Chapter 3 Constructed Wetlands - USDA · (210-VI-NEH, September 2002) 3–v Part 637 National Engineering Handbook Chapter 3 Constructed Wetlands Table 3–5 Processes involved in

(210-VI-NEH, September 2002)

United StatesDepartment ofAgriculture

NaturalResourcesConservationService

Part 637 Environmental EngineeringNational Engineering Handbook

Chapter 3 Constructed Wetlands

Part 637National Engineering Handbook

Constructed WetlandsChapter 3


Issued September 2002

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3–i(210-VI-NEH, September 2002)

Acknowledgments

Chapter 3, Constructed Wetlands for Animal Waste Treatment, was devel-oped under agreement with the Alabama Soil and Water ConservationCommission. The commission contracted with Victor W.E. Payne, envi-ronmental engineer, Payne Engineering, Auburn, Alabama, for its prepara-tion. Donald L. Stettler, environmental engineer (retired), Natural Re-sources Conservation Service (NRCS), National Water and Climate Center,Portland, Oregon, coordinated the project. Dr. Robert L. Knight, wetlandecologist and internationally known treatment wetland authority,Gainesville, Florida, is acknowledged for his detailed review and his contri-bution of the section on plant establishment and maintenance. Acknowl-edged are review and comments provided by Barry Kintzer, nationalenvironmental engineer, NRCS, Conservation Engineering Division, andDavid C. Moffitt, environmental engineer, National Water ManagementCenter, Fort Worth, Texas. Also acknowledged are the many from withinthe Natural Resources Conservation Service who added value to this chap-ter by volunteering to provide their review and comments.



3–ii (210-VI-NEH, September 2002)

3–iii(210-VI-NEH, September 2002)

Chapter 3 Constructed Wetlands

Contents:

Part 1 Animal Waste Treatment

637.0300 Introduction 3–1

(a) Purpose and scope ........................................................................................ 3–1

(b) Background ................................................................................................... 3–1

637.0301 Types of constructed wetlands 3–2

(a) Surface flow wetlands .................................................................................. 3–2

(b) Subsurface flow wetlands ............................................................................ 3–2

(c) Floating aquatic plant systems .................................................................... 3–4

637.0302 Benefits of surface flow wetlands for animal waste treatment 3–6

(a) Nutrient reductions ...................................................................................... 3–6

(b) Odor control .................................................................................................. 3–6

(c) Water quality improvement ......................................................................... 3–7

(d) Wildlife enhancement ................................................................................... 3–7

(e) Aesthetics ....................................................................................................... 3–7

(f) Economic benefits ........................................................................................ 3–8

637.0303 Treatment process 3–8

(a) Biochemical conversions ............................................................................. 3–8

(b) Accretion ........................................................................................................ 3–9

(c) Settling/filtration ........................................................................................... 3–9

(d) Volatilization .................................................................................................. 3–9

(e) Interactions with soils ................................................................................ 3–11

(f) Evapotranspiration ..................................................................................... 3–12

(g) Nutrient uptake ........................................................................................... 3–13

637.0304 Vegetation 3–13

(a) Types of aquatic and wetland plants ........................................................ 3–13

(b) Emergent herbaceous plants ..................................................................... 3–15

637.0305 Planning for a constructed wetland—the systems approach 3–20

(a) Pretreatment ................................................................................................ 3–21

(b) Wastewater characterization ..................................................................... 3–22

(c) Site evaluation ............................................................................................. 3–22

(d) Hydrologic and climatologic data ............................................................. 3–24



3–iv (210-VI-NEH, September 2002)

(e) Regulatory requirements ............................................................................ 3–25

(f) Impacts on wildlife ..................................................................................... 3–25

(g) Operation, maintenance, and monitoring ................................................ 3–26

637.0306 Design of surface flow wetlands 3–27

(a) Background ................................................................................................. 3–27

(b) Wastewater storage .................................................................................... 3–28

(c) Presumptive method .................................................................................. 3–29

(d) Field test method ........................................................................................ 3–34

(e) Designing for phosphorus removal .......................................................... 3–41

(f) Wetland configuration ................................................................................ 3–41

(g) Embankments ............................................................................................. 3–44

(h) Liners ............................................................................................................ 3–44

(i) Inlet and outlet structures ......................................................................... 3–44

(j) Water budget ............................................................................................... 3–45

(k) Operation and maintenance ...................................................................... 3–47

637.0307 Plant establishment and maintenance 3–48

(a) Plant sources ............................................................................................... 3–48

(b) Plant establishment .................................................................................... 3–48

(c) Plant maintenance ...................................................................................... 3–49

637.0308 References 3–50

Appendix 3A Typical aquatic and wetland plant species 3A–1

used in constructed wetlands

Tables Table 3–1 Composition of duckweed grown in wastewater 3–5

Table 3–2 Annual percentage change in pollutant concentrations 3–6

from two swine and three dairy facilities after treatment

of waste treatment lagoon effluent in SF constructed

wetlands

Table 3–3 Percent of un-ionized ammonia (NH3) in aqueous 3–11

solutions as related to pH and temperature

Table 3–4 Flowering aquatic and wetland plants used in 3–14

wastewater treatment

3–v(210-VI-NEH, September 2002)



Table 3–5 Processes involved in the conversion of organic and 3–18

ammonia N to nitrogen gas

Table 3–6 Example of wetland design criteria for an 11,500-head 3–40

swine finishing facility for different treatment periods

where Qa = 1,852,800 ft3/yr, Ci = 412, and Ce = 162

Table 3–7 Sample water balance spreadsheet for 2000 finisher 3–46

swine with 400- x 400-foot waste treatment lagoon

and 26,400 square foot constructed wetland

Figures Figure 3–1 Types of constructed wetlands 3–3

Figure 3–2 Water hyacinth 3–4

Figure 3–3 Duckweed 3–4

Figure 3–4 Nitrogen cycle 3–10

Figure 3–5 Cattail 3–15

Figure 3–6 Bulrush 3–15

Figure 3–7 Features of an emergent-hydrophytic plant stem that 3–16

allow movement of gases to and from the root zone

Figure 3–8 Illustration of venturi-induced convection throughflow 3–17

as demonstrated in Phragmites australis

Figure 3–9 O2 seepage and its interactions with N within the root 3–19

zone

Figure 3–10 Venn diagram of agricultural waste management system 3–21

Figure 3–11 Typical layout of waste treatment lagoon/wetland/ 3–42

storage pond system

Figure 3–12 The effect of wetland layout configuration on effective 3–43

flow distribution

Figure 3–13 Typical configuration of a water level control structure 3–46



3–vi (210-VI-NEH, September 2002)

Examples Example 3–1 Solution using presumptive method 3–31

Example 3–2 Field test method solution 3–37

3–1(210-VI-NEH, September 2002)

Chapter 3 Constructed WetlandsPart 1 Animal Waste Treatment

637.0300 Introduction

(a) Purpose and scope

The constructed wetland is a constructed, shallow,earthen impoundment containing hydrophytic vegeta-tion designed to treat both point and nonpoint sourcesof water pollution. Its principal physical componentsinclude the aquatic vegetation, substrate for plant andmicrobial growth, the basin itself, associated struc-tural devices for water management, and the waterthat flows through the system. The treatment mecha-nisms are a complex mix of physical, chemical, andbiological processes.

This chapter focuses on constructed wetlands used totreat wastewater from confined livestock operations.It addresses the types of waste treatment wetlands,treatment processes, role of vegetation, benefits andconcerns, planning considerations, design procedures,and operation and maintenance requirements.

(b) Background

Constructed wetlands have been used for treatingmunicipal, industrial, and mining wastewater fordecades. The earliest reported wetland used to treatanimal waste in this country was at a beef feedlot inIowa, which began operation in the 1930s. It was notuntil the late 1980s and early 90s, however, that animalwaste constructed wetlands came into vogue, with theearliest ones installed in Kentucky, Alabama, andMississippi.

In 1991, the Natural Resources Conservation Service(NRCS) (then the Soil Conservation Service) devel-oped technical guidelines for the design of constructedwetlands (CWs) used to treat wastewater from live-stock facilities (USDA, 1991). The design criteria inthat document were based on state-of-the-art informa-tion at that time.

In 1997, the Environmental Protection Agency's (EPA)Gulf of Mexico Program (GMP) sponsored publicationof a literature review, data base, and research synthe-sis on animal waste constructed wetlands throughoutthe United States and Canada (CH2M-Hill and Payne

Engineering, 1997). The Livestock Wastewater Wet-land data base presents information from more than 70sites including pilot and full-scale facilities.

Evaluation of the data base revealed that only part ofthe many installed systems in this country have beenthoroughly monitored. However, enough informationhas been provided to allow development of new de-sign criteria for animal waste systems. These datahave been analyzed in light of treatment wetlandperformance models that were originally developedfor municipal wastewater. Performance data fromtesting of constructed wetlands treating wastewaterfor livestock operations have been used to calibratethose models and allow performance estimation basedon flow rates and pollution concentrations. Thosemodels and parameters are described in this chapterfor design of new constructed wetlands.



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637.0301 Types of con-structed wetlands

Three principal types of constructed wetlands havebeen used for treating wastewater. They includesurface flow (SF), subsurface flow (SSF), and floatingaquatic plant (FAP) systems. Figure 3–1 provides crosssectional drawings of these wetland types.

Natural wetlands have been used to treat municipalwastewater; however, they are not used for animalwaste treatment because of the complexity of design,the difficulty of obtaining necessary permits, and therisk of degrading natural wetland resources. There-fore, only the three principal types will be describedhere.

(a) Surface flow wetlands

Surface flow wetlands are used throughout the worldto treat municipal wastewater and are the most com-monly used wetland type in North America. The SFwetland was the only one recommended by NRCS forthe treatment of livestock facility wastewater in itstechnical guidelines issued in 1991 (USDA-NRCS,1991). It still remains the primary choice for treatmentof animal waste for reasons presented here.

SF wetlands are shallow, earthen basins planted withrooted, emergent wetland vegetation. Water flowsacross the surface at depths that typically range from 6to 18 inches, depending on the type of vegetation andother design factors. The bottom slope must be flatfrom side to side, but may be flat or have a slightgradient from inlet to outlet.

Much of the treatment results from the activities ofmicro-organisms, principally bacteria and fungi, thatthrive in this type of wetland environment. Many of theorganisms become attached to submersed plant stemsand litter, while others become part of the soil/plant-root matrix. In addition, the entire water column isalive with micro-organisms that contribute to thetreatment process.

Wastewater in the SF wetland flows across the surfaceof the bed and is visible. Consequently, it is sometimes

called a free water surface (FWS) wetland. SF wet-lands have been used to treat effluent from wastetreatment lagoons, waste storage ponds, and milkhouses as well as runoff from open feedlots. They havealso been used to treat acid mine drainage and runofffrom croplands and discharges from aquaculturefacilities.

The effluent from most animal confinement facilitiesshould be pretreated to reduce the total solids andnutrients before entering an SF wetland. The highconcentrations of solids and other constituents ofwastewater that typically emanate directly from theconfinement facilities are unsuitable for most wetlandplants without pretreatment. Pretreatment is espe-cially important for reducing the high concentrationsof solids and ammonia often associated with wastewa-ter from livestock facilities.

Data on the performance of SF constructed wetlandsfor treating wastewater from livestock facilitiesthroughout the United States indicate that this type ofwetland can be highly efficient in treating wastewaterfrom confined animal feeding facilities. SF wetlandsare relatively inexpensive when compared with SSFwetlands. In addition, SF wetlands are relatively easyto manage and maintain, especially when comparedwith floating aquatic plant systems. Surface flowwetlands function year-round, although some reduc-tion in efficiency occurs in winter in colder climates.Even in the cold northern climate of Canada, SF wet-lands are successfully treating animal waste (Knight etal., 1996).

(b) Subsurface flow wetlands

The SSF wetland contains a bed of gravel, rock, or soilmedia through which the wastewater flows. The bed isplaced below ground level, and wastewater enters thebed at approximately mid-depth. Emergent, hydro-phytic vegetation is planted at the surface of the wet-land, often in a shallow layer of pinestraw, woodchips, or other mulch. The roots of the plants extendinto the saturated bed.

The water surface is maintained at an elevation justbelow the surface of the bed. The bottom slope, poros-ity of the medium, and daily average flows are criticalengineering factors that must be considered to main-tain the proper hydraulic gradient of the wastewater as

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Figure 3–1 Types of constructed wetlands

Shallow water

Surface flow constructed wetland

Subsurface flow constructed wetland

Floating Aquatic Plant (FAP) system

Lined basin

Gravel substrate

Water level

Surface of bed

Surface of bed

Water level

Water level




it passes through the bed. Failure to account for thesefactors could result in a water level that drops belowthe roots at the downstream end or a water level thatrises, resulting in ponding of water on the surface.

In areas that have shallow ground water or a seasonalhigh water table, ground water can infiltrate into thebed and disrupt hydraulic conditions and treatmentefficiency. Wastewater could also migrate from thesubsurface wetland into the surrounding soil orground water. In this case hydraulics, treatment effi-ciencies, and plant survival could be altered. For thesereasons, an impervious, fabricated liner should beinstalled in some SSF wetlands.

While SSF wetlands are successfully treating domesticwastewater, their use in treating wastewater fromlivestock facilities appears limited. The reasons forthis are twofold. First, the porous bed can be easilyplugged with solids. Even pretreated wastewater frommost livestock facilities has high concentrations ofsolids. In addition, installing a large rockbed would beprohibitively expensive for most operations. Theinstallation cost for a SSF system is expected to be atleast five times the cost of a surface flow system(Kadlec and Knight, 1996).

SSF wetlands could possibly be used to treat smallflows that have a low-solids content, such as waterused to clean milking equipment in a small dairy. Forthis use, a septic tank would need to be installedupstream of the wetland.

(c) Floating aquatic plant systems

The floating aquatic plant (FAP) system consists of apond or series of ponds in which floating aquaticplants are grown. The ponds must be deep enough toprevent emergent plants from growing, but shallowenough to ensure adequate contact between the rootsof the floating plants and the wastewater (depth range:3 to 5 ft). In FAP systems plants grow profusely andextract a large amount of nutrients from the wastewa-ter. Since harvesting is an essential managementrequirement, the number, size, arrangement of ponds,and method of harvesting must be taken into accountduring initial planning.

The most common floating plants used for wastewatertreatment are water hyacinths (Eichhornia crassipes)

(fig. 3–2) and duckweed (members of genera Lemna,

Spirodella, Wolffia, and Wolfiella) (fig. 3–3). Bothtypes of vegetation grow rapidly and generally provideenough shade to prevent the growth of algae, which, inturn, prevent large diurnal swings in pH and dissolvedoxygen concentrations.

Growth rate of water hyacinths is typically between150 and 270 pounds per acre per day (Reddy andDeBusk, 1987). Based on data from several municipalFAP systems, nitrogen was removed at an average rateof 17 pounds N per acre per day when N loadingranged from 8 to 37 pounds per acre per day (Weberand Tchobanoglous, 1985). Phosphorus removal atmunicipal treatment plants generally does not exceed30 to 50 percent, assuming an active harvesting pro-gram (Reed et al., 1995). Lower P removal is typical ofunharvested FAP systems.

Figure 3–2 Water hyacinth

Figure 3–3 Duckweed

Source: Center for Aquatic andInvasive Plants, University ofForida


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Duckweed grown in wastewater can double its area ofcoverage every 4 days at a temperature of 27 degreesCelcius (Reed et al., 1995). It is more tolerant of coldweather than hyacinths and can be grown for at least 6months of the year in all areas of the country andthroughout the entire year in Southern Coastal Statesand southern California. Water hyacinths, however,are not suitable for growth in the northern two-thirdsof the country.

Duckweed has a low-fiber, high-protein, and high-mineral content, giving it excellent potential for use aslivestock feed (table 3–1). Compared with waterhyacinths, duckweed contains at least twice as muchprotein, fat, nitrogen, and phosphorus.

Water hyacinths and duckweed contain about 92percent water. After harvesting, drying is normallyrequired depending on the requirements of the finalproduct. Plants can be dried in the sun or throughmechanical means. Mixing the dried material withother ingredients and forming a pelleted feed has beenemployed, especially with duckweed. Composting isanother viable alternative to convert these plants to auseable resource.

Research has shown that Lemna gibba, a species ofduckweed, could survive well after several days in thesupernatant for waste treatment lagoon for a swineoperation with an initial total Kjeldahl nitrogen (TKN)

concentration of 255 mg/L and an ammonia concentra-tion of 168 mg/L. However, the improvement in ammo-nia removal was significant when the wastewater wasdiluted with clean water at a ratio of 1:1 (Cheng et al.,1998).

A comparison of SF and FAP systems for municipalwastewater indicates that FAP systems have lowerreaction rates, higher construction and operatingcosts, more sensitivity to cold temperatures, and moresusceptibility to plant pests and pathogens. The prob-lem of plant pests and the need for a high level of pestmanagement might be overcome by using a combina-tion of plant species. If the FAP is considered fortreating animal waste, an economic evaluation shouldbe conducted during initial planning to determine ifthe end product, such as a high-value feed product,can offset the higher costs of installation, operation,and management.

As noted in this section, the SSF and FAP wetlandshave certain disadvantages when used to treat animalwaste. The SF wetlands have been used widely aroundthe country and are currently the preferred method oftreating animal waste. For this reason the focus ofattention in this chapter is on SF constructed wet-lands.

Table 3–1 Composition of duckweed grown in waste-water 1/

Composition - - - Percent dry weight - - -range average

Crude protein 32.7 – 44.7 38.7

Fat 3.0 – 6.7 4.9

Fiber 7.3 – 13.5 9.4

Ash 12.0 – 20.3 15.0

Carbohydrate — 35.0

TKN 4.59 – 7.15 5.91

Phosphorus-P 0.80 – 1.8 1.37

1/ Summarized by Hyde et al., 1984.




637.0302 Benefits of sur-face flow wetlands foranimal waste treatment

The surface flow constructed wetland can provideimportant benefits for confined animal operations.These benefits relate to improved nutrient manage-ment, odor control, water quality improvement, wild-life enhancement, aesthetics, and economics.

(a) Nutrient reductions

In many cases the decisionmaker wants to conservenutrients in the waste since more nutrients can meanmore value as fertilizer. However, some decision-makers need to reduce nutrient loads either out ofnecessity, such as not having enough land for properspreading, or because such reductions will providesome other advantage (see (b) Odor control and (c)Water quality improvement).

Nutrient reduction often becomes a necessity whereland area for spreading is limited. In such cases thedecisionmaker's options may be limited to:

• reducing the number of animals,• changing to a crop or cropping sequence that

allows for higher nutrient use, or• providing additional treatment of the waste-

water.In each case, economic factors will also becomeimportant.

If the decisionmaker has a liquid waste system andelects to reduce nutrient content of the waste, the SFconstructed wetland can be a viable option. Here, thewetland can be sized so that nutrients available afterits treatment are consistent with the nutrient manage-ment plan for the application site.

Table 3–2 illustrates the value of SF wetlands in re-moving nutrients and organics from wastewater. Thewetlands shown in the table differ in location, age,design, and type of wastewater; nevertheless, the dataillustrate that SF constructed wetlands can providesignificant reductions in nutrient loads.

(b) Odor control

Land application of some wastewater produces odorsthat are offensive to neighbors, even at some distancedownwind. The SF wetland can reduce these odors byreducing volatile solids concentrations. In addition, aswastewater passes through the wetland, the effluenttypically has clearer color and less intense odor thanthe raw effluent from most waste treatment lagoonsand waste storage ponds.

Where a constructed wetland is used to treat theeffluent from a waste treatment lagoon, only thesupernatant should be discharged to the wetland.Discharge of accumulated sludge from the lagoon tothe wetland may kill the plants and create operationalproblems. Thus, sludge removal and its utilizationapart from the wetland must be considered in plan-ning.

Table 3–2 Annual percentage change in pollutantconcentrations from two swine and threedairy facilities after treatment of wastetreatment lagoon effluent in SF constructedwetlands

Constituent - - - - Swine - - - - - - - - - - - - Dairy - - - - - - - - -NC 1/ AL 2/ IN 3/ MS 4/ OR 5/

- - - - - - - - - - - % reduction - - - - - - - - - - -NH4-N 91 84 89 74 46

Org-N 90 83 62 — 47

Total P 34 46 84 53 45

PO4-P 52 89 77 43 —

BOD5 — 87 92 76 63

COD 55 80 — 64 52

1/ F.J. Humenik et al.2/ T.A. McCaskey and T.C. Hannah3/ R.P. Reaves and P.J. DuBowy4/ C.M. Cooper and S. Testa, III5/ J.A. Moore and S.F. Niswander

(Summarized in Constructed Wetlands for Animal WasteTreatment, Payne Engineering and CH2M-Hill, 1997)

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(c) Water quality improvement

Proper management of livestock waste is essential toprotect surface and ground water from contaminationby nutrients, oxygen-depleting organics and ammonia,suspended and settleable solids, and microbial con-taminants. However, wastewater from livestock facili-ties, even after the treatment in waste treatment la-goon or incidental treatment in waste storage ponds,can have high levels of pollutants that can degradesurface water or ground water quality.

When wastewater from a waste treatment lagoon orstorage pond is land applied, pollutants still have thepotential to enter surface water because of over-application or through the movement of residualpollutants during storm runoff. This is especially trueif buffer zones between application sites and nearbystreams are too small.

To ensure maximum protection of surface water, thedischarge of wetland effluent to surface water is notrecommended although high treatment efficienciescan often be achieved. While reported treatmentefficiencies vary, ammonia nitrogen and biochemicaloxygen demand (BOD5) have been reduced throughwetland treatment by more than 75 percent over anextended period for some systems. Yet, despite thesehigh levels of removal, the quality of wetland effluentmay still not meet state discharge limits all year for allpollutants. Therefore, it is recommended that treatedeffluent be stored and land applied as opposed todischarging under a state-authorized permit.

The decisionmaker for a confined feeding facility whowishes to discharge treated effluent to a nearby streammust first obtain a National Pollution Discharge Elimi-nation System (NPDES) permit from the State regula-tory agency. Allowable discharge limits are basedlargely on the characteristics or waste assimilativecapacity of the receiving stream and total maximumdaily loads (TMDLs) allowed. Wastewater samplingand flow monitoring on a regular basis are typicallyrequired, which means that the treatment system mustbe reliable enough to meet discharge requirementsthroughout the year. A system permitted to dischargealso typically requires a higher level of managementand maintenance.

Although the quality of wetland effluent may not meetdischarge requirements, it may be high enough to beused for other purposes than land application. Suchuses may include flushing, cooling, and dust control.

(d) Wildlife enhancement

Constructed wetlands attract wildlife. Birds, mam-mals, amphibians, reptiles, and a variety of dragonfliesand other insects frequent the area or make the wet-land home. While any arrangement of cells enhanceswildlife habitat, the layout can be modified to attractspecific types of wildlife. In areas where bio-security isa concern, consideration should be given to excludingmigratory and other nonresident wildlife to minimizethe potential for spread of disease to other operations.

A recent EPA publication (USEPA, 1999) indicates thatmore than 1,400 species of wildlife have been identi-fied for constructed and natural treatment wetlands.They include 700 species of invertebrates, 78 speciesof fish, 21 species of amphibians, 31 species of rep-tiles, 412 species of birds, and 40 species of mammals.More than 800 species were reported in constructedwetlands alone.

(e) Aesthetics

Wetlands have a unique beauty that in many regions ofthe country changes through the seasons. Even whenplanted with typical plantings, the character of thesystem changes as natural wild plants invade thesystem. While the choice of plants may be limited forthe initial or upstream segments of the system becauseof the high concentrations of some pollutants, morecolorful and a greater variety of plant species may beplaced at downstream locations within the wetlandsystem where wastewater quality improves.




(f) Economic benefits

Each operation must be evaluated individually todetermine if the installation of a constructed wetlandwill provide an economic benefit. The benefit couldcome from reducing the land application area enoughto install a solid set system versus a more labor-inten-sive traveling gun or center pivot system. Even if aneconomic analysis shows no net benefit from installinga constructed wetland, some decisionmakers might bewilling to forgo some measure of annual benefit toreduce the amount of time spent in waste handling.

Some key factors that must be considered in an eco-nomic assessment include:

• Construction costs• Value of nutrients lost through treatment by the

wetland• Equipment and labor costs to land apply waste-

water• Value of land used by constructed wetland• Value of crop lost because of land taken out of

production by the constructed wetland• Cost of operation and maintenance

637.0303 Treatmentprocess

Many physical, chemical, and biological mechanismsoccur within treatment wetlands. Some are relativelysimple and others complex, and some are not fullyunderstood in terms of their contribution to the overalltreatment process. The principal mechanisms aredescribed in this section.

(a) Biochemical conversions

The wetland is alive with micro-organisms that con-vert chemical compounds from one form to another. Alarge fraction of these organisms are attached to plantstems and litter and to sites throughout the soil andplant root complex. Others are free floating within thewastewater stream.

Since wastewater from most livestock facilities isgenerally low in or devoid of dissolved oxygen, theprimary treatment organisms within the wetland areeither obligate anaerobes (those requiring an oxygen-free environment) or various facultative types. Theprincipal end products of anaerobic digestion arecarbon dioxide (CO2) and methane (CH4); however, avariety of other minor gases are also generated insmall quantities. Thus, the organic content of thewastewater as measured by 5-day biological oxygendemand (BOD5), chemical oxygen demand (COD), andvolatile solids (VS) can be greatly reduced throughwetland treatment.

Anaerobic bacteria also convert organic nitrogen (Org-N) to the ammonia forms, NH4

+ and NH3. Both forms,as expressed in the equilibrium equation NH4

+ ↔ NH3+ H+, are considered to be ammonia nitrogen (Sawyerand McCarty, 1967).

The conversion of ammonia to nitrite (NO2) and thento nitrate (NO3

–) requires an aerobic environment.Aerobic organisms are those requiring free-oxygen forrespiration. Such an environment may be in micro-scopic zones around the roots and rhizomes of wet-land plants and on substrates near the water surface.See details on nitrogen conversion within the rootzone in section 637.0304 Vegetation.

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As the anaerobic, ammonia-laden wastewater is drawninto the root zone, any aerobic organisms presentbegin converting ammonia to soluble nitrate. Some ofthe NO3 is used by the plants, but much of it migratesback into the surrounding anaerobic region. Withinthis region, specific types of anaerobic bacteria deni-trify the NO3, converting it to N2 gas, which is thenliberated to the atmosphere. Figure 3–4 illustrates thepathways of nitrogen conversions.

Other compounds also go through biochemical con-versions. Sulfur compounds can be converted tohydrogen sulfide under anaerobic conditions, and ironcompounds can be reduced. Some compounds are lostto the atmosphere, and others are stored in the wet-land sediment. Phosphorus does not have a gaseousstate; therefore, organic P is converted through bio-logical mechanisms to soluble P and then:

• lost in the wetland effluent,• extracted by the plants,• bound within the soil profile, or• entrapped within the permanent peat-like bed

that forms on the floor of the wetland (accre-tion).

Phosphorus is often removed in relatively high con-centrations in many surface flow wetlands duringinitial startup. However, after 1 to 5 years (Kadlec andKnight, 1995), P levels usually drop to stable long-termremoval rate. Since clay soil has a high cation ex-change capacity, a wetland constructed in clay soilwill most likely provide a longer period of high Premoval than a wetland with sandy soil. Typical re-moval rates for total P for animal waste constructedwetlands are in the range of 40 to 60 percent based onearlier NRCS design criteria (USDA-NRCS, 1991).

(b) Accretion

Accretion refers to the long-term buildup of a peat-likematerial on the floor of a SF wetland or on top of thefilter bed of a SSF wetland. This material consists ofsettleable solids from the waste stream, the remnantsof decayed plant litter, and microbial biomass. Recentadditions of loose litter or thatch are not consideredpart of the accreted material. Accretion is the primarylong-term removal process for phosphorus and metalsafter the soil has been saturated with these elements.

Design height of constructed wetland embankmentsmust consider long-term accretion. The rate of buildupis typically less than 0.5 inch (1.3 cm) per year. Whenthe depth allowance for accretion has been reached,the accumulated material should be removed to main-tain the hydraulic effectiveness of the wetland cell.However, as has been stated, accretion is a long-termprocess. As an example, with an accretion rate of 0.5inch per year, it would take 25 years to fill 1 foot.

(c) Settling/filtration

Solids entrained within the influent wastewater cansettle to the bottom of the wetland and become part ofthe accreted material or can be filtered or entrappedby the plant stems and bottom litter. The floatingmaterial and settleable solids can be retained throughthis mechanism. Any settleable organic matter iseventually converted to more stable end productsthrough biochemical conversions. Some of the mate-rial entering the wetland is relatively inert and, there-fore, degrades slowly or becomes part of the perma-nently stored material in the accretion.

(d) Volatilization

The release of a compound from the surface of a liquidto the surrounding atmosphere is called volatilization.The rate of transfer from the liquid phase to the gas-eous phase is governed by standard chemical equilib-rium equations for the compounds in question. If theconcentration of a compound in a gaseous phase islow or nonexistent, such as an extraneous compoundwould be in the Earth's atmosphere, the fractioncontained in liquid phase continues to evaporate(converted to gaseous phase) until equilibrium isreached.

Ammonia is a compound that readily volatilizes and isone of great importance in animal waste management.Ammonia concentrations in anaerobic waste treat-ment lagoons typically represent 60 to 70 percent ofthe total nitrogen concentration, with the other 30 to40 percent being in organic form. These same percent-ages apply to wastewater that enters most animalwaste constructed wetlands.




Figure 3–4 Nitrogen cycle 1/

3Atmospheric

Urineurea

Rain

Animalprotein

Organic N

AmmoniaNH

Ammonium4

NONitrites

2

Plantprotein

Organic N

NONitrates

3

Fecalmatter

Organic N

Fertilizer for plants

NAtmospheric

2

Hydrolysis of urea

Bacterialdecomposition

Volatilization

Lightnin

g

Nitrogen-fixingby bacteria & algae

NH 3

Chemical manufacture

NH

Death & decomposition by bacteria

Denitrifi

cation (b

acterial

reduct

ion)

Fertiliz

er

manufactu

re

Ani

mal

food

Mineralization

(death and bacterial oxidation)

(bacterial oxidation)N

itrification

Nitrification

(bacterial oxidation)

Denitrification

(bacterial reduction)

for plants

Fertilizer

1/ Source: United States Department of Agriculture, Natural Resources Conservation Service. 1992. Agricultural Waste Management FieldHandbook.

3–11




While some nitrogen is lost through the denitrificationprocess noted under (a) Biochemical conversions,additional N may be lost through the volatilization ofammonia. This is explained in part by the equilibriumequation for ammonia:

NH4+ + OH– ⇔ NH3 • H2O ⇔ NH3↑ + H2O

In this equation, NH3 is the gaseous phase of ammonia.The expression NH3 • H2O represents the loose attach-ment of the un-ionized NH3 molecule to the H2O mol-ecule. At the air/water interface, NH3 can be volatil-ized; in which case the equation shifts to the right. Ifno equilibrium in NH3 concentrations between air andwater is reached, NH3 is volatilized and the equationcontinues to shift toward more free NH3↑ . The equa-tion also illustrates the interrelationship between pHand the ammonia forms. Under highly alkaline condi-tions (high OH–), more NH3 becomes available insolution and more is available for volatilization.

In addition, the process is affected by temperature.Table 3–3 shows how temperature and pH affect theamount of un-ionized ammonia present in an aqueoussolution.

Wastewater entering constructed wetlands fromanaerobic waste treatment lagoons usually has pH inthe range of 7.0 to 7.5. At 25 degrees Celsius, between0.57 and 1.8 percent of the available ammonia is in theun-ionized form.

In waste treatment lagoons and constructed wetlands,only the movement of wind across the surface of thewastewater enhances volatilization. Since the pHcannot be easily raised to enhance NH3 volatilization,the process of ammonia removal in waste treatmentlagoons and constructed wetlands is naturally slower

than that in industrial and municipal systems whereaeration is provided and pH is controlled. Neverthe-less, as much as 90 percent of the original N enteringan anaerobic waste treatment lagoon is lost, mostlythrough volatilization of ammonia. It is believed that aconsiderable amount of N is also lost in constructedtreatment wetlands as a result of this process.

Research on ammonia losses from rice fields fertilizedwith ammonium indicates that loss rates were compa-rable to plant uptake for dense stands of macrophytes(Freney et al., 1985). In addition, Kadlec and Knight(1996) summarized various studies on the subject ofammonia volatilization and concluded that "volatiliza-tion typically has limited importance, except in spe-cific cases where ammonia is present at concentra-tions greater than 20 mg/L."

The influent ammonia concentration to constructedwetlands from livestock operations generally exceeds20 mg/L. For wastewater from swine operations thathas been pretreated with a waste treatment lagoon,this influent ammonia concentration ranges from 200to 300 mg/L. Because of this, it would appear thatammonia volatilization is a significant pathway for theloss of N in this type of wetland. Further research onthis issue is needed to quantify amounts lost undervarious climatic conditions.

(e) Interactions with soils

When wastewater enters the soil/plant-root matrix,various reactions can take place depending on the typeand amount of clay, hydrous oxide, and organic matterpresent. In addition, the nature and type of chemicalconstituents in the solute as well as the pH and cationexchange capacity of the soil play important roles inthe retention and conversion of pollutants.

Reactions within the soil complex include ion ex-change, adsorption and precipitation, and complex-ation (Keeney and Wildung, 1977). Cation exchange isthe dominant exchange process in soils. In this pro-cess positively charged particles (cations) that arebound electrostatically to negatively charged (anionic)sites on soil colloids are exchanged with cations in thesoil solution with little or no alteration of the solids.Since soil colloids have a net negative charge, manypositively charged molecules in wastewater are readilybound within the soil profile.

Table 3–3 Percent of un-ionized ammonia (NH3) inaqueous solutions as related to pH andtemperature

Temperature - - - - - - - - - - - - - - - - - - - - pH - - - - - - - - - - - - - - - - - - - -(oC) 6.0 6.5 7.0 7.5 8.0 8.5

15 0.0027 0.087 0.27 0.86 2.7 8

20 0.040 0.13 0.4 1.2 3.8 11

25 0.057 0.18 0.57 1.8 5.4 15

30 0.080 0.25 0.80 2.5 7.5 20




Adsorption refers to the "adhesion of gas molecules,dissolved substances, or liquids to the surface of solidswith which they come in contact," while precipitationdenotes the formation of "a sparingly soluble solidphase" (Keeney and Wildung, 1977). These two pro-cesses are often in competition, and determiningwhich one dominates is often difficult.

Sorption, a term often used to describe adsorption andabsorption, can involve weak atomic and molecularinteractions (physical sorption) or stronger ionic-typebonds similar to those holding atoms in a molecule(chemisorption). The latter process is thought to bethe primary mechanism for phosphate retention inacid (Seyers et al., 1973; Mattingly, 1975).

A host of other interactions can occur within the soil.Metals, for instance, can react with soil in a variety ofways. In addition to the inorganic reactions that occur,metals may be subject to complexation, chelation, andbiological transformations in organic soils.

The purpose of this section is not to explain the oftencomplex interactions that can occur when wastewaterenters the soil profile. This section simply illustratesthat the soil is a vitally important and intriguing part ofthe treatment process within constructed wetlands.

(f) Evapotranspiration

Losses of water to the atmosphere from a wetland'swater surface and soil (evaporation) and from theemergent part of the wetland plants (transpiration) arereferred to collectively as evapotranspiration (ET).Since ET affects the overall water balance of a wastetreatment system, it becomes an important factor indesign. Factors that affect the rate of ET includeincoming solar radiation, back radiation, cloud cover,time of year, latitude, wind velocity, amount of openwater exposed to winds, and percent of water surfacecovered by litter or occupied by emergent plants,(Kadlec, 1989). Differences in evaporation related towetland plant type appear to be relatively unimportant(Linacre, 1976).

Any attempt to predict ET losses based on energybalances could be a difficult task and could result inoutcomes that may be no better than using empiricalmethods. With this in mind, the following guidelinesare presented for estimating ET:

• Wetland ET over the growing season is nearlyequivalent to 0.8 times Class A pan evaporation.Climate apparently has little effect on this rela-tionship. Monthly and yearly Class A pan evapo-ration data can be obtained from data publishedby the U.S. National Oceanic and AtmosphericAdministration (NOAA).

• Wetland ET and lake evaporation are approxi-mately equal. This is simply a corollary of theparagraph above because Class A pan evapora-tion is roughly 1.4 times lake evaporation.

• For small wetlands, the ratios to pan and lakeevaporation may not be adequate for predictingET. While these ratios can be applied effectivelyto wetlands as small as 0.25 acre (0.1 ha), theymay not be reliable for smaller wetlands becauseof the advective influences of the surroundingclimate. In other words, ET is enhanced in smallwetlands much as it is with potted plants.

The importance of ET can be seen in a simple calcula-tion for a wetland with a 2-acre surface area. Assum-ing, based on climatic data, a lake evaporation of 36inches (92 cm) per year, the annual ET would be about261,360 cubic feet (7,396 m3) per year, or nearly 2million gallons. This yearly value is somewhat mislead-ing because ET is not evenly distributed throughoutthe year: ET rates are typically much higher during thesummer than during winter. Even in northern climates,all wastewater applied to a treatment wetland can belost through ET during a dry summer, as occurredtwice in 10 years at a municipal treatment wetland inMichigan (Kadlec, 1989). For this reason, consider-ation should be given to supplemental water that maybe needed for the system.

Given the choice between the more detailed andrigorous method of determining ET and the use ofempirical methods, the latter is recommended forestimating ET for animal waste treatment wetlands.Regardless of the method used, it should be noted thatET can result in a high degree of variability in hydro-dynamics throughout any single growing season.

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(g) Nutrient uptake

Wetland plants extract nitrogen, phosphorus, potas-sium, and various minor nutrients and metals fromlivestock wastewater. These constituents of wastewa-ter may be used in the development of plant stems andleaves, or they may be stored for an extended periodin the roots and rhizomes. Emergent plants used in SFand SSF wetlands remove nutrients during the grow-ing season, but a large part of these nutrients arereturned to the litter mass as plants die back in winter.A fraction of the decaying litter is released in thewetland effluent. However, some of the nutrientsbecome part of the accretion, while others are perma-nently or semipermanently stored in the subsurfacestructure of the plants.

Harvesting plants in SF and SSF wetlands will removeonly a minor amount of nutrients and other pollutantsrelative to the other processes noted above. Therefore,harvesting is not recommended. However, in FAPsystems, nutrient removal by plants is significantsimply because the plants and, hence, the nutrients areharvested and removed from the system.

637.0304 Vegetation

The U.S. Fish and Wildlife Service (USFWS) lists morethan 6,700 plant species that are identified with wet-lands. These include the obligate species that areexclusively in wetland habitats and facultative speciesthat are in either wetland or upland areas. Only afraction of this number is suitable for use in treatmentwetlands, and fewer still would be suitable for use intreating high-strength wastewater, such as that frommost confined livestock facilities. Nonetheless, avariety of wetland plant species has been used in thetreatment of wastewater. Some have been purpose-fully introduced, and some are natural invaders.Guntenspergen, et al. (1989) listed 17 emergent spe-cies, 4 submergent species, and 11 floating species thathave been used in wetlands for treating municipalwastewater. Kadlec and Knight (1996) listed 37 fami-lies of vascular plants that have been used in waterquality treatment. Be alert to using any plant speciesthat may be considered invasive.

(a) Types of aquatic and wetlandplants

The four major groups of macrophytic plants associ-ated with wetlands in general are mosses, ferns, coni-fers, and flowering plants. However, the vast majorityof plants used in wastewater treatment wetlands areflowering plants. Table 3–4 describes plants within theflowering plant group.

The emergent herbaceous plants are used extensivelyin municipal waste treatment systems throughout theworld and are the most widely used plants in animalwaste constructed wetlands. Although floating plants,such as duckweed, often fill open areas of surface flowwetlands, their contribution to the overall treatmentprocess in this type system is incidental to that pro-vided by the emergent herbaceous plants. Therefore,the focus in this publication is on the emergent herba-ceous varieties.




Table 3–4 Flowering aquatic and wetland plants used in wastewater treatment

Growth habit Description Typical plants

Rooted plants

Submerged Main vegetative structure is completely underwater. Flowers hydrilla (Hydrilla)

or inflorescence generally extend above the water. Through egeria (Egeria elodea)

photosynthesis, these plants produce volumes of dissolved frog's-bit (Limnobium)

oxygen, which facilitates aerobic decomposition. They may pondweed (Potamogeton spp.)be shaded out where free floating plants are plentiful. Bestadapted to deep water zones.

Floating Roots extend into the bottom soil or may be attached at the water lily (Nymphaea spp.)(stems and leaves) shoreline. Plants may cover large areas in shallow water spatterdock (Nuphar spp.)

regimes. The shade they provide may affect water tempera- pondweed (Potamogeton spp.)ture. Such coverage may also reduce the population of pennywort (Hydrocotyle spp.)algae and, thereby, reduce suspended solids concentrationsin wetland effluent. Pennywort, attached at the shoreline,has spread profusely in open areas between emergent plantsin some treatment wetlands.

Emergent Plants are rooted in the soil and have structures (stems and bulrush (Scirpus spp.)herbaceous leaves) that emerge or stand upright above the water surface. cattail (Typha spp.)

As herbaceous plants, their structures are nonwoody yet common reed (Phragmites)

they stand erect above the water surface. They are the duckpotato arrowhead primary plants used in constructed wetlands for (Sagittaria spp.)treating animal waste. giant cutgrass (Zizaniopsis

spp.)southern wild rice (Zizania)

rush (Juncus spp.)

Emergent woody Includes shrubs, trees, and woody vines. Distinguishing cypress (Taxodium spp.)characteristics include bark, nonleafy vascular structure, willow (Salix spp.)decay-resistant tissues, and relatively long life. Used in ash (Fraxinus spp.)municipal treatment wetlands. Their effectiveness in treating gum (Nyssa spp.)wastewater from confined livestock operations is uncertain. birch (Betula spp.)

alder (Alnus spp.)

Free-floating plants

Free-floating to Plants may be rootless (Wolffia spp.) or have a root duckweed (Lemna spp.)partly submerged system that ranges from a single hair-like root (Lemna spp.) water meal (Wolffia spp.)

to roots that are several feet long (Eichhornia spp.). water hyacinth (Eichhornia

Roots, when present, are not attached to the soil, but extend crassipes)

into the water column. Plants reproduce rapidly, especiallyin a nutrient-rich environment. When used for wastewatertreatment, harvesting is essential.

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(b) Emergent herbaceous plants

Emergent herbaceous plants (EHPs) are the dominanttype vegetation used in wetland treatment systems,mainly because most treatment wetlands are surface-flow systems and the shallow water of these systemsis ideal for this type vegetation. EHPs are also thedominant type vegetation in SSF wetlands. Whilefloating plants (free-floating or attached) frequentlyenter SF wetlands through natural means, their pres-ence is usually incidental.

Another factor favoring the use of emergent wetlandplants is that they function in all latitudes of theUnited States, unlike some major floating plants. Inaddition, the best known and most versatile of thewetland plants (i.e., cattails, fig. 3–5, and bulrushes,fig. 3–6) are often available locally; thus, starter plantscan sometimes be gotten onfarm or from county andstate highway departments when they are cleaning outroad ditches.

Although these considerations are important, the twospecial reasons that make the emergent wetland plantsimportant are

• the special structural properties that allow theseplants to survive in an otherwise hostile environ-ment and

• the plants' special ability to facilitate the treat-ment process.

The structural functionality of these plants and theirrole in the treatment process are presented here.

(1) Structural functionality

All plants require oxygen, nutrients, and water forvarious metabolic processes. When plant roots remainin saturated soil, the normal diffusion of gases to andfrom the plant roots is inhibited. Such gas transferscan still take place within the root zone if the water isoxygenated, but the process is much slower than inwell aerated, but unsaturated soils. If the soils aresaturated and also enriched with organic matter,anaerobic condition undoubtedly exists. In this casethe roots are in competition with local microbialcommunities for any meager supplies of dissolvedoxygen (DO) available; for most terrestrial plantspecies, the result is certain death.

Figure 3–5 Cattail Figure 3–6 Bulrush






Many emergent wetland plants have adaptations thatallow life to go on even in soil that is both continu-ously flooded and saturated with a high level of oxy-gen demanding organic material, more specifically,wastewater. These adaptations ensure that oxygen istransported to the roots and rhizomes to satisfy theplant’s respiratory demands.

Vascular wetland plants are equipped with aeren-

chyma or aerenchymous tissues containing lacunae,or a network of tiny hollow tubes that traverse thelength of the plant allowing gases to move from theabove-water part of the plant to the roots and rhi-zomes, and vice versa. In addition, these plants havelenticels, or small openings along the plant stems thatfacilitate the flow of gases in and out (see figure 3–7).Lenticels may also be located on adventitious rootsthat develop from the stalk or stem of the plant withinthe water column. Other structural components in-clude "knees" on cypress trees (an emergent woodyplant) and buttresses, also on certain woody species.

The transfer of gases and in particular of oxygen fromthe above-water part of the emergent herbaceousplants to the root zone can occur in two basic ways:

• passive molecular (gas-phase) diffusion• bulk flow of air through internal gas spaces of

the plant, resulting from internal pressurization(Brix, 1993)

(2) Molecular diffusion

Brix, 1993, describes molecular diffusion as follows:Diffusion is the process by which matter istransported from one part of a system to anotheras the result of random molecular movement.The net movement of matter is from sites withhigh concentrations (or partial pressures) tosites with lower concentrations. The rate ofdiffusion of a gas depends on the medium inwhich the diffusion occurs, the molecular weightof the gas, and the temperature.

Diffusion within the emergent herbaceous plantsinvolves reverse gradients of O2 and CO2 partial pres-sures in the lacunae. Researchers have shown that insome plants a large decrease in O2 concentrationoccurs between the aerial parts of the plants and theroot zone, while gradients of CO2 and CH4 occur in thereverse direction (Brix, 1993). The decrease in O2concentration was shown to range from 20.7 percentin the aerial stems to 3.6 percent in the lacunal air ofthe deepest-growing rhizomes, with the drop resultingfrom O2 extracted for respiration (Brix, 1993). In thesame manner, CO2 produced by respiration in theroots and rhizomes and CH4 produced in the anoxicsediment diffuse along a reverse path with an increas-ing concentration gradient until these gases are ex-pelled from the aerial part of the plant.

(3) Pressurized ventilation

The bulk flow of air into and through a plant can resultfrom differences in temperature and water vaporpressure across porous partitions (i.e., plant leaves).Pressure is higher on the warm side and on the humidside of a partition, which can result in pressurizationand airflow within the plant. In a study of water lilies,the external pressure was greatest in the youngestleaves, causing airflow into the leaves, down thepetioles to the rhizomes, and back up to the olderleaves where the air was vented back to the atmo-sphere. Internal pressurization and convectivethroughflow driven by gradients in temperature andwater vapor pressure seem to be common attributes ofa wide range of wetland plants, including species withcylindrical and linear leaves (e.g., Typha, Schoenop-

lectus, Eleocharis) (Brix, 1993).

Another type of pressurization is called venturi-induced convection. Wind passing over the wetlandflows at different velocities, with lower velocitiesoccurring near the water surface because of drag. At

Lacunae

Lenticels

Aerenchymoustissues

Figure 3–7 Features of an emergent-hydrophytic plantstem that allow movement of gases to andfrom the root zone

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lower wind speeds, the pressure is greater. Thus, air isdrawn into broken stems and culms closest to thewater, circulated within the root system, and movedthrough the lacunae to points of lower pressure in theupper leaves and shoots. From there it is exhausted tothe surrounding atmosphere (see figure 3–8).

The special structural features noted here do morethan provide a means of respiration in the roots andrhizomes. In some cases an amount of O2 exceedingthe respiratory requirements of the roots and rhizomesoccurs, resulting in O2 exuding into the adjacent soiland creating microscopic aerated zones amid other-wise anaerobic conditions. The amount of O2 leakagefrom diffusion has been reported to be in the range of0.02 to 12 g O2/m

2/day (Brix and Schierup, 1990; Brix,1993; and Armstrong et al., 1990) although highervalues have been reported. Wetland plants that have apressurized flowthrough mechanism for transportingoxygen to the roots and rhizomes have a greaterpotential for leakage and rhizosphere oxidation thanthose based on passive diffusion or pressurizedmechanisms without flowthrough (Brix, 1993).

(4) Role of emergent macrophytes in the

treatment process

The primary function of emergent herbaceous vegeta-tion is not to remove nutrients and other pollutantsthrough plant uptake; rather, it is to facilitate wastetreatment. As facilitators, these plants play severalroles in the treatment process:

• source of microbial substrate• facilitator of nitrification/denitrification• water and pollutant transporter• users of nutrients• filter• source of shade• source of new soils and sediment

Source of microbial substrate—Wetland plantsprovide solid surfaces or substrate on which bacteriaand fungi grow. Fallen leaves, stems, flowers, andother residue from aging plants provide a large amountof surface area on which the treatment organismsthrive.

Wind velocity (v)

Air is drawninto the rootzone throughbroken stems

V1, P1

V1>V2P1<P2V1, P1=V2, P2

V2, P2

Figure 3–8 Illustration of venturi-induced convection throughflow as demonstrated in Phragmites australis (modified fromBrix, 1993)




The populations of organisms that inhabit the sub-strate are the driving force in the treatment process,causing pollutant concentrations to dramaticallydecrease as wastewater passes through the wetland.Reed et al. (1995) indicates that the micro-organismsthat populate the submerged plant stems, fallen leaves,roots, and rhizomes are responsible for much of thetreatment within the wetland. Kadlec and Knight(1996) state the complex mixture of plant litter invarious stages of decomposition and its highly produc-tive biological communities are responsible for 90percent of the overall treatment within surface flowwetlands. Thus, the principal function of the emergentherbaceous vegetation is to provide substrate essentialto the treatment process.

It becomes evident that the greater the surface area ofthe wetland, the greater amount of substrate presentand, hence, the greater the effectiveness of the wet-land. This assumes complete submergence of the litterand adequate contact time between wastewater andattached micro-organisms.

Facilitator of nitrification/denitrification—Animportant function of the treatment wetland is toremove nitrogen. A large fraction of the nitrogen inanimal waste treatment wetlands is lost through vola-tilization (see 637.0303). However, nitrogen can alsobe lost through a series of processes that lead tonitrate (NO3) being converted to N2 gas, which isliberated to the atmosphere. (Refer to figure 3–4, thenitrogen cycle, and table 3–5.)

Wastewater entering a surface flow wetland from awaste treatment lagoon or waste storage pond gener-ally has little or no dissolved oxygen. Therefore, thenitrogen entering the wetland is either in the form of

organic N or ammonia. The conversion from ammoniato nitrate is impossible unless the wastewater is some-how aerated, since aerobic bacteria are needed tomake this conversion. Here is where the unique prop-erties of the wetland plants become important, asexplained in the conceptual model that follows.

As wastewater is drawn into the soil profile to satisfythe water requirements of the plants, it enters a zonethat is basically devoid of oxygen (anaerobic), thusprohibiting the oxidation of ammonia to the nitrateform (NO3). However, some O2 seeps from the rootsand rhizomes of the plants to form microscopic zonesof aeration within the root complex (fig. 3–9). Withinthese aerobic zones, conditions are conducive for thegrowth of aerobic, nitrifying organisms that convertammonia to NO3. Some of this soluble form of nitro-gen is used by the plants, but some migrates back intothe surrounding anaerobic environment. Within theanaerobic zone, special types of bacteria calleddenitrifiers use NO3 as a source of oxygen for respira-tion and, in the process, convert the NO3 to N2 gas,which then passes from the soil to the water columnand then to the atmosphere.

Field-scale research to determine the actual amountsof O2 exuded into the root zone and the extent towhich nitrifying and denitrifying organisms make theconversions is still limited. Wetland systems are socomplex in terms of types of plants, soils, and a hostof other related factors that could influence oxygentransfer and biological activity, that the loss of N,however it occurs, is currently explained in terms ofgeneral rate constants based on influent and effluentsampling rather than on kinetics of individual micro-bial processes (Kadlec and Knight, 1996).

Table 3–5 Processes involved in the conversion of organic and ammonia N to nitrogen gas

Process - - - - - - - - - - - - - - - - - - - - - - - - - Conversion of N - - - - - - - - - - - - - - - - - - - - - - - - - Condition requiredfrom to

Ammonification Organic N (Org-N) Ammonia (NH3 + NH4) Anaerobic or aerobic

Nitrification Ammonia (NH3 + NH4) Nitrite (NO2) and Nitrate (NO3) Aerobic

Denitrification Nitrate (NO3) Nitrite (NO2) and N gas (N2) Anaerobic

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Water and pollutant transporter—As plants drawwater into the soil profile to satisfy their normal waterrequirements, they also bring various ionized pollut-ants into the matrix. As noted in section 637.0303,Treatment process, these potential pollutants can beinactivated through ion exchange, adsorption andprecipitation, complexation, and oxidation and reduc-tion. Without the plants serving as pumps to draw thewastewater into the soil, these reactions would notoccur.

Users of nutrients—Plants use nitrogen, phospho-rus, and the full range of minor nutrients. The amounttaken up by the plants is generally small in relation tothe full nutrient load in animal waste constructedwetlands. Nutrient utilization becomes especiallyimportant if plants are harvested. Otherwise, a highpercentage of nutrients taken up by the plants arereturned to the system as leaves and stems die anddecay during senescence. A small percentage becomesstored in the accretion, some is stored within the rootsand rhizomes, and some escapes the wetland in theeffluent.

Filter—The matrix of plant stems and litter traps andretains a large fraction of the solids that enter thewetland. In addition, the plant/litter matrix slows themovement of water as it passes through the wetland,causing solids to settle. Thus, the plants facilitate the

breakdown of organic matter by allowing more timefor biochemical conversions to take place.

Source of shade—By shading the water, plants helpregulate water temperature and reduce algal popula-tions. The reduced concentration of algae preventslarge daily swings in pH and dissolved oxygen concen-trations. It also results in a lower concentration ofsuspended solids in the wetland effluent. This is espe-cially important if the wetland has a permitted dis-charge. If the effluent is land applied using sprinklerirrigation equipment, the reduction of algae, especiallythe filamentous varieties, will reduce problems relatedto clogged pumps and nozzles.

Source of new soils and sediment—Over time, alayer of peat-like material gradually builds up on thefloor of the wetland through a process called accre-tion. This material, sometimes referred to as new soilor deposited sediment, consists of plant residue, theremnants of the microbial organisms that were part ofthe treatment process, and nondegradable or slowlydegradable solids trapped by the plants. The accretionrate is typically 0.08 to 0.39 inch per year for lightlyloaded surface flow wetlands for municipal wastewa-ter treatment (USEPA, 1999). While TSS concentra-tions in pretreated influent to animal waste SFwetlands are typically higher than those for mostmunicipal systems, the total annual sediment load to

Figure 3–9 O2 seepage and its interactions with N within the root zone

O2

O2 seepagefrom roots

O2

O2

N2

NH3

O2

O2

NO3

Anaerobiczone

Aerobiczone

Conversion of NH3 to N2 gas

NH4 to NO3 = nitrificaiton (aerobic)NO3 to N2 = denitrification (anaerobic)




municipal wetlands is expected to be higher becauseof a much greater annual influent volume. Although nodata are available on long-term accretion rates foranimal waste constructed wetlands, a rate of 0.5 inchper year appears ample based on a comparison of datafrom municipal and animal waste systems. Some ofthe phosphorus, nondegradable solids, and metals arepermanently trapped in this layer. Accretion should beconsidered when designing embankment heights.

637.0305 Planning for aconstructed wetland—thesystems approach

An agricultural waste management system (AWMS)may have numerous components. If treatment isneeded, a constructed wetland could be integratedinto the total system along with other structural,vegetative, and management components. Like othercomponents, the wetland must be examined in light ofother considerations, such as economics, odor control,wildlife enhancement, and regulations. Figure 3–6illustrates the interrelationship of the key functionalcomponents of the AWMS and shows, through a Venndiagram, how the functional components are envel-oped by other considerations.

All three of the key functional components are part ofa constructed wetland. The embankments and waterlevel controls are structural components. The wetlandplants and grass on the embankments are vegetativecomponents, while all aspects of controlling waterlevels and maintaining vegetation and embankmentsare management considerations. In the Venn diagram,note the overlap between components. The wetland isonly one component of the total system, and interac-tion of all components should be addressed in anoverall AWMS plan. Water management, nutrientmanagement, and other aspects of the system aresubsets of the AWMS plan. For a more detailed de-scription of agricultural waste management systemsplanning, see the NRCS Agricultural Waste Manage-ment Field Handbook (USDA, 1992).

Although the constructed wetland is part of a system,some planning factors specific to the wetland compo-nent must be addressed. Listed below are some keyfactors to consider, with a brief explanation of each.An interdisciplinary team, consisting of engineers, soilscientists, geologists, agronomists, biologists, andothers, must be involved in the site-specific details andmethods for integrating this component into the sys-tem.

3–21




(a) Pretreatment

Wastewater from all confined animal feeding opera-tions must be treated before it is discharged to aconstructed wetland. Raw, untreated effluent typicallycontains concentrations of solids, organic matter, andnutrients high enough to kill most wetland plants.

Waste treatment lagoons, waste storage ponds, andsettling basins have been used for pretreatment, butthe selection depends on the characteristics of the rawwastewater and the desired level of treatment. For

instance, an underground tank has been used to col-lect runoff from an open lot at a small dairy before theeffluent is discharged to a wetland, and the resultswere satisfactory. However, solids must be removedregularly in such situations, and the use of a septictank or a small settling basin is impractical in mostsituations where a large number of animals are in-volved or where the solids cannot be removed on aregular basis.

S

M V

SVM

VM

SM SV

VVegetation

MManagement

SStructures

Examples of structures include

• Lagoons• Constructed wetlands• Waste storage ponds

Examples of vegetation include

• Cropping sequence• Wetland vegetation• Critical area treatment

Examples of management include

• Water management• Water level control• Irrigation scheduling• Nutrient management• Soil testing• Wastewater analysis

Components include

• Structures• Vegetation• Management

Other considerations include

• Economics• Water quality• Air quality• Wildlife• Regulations/permits• Social factors• Aesthetics

Figure 3–10 Venn diagram of agricultural waste management system




(b) Wastewater characterization

The characteristics of the wastewater being dis-charged to a wetland must be determined in advanceto see first if the pollutant load will be too great for thewetland and then for the purpose of designing thewetland. The wastewater characterization shouldaddress both the pollutant load and the volume pro-duced. Laboratory testing should be used to deter-mined the pollutant loads, and measurements made todetermine volumes produced. Estimates for pollutantload and volume produced are necessary for newsystems. A further explanation of the influent charac-terization process follows.

(1) Pollutant load

For purposes of design, the wastewater pollutant loadcan be characterized by estimating techniques or byanalyzing the supernatant of the pretreatment facility.Estimates must be used if the system is new and thepretreatment facility has not yet been installed or isnot fully operational. However, for design of a con-structed wetland that will be added to an alreadyoperational waste management system, it is alwaysbest to use laboratory test data for the actual wastewa-ter proposed to be treated by the wetland.

If a waste treatment lagoon or other pretreatmentfacility is in place and nearly full, a representativesample of the supernatant should be collected andanalyzed for total Kjeldahl nitrogen (TKN), ammonianitrogen (NH3 + NH4

+ – N), total phosphorus (TP),total suspended solids (TSS), pH, and 5-day biochemi-cal oxygen demand (BOD5). Ideally, samples should becollected during several months to reflect both warm-season and cool-season conditions. Samples mustrepresent the conditions when the pretreatment com-ponent will discharge to the wetland.

Estimates of wastewater strength can be made usingtables and other information in the NRCS AgriculturalWaste Management Field Handbook or in other profes-sional engineering publications. The estimates shouldonly include the supernatant or that part of the waste-water stream that will be discharged to the con-structed wetland. For instance, data tables may indi-cate that the nitrogen load can be reduced by 80percent in an anaerobic waste treatment lagoonthrough volatilization. However, half of the remaining20 percent may be retained in the settled sludge. Inother words, only about 10 percent of the original N

may be available for discharge to the wetland throughthe supernatant.

(2) Volume produced

A reasonable degree of accuracy is needed in deter-mining annual and seasonal wastewater flows. Infor-mation about volumes is needed not only for designingthe wetland, but also for planning effluent storage andland application requirements. The total volume ofwastewater produced and entering the wetland in-cludes input from such sources as manure, whichdisplaces water in the pretreatment facility, flush-water, and rainwater. (For further information, seesection 637.0306(k), Design of surface flow wetlands,Water budget.)

(c) Site evaluation

An onsite evaluation is essential to determine if anyphysical restrictions will prevent installation of thewetland or require modifications in design, layout, andoperation. Soil maps, contour maps, aerial photos, andother "office" tools should be used in the evaluation.Some of the factors that should be considered duringthe onsite evaluation are noted in this section.

(1) Soils

Soil borings or backhoe pits should be dug at severallocations within the boundaries of the proposed wet-land site. Borings or pits should extend to a depth of atleast 2 feet below the proposed constructed bottomelevation of the wetland to determine if permeableseams, shallow bedrock, or high water table arepresent and to evaluate soil permeability.

The hydraulic head (h) is relatively small for con-structed wetlands (usually less than 18 inches); there-fore, the potential for seepage is expected to be mini-mal, assuming a moderately clayey soil is available ora well-compacted liner is installed. However, a de-tailed evaluation of potential seepage should be con-ducted at questionable sites (sandy soils, underlyinglimestone rock). To reduce the potential for seepage,soils should contain a relatively high concentration ofclayey material. Soil classified as clay, sandy clay,sandy clay loam, or clay loam is suitable for use in awetland. Clayey soil may inhibit the growth of somewetlands vegetation, but traditional plants, such ascattails, bulrushes, and reeds, have adapted to thistype soil.

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If the soil in the top 12 to 15 inches (30.5 to 38 cm) ishighly permeable (i.e., sandy) or a sand or gravel seamis located within this layer, the surface material shouldbe removed and a compacted clay or fabricated linerinstalled. Once the liner is installed, the original mate-rial can be replaced. Specific guidance for determiningwhen a liner is needed and details for its design are inthe NRCS Agricultural Waste Management Field Hand-book, appendix 10D.

Since the rooting depth of most surface flow wetlandplants is typically less than 12 inches (30 cm) andabout 80 percent of the root mass for most emergentplants is in the top 6 inches (15 cm) of soil, the top ofthe liner should be 12 to 15 inches (30 to 38 cm) belowthe intended surface of the wetland. In other wordsthe medium for plant growth that overlies the linershould be at least 12 inches thick.

A soils investigation also determines the depth to andtype of bedrock. A liner should be considered if bed-rock consists of easily solubilized limestone or iffractured sandstone is within 3 feet of the proposedwetland bottom. The characteristics of the soil andsoil depth should be carefully evaluated in this case.

(2) Effluent storage

Wetland effluent must be stored unless permits havebeen obtained to allow for its discharge to surfacewater. The storage facility, at a minimum, must belarge enough to contain the effluent volume from thewetland between land application events or otheruses. The storage facility, of course, must also bedesigned to contain runoff water, direct precipitationon its surface, and the input from other sources. Analternative to this type storage is returning the effluentto the upstream pretreatment facility.

A water budget is needed to determine the requiredcapacity of the storage facility, whether it is located ina downstream pond or in the pretreatment facility. Seesection 637.0305(d) Hydrologic and climatologic data,and section 637.0306(k), Water budget.

(3) Topography

The lay of the land impacts the size and layout of thewetland system and the construction costs. All wet-land cells should have a level bottom side-to-side and aflat or nearly level bottom lengthwise. If the land hasconsiderable slope, several cells may need to be in-stalled in series to maintain a relatively constant water

depth. A new embankment is needed with each newcell; thus, more area is needed for the system.

The wetland should fit within the existing topographyin such a way that, wherever possible, earthwork cutsand fills can be balanced during construction. A slightslope in the direction of the outlet end of each cellallows for complete drainage of the cell for mainte-nance. However, the same purpose can be achieved byinstalling a deep zone at the end of the cell that can beused as a sump for pumping and draining the cell. Forfurther information see section 637.0306(f)(1) Wetlandconfiguration, Bottom gradient/maximum length.

(4) Land area

The amount of land used for the wetland and down-stream storage pond depends on the level of treatmentdesired and the topography, as noted above. In somecases the amount of land needed for the wetlandcomponent includes more dry land for embankmentsthan actual wet land or surface water area. The eco-nomic consequences of replacing productive land witha treatment wetland should be evaluated in light ofproduction lost as well as benefits gained. In addition,the installation of the constructed wetland will mean areduction in nutrient content and, therefore, less landneeded for spreading waste at the final applicationsite.

(5) Surface water

The proximity of the wetland to the nearest stream orwaterbody should be noted in the AWMS plan.

(6) Ground water

The depth to ground water and the distance to anddepth of nearby wells must be established. The place-ment of the wetland must conform to state regulatoryrequirements concerning setback distances fromwells.

If the wetland location satisfies the separation dis-tance from a well, but only marginally so, well watersamples should be collected prior to construction andevaluated for fecal coliform and fecal streptococcusbacteria (or other bacteria that may be specified bythe state regulatory office), nitrates (NO3-N), andammonia nitrogen (NH3 + NH4-N). Without precon-struction sampling and testing, it cannot be estab-lished whether the wells were contaminated beforeoperation of the constructed wetland.




If shallow depth to ground water is noted, installationof at least one monitoring well downslope of thewetland or in an area selected by a qualified geologistis suggested. State regulatory officials should beconsulted if a seasonal high water table will be in closeproximity to the bottom of the wetland.

(7) Flood plains

Flood plains are lowland areas that are adjacent torivers, lakes, and wetlands and are covered by waterduring a flood. The ability of the flood plain to carryand store floodwater should be preserved and re-spected to protect human life and property from flooddamage. Preservation of an active flood plain withadequate capacity is also important in maintenance ofstream/riparian ecological function. For this reasonconstructed wetlands should be placed outside theflood plain if possible. Another reason for placingconstructed wetlands outside the flood plains is sothey will not be subject to inundation and damage.

Flood plains are delineated by the frequency that aflood of a given magnitude has the probability ofoccurring, such as the 1-year, 25-year, 50-year, and100-year flood events. If site conditions require loca-tion of constructed wetland within a flood plain, itshould be protected from inundation or damage fromat least the 25-year storm event. Of course, if planningand design for a larger flood event is required by laws,rules, and regulations, such an event should be the oneused. Important questions to consider if a constructedwetland is being planned within a flood plain are

• Will the installation of the wetland cause up-stream or cross-stream flooding during a floodevent?

• How much will it cost to protect the wetland anddownstream storage pond from being over-topped by the design flood event?

The state regulatory agency and, possibly, the Corps ofEngineers and the Federal Emergency ManagementAgency (FEMA) may need to be consulted whenconsidering placement of the wetland and storagepond within the flood plain.

(8) Fencing

Fencing around the wetland may be required by stateregulations, or it may be needed because grazinganimals could have access to the area. Grazing animals(cattle, goats, sheep) can seriously damage wetlandplants and the embankments. Fencing or other

preventive measures may be used to exclude burrow-ing animals, such as nutria and muskrats, both ofwhich have been a problem in constructed wetlands.While there are cost benefits to not including fencing,there are also advantages to having it.

(9) Jurisdictional wetlands

The constructed wetland should not be planned for anarea defined as a jurisdictional wetland. A technicalspecialist trained in how to make wetland determina-tions should evaluate the site if there is any doubtabout this issue.

(10) Sociological factors

If the livestock facility and other waste managementcomponents are already in place, the addition of atreatment wetland should be of little concern to neigh-bors as compared with other more noticeable compo-nents. Since odors are often the major issue withlivestock facilities, the addition of the wetland shouldbe promoted for its benefits to air quality. (See section637.0302, Benefits of SF wetlands for animal wastetreatment.) Nevertheless, the location of the wetlandcan still be a concern simply because of its proximityto property lines or because of the types of wildlifethat might be attracted to these systems.

Although serious mosquito problems have not beenreported at most animal waste constructed wetlands,the possibility for problems exists. Mosquitofish maybe able to survive in some wetlands for treating live-stock wastewater and provide a natural control ofmosquito breeding. If mosquito problems occur, con-trols may include scheduled manipulation of waterlevels or the application of a bacterial insecticide, suchas Bacillus sphaericus.

(d) Hydrologic and climatologicdata

Data on precipitation, pan evaporation, and tempera-ture are needed for design of the wetland and thedownstream storage pond. The data must be gatheredduring the planning process. Rainfall and evaporationdata, along with other inputs, are used to determine

• annual flow through the wetland, which is usedin the Field Test Method to size the wetland

• hydraulic retention time in the wetland

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• effluent volumes and, hence, the size of theeffluent storage facilities, whether locateddownstream or upstream

• overall water budget, which is important inplanning the land application component of thesystem

All sources of direct precipitation and runoff must beconsidered in determining the annual flow rate for thedesign equation. This may include direct rainfall on thewaste treatment lagoon and wetland as well as runofffrom embankments, roofs, open lots, and other areasdraining into the system. This information is combinedwith data on manure and flushwater volumes to deter-mine monthly and annual flows into the wetland. It isalso key to designing for dormant-season storage andestablishing land application requirements.

The annual ET within a wetland is presumed to beequivalent to lake evaporation. Lake evaporation isgenerally considered to be about 80 percent of panevaporation. ET losses in a constructed wetland canexceed a livestock facility's wastewater productionduring the warm season of the year. Where this willoccur, a continuous flow through the wetland must beassured by managing the upstream treatment facilityor by introducng water from another source to preventthe wetland from drying out.

Temperature data are used in equations to size thewetland. If the wetland is being designed for a dis-charge, average monthly ambient temperature for thecoldest month should be used for water temperature.

A wetland system can be designed for year-roundoperation even where ice will cover the wetlandthroughout most of the winter. In these cases, theanticipated thickness of the ice and expected maxi-mum depth of wastewater flow are considered alongwith other factors. However, this type operation is notrecommended for animal waste constructed wetlands.

If wastewater is stored during the winter months andif a discharge is planned, the average monthly tem-perature for the coldest month during the dischargeperiod should be used for design. However, if thewastewater is released to the wetland only during thewarmer months and if the wetland is used to reducenutrients to a specific level required by the nutrientmanagement plan for the land application area, then

the average temperature over all months of the warmseason should be used in design.

No hard and fast recommendations are provided in theliterature for hydraulic detention time. However, it isobvious that some fraction of time is necessary forbiological processes to reduce concentrations of mostpollutants. Reed, et al. (1995) have suggested that ahydraulic retention time of 6 to 8 days is necessary toprovide for oxygen transfer in fully developed rootzones to affect desired levels of nitrification. This andother limited information for other pollutants suggestthat a minimum detention time should be 6 days.

(e) Regulatory requirements

Planning must consider applicable regulations govern-ing the installation of constructed wetlands. Theywould include regulations pertaining to jurisdictionalwetlands, odors, and setback distances from propertylines, wells, neighboring houses, streams, roads, andother areas of concern.

(f) Impacts on wildlife

Some concern may exist regarding the potential fortransmission of diseases and the impact of the bio-accumulation of toxic substances to migratory ani-mals. The USEPA (USEPA, 1999) indicates that "quan-titative data of direct or indirect toxic effects towildlife in treatment wetlands are generally lacking."However, the document acknowledges that somepotential for detrimental effects to wildlife may existbecause of the chemical forms of some toxic sub-stances. However, they also indicate that "wetlandenvironments are typically dominated by plant andanimal species that are hardier and less sensitive topollutants than more sensitive species that may occurin other surface water."

Given the wide use of municipal and industrial treat-ment wetlands throughout the world and the paucityof data reflecting damage to wildlife, it appears thattreatment wetlands present a low risk for transmissionof disease or for bio-accumulation in any migratoryanimals, especially those that may be associated withanimal waste. Planners might also take into accountthe fact that migratory animals have traditionally had




Operation, Maintenance, and Monitoring Checklist

Suggested time Check Action

Daily Inlet and outlet pipes, water level (Water levels may Adjust as needed.be a clue to short circuiting caused by burrowinganimals.)

Monthly Embankments, emergency bypasses, and fences Record dates that embankments(Ensure that no damage has occurred from animals.) were mowed.

Quarterly Wastewater sampling at inlets and outlets. Check for When samples are collected fornutrient concentrations (TKN, NH3+NH4-N, NO3-N, analysis, measure flow rates atand TP) using a composite sample approach. inlets and outlets using a bucket

and stopwatch.

As desired Identify wildlife. Record wildlife identified, includingbirds, amphibians, reptiles, andinsects (a good family or youthgroup project).

When needed Recordkeeping required as part of the comprehensivenutrient management plan.

access to other types of animal waste practices (openfeedlots, treatment lagoons), and the installation of aconstructed wetland would probably provide nogreater danger than existing systems.

(g) Operation, maintenance, andmonitoring

The decisionmaker needs to keep certain records onoperation and maintenance as an aid to ensuring thatthe system continues to function as required. At aminimum, the inlet and outlet pipes should be checkeddaily because clogging by various types of debris canbe a problem. A limited checklist schedule follows:

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637.0306 Design of sur-face flow wetlands

(a) Background

The design of wetlands for animal waste treatment, aspresented here, uses best available technology basedon data from a number of animal waste treatmentwetlands throughout North America and on proventechnology in the field of municipal waste treatmentwetlands. As with the design of other biological treat-ment processes, the design of treatment wetlands isnot an exact science because biological processes areoften subject to influences that are highly unpredict-able and variable, such as climatic changes. Neverthe-less, the state of the art has advanced considerably,and wetlands can be sized and treatment performancepredicted within a fairly high degree of accuracy, giventhe fact that anomalies occur from time to time.

In the early 1990's, the Agricultural Stabilization andConservation Service, now the Farm Service Agency,initiated a trial cost-share program for constructedwetlands to treat wastewater from livestock andaquaculture facilities. Technical guidance was neededto support this program. Only a few animal wasteconstructed wetlands were in place at that time so theamount of data on treatment efficiencies on which tobase this guidance was limited. Therefore, to meet theneed for technical guidance, the NRCS National Head-quarters formed an interdisciplinary team to reviewavailable information on constructed wetlands anddevelop requirements for planning, design, construc-tion, operation and maintenance, and monitoring ofconstructed wetlands. The document resulting fromthis effort, Constructed Wetlands for Agricultural

Wastewater Treatment Technical Requirements, waspublished August 9, 1991. This chapter and PracticeStandard 656, Constructed Wetland, replace thesetechnical requirements.

The technical requirements were issued with a cau-tion: "Significant parts of the technology are not wellunderstood. Consequently, caution should be exer-cised in approving constructed wetlands outside theASCS cost sharing program." They further indicate thatthe performance of constructed wetlands developed

under the program should be monitored with assis-tance of university personnel and State natural re-source and regulatory agencies.

Two procedures were presented: presumptive methodand field test method. The presumptive method isbased on estimates or presumptions about certainpollutants entering the wetland. With this approach anestimate is made of the amount of BOD5 or nitrogenproduced by the animals and the amount lost throughtreatment before entering the wetland. The presumedamount of influent BOD5 or N was then applied to agiven areal loading rate (i.e., 65 lb BOD5/ac/d) todetermine wetland size. This methodology was takenfrom design information developed by TVA and usedin 1989 to design a treatment wetland for a swineresearch facility at Auburn University's Sand MountainExperiment Station in Alabama. The design was basedon a fixed areal loading rate that is intended to providetreatment to the level required for municipal con-structed wetland effluent to be discharged meeting thestandard discharge limit of 30 mg/L of BOD5 or less.Since constructed wetlands for animal waste treat-ment are generally not designed for discharge, use of adesign loading rate meant to provide treatment to alevel to allow discharge may be treatment in excess ofwhat is actually needed.

The field test method was based on equations devel-oped by Reed et al. (1988). This approach was typi-cally applied to municipal treatment wetlands. Itassumes that samples of wastewater in the pretreat-ment facility can be analyzed before designing thewetland. Information on a given influent and expectedeffluent BOD5 or total nitrogen (TN) concentration,average daily flow rate, temperature data, decay rateconstants for given pollutants, average depth of thewetland, and an effective wetland volume factor wouldbe entered into an equation to determine the surfacearea. The effective wetland volume factor, sometimescalled porosity, is the amount of wetland water vol-ume not occupied by plants and expressed as a deci-mal.

The methods presented in the NRCS technical require-ment assumed that the effluent concentration wouldnot exceed typically allowed discharge limits forBOD5, ammonia, and total suspended solids. Establish-ment of these limits for designing the wetland was notintended to encourage discharges, but was, rather, toserve as a benchmark and to promote consistency in




design throughout the country. Moreover, the NRCSguidelines stated that effluent could be dischargedonly if appropriate Federal, State, and local permitrequirements were satisfied. Otherwise, the guidelinesrequired that the wetland effluent be collected in astorage facility and held until it could be land appliedor recycled.

After several years of evaluation and after the nationaldata base on animal waste constructed wetlands wascompiled (CH2M Hill and Payne Engineering, 1997), itbecame apparent that the original design methodswere in need of modification. It was also clear thatwetlands could be sized for nutrient management orodor control (see section 637.0302, Benefits of surfaceflow wetlands) rather than sizing to satisfy regulatorydischarge requirements (Payne and Knight, 1997;Payne and Knight, 1998).

As a result of these findings, a modified presumptivemethod and a new field test method were developed.These methods are based on new equations advancedin the larger field of wetland design (Kadlec andKnight, 1996) and on data from many animal wasteconstructed wetlands (CH2M Hill and Payne Engineer-ing, 1997; Payne and Knight, 1998). The revision ofthese approaches to design is presented here.

The primary goal of both approaches is nutrient man-agement, as described in section 637.0302, Benefits ofsurface flow wetlands for animal waste treatment. Inother words, the wetland is sized so that the totalannual nutrient load (TN or TP) in the wetland effluentmatches the annual needs of the crops at the final landapplication site. The land area available for spreadingwastewater is assumed to be the limiting factor.

The earlier presumptive model (USDA, 1991) was aone-size-fits-all approach with the goal being to reducepollutant levels to those allowed for discharge (i.e., 30mg/L BOD5). No provision was made for adjusting theoutflow concentrations to some value other than thosefixed by NPDES permit requirements. The previousfield test model could be used for that purpose, butprocedures for doing so were not discussed.

The newer models use an areal loading technique todetermine wetland size versus volumetric loading. Theearlier presumptive method used this approach, butthe earlier field test method was based only on volu-metric loading.

Areal loading is based on the premise that a largefraction of the biological treatment within the wetlandis associated with micro-organisms attached to thesurfaces of submerged litter, fallen leaves, soil, andplant stems. As noted in section 637.0304, Vegetation,as much as 90 percent of the treatment may be associ-ated with vegetative surface area. Thus, raising thewater level to increase detention time does not pro-duce a proportional increase in treatment perfor-mance. This is because the additional substrate addedfrom the newly submerged plant stems is small incomparison to the amount of substrate already sub-merged.

Therefore, it has been concluded that surface area ofthe wetland is paramount to effective treatment asopposed to water depth. Consequently, surface area ofthe wetland is determined by theoretically applying agiven amount of a particular pollutant over some unitof surface area per unit of time. Units of loading areexpressed in such terms as pounds per acre per day. Itshould be understood, of course, that the use of suchunits does not imply that influent wastewater issprayed uniformly over the entire surface area of thewetland; rather, it is simply an expression needed toquantify the relationship between rate applied andsurface area of the treatment unit.

(b) Wastewater storage

Unlike municipal wetland systems that typically havepermits to discharge to surface water, constructedwetlands for treating livestock facility wastewater aregenerally not designed for discharge. Rather, theeffluent from an animal waste constructed wetland iscollected, stored, and then applied to the land or usedfor other purposes. The storage period may be thedormant season when wastewater cannot be landapplied, or in warmer climates where year-roundapplication occurs, it may simply be the plannedperiod between applications.

(1) Dormant season storage

Wastewater, whether treated or not, must be storedduring the dormant season when conditions do notallow its environmentally safe land application. Since aconstructed wetland is capable of providing treatment,although at a reduced level, during the dormant sea-son, its operation can continue even though the efflu-ent cannot be immediately land applied. However, a

3–29




downstream storage must be provided for the treatedeffluent generated during this period. On the otherhand, if it is desired to operate the wetland only whenits treatment performance will be at or near optimum,the wetland's operation is ceased during the dormantseason. This requires that the wastewater generated bythe livestock operation be stored in a facility upstreamof the wetland. Even then a storage facility down-stream of the wetland may be needed.

Developing water budgets based on how the wetlandwill be managed is essential in determining this stor-age requirement. If the wetland is managed to beeither empty or nearly empty at the beginning of thedormant season, the wetland itself may be capable ofstoring all or part of the precipitation falling on itssurface and embankments. Downstream storage mustbe provided for the part the wetland itself cannotstore. Of course, if the wetland is operated so it is atfull depth at the beginning of the dormant season,downstream storage requirements will not be offset bystorage capabilities of the wetland.

Operating the wetland during the dormant season willresult in some reduction in treatment efficiency. Thismust be accounted for with a temperature adjustmentfactor in the Field Test Method of design. Design forcold weather operation must also counter the effectsof freezing on pipes and on the overall hydraulics ofthe system.

(2) No dormant season storage (annual

operation)

When the constructed wetland is operated for theentire year (annual operation), dormant season stor-age is not required upstream of the wetland. However,pretreatment ahead of the wetland is still needed toremove settleable solids and reduce the concentrationof other pollutants. The volume of wastewater flowinto the wetland is spread evenly over the year. Con-structed wetland effluent storage would include thatvolume necessary to facilitate managing land applica-tion or other uses and provide management flexibility.

(c) Presumptive method

The presumptive method allows sizing a wetland whenthe animal production facility or pretreatment facilityis not already on hand, and, hence, the actual concen-trations of a given pollutant are not immediately

known. In this case design is based on estimates(presumptions) about the amount of a given pollutantthat will enter the wetland on an average daily basis.Information on pollutant loads is derived from wasteproduction tables and predicted levels of treatmentoccurring within a particular type of pretreatmentfacility. Such information is available in the NRCSAgricultural Waste Management Field Handbook(USDA, 1992) and other recognized technical sources.It should be noted that for an existing system wherethe addition of a constructed wetland is being consid-ered, final planning and design should be made basedon laboratory analysis of the pretreatment facility'seffluent and with use of the field test method.

(1) Procedure

The following steps are taken to design a SF wetlandusing the presumptive method. Example 3–1 demon-strates calculations for each step. The size of thewetland for this example is based on nitrogen as beingthe controlling nutrient. The procedure is given forEnglish units only. If different units are used thanthose suggested, appropriate conversions must bemade.

Step 1 Estimate the average daily and annual TN

loading to the constructed wetland, TNd (lb TN/

d) and TNa (lb TN/yr).

A standard estimating technique, such as those pro-vided in the USDA NRCS Agricultural Waste Manage-ment Field Handbook (1992) or other technical publi-cations, should be used. The estimated influent TN isbased on the amount of TN produced by the animalsless losses occurring during handling, storage, ortreatment prior to discharge to the constructed wet-land.

Step 2 Determine cropland requirement to uti-

lize TNa loading (acres).

This step allows determination of whether furthertreatment of the proposed wetland is needed becauseof excess nutrients. If the computation shows that lessacreage is needed based on nitrogen than is actuallyavailable, then no wetland is needed. However, thefact that the decisionmaker may have a goal thatrequires even more treatment than may be required fornutrient management should be noted and empha-sized. For example, a high quality flushwater may bethe goal.




The recommended method for determining the acre-age needed for land application is to base it on soiltests and accompanying fertilization recommenda-tions. If these recommendations are not available, anestimate can be made following the nutrient budgetingprocedures of AWMFH Chapter 11, Waste Utilization.Regardless of the method used, the losses occurringduring application and the nutrients in the organicform that will not be available during the first yearafter application need to be considered.

Equation 3–1 may be used for this computation. Theannual TN loading to the constructed wetland, TNa, isin terms of pounds per year as determined in step 1.Crop TN requirement is in terms of pounds per acreper year determined as described above. The croprequirement is adjusted to compensate for losses bymultiplying the crop requirement by the percentageremaining after losses occurring during applicationand those following application, such as leaching.

Acreage =TN

Crop TN requirement%TN remaining after losses

100

a

[3–1]

Step 3 Estimate daily total TN required for the

available cropland, Ni (lb/d).

The estimated total daily TN required for the availablecropland, Ni, is determined by multiplying the avail-able cropland acreage by the crop requirement ad-justed to compensate for losses. The crop TN require-ment is in terms of pounds per acre per year and isdetermined as described in step 2. Again, the croprequirement is adjusted for losses as described earlier.

N =Available cropland Crop TN requirement

3%TN remaining after losses

i×

×65100

d yr/ [3–2]

Step 4 Estimate the average daily constructed

wetland influent volume, Qd (gal/d).

Appropriate technical references and local climaticdata are used to estimate the volume of wastewater tobe discharged to the constructed wetland on a dailybasis. Wastewater inputs to the wetland occur fromsuch things as manure displacement, precipitation less

evaporation on the surface from the pretreatmentfacility, precipitation, runoff, flushwater, and otherinputs. Superior to making estimates based on pub-lished data is to measure the volume of wastewatergenerated.

Step 5 Calculate the average daily total TN

effluent concentration needed from the wetland

to satisfy daily input on the available acreage, Ce

(mg/L).

Using the daily TN required for the available cropland,Ni, in terms of pounds per day (step 3), the averagedaily wastewater volume loading, Qd, in gallons perday (step 4), and applying the appropriate conversionfactors, the constructed wetland effluent N concentra-tion (mg/L) is determined.

CN

Qe

i

d

=( )( )

( )119 826,

[eq. 3–3]

where:Ni = TN required for the available cropland (lb/

d) – Step 3Qd = Average volume of wastewater entering

the wetland daily (gal/d) – Step 4119,826 = conversion factor for lb/gal to mg/L

= ××

lb d mg lbgal d L gal

/ . // . /

453592 43 785412

Step 6 Determine areal loading rate to the con-

structed wetland, LR (lb/ac/d or kg/ha/d).

The following equation, in English or metric units asappropriate, is used to determine the constructedwetland areal loading rate (Payne and Knight 1998).

English: LR = 0.609(Ce) – 7.0 [eq. 3–4]

Metric: LR = 0.68(Ce) – 7.88

where:LR = areal loading rate (lb/ac/d or kg/ha/d)Ce = desired wetland effluent concentration (mg/L)

– Step 5

Equation 3–4 is not valid for values of Ce less than 11mg/L. If such high levels of treatment are desired,possibly to meet discharge requirements, use of theField Test Method is recommended.

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Given: A confined swine finishing facility that has 11,500 animals with an average weight of 135 poundsper animal live weight (LW). The wastewater will be pretreated in an anaerobic waste treatmentlagoon with its supernatant containing 20 percent of the original as-excreted TN.

Annual volume of wastewater discharged to the wetland from thewaste treatment lagoon ..............................................................................1,852,800 ft3/yr

Cropland available for wastewater application ...........................................80 acresCrop requirement for TN per acre per year .................................................150 lbNitrogen application losses using sprinkler irrigation equipment ............25% (estimate)

(table 11-6, AWMFH)Losses of nitrogen through leaching .............................................................5%

(table 11-7, AWMFH)Storage for effluent from the wetland ..........................................................45-day storage pond

(results in an additional 10% nitrogen loss)

The proposed constructed wetland is in a climatic region that allows year-round operation. Thephosphorus index determination indicates that wastewater may be applied on the basis ofnitrogen as opposed to applying it based on phosphorus.

Required: The surface area for a constructed wetland to reduce nutrients as required for nutrient manage-ment.

Solution: Step 1 Estimate the average daily and annual TN loading to the constructed wetland,TNd (lb TN/d) and TNa (lb TN/yr):

From the AWMFH, select an average daily production of 0.42 pound TN/1,000-lb LW.

TN = Number of animals Avg. LW TN production N remainingd d( )( )( )( )= ( )( )( )( )=

11 500 135 0 42 1 000 0 2

130 4

, / . / / , .

. /

hogs lb hog lb TN d lb

lb TN d

TN = TN 365 d / yr

365 d / yra d( )( )

= ( )( )=

130 4

47 596

. /

, /

lb TN d

lb TN yr

Example 3–1 Solution using presumptive method

Step 7 Determine surface area of the wetland

(acres).

Determination of the surface area of the constructedwetland is based on the daily TN input from the pre-treatment facility in terms of pounds N per day (step1) and the areal loading rate, LR, in terms of poundsper acre per day (step 6) using the equation:

Surface area =TNLR

d [eq. 3–5]

The equation computes the water surface area for thewetland. The total area required by the constructedwetland is water surface area, embankment arearequirement, and maintenance access area require-ment.




Step 2 Determine cropland requirement to utilize TNa loading, acres:

Acreage =TN

Crop TN requirement

remaining after losses

47, 596 lb TN / yr

acres of available cropland — a CW is needed

a

%

/ /

TN

lb TN ac yr

acres

( )

=

( )

= >

100

150

75

100

95

100

226 80

Note: TN remaining after losses for application is 100% – 25% loss = 75%and for leaching is 100% – 5% loss = 95%

Step 3 Estimate daily TN required for the available cropland:


3%TN remaining after losses

N =80 ac

N = 51.3 lb TN / d

i

i

i

×

×

( )( )( )

65100

150

36575

10095

10090

100

d yr

lb TN ac yr

d yr

/

/ /

/

Note: TN remaining after losses includes:application losses—100% – 25% = 75%leaching losses—100% – 5% = 95%waste storage pond losses after CW treatment—100% – 10% = 90%

Step 4 Estimate the average daily constructed wetland influent volume:The annual volume of discharge to the constructed wetland is given as 1,852,800 ft3/yr

Q ft yr yr d gal ft gal dd = ( ) × ( ) × ( ) =1 852 800 1 365 7 48 37 9703 3, , / / . / , /

Example 3–1 Solution using presumptive method—Continued

3–33




Step 5 Calculate the average daily TN concentration needed from the wetland to satisfy dailyinput for the available acreage, Ce:

CN

Q

lb TN d

gal d

mg L

ei

d

=( )( )

( )=

( )( )( )

=

119 826

51 3 119 826

37 970

162

,

. / ,

, /

/

Step 6 Determine areal loading rate to the constructed wetland, LR:

LR C

mg L

lb TN ac d

e= ( ) −

= ( )( )[ ] −

=

0 609 7 0

0 609 162 7 0

91 7

. .

. / .

. / /

Step 7 Determine surface area of the wetland:

Surface area =TNLR

d

=( )

( )== × =

130 4

91 71 42

1 42 43 560 61 8552 2

. /

. / /.

. , / ,

lb TN d

lb N ac dac

ac ft ac ft

For a wetland with a length to width ratio of 4:1, the required surface water dimensions of thiswetland would be W = 124 ft and L = 497 ft.

Let x = width and 4x = length, then:

4 61 855

61 8554

15 463

124

4 4 124

497

2

22

0 5

x x ft

xft

x

x ft

Length x

ft

( )( ) =

=

= ( )== = ( )( )=

,

,

,.

Example 3–1 Solution using presumptive method—Continued




(d) Field test method

Field testing provides the most accurate way to deter-mine the size of the wetland. Samples of the pretreat-ment wastewater are collected and analyzed, and theinformation is applied to the following equation forboth English and metric units:

English unit:

AQk

C C

C Cta

T

e

i

cw= −( )

−( )−( )

( )0 305 365. ln /

*

* [eq.3–6]

Metric unit:

AQk

C C

C Cta

T

e

i

cw=

−( )−( )

( )ln /

*

*365

where:A = wetted surface area of the wetland (ft3 or m3)0.305 = factor to convert original metric equationQa = annual flow into the wetland (ft3/yr or m3/yr)kT = k20θT-20, rate constant adjusted for tempera-

turek20 = 14 for TN, 10 for NH4-N, and 8 for TP (m/yr)θ = 1.06 for TN, 1.05 for NH4-N, and 1.05 for TP

(dimensionless)T = average operating temperature (°C)Ci = wetland influent concentration (mg/L)Ce = wetland effluent concentration (mg/L)C* = background concentration (mg/L), assumed

to be 10 for TN and 3 for NH4-N (based on anationwide analysis of animal waste con-structed wetlands)

365 = days of the year (d)tcw = days that the wetland will be in operation

(i.e., the length of the growing season)

The basic equation (less the factor 365/tcw) was devel-oped originally for municipal treatment wetlands(Kadlec and Knight, 1996). Rate constants specific toanimal waste constructed wetlands were developedfrom the national data base on animal waste con-structed wetlands (CH2M Hill and Payne, 1997) andapplied to the Kadlec and Knight equation, also calledthe k-C* model.

This model should be used where a pretreatmentfacility is already in place and samples can be readilycollected. An alternative would be to collect samplesfrom the pretreatment facility at a nearby facility thatis expected to have the same characteristics (numberof animals, size of pretreatment facility) and, there-fore, the same wastewater characteristics.

Samples from the pretreatment facility are analyzedfor the constituent of concern (TN, NH4–N, or TP) todetermine wetland influent concentration (Ci). Inaddition, the annual flow (Qa) from the pretreatmentfacility must be calculated as well as the wetlandeffluent concentration for the nutrient of concern.

Average operating temperature used in the equation isbased on the site temperatures when the constructedwetland will be actually operated. For example, if theconstructed wetland is operated only during the grow-ing season with the wastewater stored upstreamthrough the dormant season, the temperature for theequation will be the average for the growing season.This, of course, will require that the stored volume ofwastewater be treated in addition to what is generatedduring the growing season. Provisions for storage havebeen included in the equation with the factor 365/tcw.

The field test method differs from the original fieldtest method presented in the NRCS technical require-ment (USDA, 1991) in that the size of the wetland isbased on areal loading as opposed to volumetricloading. The same is true of both the original and newpresumptive methods. (See prior information on arealversus volumetric loading and the information thatfollows the field test method example.)

(1) Procedure

The following steps are taken to determine the surfacearea for a SF wetland using the field test method.Subsequently, example 3–2 demonstrates the calcula-tions for each step. This example uses English units. Ifmetric units are desired, use the proper units andconversion factors for the equations chosen.

Step 1 Estimate the average daily and annual

constructed wetland influent volumes, Qd (gal/d

and ft3/d) and Qa (ft3/yr).

This step is the equivalent of step 4 in the presumptivemethod. Appropriate technical references and localclimatic data are used to estimate the volume of

3–35




wastewater to be discharged to the constructed wet-land on a daily basis. Wastewater inputs to the wetlandoccur from such things as manure displacement,precipitation less evaporation on the surface from thepretreatment facility, storm runoff water, flushwater,and other inputs.

Step 2 Estimate the average daily and annual TN

loading to the constructed wetland, TNd (lb TN/

d) and TNa (lb TN/yr).

This computation is based on laboratory results ofpretreatment facility effluent and the volume of waste-water in gallons per day (step 1) entering the wetland.

TN TNd i= ( )( ) ×( )−Qd 8 34 10 6.

where:Qd = average daily constructed wetland influent

volume, gal/d (from step 1)TNi = wetland influent TN concentration, mg/L8.34 x 10-6 = conversion factor for mg/L to

lb/gal

TNa = TNd x 365

Step 3 Determine cropland requirement to uti-

lize the annual total N loading (acre).

This is the equivalent of step 2 in the presumptivemethod. If treatment for nutrient management is thegoal of constructed wetland treatment, this step allowsthe determination of whether further treatment of theproposed constructed wetland is needed. If the com-putation shows that less acreage is needed based onnitrogen than is actually available, then no wetland isneeded for nutrient concentration reduction. As notedin the presumptive method, the decisionmaker’s goalmay be something other than nutrient management.The goal could be to improve the water quality forsuch a purpose as a high quality flushwater or dustcontrol. In such cases the issue as to whether thetreatment of a constructed wetland is needed is not anissue and this step could be skipped.

The general equation for determining the croplandarea requirement without a constructed wetlandfollows. The annual TN loading is determined bymultiplying the daily TN loading to the constructedwetland in pounds of TN per day taken from step 2 by365, the days in a year. The crop N requirement is best

based on soil test and fertilizer recommendations. Ifthese recommendations are not available, an estimatecan be developed using the procedure in AWMFHchapter 11. The crop TN requirement is in terms ofpounds of N per acre per year. Regardless of how thecrop requirement is established, the amount must beadjusted for anticipated losses, such as from applica-tion and leaching. In the equation that follows, this isgiven as a percentage of TN remaining after the losses.

Cropland requirement =

TN

Crop TN requirement%TN remaining after losses

a

×100

TNa is the annual TN loading in pounds per year (step2), crop requirement in pounds per acre per year, andTN remaining after losses expressed as a percentage.

Step 4 Estimate daily TN required for the avail-

able cropland, Ni (lb/d).

This is the equivalent of step 3 in the presumptivemethod. The general equation for making this estimatefollows. The crop TN requirement was established instep 3 as was the percentage of TN remaining afterlosses.


365 d / yr%TN remaining after losses

i×

×100

Available cropland is in acres, crop TN requirement isin pounds N per acre per year, and TN remaining afterlosses is expressed as a percentage.

Step 5 Calculate the average daily total N efflu-

ent concentration needed from the wetland to

satisfy daily input on the available acreage, Ce

(mg/L).

Using the daily TN required for the available croplandin pounds per day, Ni, from step 4 and the averagedaily wastewater volume loading in gallons per day(step 1), the appropriate conversion factors are ap-plied to determine the constructed wetland effluent Nconcentration (mg/L).

CN

Qe

i

d

=( )( )

( )119 826,




where:Ni = daily total N required for the available

cropland, lb/d (step 4)Qd = daily total N required for the available

cropland, gal/d (step 1)119,826 = conversion factor for lb/gal to mg/L

= ××

lb d mg lbgal d L gal

/ . // . /

453592 43 785412

Step 6 Calculate kT.

k kTT= −

2020θ [eq. 3–10]

where:kT = rate constant adjusted for temperaturek20 = 14 for total N and 10 for NH4–Nθ = 1.06 for total N and 1.05 for NH4–N (dimension-

less)T = average operating temperature (°C)

Step 7 Determine surface area of the wetland, A

(ft2).

AQk

C C

C Cta

T

e

i

cw= −( )

−( )−( )

( )0 305 365. ln /

*

* [eq. 3–6]

where:Qa = annual flow into the wetland, ft3/yr or m3/yr

(step 1)Ci = wetland influent concentration, mg/L (from

laboratory test results)Ce = wetland effluent concentration, mg/L (step 5)C* = background concentration (mg/L), assumed to

be 10 for total N and 3 for NH4-N based on anationwide analysis of animal waste con-structed wetlands

365 = days of the year, dtcw = days that the wetland will be in operation

(i.e., the length of the growing season)

Step 8 Compute theoretical hydraulic detention

time, td.

t A Dn

Qdd

= × ×

where:A = surface area of constructed wetlandD = depth of water in constructed wetlandn = wetland porosityQd = average daily constructed wetland influent

volume, gal/d

Step 9 Compute winter storage.

Winter storage volume = −( )( )365 t Qcw d

where:tcw = days that the wetland will be in operation (i.e.,

the length of the growing season)Qd = average daily constructed wetland influent

volume, gal/d

3–37




Example 3–2 Field test method solution

Given: The same confined swine finishing operation as the example for the presumptive method withthe following additional information:• Water depth in the constructed wetland is 8 inches. This depth is selected based on plant

species to be used and other design factors.• A wetland porosity, n, of 0.90• The pretreatment effluent contains 412 mg/L of total nitrogen based on testing. Average

temperatures for the site are as follows:

May – Sept Apr – Oct Mar – Nov Jan – Dec(tcw=150) (tcw=210) (tcw=270) (tcw=365)

Average temp (oC) 24.6 22.5 20.3 17.1

Required: The surface area for a constructed wetland for April to October operation with the treatmentgoal of nutrient management to the available cropland.

Solution: Step 1 Estimate the average daily and annual constructed wetland influent volumes:

Q ft yr

Q ft yr yr days ft d

ft d gal ft gal d

a

d

=

= × =

= × =

1 852 800

1 852 800 1 365 5 076

5 076 7 48 37 970

3

3 3

3 3

, , /

, , / / . /

, / . / , /

Step 2 Estimate the average daily and annual total N loading to the constructed wetland:From the laboratory test results, the N concentration = 412 mg/L

TN N concentrationd = ( )( ) ×( )= ( )( ) ×( )=

−

−

Q

gal d mg Llb N d

d 8 34 10

37 970 412 8 34 10130 5

6

6

.

, / / .. /

T

lb N d d yrlb N yr

N TNa d= ( )( )= ( )( )=

365

130 5 36547 632

. / /, /




Step 3 Determine cropland requirement to utilize the annual total N loading:

Cropland requirement =TN

Crop TN requirement% N remaining after losses

=47,632 lb N / yr

150 lb N / ac / yr

75100

acres of available cropland a CW needed

a

×

( )

= > ∴

100

95100

226 80acres

Step 4 Estimate daily total N required for the available cropland


365 d / yr%TN remaining after losses

=lb N / yr

i×

×

( )( )( )

=

10080 150

36575

10095

10090

10051 3

ac

d yr

lb N d

/

. /

Step 5 Calculate the average daily total N effluent concentration needed from the wetlandto satisfy daily input on the available acreage:

CN

Q

lb N d

gal dmg L

ei

d

=( )( )

( )=

( )( )( )

=

119 826

51 3 119 826

37 970162

,

. / ,

, //

Step 6 Calculate kT: For April to October

k kTT=

= ( )( )=

−

−( )20

20

22 5 2014 1 06

16 2

θ

.

.

.

Example 3–2 Field test method solution—Continued

3–39




Step 7 Determine surface area of the wetland: The surface area required for April toOctober operation:

AQk

C C

C C t

ft mg L mg Lmg L

a

T

e

i cw= −( )

−( )−( )

= −( )

−−

= −

0 305365

0 3051 852 800

16 2162 10

412 10365210

3

. ln

., ,

.ln

/ //

*

*

3434 883152402

1 74

34 883 0 378 1 74

34 883 0 9726 1 74

58 967

58 967

43 5601 4

2

2

2

, ln//

.

, ln . .

, . .

,

,

, /.

( )

( )

= −( ) ( )[ ]( )= −( ) −( )( )=

= =

mg Lmg L

ft

ft

ft acacres

Step 8 Compute theoretical hydraulic detention time, td:

tA D n

Q

ft in in ft

ft d

ft

ft d

days

dd

=× ×( )

=( )( )

=( )

=

58 967 8 12 0 90

5 076

35 380

5 076

6 9

2

3

3

3

, / / .

, /

,

, /

.

This satisfies the minimum requirement of 6.0 days. See 637.0305(d).

Step 9 Compute winter storage requirement:

Winter storage requirement = −( )( )= −( )( )= ( )( )=

365

365 210 5 076

155 5 076

786 780

3

3

3

t Q

ft d

d ft d

ft

cw d

, /

, /

,

Example 3–2 Field test method solution—Continued




(2) Summary of field test method

Table 3–6 illustrates how different treatment periodsused in the field test method affect wetland size for agiven set of inflow and outflow concentrations of totalnitrogen. The results are based on the same scenarioas the design in example 3–2.

Values for hydraulic detention time (dt) shown in thistable are based on a wetland porosity (n) of 0.90, anaverage water depth of 8 inches, and a daily flow of5,076 cubic feet per day. The wetland porosity is thevolume of water not occupied by wetland plants andwas originally assumed to be between 0.65 and 0.75.These values, from Reed et al. (1988), were used in theearlier NRCS field test method. However, TVA re-searchers found in one study that plant fill rates forcattails (Typha spp.) were 10 percent; bulrush(Scirpus validus), 14 percent; reeds (Phragmites), 2percent; and woolgrass (S. cyperinus), 6 percent(Watson and Hobson, 1989). In addition, Rogers et al.(1995) reported fill rates of 10 percent for Sagittaria

lancifolia and 7 percent for Phragmites australis.

These data indicate that fill rates presented in theearlier NRCS Technical Requirements (USDA, 1991)were probably too high and, consequently, the valuesfor wetland porosity were too low.

The earlier field test method (a volumetric method)required a determination of dt, which meant that an

accurate measure of water volume within the wetlandbe known. However, its value can be estimated withonly a limited degree of accuracy (as was done in table3–6). This is because mats of vegetation, growth habitof various plants, and other factors can reduce volumeand either impede flow or cause short-circuiting.Estimates of dt can be quite different from measure-ments using more sophisticated approaches, such asdye testing.

For the field test example, the wetland surface area orwetted area ranges from 1.1 to 1.7 acres, with treat-ment period and associated changes in temperaturesignificantly affecting size. Of interest is that the areadetermined with the presumptive model, using thesame number of animals with average weight of 135pounds, was about 1.4 acres. This is the same as thatcalculated for a 210-day operating period for the fieldtest model shown in example 3–2. This does not meanthat the presumptive method and field test methodsare considered comparable for any wetland with a 210-day storage period; it happens to be the same onlybecause of the influent concentration selected for thefield test example. If, for example, Ci for the fieldexample had been 380 mg/L instead of 412 mg/L, withall other factors the same, the wetland surface areawould have been 1.2 acres, while the presumptivemethod acres would remain at 1.4 acres.

Table 3–6 Example of wetland design criteria for an 11,500-head swine finishing facility for different treatment periodswhere Qa = 1,852,800 ft3/yr, Ci = 412, and Ce = 162

May – Sept Apr – Oct Mar – Nov Jan – Dec(tcw=150) (tcw=210) (tcw=270) (tcw=365)

Average temp. (oC) 24.6 22.5 20.3 17.1

kT for TN (m/yr) 18.3 16.2 14.2 11.8

Wetland area (ac) 1.7 1.4 1.2 1.1

td (days) @ depth = 8 in 8.6 7.0 6.2 5.5

Winter storage (ft3) 1,091,375 786,805 482,236 as needed forland application

3–41




(e) Designing for phosphorusremoval

The presumptive method and the field test method canbe used to design for P removal. The changes neededin the two models follow:

Presumptive method:

• Replace the loading rate equations in step 6 withthe following:

English:LR = 0.49(Ce) + 0.51Metric: LR = 0.6(Ce) + 0.6

where:Ce = total phosphorus concentration in mg/L

• Replace other TN-based calculations with valuesfor TP.

Field test method:

• Use the following values for TP in the equationsin steps 6 and 7:

k20 = 8 m/yrθ = 1.05C* = 2 mg/L

(f) Wetland configuration

(1) Bottom gradient/maximum length

Early guidance on constructed wetlands indicated thata gradient in the lengthwise direction is beneficial tofacilitate emptying the wetland for repairs or mainte-nance. While providing a gradient can facilitate empty-ing, the effect it will have on water depth should beconsidered. For instance, a wetland cell with a 0.5percent grade and a water depth of 6 inches at theupstream end will have a water depth of 12 inches at alength of 100 feet and 15 inches at 150 feet. Therefore,if a bottom gradient is used, either by choice or out ofnecessity because of the site conditions, the maximumlength is dependent on the allowable water depth forthe wetland plants that will be used. If a level-bottomwetland is used, length is not an important consider-ation for most animal waste treatment wetlands.However, if large volumes of water are used and thiswater is pumped to a long, narrow wetland cell, resis-tance of the vegetation to the flowing water couldcause incoming water to back up. At one municipalwetland having a 20:1 length-to-width ratio, flow wasso restricted that wastewater overflowed the embank-ment at the inlet end of the system (Reed et al., 1995).

An acceptable alternative to providing a bottom gradi-ent to facilitate emptying is a flat bottom with a deepzone that acts as a sump. The deep zone provides thesubmergence on the suction pipe necessary for thepump to transfer the wetland effluent to land applica-tion, to a downstream holding storage facility, or to anupstream waste treatment lagoon. If an exceptionallylong, level-bottom wetland is planned, intermediatedeep zones should be used. This not only facilitatesdraining the wetland, but also allows effective lateraldistribution of flow during normal operation.

(2) Layout of the wetland

The layout or configuration of a constructed wetlandmay be affected by site conditions. Shape of the site,area available, and lay of the land can influence how aconstructed wetland is configured.

Surface-flow wetlands are generally designed to havemore than one cell. For these multicelled wetlands, thecells are typically arranged in series (end-to-end) or inparallel (side-by-side). The parallel arrangement al-lows two or more cells to receive influent at the sametime; thus, if the inlet on one cell plugs or if a cell isclosed for maintenance, the other cell(s) can keepoperating. The parallel arrangement can also be usedfor alternating treatment, allowing wetting and dryingof cells and, thereby, enhancing treatment perfor-mance. However, this method of treatment requires ahigher level of management. Figure 3–11 is a typicallayout of cells in parallel.

An efficiently designed system has limited short-circuiting of wastewater between inlets and outlets. Inthe ideal system, wastewater flows evenly across thewetland cell throughout its entire length with no stag-nant pools. An inlet consisting of a gated or slottedpipe across the upstream end helps to ensure initialdistribution of flow. Figure 3–12 illustrates efficientand inefficient layouts as related to inlet and outletstructures. (More details about inlets follow.) As watermoves through the plants and detritus, however,channelization of water may occur as a result of thebuildup of islands of roots, rhizomes, and dead vegeta-tion. For long, wide wetland cells, uneven distributionis more apt to occur, resulting in a need to redistributeflow. This can be accomplished by using shorter cellsin series and discharging the effluent of one into adistribution header pipe or deep trench at the up-stream end of a receiving cell. For long cells that havea flat bottom, flow can be redistributed laterally along




the flow path by installing deep zones or trenchesacross the width of the cell at appropriate points. Inlettrenches and redistribution sumps should be at least 3feet deeper than the constructed bottom of the cell toinhibit growth of rooted vegetation (Kadlec andKnight, 1996).

As a rule, the length-to-width ratio for the systemshould be in the range of 1:1 to 4:1. Individual cells

within this overall system may have ratios as high as10:1. In fact, 20:1 length-to-width ratios have been usedsuccessfully. From the standpoint of constructioncosts, however, the square (1:1) wetland is most effi-cient. The cost advantage of the square wetland isoffset by the critical need to provide for distribution offlow to prevent short-circuiting.

Set pipe oulet elevationat bottom elevationfor winter

Pump for recycleand irrigation

1st Stage cells 2nd Stage cells Irrigationline

Recycle line

Animalhousing

Valve

Winter storage

Treatment

Lagoon PondConstructed wetlands

Figure 3–11 Typical layout of waste treatment lagoon/wetland/storage pond system

3–43




Figure 3–12 The effect of wetland layout configuration on effective flow distribution (modified from Kadlec and Knight, 1997)

Inlet

Outlet

Wetlandplants

A. Bad: Preferential flowchannel from inlet to outlet

B. Poor: Large dead zones in corners not in flow path

C. Good: Header pipe with multipleoutlets and footer pipe in rockfilled trench with single outlet pipe

D. Better: Multiple inlets and flowcontrol dikes




(g) Embankments

(1) Design height

Wetland embankments are often the same height.However, a distinction can be made between the outerembankments, which surround the entire system, andinner embankments or dikes that divide the systeminto cells. The outer embankment must be highenough to protect the system from overtopping duringa specific design storm (i.e., 25-year, 24-hour). Theseembankments must have an ungated overflow deviceset at an elevation such that any precipitation thatexceeds the design will pass through it.

Design height for the outer embankment should bebased on the following increments of depth:

• Normal design flow—Based on type of vegeta-tion; typically 8 to 12 inches.

• Accretion—Based on buildup during the designlife of the system; allow 0.5 inch per year.

• Design storm—Includes direct precipitation onthe wetlands plus runoff from embankments and,if inflow to the wetland is unrestricted, precipita-tion on the pretreatment surface, includingembankments.

• Ice cover—If the system will operate under icecover in winter, allow depth equal to ice thick-ness expected during some design period (i.e.,once in 25 years).

• Freeboard—A safety factor of at least 12 inchesis recommended.

• Overflow device—As required by type (i.e., pipe,earthen spillway).

Design height for interior divider embankments mustinclude at least the first three items listed for designheight for outer embankment.

(2) Top width

The top width of dikes used to surround and divide theconstructed wetland must be wide enough to accom-modate the requirements of construction and opera-tion and maintenance. Outer embankments should beat least 15 feet at the top to prevent burrowing animalsfrom draining the system to the surrounding area. Therecommended top width for inside dikes is 8 to 10 feet.This width allows grass to be mowed with tractor-driven equipment and reduces the potential for ani-mals burrowing through the dikes. Narrower dikes orembankments must be cut with a hand mower and areeasily breached by muskrats.

(3) Side slopes

Side slopes should not be steeper than 2 horizontal to1 vertical. Consideration should be given to flatterslopes if needed for slope stability or to accommodatemaintenance.

(h) Liners

The bottom of all wetland cells should be lined eitherwith a compacted clay liner or with a fabricated liner ifthere is potential for ground water contamination.Although the wetland operates under a low hydraulichead environment, seepage is still possible. A liner canhelp to avoid ground water contamination by nitrates.Detailed information on evaluation of soils to protectground water is in the NRCS Agricultural Waste Man-agement Field Handbook, appendix 10D.

If a fabricated liner is needed, the top 12 inches of soilfrom the construction site should be removed andstockpiled. After the liner has been installed, thestockpiled soil is placed on top of the liner to serve asthe rooting medium for the wetland plants. To preventpuncture of the liner during construction, consider-ation should be given to placing 6 to 8 inches of sandon top of the liner before installing the stockpiled soil.Overexcavation or additional fill height, or a combina-tion of both, will be needed to accommodate the sandlayer. Where a liner is installed, care must be taken toensure that it ties in vertically at the embankments,thus preventing any lateral movement under orthrough the embankments. This requirement is thesame for soil and fabricated liners.

(i) Inlet and outlet structures

(1) Inlet structures

A variety of inlet control structures can be used atconstructed wetlands used to treat animal waste. Theymay include an ungated gravity flow overflow pipefrom the pretreatment facility to the first cells of theconstructed wetland, pipes with orifice controls,swivel pipes, and valves.

Inlets may discharge at a point centered on the widthof the upstream end of the cell if the cells are rela-tively narrow and dead zones will not be a problem inthe adjacent corners. Gated pipe that spans the widthof the cell can ensure even distribution and eliminate

3–45




dead zones in the corners. This pipe has precut holesor slots, or it may have gated openings so flow can bemore accurately distributed. Plugging is sometimes aproblem at the inlet to the first cell where influentwastewater is from the pretreatment facility. If this is aconcern, an alternative to a gated pipe is a deep trenchacross the width of the upper end of the cell. An elbowcan be placed on the inlet pipe so that influent water isdischarged downward into the middle of the trench;wastewater should then discharge into the vegetationacross the width of the cell. If the cell is wide, a shal-low dam with multiple slots or weirs across the topcan be placed immediately downstream of the trench.

If wastewater will be stored in the pretreatment facil-ity during winter, the invert elevation at the entranceto the effluent pipe leading to the wetland should be inline with the bottom elevation of winter storage. If thedesign calls for winter storage in the upstream pre-treatment facility, some positive control is needed toprevent discharge to the wetland during this period(i.e., a closed valve). In addition, some positive controlis also needed to ensure that stored wastewater isreleased to the wetland according to a water budgetfor the system. This may mean manually opening andclosing of valves on a daily basis or using a properlysized orifice control based on daily requirements ofthe water budget. Note: Reliance on manually openingand closing valves can be a dangerous option becausethe operator may forget to close a valve, which couldresult in a discharge from the system.

All control devices should be checked daily sinceplugging of pipes and controls can be a problem. Abuildup of a crystalline substance on pipe walls is aproblem in some orifice-control devices. An inletscreen or box screen used around the inlet pipes to thefirst cell can prevent floating debris from entering theline. Small turtles have been known to enter an unpro-tected inlet and clog the pipe. For these reasons, largediameter pipe is preferred over smaller diameter pipe.

(2) Outlet structures

The outlet structure is used to maintain the properwater level in the upstream cell and to control flowrate. Several types of outlet controls are possible. Theyinclude slotted pipes laid across the downstream endof the cell or slotted pipes buried in a shallow trenchof gravel. In each case a T section is placed in themiddle of the pipe to carry water through the embank-ment to a water-level control structure.

The most common water-level control structure usedon wetlands for treating animal waste is an elbowattached with a swivel joint located downstream of thecell for which water level is being controlled (fig.3–13). In other words, water level in the upstream cellwill be at the same elevation as the invert of the down-stream outlet pipe. As the pipe is turned on the swivel,the invert of the pipe is raised or lowered, thus settingwater depth in the upstream cell.

Water can be discharged to a point centered on thewidth of the upstream end of the next cell if the cell isrelatively narrow. If it is wider and there is concern fordead zones in the corners (see fig. 3–12), the swivelpipe can be attached to a header pipe, forming a Ubetween the pipe that exits the embankment and theheader.

Another water level control device is a flashboarddam. This provides a simple way to control upstreamwater level without the problem of plugging pipes.However, the embankment on the downstream sidemust be adequately protected from erosion, and adeep-zone distribution trench may be needed if thedownstream cell is wide.

(j) Water budget

A water budget is essential as it is used in• Determining annual and daily flow rates needed

to determine wetland surface area using thepresumptive and field test design equations

• Sizing the embankments• Scheduling land application• Determining release rates or pumping rates to

the wetland for the in-use period, and sizingpipes, pumps, orifice controls, and other devicesaccordingly

• Sizing the downstream storage pond• Sizing storage for the upstream pretreatment

facility• Determining detention time in the wetland

If several treatment wetlands will be designed, acomputer spreadsheet is recommended to speedrepetitive calculations and assist with accuracy indesign. A sample spreadsheet is shown in table 3–7.




Table 3–7 Sample water balance spreadsheet for 2000 finisher swine with 400- x 400-foot waste treatment lagoon and26,400 square foot constructed wetland

Climate Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec total

Precip. 5.60 5.40 6.00 5.90 4.90 5.00 4.50 4.00 3.80 4.20 5.00 5.20 59.50Pan Evap 3.20 3.80 4.00 4.00 4.30 5.10 5.60 6.20 4.90 4.30 4.00 3.80 53.20Lake Evap 2.20 2.70 2.80 2.80 3.00 3.80 3.90 4.30 3.40 3.00 2.80 2.70 37.4

Items - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Volume (1,000 ft3/mo) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Input Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec total

Manure 11.20 10.10 11.2 10.80 11.20 10.80 11.20 11.20 10.80 11.20 10.80 11.20 131.70Precip. lagoon 74.70 72.00 80.00 78.70 65.30 66.70 60.00 53.30 50.70 56.00 66.70 69.30 793.40Precip. CW 12.30 11.90 13.20 13.00 10.80 11.00 9.90 8.80 8.40 9.20 11.00 11.40 130.90Flush* 0.00 0.00 0.00 120.30 124.30 120.30 124.30 124.30 120.30 0.00 0.00 0.00 733.80Runoff 4.70 4.50 5.00 4.90 4.08 4.17 3.75 3.33 3.16 3.50 4.16 4.33 49.58

Total 102.90 98.50 109.40 227.70 215.68 212.97 209.15 200.93 193.36 79.90 92.66 96.23 1,839.38

Output Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec total

Evap. - lagoon 29.90 35.50 37.30 37.30 40.10 47.60 52.20 57.80 45.70 40.10 37.30 35.50 496.30Evap. CW 4.93 5.85 6.16 6.16 6.62 7.85 8.62 9.55 7.55 6.62 6.16 5.85 81.92

Net Annual w.w. = Total Input = Total Output

Land 0 0 0 210.19 210.19 210.19 210.19 210.19 210.19 0 0 0 1,261.16application(1,000 ft3)

* Fresh flushwater at 15 gal/head/day. If recycled wastewater from the constructed wetland is used, flush = 0.

Figure 3–13 Typical configuration of a water-level control structure

Water level

Rock trench

Embankment top

Swivelelbow

Top of embankment for upstream cell

Elevation of upstream water level

Swivel elbow Water flow from outlet pipe

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(k) Operation and maintenance

Written operation and maintenance (O&M) require-ments for a constructed wetland must be incorporatedinto the AWMS plan to which the wetland becomes acomponent. In addition to the O&M requirement forthe wetland itself, coordination of its operation withother components of the AWMS must also be de-scribed. For further information on developmentAWMS plan see AWMFH, Chapter 13, Operation,Maintenance, and Safety. Recommended requirementsto be included in the AWMS plan for a constructedwetland are described in this section.

(1) Operation

Operation of a constructed wetland includes theadministration, management, and performance ofnonmaintenance actions needed to keep the wetlandsafe and functioning as planned. Annual operationalrequirements are dictated by the water budget, byvisual inspection, by wastewater testing, and by com-mon sense. Some key operational requirements in-clude:

• Maintaining water levels in the wetland cells asappropriate for the vegetation. In cold climateswhere continuous winter operation is involved,increase water levels as needed prior to the firstfreeze.

• Controlling flows into the wetland in accordancewith water budget requirements. Adjust asneeded for drought periods, increasing inflowrates to ensure vegetation at the downstream endof the wetland is kept wet during dry times.

• Ensuring that water levels in the pretreatmentfacility and downstream storage pond are low-ered to appropriate levels in preparation forwinter storage.

• Monitoring treatment performance. Collectsamples and measure flow rates into and out ofthe wetland regularly. Determine treatmentefficiencies and nutrient mass loadings for use inadjusting application rates. Typically, samplesshould be analyzed for total Kjeldahl nitrogen(TKN), total ammonia nitrogen (NH3 + NH4-N),combined nitrite plus nitrate nitrogen (NO2

+ NO3-N), total phosphorus (TP), and ortho-phosphorus (ortho-PO4-P). If a wastewaterdischarge is being considered or if additionalinformation on water quality improvement issought, 5-day biochemical oxygen (BOD5),

chemical oxygen demand (COD), total sus-pended solids (TSS), temperature, and pH maybe required by the state regulatory agency.

(2) Maintenance

Maintenance of a constructed wetland includes ac-tions taken to prevent deterioration of the wetlandcomponents and to repair damage. Regular mainte-nance of the wetland system is essential. If frequentinspections are ignored, rodents can destroy vegeta-tion and embankments, pipes can become clogged,wastewater can short circuit through the cells, and thesystem can become nonoperational in a short time.

A short list of important maintenance items follows.This is not intended to be an all-inclusive list:

• Inspect inlet and outlet structures daily forplugging and damage.

• Inspect embankments at least weekly for dam-age, and make repairs as needed. Control rodentpests through removal or deterrents, such aselectric fences.

• Mow embankments regularly to allow for inspec-tions and to enhance visual appeal.

• Inspect and repair fences as needed.• Inspect vegetation throughout the growing

season, and replace plants that are not perform-ing as expected.

• Inspect and repair pumps and piping systems asneeded.




637.0307 Plant establish-ment and maintenance

Successful plant establishment requires adequate soilpreparation, intact plant materials, appropriate plantspacing, proper planting methods, good timing, suffi-cient soil moisture, and proper water depth. Failure toprovide any of these can be problematic to establish-ment of a successful wetland planting (Kadlec andKnight, 1996). Wetland vegetation maintenance bycomparison to initial plant establishment is not nearlyas simple. Perpetuation of dominance by desiredspecies, maintenance of desired plant cover density,and exclusion of undesirable plant species are allcomplex, problematic goals that cannot always beachieved (Kadlec and Knight, 1996).

(a) Plant sources

In recent years, commercial supplies of wetland plantmaterial have become relatively common. Regulationsrequiring entities that remove or manipulate wetlandsto mitigate the wetland losses have created a highdemand for live, healthy plants for revegetation. Mostcommonly used plants for treatment wetlands can bepurchased for planting or can be harvested locallyfrom existing roadside ditches or pond margins. De-pending on the morphology of individual plants, theplant can be purchased as a bare-root seedling, asterile propagule from a micropropagation laboratory,a senesced root or rhizome, a potted seedling, or anindividual taken from an established stand. Somewetland plants can be established from seed. Seedscan be planted by hand broadcasting or automatedbroadcasting using a tractor.

Another method of establishing plants in a newlyconstructed wetland is reliance on volunteer coloniza-tion from an existing or imported seed bank. Mostconstructed treatment wetlands require some type oforganic soil augmentation for successful plant estab-lishment. Removing a layer of soil from another exist-ing wetland and evenly distributing the soil throughoutthe newly constructed wetland allow the natural seedbank in the existing soil to germinate and establish thevegetation in the new treatment wetland.

The most common form of plant seedlings is bare-rootpropagules. Bare-root seedlings are easily planted inthe field using a small shovel, trowel, or dibble. Thesurvival rate of bare-root seedlings is significantlyhigher than that for field germinated seeds and gener-ally can be maintained at 80 percent or higher withhealthy plant stock and an adequate moisture regime.Since bare-root stock has already had a sufficientperiod of initial growth, successful planting can lead toa rapid plant cover.

Field-harvested plants, in some cases, offer the mostsuccessful option for planting treatment wetlands.These plants can be collected in nearby retentionponds, roadside ditches, and canals and then plantedin suitable substrate in the newly constructed wetland.Planting of field-harvested plants may be more diffi-cult than planting bare-root propagules because of thesize differences of the plants. Planting can be accom-plished by using a shovel or post-hole digger to buryall roots and associated belowground structures.Stresses to the plants, such as extreme shifts in tem-perature, moisture, and light, should be limited wherepossible. The advantages of field-harvested plants overnursery grown stock (Kadlec and Knight, 1996) in-clude:

• Larger roots, rhizomes, and/or corms for energystorage allow the plant to produce abovegroundstructures faster once they are planted.

• They are adapted to local environmental condi-tions.

• Additional volunteer plant species are introducedwith the harvested plant species

(b) Plant establishment

Wetland plants have various environmental adapta-tions as part of their normal routines of germination,growth, reproduction, and senescence/decay. A gen-eral understanding of these components of plantbiology is important in planning and operating con-structed wetlands.

Most emergent wetland plants produce seeds thatgerminate and initially develop best in wet, butunflooded loamy soil. Excessive flooding kills mostwetland plant seedlings. Tight, clayey soil may be in-hospitable for root development and aeration. Highlydrained sandy soil and gravel may not provide ad-equate moisture for initial plant development. Rapid

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development of herbaceous wetland plants in manyconstructed wetlands is normally accomplishedthrough adequate spacing of healthy plants into moist,loamy to sandy soil, followed by gradual increases inthe water level during plant establishment. Rapidincreases in water level within newly planted treat-ment wetlands may kill the plantings.

Plants require nutrients in proper proportions forhealthy growth. The two major nutrients most likely tolimit plant growth in wetlands are phosphorus andnitrogen, respectively. Other nutrients especiallyimportant for plant growth are carbon (typicallysupplied from atmospheric or dissolved carbon diox-ide), potassium, calcium, and sulfur. In addition,wetland plants require several minor nutrients fornormal growth and development. Some essential plantmicronutrients are magnesium, iron, manganese,boron, zinc, copper, and molybdenum. While livestockwastewater supplies adequate quantities of thesenutrients, some industrial wastewater and agriculturalrunoff water do not provide ample nutrition for pro-ductive wetland plant growth. In such cases nutrientsupplements may be required for rapid plant develop-ment and for sustained wetland plant growth. Soiltests during predesign can identify fertilization require-ments for rapid plant establishment. In a relatively fewinstances, supplements of plant micronutrients mustbe added to wetlands to provide adequate plantgrowth.

(c) Plant maintenance

Wetland plant species have a variety of growth strate-gies that provide a competitive advantage in theirnatural habitats. Emergent herbaceous marsh speciesin temperate climates generally grow vegetativelywithin a single growing season to a maximum totalstanding live biomass in late summer or early fall. Thisbiomass may represent multiple growth and senes-cence periods for individual plants during the courseof the growing season, or a single emergence of plantstructures. Standing senesced biomass provides at-tachment sites for microbial species important inwetland treatment performance throughout the annualcycle. It is also important for maintaining root viabilityunder flooded, winter conditions.

Excess solids can stress or kill wetland plants. Sinceuntreated livestock wastewater typically contains highconcentrations of solids, adequate pretreatment of thewastewater is important. This can be accomplished bysettling solids in lagoons or storage ponds or by usingspecial solids separators.

Other environmental factors that may stress the wet-land plants include excessive water depth (any con-stant depth over about 12 to 18 inches is stressful toemergent wetland plants), excessive drought condi-tions, extremely hot or cold conditions, insect pests,and plant pathogens. Some emergent wetland plantspecies, such as cattails, can quickly recover from pestoutbreaks and excessive water levels if their rootsremain alive and healthy and conditions become morefavorable. Healthy wetland plant communities thatsenesce during freezing winter conditions quicklyregrow from below-ground structures during the nextgrowing season as long as their standing dead stemsremain above the water level during the nongrowingseason.




637.0308 References

Armstrong, W., J. Armstrong, and P.M. Beckett. 1990.Measurement and modeling of oxygen releasefrom roots of phragmites australis. In Con-structed Wetlands in Water Pollution Control,P.F. Cooper and B.C. Findlater, eds., PergamomPress, Oxford, UK.

Brix, H. 1993. Macrophyte-mediated oxygen transfer inwetlands: transport mechanisms and rates. InConstructed Wetlands for Water Quality Im-provement, G.A. Moshir, ed., Lewis Pub., BocaRaton, FL.

Brix, H., and H.H. Schierup. 1990. Soil oxygenation inconstructed reed beds: the role of macrophyteand soil-atmosphere interface oxygen transport.In Proceedings of the international conferenceon the use of constructed wetlands in waterpollution control. P.F. Cooper and B.C. Findlater,eds., Pergamom Press, Oxford, UK, pp. 53-66.

CH2M Hill and Payne Engineering. 1997. Constructedwetlands for livestock wastewater management:literature review, data base, and research synthe-sis. Prepared for United States EnvironmentalProtection Agency, Gulf of Mexico Program, andpublished by Alabama Soil and Water Conserva-tion Committee, Montgomery, AL.

Freney, J., R. Leuning, J.R. Simpson, O.T. Denmead,and W.A. Muirhead. 1985. Estimating ammoniavolatilization from flooded rice fields by simpli-fied techniques. Soil Sci. Soc. Am. Jour., Vol. 49.

Guntenspergen, G.R., F. Stearns, and J.A. Kadlec. 1989.Wetland vegetation. In Constructed Wetlandsfor Wastewater Treatment: Municipal, Industrialand Agricultural, ch. 5, D.A. Hammer, ed., LewisPub., Chelsea, MI, pp. 73-88.

Jiang, C., A-M Stomp, J.J. Classen, J.C. Barker, andB.A. Bergmann. 1998. Nutrient removal fromswine wastewater with growing duckweed.ASAE Paper 984122, 1998 ASAE InternationalMtg., Orlando, FL, ASAE, St. Joseph, MI.

Kadlec, R.H. 1989. Hydrologic factors in wetland watertreatment. In Constructed Wetlands for Waste-water Treatment: Municipal, Industrial andAgricultural, ch. 5, D.A. Hammer, ed., Lewis Pub.,Chelsea, MI.

Kadlec, R.H., and R.L. Knight. 1996. Treatment wet-lands. Lewis Pub., Boca Raton, FL.

Keeney, D.R., and R.E. Wildung. 1977. Chemical prop-ertied of soils. In Soils for Management ofOrganic Wastes and Waste Waters. Soil Sci. Soc.of Am., Am. Soc. of Agron., and Crop Sci. Soc. ofAm.; Madison, WI.

Knight, R.L., V. Payne, R.E. Borer, R.A. Clarke, Jr., andJ.H. Pries. 1996. Livestock waste treatmentwetlands data base. Paper, second Natl. Work-shop for Constructed Wetlands for Animal WasteTreatment, Fort Worth, TX.

Linacre, E.T. 1976. Swamps. In Vegetation and Atmo-sphere, Vol. 2: Case Studies, J.L. Montieth, ed.,Academic Press, London.

Mattingly, D.E.G. 1975. Labile phosphate in soils. SoilScience 119:369-375.

Payne, V.W.E., and R.L. Knight. 1997. Constructedwetlands for treating animal waste treatment.Sec. 1, Performance, design and operation.Prepared for the Gulf of Mexico Program Nutri-ent Enrichment Committee under contract toAlabama Soil and Water Conservation Commit-tee and National Council of the Pulp and PaperIndustry for Air and Stream Improvement byPayne Engineering and CH2M Hill.

Payne, V.W.E., and R.L. Knight. 1998. New designprocedures for animal waste constructed wet-lands. ASAE Paper No. 982089, 1998 ASAEInternational Mtg., Orlando, FL, ASAE, St. Jo-seph, MI.

Reddy, K.R., and T.A. DeBusk. 1987. State-of-the-artutilization of aquatic plants in water pollutioncontrol. Water Science and Technology, Vol. 19,No. 10, pp. 61-79.

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Reed, S.C., R.W. Crites, and E.J. Middlebrooks. 1995.Natural systems for waste management andtreatment (2nd ed.). McGraw-Hill, NY.

Rogers, J.W., D.T. Hill, V.W.E. Payne, and S.R. Kown.1995. A biological treatment study of constructedwetlands treating poultry wastes. In Versatility ofWetlands in the Agricultural Landscape, ASAEand AWRA Proceed., Tampa, FL.

Sawyer, C.N., and P.L. McCarty. 1967. Chemistry forsanitary engineers, 2nd ed. McGraw-Hill BookCo., NY.

Seyers, J.K., G.W. Smille, and R.B. Corey. 1973. Phos-phate sorption in soils evaluated by Langmuiradsorption equation. Soil Sci. Soc. Am., Proc.37:358-363.

United States Department of Agriculture, NaturalResources Conservation Service. 1991. Con-structed wetlands for agricultural wastewatertreatment. Technical Requirements, Washington,DC.

United States Department of Agriculture, NaturalResources Conservation Service. 1992. Agricul-tural waste management field handbook.Washington, DC.

United States Environmental Protection Agency. 1976.Quality criteria for water. Washington, DC.

United States Environmental Protection Agency. 1999.Treatment wetland habitat and wildlife useassessment. Executive summary, EPA 832-S-99-001, Washington, DC.

Watson, J.T., and J.A. Hobson. 1989. Hydraulic designconsiderations and control structures for con-structed wetlands for wastewater treatment. InConstructed Wetlands for Wastewater Treat-ment, D.A. Hammer, ed., Lewis Pub., Chelsea, MI.

Weber, A.S., and G. Tchobanoglous. 1985. Nitroficationin water hyacinth treatment systems. J. Environ.Eng. Div., ASCE, 11(5):699-713.


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Accretion Refers to the long-term buildup of a peat-like material consisting of settle-able solids from the waste stream, the remnants of decayed plant litter, andmicrobial biomass on the floor of a surface flow wetland or on top of thefilter bed of a subsurface flow wetland.

Adsorption The process by which chemicals are held on a solid surface, such as thepositively charged ammonium ion (NH4

+) bonding with negatively chargedclay particles.

Aerobic Living, active, or occurring only in the presence of free oxygen. A conditionof having free oxygen.

Agricultural waste A combination of conservation practices formulated to appropriatelymanagement system manage a waste product that, when implemented, will recycle waste con-

stituents to the fullest extent possible and protect the resource base in anonpolluting manner.

Agricultural waste Waste normally associated with the production and processing of food andfiber on farms, feedlots, ranches, and forests that may include animalmanure, crop and food processing residue, agricultural chemicals, andanimal carcasses.

Algae Algae are photosynthetic organisms that occur in most habitats, rangingfrom marine and freshwater to desert sands and from hot boiling springs tosnow and ice. They vary from small, single-celled forms to complex, multi-cellular forms, such as the giant kelps of the eastern Pacific that grow tomore than 60 meters in length and form dense marine forests.

Ambient Environmental or surrounding conditions.

Ammonification The production of ammonia by micro-organisms through the decomposi-tion of organic matter.

Anaerobic Living, active, or occurring only in the absence of free oxygen. A conditionof being without free oxygen.

Anoxic sediment Sediment devoid of oxygen.

Biochemical oxygen demand The amount of oxygen (measured in mg/L) required in the oxidation oforganic matter by biological action under specific standard test conditions.Widely used to measure the amount of organic pollution in wastewater andstreams.

Biomass The total mass of living tissue of both plants and animals.

BOD See Biochemical oxygen demand.

BOD5

Biochemical oxygen demand measured over a standard 5-day test period;distinguished from BODN (nitrogenous oxygen demand) and BODU (ulti-mate oxygen demand). See Biochemical oxygen demand.

Glossary




Cation exchange The interchange between a cation in solution and another cation in theboundary layer between the solution and surface of negatively chargedmaterial, such as clay or organic matter.

Center pivot An automated irrigation system consisting of a sprinkler line rotating abouta pivot point at one end and supported by a number of self-propelled tow-ers. The water is supplied at the pivot point and flows outward through theline supplying the individual outlets.

Chelation A chemical complexing (forming or joining together) of metallic cationswith certain organic compounds.

Class A pan evaporation Evaporation as measured using a standard U.S. Weather Bureau Class Aevaporation pan that has a depth of 10 inches and a diameter of 48 inches.The depth of water that evaporates is measured, and coefficients can beapplied to estimate evaporation amounts from waterbodies. A typicalcoefficient for lakes is 0.7.

Complexation A reaction in which a metal ion and one or more anionic ligands chemicallybond. Complexes often prevent the precipitation of metals.

Composting A facilitated process of aerobic biological decomposition of organic mate-rial characterized by elevated temperature that, when complete, results in arelatively stable product suitable for a variety of agricultural and horticul-tural uses.

Constructed wetland A synthetic, shallow earthen impoundment containing hydrophytic vegeta-tion designed to treat both point and nonpoint sources of water pollution.

Culm An aerial stem bearing the inflorescence, in grasses, rushes, and other suchplants.

Deciduous Plants that shed all their leaves annually, generally in the fall.

Decisionmaker An individual, group, unit of government, or other entity that has the au-thority by ownership, position, office, delegation, or otherwise to decide ona course of action.

Denitrification Reduction of nitrogen oxides (usually nitrate and nitrite) to molecularnitrogen or nitrogen oxides with a lower oxidation state of nitrogen bybacterial activity (denitrification) or by chemical reactions involving nitrite(chemodenitrification). Nitrogen oxides are used by bacteria as terminalelectron acceptors in place of oxygen in anaerobic or microaerophilicrespiratory metabolism.

Diffusion The process by which matter, typically a gas, is transported from one partof a system to another as the result of random molecular movement; move-ment is from areas of high concentration to areas of low concentrationinfluenced by temperature and the nature of the medium.

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Dissolved oxygen The molecular oxygen dissolved in water, wastewater, or other liquid;generally expressed in milligrams per liter, parts per million, or percent ofsaturation.

DO See Dissolved oxygen.

Effluent Water or some other liquid—raw, partially or completely treated—flowingfrom a waste storage or treatment facility.

Emergent plant An aquatic or wetland plant with its lower part submerged and its upperpart extending upright above the water.

ET See Evapotranspiration.

Evapotranspiration The combination of water transpired from vegetation and evaporation fromsoil and plant surfaces. Sometimes called consumptive use.

Facultative species In the context of wetland plants, the term refers to species of plants thatcan grow under natural conditions in both wetlands and uplands. SeeObligate species.

Field test method An approach to sizing constructed wetlands based on loading determinedfrom laboratory test results of the influent proposed for the wetland.

Floating aquatic plants Aquatic plants that are not attached to the soil, but rather float freely on ornear the water surface, such as duckweed and water hyacinths.

Floating aquatic plant Consists of a pond or series of ponds in which floating aquatic plants are(FAP) systems grown for the purpose of treating wastewater.

Flushwater Water used to clean or rinse surfaces.

Free-floating plants Plants that float at or beneath the water surface without attachment to thesubstrate. Free-floating aquatics are transported freely by wind and cur-rents, so they are normally found in abundance only in calm, shelteredwater. Duckweed (Lemna spp.), bladderwort (Utricularia vulgaris), andcoontail (Ceratophyllum demersum) are common examples of free-float-ing aquatics.

Gated pipe Portable pipe that has small gates installed along one side for distributingwater across the width of the inlet end of a constructed wetland cell or tosurface irrigation corrugations or furrows.

Ground water Water that flows or seeps downward and saturates soil or rock, supplyingsprings and wells. The upper level of the saturated zone is called the watertable. Water stored underground in rock crevices and in the pores of geo-logic material that makes up the Earth's crust. That part of the subsurfacewater that is in the zone of saturation; phreatic water.

Herbaceous vegetation Plants that are herbs with soft, nonwoody stems and no secondary growth.




Hydraulic detention time The period that wastewater flow is retained in the constructed wetland forcompletion of physical, chemical, or biological reaction. The theoreticaldetention time is equal to the volume of water in the constructed wetlanddivided by the flow rate.

Hydraulic gradient The slope of the surface of open or underground water.

Hydrophytic vegetation Any plant that can grow in water or on a substrate that is at least periodi-cally deficient in oxygen as a result of excessive water content.

Influent Water or other liquid—raw or partly treated—flowing into a reservoir,basin, treatment process or treatment plant.

Ion An electrically charged atom, radical, or molecule formed by the loss orgain of one or more electrons.

Ion exchange A process that involves substitution of one ion, either cation or anion, foranother of the same charge when a solution containing ions is passed into amolecular network having either acidic or basic substituent groups that canbe readily ionized. The ions in the solution attach themselves to the net-work, replacing the acidic or basic groups.

Jurisdictional wetlands Those wetlands defined as water of the U.S. They include all that are cur-rently used or were used in the past or may be susceptible to use in inter-state commerce, including: all water that is subject to ebb and flow of thetide; all interstate water including interstate wetlands; all other water, suchas intrastate lakes, rivers, streams including intermittent streams, mudflats,sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, ornatural ponds, the use, degradation, or destruction of which would orcould affect interstate or foreign commerce; all impoundments of waterotherwise defined as water of the U.S. under this definition; tributaries ofwater defined above; the territorial sea; and wetlands adjacent to water(other than water that is itself wetlands) identified above. See Wetlands.

Kjeldahl nitrogen Nitrogen in the form of organic proteins or their decomposition productammonia, as measured by the Kjeldahl Method.

Lacuna A gap or cavity.

Lake evaporation The rate of evaporation from a water surface like that of a lake too large tobe much affected by the additional evaporation that occurs at the edge.

Land application Application of manure, sewage sludge, municipal wastewater, and indus-trial wastewater to land for reuse of the nutrients and organic matter fortheir fertilizer and soil conditioning value.

Leaching The removal of soluble material from one zone in soil to another via watermovement in the profile.

Lenticel A small, raised, corky spot or line appearing on young bark, through whichgaseous exchange occurs.

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Liner A relatively impermeable barrier designed to prevent seepage into the soilbelow. Liner material includes plastic and dense clay.

Livestock Animals kept or raised for use or pleasure, especially farm animals kept foruse and profit. Includes cattle, swine, poultry, and horses.

Loading The quantity of a substance entering the environment or facility, such asthe quantity of a nutrient to a constructed wetland.

Macrophyte A macroscopic vascular plant; a multicellular aquatic plant, either free-floating or attached to a surface.

Nonpersistent plant A plant that breaks down readily after the growing season.

Nonpoint source Pollution sources that are diffuse and do not have a single point of origin orare not introduced into a receiving stream from a specific outlet.

Nutria Aquatic, plant-eating rodent, Myocastor coypus, native of South America,resembling a small beaver with a ratlike tail. These rodents inhabit wet-lands throughout the continental United States and are considered destruc-tive pests.

Nutrient Elements or compounds essential as raw material for organism growth anddevelopment.

Obligate species Species that in nature can grow and multiply in only specific environment.

Organic matter Mass of matter that contains living organisms or nonliving material derivedfrom organisms. Sometime refers to the organic constituents of soil.

Oxidation The addition of oxygen, removal of hydrogen, or the removal of electronsfrom an element or compound. In the environment, organic matter isoxidized to more stable substances.

Pathogen Micro-organisms that can cause disease in other organisms or in humans,animals, and plants. They may be bacteria, viruses, fungi, or parasites.

Perennial plant A plant that lives through several growing seasons.

Point source A stationary location or fixed facility from which pollutants are dischargedor emitted.

Presumptive method An approach to sizing a constructed wetlands based on estimates of influ-ent loadings.

Pretreatment Treatment of waste or wastewater to reduce the concentrations of solidsand other constituents of waste and wastewater before discharge to afacility for further management.

Propagules Any of various portions of a plant, such as a bud or other offshoot, that aidin dispersal of the species and from which a new individual may develop.




Rhizome A root-like stem that produces roots from the lower surface and leaves, andstems from the upper surface.

Seepage The loss of water by percolation into the soil from a canal, ditch, lateral,watercourse, reservoir, storage facility, or other body of water, or from afield.

Senescence The plant growth phase from full maturity to death that is characterized byan accumulation of metabolic products, increase in respiratory rate, andloss in dry weight, especially in leaves and fruit.

Settleable solids Solids in a liquid that can be removed by stilling a liquid. Settling times of atleast 1 hour are generally used.

Short circuiting When water finds a more direct course from inlet to outlet than was in-tended. This is generally undesirable because it may result in short contact,reaction, or settling time in comparison with the theoretical or presumeddetention times.

Sludge The accumulation of solids resulting from chemical coagulation, floccula-tion, and sedimentation after water or wastewater treatment.

Solids See Total solids.

Solid set system An irrigation system that covers the complete field with pipes and sprin-klers in such a manner that all the field can be irrigated without moving anyof the system.

Sorption The removal of an ion or molecule from solution by adsorption and absorp-tion. It is often used when the exact nature of the mechanism of removal isnot known.

Stolon A trailing aboveground stem or shoot, often rooting at the nodes and form-ing new plants.

Substrate A supporting surface on which organisms grow. The substrate may simplyprovide structural support, or may provide water and nutrients. A substratemay be inorganic, such as rock or soil, or it may be organic, such as vegeta-tion surfaces.

Subsurface flow (SSF) wetlands Constructed wetlands consisting of a bed of gravel, rock, or soil mediathrough which the wastewater flows. Emergent, hydrophytic vegetation isplanted at the surface of the wetland. The water surface is maintained at anelevation just below the surface of the bed.

Supernatant The liquid fraction in a waste impoundment, such as a waste treatmentlagoon or waste storage pond, that overlies the sludge or settled solids.

Surface flow (SF) wetlands A constructed wetland consisting of shallow earthen basin planted withrooted, emergent vegetation in which water flows across the soil surface.

3–59




Suspended solids Organic or inorganic particles that are suspended in and carried by thewater. The term includes sand, mud, and clay particles, as well as solids inwastewater.

TKN Total Kjeldahl nitrogen. See Kjeldahl nitrogen.

Total maximum daily load (TMDL) The sum of the individual wasteload allocations for point sources and loadallocations for nonpoint sources and natural background.

TMDL See Total maximum daily load.

Total solids The weight of all solids, dissolved and suspended, organic and inorganic,per unit of volume of water or wastewater. It is the residue remaining afterall water has been removed by evaporation.

Traveling gun An irrigation system using a high volume, high pressure sprinkler (gun)mounted on a trailer, with water being supplied through a flexible hose orfrom an open ditch along which the trailer passes.

Treatment Chemical, biological, or mechanical procedures applied to sources ofcontamination to remove, reduce, or neutralize contaminants.

Tuber An enlarged, fleshy, underground stem with buds capable of producingnew plants.

Vascular plants Plants that possess a well-developed system of specialized tissues thatconduct water, mineral nutrients, and products of photosynthesis throughthe plant, consisting of the xylem and phloem.

Venn diagram A diagram where sets are represented as simple geometric figures, withintersections and unions of sets represented by intersections and unions ofthe figures.

Volatile solids That part of total solids driven off as volatile (combustible) gases whenheated to 1,112 degrees Fahrenheit.

Volatilization Loss of gaseous components, such as ammonium nitrogen, from animalmanure.

Waste storage facility A waste storage impoundment made by constructing an embankment and/or excavating a pit or dugout or by fabricating a structure for the tempo-rary storage of animal or other agricultural waste.

Waste treatment lagoon A waste treatment impoundment made by constructing an embankmentand/or excavating a pit or dugout for the biological treatment of animal andother agricultural waste.

Wastewater The used water and solids from a confined livestock or aquaculture facilitythat is usually not suitable for reuse unless it is treated.




Water budget An accounting of the inflow to, outflow from, and storage changes of waterin a hydrologic unit.

Water quality The excellence of water in comparison with its intended use or uses.

Water table The upper surface of ground water in the zone of saturation.

Wetland porosity The amount of wetland water volume not occupied by plants, expressed asa decimal.

Wetlands Land transitional between terrestrial and aquatic systems that has a watertable at or near the surface or a shallow covering of water, hydric soil, anda prevalence of hydrophytic vegetation. Note that there are several ver-sions of this definition. Refer to agency definitions (U.S. EPA/Army Corpsof Engineers, U.S. Fish and Wildlife Service) for a more precise definition.

3A–1(210-VI-NEH, September 2002)

(From Constructed Wetlands for Animal Waste Treatment, A Manual on Performance, Design, and Operation

with Case Histories, Gulf of Mexico Program, Nutrient Enrichment Committee, June 1997; adapted with modifica-tions from Thunhorst, 1993)

Plant species Common name Growth form Persistence Rate Method Spacing

Acer negundo Box elder Tree Perennial, Fast, 4.5 todeciduous 6 m in 5 yrs

Acer rubrum Red maple Tree Perennial, Medium to fast,deciduous 5 to 7 m in 10 yr

Acorus Sweet flag Emergent, Perennial, Moderate, Rhizome 0.3 to 0.9 m O.C.calamus herbaceous nonpersistent 15 cm/yr

Alnus serrulata Smooth alder Shrub Perennial, Rapid,deciduous 60 cm/yr

Carex spp. Sedges Emergent, Perennial, Slow to rapid Rhizome 0.15 to 1.8 mherbaceous nonpersistent O.C.

Cephalanthus Buttonbush Shrub Perennial, Medium, 30occidentalls deciduous to 60 cm/yr

Ceratophyllum Coontail Submerged Perennial Rapid Fragmentationdemersum aquatic

Cyperus Chufa Emergent, Perennial, Rapid Rhizomeesculentus herbaceous nonpersistent

Eichhornia Water hyacinth Nonrooted Perennial, Rapid Stolonscrassipes floating aquatic nonpersistent

Hydrocotyle Water- Emergent to Perennial, Rapid Stolons orumbellata pennywort floating, nonpersistent rhizomes

herbaceous

Iris versicolor Blue flag Emergent, Perennial, Slow, Bulb 0.15 to 0.45 mherbaceous nonpersistent <60 cm/yr O.C.

Juncus effusus Soft rush Emergent, Perennial, Slow, <6 cm/yr Rhizome 0.15 to 0.45 mherbaceous persistent O.C.

Lemna minor Common Nonrooted Perennial, Rapid Fragmentationduckweed floating aquatic nonpersistent

Nuphar luteum Spatterdock Rooted floating Perennial, Slow, <6 cm/yr Rhizome 0.15 to 0.45 mto emergent, nonpersistent O.C.herbaceous

Nymphaea Fragrant Rooted, Perennial, Rhizomeodorata water lily floating aquatic nonpersistent

Nyssa sylvatica Black gum Tree Perennial, Slow Suckersdeciduous

Appendix 3A Typical Aquatic and Wetland PlantSpecies Used in Constructed Wetlands



3A–2 (210-VI-NEH, September 2002)

Appendix 3A Typical aquatic and wetland plant species used in constructed wetlands—Continued

Plant species Common name Growth form Persistence Rate Method Spacing

Phragmites Common reed Emergent, Perennial, Rapid, Rhizome 0.6 to 1.8 m O.C.australis herbaceous persistent >30 cm/yr

Pontederia Pickerelweed Emergent, Perennial, Moderate, Rhizome 0.3 to 0.9 m O.C.cordata herbaceous nonpersistent 15 cm/yr

Populus Eastern Tree Perennial, Fast, 1.2 todeltoides cottonwood deciduous 1.5 m/yr

Potamogeton Long-leafed Rooted sub- Perennial, Rapid Rhizome 0.6 to 1.8 m O.C.nodosus pond weed merged aquatic nonpersistent

Quercus Swamp white Tree Perennial, Fast, 0.4 tobicolor oak deciduous 0.6 m/yr

Rosa palustris Swamp rose Shrub Perennial,deciduous

Sagittaria Duck potato Emergent, Perennial, Rapid, Runners, 0.6 to 1.8 m O.C.latifolia herbaceous nonpersistent >30 cm/yr tubers

Salix nigra Black willow Tree Perennial, Fast, 0.9 to Suckersdeciduous 1.8 m/yr

Scirpus acutus Hardstem Emergent, Perennial, Rapid Rhizome 0.9 to 1.8 m O.C.bulrush herbaceous persistent >30 cm/yr

Scirpus Olney's bulrush Emergent, Perennial Rapid, Rhizome 0.6 to 1.8 m O.C.americanus herbaceous semi-persistent >30 cm/yr

Scirpus Wool grass Emergent, Perennial, Moderate, Rhizome 0.3 to 0.9 m O.C.cyperinus herbaceous persistent 15 cm/yr

Scripus Soft stem Emergent, Perennial, Rapid, Rhizome 0.6 to 1.8 m O.C.validus bulrush herbaceous persistent >30 cm/yr

Sparganium Giant burreed Emergent, Perennial, Rapid, Rhizome 0.6 to 1.8 m O.C.eurycarpum herbaceous nonpersistent >30 cm/yr

Taxodium Bald cypress Tree Perennial, Medium, 0.3 todistichum deciduous 0.6 m/yr

Typha Narrowleafed Emergent, Perennial, Rapid, Rhizome 0.6 to 1.8 m O.C.angustifolia cattail herbaceous persistent >30 cm/yr

Typha latifolia Broadleafed Emergent, Perennial, Rapid, Rhizome 0.6 to 1.8 m O.C.cattail herbaceous persistent >30 cm/yr

3A–3




Continuation of same plant species list as above with additional characteristics

Plant species Propagules Habitat Shade tolerance Wildlife benefits Water regime Salinity tolerance

Acer negundo Container Forested Full sun Songbirds, Irregular to Fresh water,wetlands waterbirds, regular inun- resistant to salt

small dation or watermammals saturation

Acer rubrum Seed, whip, Fresh marsh, Partial shade Gamebirds, Irregular to Fresh water,bare root swamp, alluvial songbirds, seasonally <0.5 ppt

woods browsers inundated orsaturated

Acorus Rhizome, bare Fresh to brack- Partial shade Waterfowl, Regular to Fresh tocalamus root plant ish marshes muskrat permanent brackish water

inundation <10 ppt<15 cm

Alnus Container Fresh marshes Full sun Songbirds, Seasonal to Fresh water,serrulata and swamps gamebirds, regular inun- <0.5 ppt

ducks, wood- dation, up tocock, black- 7 cmbirds, beaver

Carex spp. Seed, bare root Fresh marshes, Full shade to Rails, sparrows, Irregular to Fresh water,plant swamps, lake full sun snipe, song- permanent <0.5 ppt

edges birds, ducks, inundation,moose <15 cm

Cephalanthus Seedling, bare Fresh marshes, Full shade to Ducks, deer, Irregular to Fresh water,occidentalls root plant swamps, edge full sun rails, black- permanent tolerates infre-

of ponds birds, musk- inundation, quent salt waterrat, beaver up to 90 cm

Ceratophyllum Whole plant Lakes, slow Ducks, coots, Regular to Fresh water,demersum streams geese, grebes, permanent in- <0.05 ppt

swans, marsh- undation, 0.3birds, muskrat to 1.5 m

Cyperus Seed, tuber Fresh marshes, Full sun Waterfowl, Irregular to Fresh water,esculentus wet meadows songbirds, regular inun- <0.5 ppt

small mammals dation, <0.3 m

Eichhornia Whole plant Fresh water Full sun Coots, cover for Permanent Fresh water,crassipes ponds and slug- invertebrates inundation <0.5 ppt

gish streams and fish

Hydrocotyle Bare root plant, Shorelines, Partial shade Wildfowl, Regular to Fresh water,umbellata whole plant shallow waterfowl permanent <0.5 ppt

marshes inundation<30 cm






Iris versicolor Seed; bulb, Marshes, wet Partial shade Muskrat, wild- Regular to Fresh to moder-bare root plant meadows, fowl, marsh- permanent ately brackish

swamps birds inundation, water<15 cm

Juncus effusus Seed, rhizome, Marshes, shrub Full sun Wildfowl, Regular to Fresh water,bare root swamps, wet marshbirds, permanent <0.5 pptplants meadows songbirds, inundation,

waterfowl <30 cm

Lemna minor Whole plant Lakes and Partial shade Ducks, galli- Permanent Fresh water,ponds nules, coots, inundation <0.05 ppt

rails, geese,beaver, musk-rat, smallmammals

Nuphar luteum Bare root plant Marshes, Partial shade Ducks, musk- Regular to Fresh toswamps, ponds rat, fish permanent infrequent

inundation, brackish waterup to 1.8 m

Nymphaea Bare root Ponds and Partial shade Cranes, ducks, Permanent Fresh water,odorata seedling lakes beaver, musk- inundation, <0.05 ppt

rat, moose 0.3 to 0.9 m

Nyssa Seed, bare root Forested wet- Partial shade Ducks, wood- Irregular to Fresh to infre-sylvatica plant lands, swamps peckers, song- permanent quent brackish

birds, aquatic inundation waterfurbearers

Phragmites Bare root plant Fresh to brack- Full sun Songbirds, Seasonal to Fresh to brack-australis ish marshes, marshbirds, permanent in- ish water, up to

swamps shorebirds, undation, up 20 pptaquatic fur- to water, up tobearers 60 cm

Pontederia Rhizome, bare Fresh to brack- Partial shade Ducks, musk- Regular to Fresh to moder-cordata root plant ish marshes, rat, fish permanent ately brackish

edges of ponds inundation up water, up toto 30 cm 3 ppt

Populus Bare root plant Forested wet- Full sun Gamebirds, Seasonal inun- Fresh to infre-deltoides container lands songbirds, dation or quent brackish

waterfowl, saturation wateraquatic fur-bearers,browsers


3A–5





Potamogeton Seed, bare Streams, lakes, Waterfowl, Regular to Fresh water,nodosus root plant ponds marshbirds, permanent <0.05 ppt

shorebirds, inundation,aquatic fur- 0.3 to 1.8 mbearers,moose, fish

Quercus Bare root Forested Partial shade Waterfowl, Irregular to Fresh to infre-bicolor plant, container wetlands marshbirds, seasonal quent brackish

shorebirds, inundation or watergamebirds, saturationsongbirds,mammals

Rosa palustris Container Fresh marshes, Full sun Songbirds, Irregular to Fresh water,shrub swamps gamebirds regular soil <0.5 ppt

saturation

Sagittaria Tuber, bare Fresh marshes, Partial shade Ducks, swans, Regular to Fresh water,latifolia root plant swamps, edge rails, muskrat, permanent <0.5 ppt

of ponds beaver inundation,up to 60 cm

Salix nigra Bare root, Fresh marshes, Full sun Gamebirds, Irregular to Fresh water,container swamps ducks, song- permanent <0.5 ppt

birds, wood- inundationpeckers, aqua-tic mammals

Scirpus acutus Seed, rhizome Fresh to Full sun Ducks, geese, Regular to Fresh to brack-brackish swans, cranes, permanent, ish watermarshes shorebirds, up to 90 cm

rails, snipe,muskrat, fish

Scirpus Rhizome, bare Brackish and Full sun Ducks, geese, Regular to Fresh to brack-americanus root plant alkali marshes swans, cranes, permanent, ish water, up to

shorebirds, up to 30 cm 15 pptrails, snipe,muskrat, fish

Scirpus Rhizome, bare Fresh marshes, Full sun Ducks, geese, Irregular to Fresh water,cyperinus root plant wet meadows, swans, cranes, seasonal <0.5 ppt

sloughs, swamps shorebirds, inundationrails, snipe,muskrat, fish






Scirpus Rhizome, bare Fresh and Full sun Ducks, geese, Regular to Fresh to brack-validus root plant brackish swans, cranes, permanent ish water, up to

marshes shorebirds, inundation, 5 pptrails, snipe, up to 30 cmmuskrat, fish

Sparganium Seed, rhizome, Marshes, Partial shade Ducks, swan, Regular to Fresh water,eurycarpum bare root swamps geese, beaver, permanent <0.5 ppt

plant muskrat inundationup to 30 cm

Taxodium Seed, bare Fresh water Partial shade Perching and Irregular to Fresh water,distichum root swamps, pond nesting site permanent <0.5 ppt

and lake for birds inundationmargins

Typha Rhizome, Fresh and Full sun Geese, ducks, Irregular to Fresh to brack-angustifolia bare root brackish muskrat, permanent ish water, up to

marshes, beaver, black- inundation, 15 ppmpond edges birds, fish up to 30 cm

Typha latifolia Rhizome, bare Fresh marshes, Full sun Geese, ducks, Irregular to Fresh water,root plant pond margins muskrat, permanent <0.5 ppt

beaver, black- inundation,birds, fish up to 30 cm


Documents

Chapter 3 Constructed Wetlands - USDA · (210-VI-NEH, September 2002) 3–v Part 637 National Engineering Handbook Chapter 3 Constructed Wetlands Table 3–5 Processes involved in