Fate and Transport of Soluble Reactive Phosphorus in the North …tiaer.tarleton.edu/pdf/TR0101.pdf · 2002. 1. 23. · Fate and Transport of Soluble Reactive Phosphorus 3 Abstract

USDALake Waco-Bosque River Initiative

Fate and Transport of SolubleReactive Phosphorus in the North

Bosque River of Central Texas

Anne McFarland, Larry Hauck, and Richard Kiesling

TR0101

February 2001

Texas Institute for Applied Environmental ResearchTarleton State University • Box T0410 • Tarleton Station • Stephenville, Texas 76402254.968.9567 • FAX 254.968.9559 • [email protected]

Fate and Transport of Soluble Reactive Phosphorus

Acknowledgements

Funding sources for this study include the United States Department of Agriculture - Natural Resources Conservation Service, the Clean Rivers Program of the Texas Natural Resource Conservation Commission, the United States Environmental Protection Agency, and the State of Texas. The authors acknowledge the support and dedicated work of the many field personnel and laboratory chemists involved with the monitoring program, particularly since rain often falls on weekends requiring staff to be on call seven days a week.

Mention of trade names or commercial products does not constitute their endorsement.

For more information about this document or any other TIAER documents, send e-mail to [email protected].

Authors

Anne McFarland, Research Scientist, TIAER, [email protected]

Larry Hauck, Assistant Director of Environmental Sciences, TIAER, [email protected]

Richard Kiesling, Research Scientist, TIAER, [email protected]

USDA02.06

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Abstract

Phosphorus (P) forms at sampling sites along the North Bosque River in central Texas were evaluated to determine the fate of soluble reactive phosphorus (SRP) at different points along the river during base and storm flow. Base flow samples were evaluated at eight sites and storm event samples at five sites for data collected between February 4, 1997 and July 31, 1998. The highest concentrations of soluble reactive phosphorus (SRP) and total P (TP) and higher proportions of SRP to particulate P (PP) occurred in the upper portion of the North Bosque River during base and storm flow. About 95 percent of all P transported along the North Bosque River occurred during storm events. Although loadings increased with flow along the North Bosque River, a general decrease in SRP and TP concentrations was indicated from upstream to downstream sites for base and storm conditions. To assess the potential for P transformations in transport along the North Bosque River, inflow contributions between two sets of upstream and downstream sites were evaluated for selected storm events and for cumulative daily loadings for an extended time period of November 1, 1995 through July 31, 1998. During storm events, dilution from contributing tributaries appeared to explain most of the noted decrease in P concentrations between upstream and downstream sites. At base flow, dilution as well as retention via transformations were involved in explaining the decrease in P concentrations. At base flow, a noticeable depletion of SRP occurred in cumulative daily loadings. This depletion in SRP is most likely associated with uptake by aquatic plants and algae and the binding of SRP with sediment particles. A depletion of TP was also indicated during base flow. This depletion of TP was expected with removal of SRP from the water column by attached plants and algae. The depletion of TP was also associated with an increased settling of sediment bound PP as noted by a slight depletion in cumulative TSS loadings during low flow conditions. The cumulative depletion or retention of P in the North Bosque River at base flow is temporary, because storm events resuspend and transport retained PP downstream. While some transformations of soluble P to PP occur under low flow conditions, the majority of the SRP transported along the North Bosque River occurs during storm events and appears to arrive at Lake Waco, the receiving water body, without undergoing significant biological or geochemical transformations.

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4

Contents

Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Chapter 2 Sites on the North Bosque River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Chapter 3 Data Collection and Laboratory Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Chapter 4 Data Analysis Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Chapter 5 Precipitation Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Chapter 6 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Spatial Variability in P Concentrations and Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Correlation of Water Quality to Flow Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32P Loading During Base Flow Versus Storm Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Inflow Impacts During Storm Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Cumulative Daily Volumes and Loadings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Chapter 7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Appendix A Summary of Storm Events Monitored Between February 1997 and July 1998 . . . . . . 61

Appendix B Summary of Storm Events Monitored Between November 1995 and January 1997 . . 65

Appendix C Average Monthly Discharge from WWTPs along the North Bosque River . . . . . . . . 67

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6

Tables

Table 1 Permitted point source discharges to the North Bosque River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Table 2 Land uses above sampling sites along the North Bosque River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Table 3 Monitoring history for sampling sites along the North Bosque River. . . . . . . . . . . . . . . . . . . . . . . . . . . 23Table 4 Total monthly rainfall for selected National Weather Service Observer Stations. . . . . . . . . . . . . . . . . . 27Table 5 Basic statistics of stream flow associated with routine grab samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Table 6 Municipal wastewater treatment plant effluent characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 7 Cross correlation of flow and concentration data for base flow samples at BO020. . . . . . . . . . . . . . . . 33Table 8 Cross correlation of volume and concentration data for storm events at BO020. . . . . . . . . . . . . . . . . . 33Table 9 Cross correlation of flow and concentration data for base flow samples at BO040. . . . . . . . . . . . . . . . 34Table 10 Cross correlation of volume and concentration data for storm events at BO040. . . . . . . . . . . . . . . . . . 34Table 11 Cross correlation of flow and concentration data for base flow samples at BO070. . . . . . . . . . . . . . . . 35Table 12 Cross correlation of volume and concentration data for storm events at BO070. . . . . . . . . . . . . . . . . . 35Table 13 Cross correlation of flow and concentration data for base flow samples at BO090. . . . . . . . . . . . . . . . 36Table 14 Cross correlation of volume and concentration data for storm events at BO090. . . . . . . . . . . . . . . . . . 36Table 15 Cross correlation of flow and concentration data for base flow samples at BO100. . . . . . . . . . . . . . . . 37Table 16 Cross correlation of volume and concentration data for storm events at BO100. . . . . . . . . . . . . . . . . . 37Table 17 Flow at North Bosque River sites categorized as storm, base, or dry . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Table 18 Estimated loadings by type of flow along the North Bosque River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Table 19 Drainage area and river miles between sites BO040 and BO070 and sites BO070 and BO090 . . . . . . . 41Table 20 Storm concentrations for tributaries between sites BO040 and BO070 . . . . . . . . . . . . . . . . . . . . . . . . . . 42Table 21 Land use of monitored tributaries compared to drainage area between BO040 and BO070. . . . . . . . . 42Table 22 Calculated inflow storm volume (equation 1) and concentrations (equation 2) . . . . . . . . . . . . . . . . . . 43Table 23 Storm concentrations for tributaries between sites BO070 and BO090 and area-weighted inflow. . . 44Table 24 Land use of monitored tributaries compared to drainage area between sites BO070 and BO090 . . . . 44Table 25 Calculated inflow storm volume (equation 1) and concentrations (equation 2) . . . . . . . . . . . . . . . . . . 45

Table A–1 Summary of storm events monitored between February 1997 and July 1998 . . . . . . . . . . . . . . . . . . . 61

Table B–1 Summary storm events monitored between November 1995 and January 1997 . . . . . . . . . . . . . . . . . 65

Table C–1 Average monthly effluent discharge from municipal wastewater treatment plants . . . . . . . . . . . . . 67

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Figures

Figure 1 TIAER sampling sites on the North Bosque River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Figure 2 Classified stream segments within the Bosque River watershed. . . . . . . . . . . . . . . . . . . . . . . 12Figure 3 Monthly precipitation and departure from normal for Stephenville and Waco Dam.. . . . . 28Figure 4 Geometric mean values for SRP, TP, and TSS at sites along the North Bosque River.. . . . . 30Figure 5 Percent of TP represented by soluble (SRP) and particulate (PP) forms. . . . . . . . . . . . . . . . . 32Figure 6 Volume-weighted mean concentrations and mass loadings as a percent of total. . . . . . . . . 40Figure 7 Cumulative daily volume of flow for sites and the inflowing area between sites . . . . . . . . 46Figure 8 Daily average flow at sites BO040, BO070 and BO090 on the North Bosque River. . . . . . . . 47

Figure 9 Cumulative daily loading of SRP for sites and the inflowing area between sites . . . . . . . . . 48Figure 10 Cumulative daily loading of TP for sites and the inflowing area between sites . . . . . . . . . . 49Figure 11 Relationship of daily SRP loading for the inflow between sites BO040 and BO070 . . . . . . . 50Figure 12 Cumulative daily loading of TSS for sites and the inflowing area between sites . . . . . . . . . 51Figure 13 Impact of WWTP discharge on cumulative daily volume and loadings . . . . . . . . . . . . . . . . 52

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10

CHAPTER 1

Introduction

The North Bosque River begins just north of Stephenville, Texas, and continues to Lake Waco near Waco, Texas, a length of over 257 kilometers (160 miles; Figure 1). The North Bosque River watershed encompasses nearly 316,600 hectares (782,000 acres) in north central Texas and represents 74 percent of the drainage area to Lake Waco. The North Bosque River is important as the dominant source of water to Lake Waco, a public water supply for a service population of about 150,000 people. With increasing concerns about the availability of ground water, small municipalities along the North Bosque River are exploring the use of surface water. For example, Clifton (estimated population 3,600) has built an off-stream reservoir to take advantage of surface water from the North Bosque River, and Meridian (estimated population 1,500) is considering the use of surface water from the North Bosque River for public water supply.

Figure 1 TIAER sampling sites on the North Bosque River.

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An increasing focus on water quality within the North Bosque River has accompanied increasing interest in its use. In 1990, the North Bosque River watershed was identified as an impacted watershed due to nonpoint source pollution (Texas Water Commission and Texas State Soil and Water Conservation Board, 1991). Segments 1226 and 1255 along the North Bosque River have been on the Texas 303(d) list of impaired waters prepared by the Texas Natural Resource Conservation Commission (TNRCC) since 1992 (Figure 2). Segment 1226 is defined as the North Bosque River from a point 100 meters (328 feet) upstream of Farm-to-Market Road 185 in McLennan County near Lake Waco to a point immediately above the confluence of Indian Creek in Erath County (TNRCC, 1996). Designated water uses for segment 1226 include contact recreation, high aquatic life, and public water supply. Segment 1255 is defined as the North Bosque River from a point immediately above its confluence with Indian Creek to the confluence of the North and South Forks of the North Bosque River above Stephenville. Designated uses for segment 1255 include contact recreation and intermediate aquatic life use.

Figure 2 Classified stream segments within the Bosque River watershed.

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Chapter 1 Introduction

Segments 1226 and 1255 were included in the Clean Water Act Section 303(d) list for Texas as impaired water bodies under narrative water quality standards related to nutrients and aquatic plant growth (TNRCC, 2000). The TMDL effort for segments 1226 and 1255 is focusing on nutrients due to the role of nutrients in promoting excessive algae growth as indicated by elevated chlorophyll-α levels all along the North Bosque River (TNRCC, 1999). In September 2000, the TNRCC released two TMDLs for the North Bosque River for public review (TNRCC, 2000). Phosphorus is identified as the nutrient limiting the growth of aquatic plants, and about a 50 percent reduction in loading of soluble reactive P is proposed along both segments.

Nutrients are a concern in surface waters because excessive nutrients can cause accelerated or “cultural” eutrophication. Eutrophication refers to increased productivity of algae associated with nutrient enrichment and is a natural process in aquatic systems, but when accelerated by humans, eutrophication can lead to an overabundance of aquatic plant biomass or algal blooms. From a water quality perspective, algal blooms are undesirable because they can significantly increase water treatment costs, particularly in small reservoirs, by increasing filtration and disinfecting requirements (Walker, 1983). Some algae release undesirable substances, such as geosmin from Oscillatoria chalybea or 2-methylisoborneol (MIB) from Anabaena circinalis (Izaguirre et al., 1982). Geosmin and MIB are associated with taste and odor problems in drinking water that are very costly to treat. Further, the chlorination step often used in water treatment may form chlorinated hydrocarbons, such as trihalomethanes, which are a potential health risk because they exhibit, or are suspected of having, carcinogenic and/or mutagenic properties (Palmstrom et al., 1988; Martin and Cooke, 1994). These undesirable chlorination by-products increase with increases in organic matter and ammonia from the decay of algae (Rook, 1976). From an ecosystem perspective, algal blooms can cause large diurnal swings in the amount of dissolved oxygen in a water body. Algae continuously use oxygen for respiration, but only during the day do algae replenish oxygen to the water via photosynthesis. As the algae from a bloom die off, the decomposition of large amounts of dead algae can further deplete oxygen supplies. These decreased oxygen levels can cause fish kills (Boyd, 1990). Decomposition of cyanobacteria (blue-green algae) blooms are further detrimental in that they may release toxins that are threatening to livestock and humans if consumed (Codd, 1995).

While the presence of some algae is necessary in maintaining a balanced aquatic ecosystem, avoiding eutrophic situations is generally desirable. It is thus helpful to understand some of the factors regulating algal growth. In most freshwater systems, phosphorus (P) is the limiting nutrient to the growth of algae (Gibson, 1997). Although nitrogen and even carbon limitation can occur, particularly in smaller pond systems (Boyd, 1990), P limitation is most often documented in freshwater lake and stream systems (Klotz, 1991). Relatively little P is required for the biomass production of algae. An average molar equivalent often quoted for algal tissue is the Redfield Ratio of carbon (C), nitrogen (N), and P of 106C:16N:1P (Redfield, 1958). Although the actual ratio of C:N:P will vary by species and even trophic status of the water body (Harris, 1986), the Redfield Ratio remains a good general relationship for evaluating the nutrient needs of algae. Algal bioassay experiments for limiting nutrients further indicate that phosphorus supplies most likely limit the growth of algae in Lake Waco (Dávalos-Lind and Lind, 1999) and at sites along the North Bosque River (Matlock and Rodriguez, 1999). The bioavailability of phosphorus within the North Bosque River and that reaching Lake Waco is, thus, a very important consideration in evaluating the potential for accelerated algal growth along the North Bosque River and in Lake Waco.

Forms of phosphorus are non-conservative and can undergo many biogeochemical changes during transport along a waterway. In rather rough terms, phosphorus can be categorized as soluble phosphorus and particulate phosphorus (PP). Soluble phosphorus is approximated in this research as soluble reactive phosphorus (SRP) or phosphorus that will pass through a 0.45 µm pore filter and is reactive with molybdate (NRC, 1993). SRP primarily consists of

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orthophosphate and is also referred to as dissolved reactive phosphorus (NRC, 1993). Inorganic PP is associated with the mineral fraction and primarily involves the binding of P with aluminum, iron, or calcium compounds. Organic PP forms include such compounds as phospholipids, nucleic acids, and humic acids (Nelson and Logan, 1983). The pools of PP and SRP are not static in surface waters. SRP may be taken up by plants, algae, and/or bacteria or bound by minerals on and into sediment particles. Portions of PP are moderately labile and may flux between soluble and particulate forms. P has no significant atmospheric fluxes, unlike N, and exists in only one valance state in its solid and liquid phases (Stevenson, 1986). P characterization in aquatic systems, thus, deals primarily with fluxes of P between sediments and solution, and plant and animal uptake and decay.

There are two primary modes of interaction of dissolved phosphate with fluvial inorganic sediments (Froelich, 1988). One mode is via adsorption and desorption on particle surfaces primarily through interactions with reactive iron and aluminum hydroxyoxides associated with natural clay particles. This reaction is generally fast (minutes to hours) and easily reversible creating a moderately labile PP pool. The second mode is via solid-state diffusion of adsorbed phosphate from the surface to the interior of sediment particles. This reaction has a much slower kinetic rate (days to months) and depends on the previous history of the sorption surface in relation to its sorption capacity and the chemistry of the solid diffusion layer. The movement of P into the interior of sediment particles leads to a more stable and less easily reversible state that is generally considered unavailable for uptake by aquatic plants or animals.

P forms may also change via biological uptake and release. SRP or loosely bound PP may be taken up by aquatic plants and animals and converted to organic P. As aquatic plants and animals die and decay, this organic P is mineralized or reconverted to inorganic P as a cycling process. While nutrient cycling occurs via the uptake, release, and re-uptake of nutrients, very little cycling occurs in place. Nutrients generated at one place on a stream are generally transported downstream prior to reutilization (Newbold et al., 1983). Downstream transport and nutrient cycling are interrelated processes jointly referred to as nutrient spiralling due to the continuous downstream displacement of nutrients as they cycle within the system (Mulholland et al., 1985). The amount of recycling that occurs generally depends on the rate of flow and the length of the river reach (Newbold et al., 1983).

The purpose of this study is to determine the influence of natural assimilative processes in the North Bosque River on its loading of bioavailable P to Lake Waco. The significance of this study arises from several interrelated facts and concerns. Facts known about the watershed include:

• The algal community within Lake Waco is limited by P (Dávalos-Lind and Lind, 1999)

• The North Bosque River is the major source of P to Lake Waco (McFarland and Hauck, 1999)

• The two major sources of bioavailable P in the North Bosque River are dairy operations and the Stephenville wastewater treatment plant, both of which are located in the upper portion of the watershed (McFarland and Hauck, 1999)

In relation to these facts, further investigation is needed to assess the following questions:

• Is soluble phosphorus, which is loaded in the upper portion of the watershed, still soluble and bioavailable to algae by the time it reaches Lake Waco or do transformations occur making this phosphorus less available?

• Are in-stream processes important to include in watershed nutrient loading models for predicting the impact of land use changes on water quality?

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Chapter 1 Introduction

• Do differences in flow (i.e., base versus storm flow) influence differently the impact of river transport and assimilation on the delivery of bioavailable P within the North Bosque River watershed?

• Are the type of soluble P loading (continuous point source versus stochastic nonpoint source contributions) and the location of the source contribution important factors in the delivery of bioavailable P to Lake Waco?

While it is beyond the scope of this study to completely answer these questions, the monitoring data set collected by the Texas Institute for Applied Environmental Research (TIAER) does allow a preliminary investigation. Monitoring data of flow and water quality collected during base flow and storm events will be used to evaluate the following questions:

• Is there spatial variability in P concentrations and forms at sites on the North Bosque River?

• Are P concentrations of SRP, PP, and total-P correlated to flow conditions?

• How much of the P load (TP and SRP) in the North Bosque River is transported during base flow versus storm events?

• Is dilution from inflowing tributaries or P transformations responsible for the decrease in SRP concentrations from upstream to downstream sites during storm events?

• Do transformations of soluble P to particulate P occur during storm events and/or base flow and, if so, what is the magnitude of these transformations?

While the monitoring program was not designed to directly answer these questions, important insights may be gleaned through prudent data evaluation. The purpose of this report is to evaluate monitoring data collected by TIAER at sites along the North Bosque River within the context of known in-stream transport and biogeochemical processes for phosphorus. The goal is to ascertain the fate of phosphorus, particularly SRP, at different points in the North Bosque River during base flow and storm events and to discuss the potential impact of in-stream transformations and transport processes on P loadings and bioavailability from the North Bosque River to Lake Waco.

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CHAPTER 2

Sites on the North Bosque River

Sampling on the North Bosque River is conducted at eight sites (BO020, BO040, BO070, BO060, BO080, BO085, BO090, and BO100) beginning upstream at BO020, located above Stephenville, and continuing downstream to BO100, located near Valley Mills (Figure 1). Routine grab samples are collected at all eight sites. Storm sampling using automatic samplers occurs at five sites—BO020, BO040, BO070, BO090, and BO100. The land within the North Bosque River watershed is primarily rural, although six cities are located along the North Bosque River. These cities in an upstream to downstream order are Stephenville (16,000),1 Hico (1,500), Iredell (370), Meridian (1,500), Clifton (3,600), and Valley Mills (1,200). Each of these cities is permitted to discharge wastewater treatment plant (WWTP) effluent into the North Bosque River (Table 1). Biweekly grab samples of the WWTP effluents are collected to characterize these discharges.

General land use descriptions indicate a decreasing trend in the amount of permanent pasture and dairy waste application fields and an increasing trend in the amount of land categorized as wood/range and cropland from BO020 to BO100 (Table 2). Land use for the watershed is based on Landsat Thematic Mapper imagery classification processed into a Geographic Information System (GIS) layer by the U.S. Department of Agriculture (USDA)-Natural Resources Conservation Service Texas State Office in Temple, Texas. The land use data layer was developed from an August 1992 overflight for Erath County and a June 1996 overflight for Bosque, Coryell, Erath, Hamilton, and McLennan counties which were updated with extensive ground truthing occurring in January through April 1998. Information on dairy waste application fields was obtained from dairy permits and dairy waste management plans on file with TNRCC and overlaid on the general land use data layer to represent a separate land use category. The data on dairy waste application fields represents information as of January 1995. The size of the drainage area above sampling sites was delineated from an U.S. Geological Survey (USGS) 1:24,000 digital elevation map.

1 Numbers in parentheses represent the estimated population of each city as presented in the 1998-99 Texas Almanac (Dallas Morning News, 1997).

Table 1 Permitted point source discharges to the North Bosque River.

Wastewater Treatment Plant

Permitted Daily Average Discharge(m3/day)

Permitted Daily Average Discharge

(million gallons per day)

Stephenville 11,355 3.00

Hico 757 0.20

Iredell 189 0.05

Meridian 1,703 0.45

Clifton 2,460 0.65

Valley Mills 1,363 0.36

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The location of each sampling site is described below.

North Bosque River above Stephenville (site BO020) Site BO020 is located on the North Bosque River below the confluence of the North and South Forks at the crossing of State Highway 8 on the northeast boundary of Stephenville. Site BO020 is located near the beginning of the North Bosque River and contains a small portion of the city of Stephenville in its drainage area.

North Bosque River below the Stephenville Wastewater Treatment Plant (site BO040) Site BO040 is located on the North Bosque River about 400 meters (1,300 ft) below the Stephenville wastewater treatment plant (WWTP). Site BO040 is located at the crossing of County Road (CR) 454 about 8 river kilometers (5 river miles) below site BO020.

North Bosque river near Green Creek (site BO060) Site BO060 is located on the North Bosque River about 23 river kilometers (14 river miles) downstream of site BO040 at the crossing of CR 248.

North Bosque River at Hico (site BO070) Site BO070 is located near USGS station 08094800 on the North Bosque River at the crossing of U.S. Highway 281 in Hico, Texas. The drainage area of this site is referred to as the upper North Bosque River watershed in most TIAER data analysis reports (e.g., McFarland and Hauck, 1995; 1997). BO070 is located about 34 river kilometers (21 river miles) downstream of site BO040. Site BO070 is above the Hico WWTP effluent discharge.

North Bosque River at Iredell (site BO080) Site BO080 is located on the North Bosque River below the confluence of Duffau Creek and above the WWTP effluent discharge for the city of Iredell. BO080 is located about 23 river kilometers (14 river miles) downstream of site BO070.

North Bosque River at Meridian (site BO085) Site BO085 is located on the North Bosque River at Farm-to-Market (FM) Road 2840, west of Meridian, above the Meridian WWTP effluent discharge. BO085 is located about 27 river kilometers (17 river miles) downstream of BO080.

North Bosque River at Clifton (site BO090) Site BO090 is located near USGS station 08095000 on the North Bosque River near the crossing of FM Road 219 about a kilometer northeast of Clifton, Texas. BO090 is located about 23 river kilometers (14 river miles) downstream of BO085. Site BO090 is located above the Clifton WWTP effluent discharge.

Table 2 Land uses above sampling sites along the North Bosque River.

SiteWood/ Range

(%)Pasture

(%)Cropland

(%)

Dairy Waste Appl. Fields

(%)

Urban (%)

Other (%)

Drainage Area (hectares)

BO020 49.4 30.1 6.4 12.3 0.8 1.0 21,572

BO040 51.1 23.8 8.4 11.7 3.8 1.2 25,719

BO060 60.5 19.1 7.3 9.2 2.8 1.1 48,979

BO070 68.2 15.4 6.5 7.2 1.7 1.0 93,248

BO080 69.0 16.0 6.6 6.4 1.7 0.3 146,211

BO085 71.3 14.5 7.3 5.0 1.6 0.3 189,587

BO090 71.9 13.8 8.9 3.7 1.5 0.2 253,740

BO100 72.4 13.6 9.4 3.1 1.4 0.1 302,320

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Chapter 2 Sites on the North Bosque River

North Bosque River at Valley Mills (site BO100) Site BO100 is located south of the USGS station 08095200 on the North Bosque River near the crossing of FM Road 56 northeast of Valley Mills. BO100 is located about 19 river kilometers (12 river miles) downstream of BO090 and about 45 river kilometers (28 river miles) upstream from the mouth of the North Bosque River at Lake Waco. BO100 is located above the Valley Mills WWTP effluent discharge.

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CHAPTER 3

Data Collection and LaboratoryMethods

Routine grab sample collection consists of a single, representative sample taken at 0.1 to 0.3 meters (0.25 to 1.0 ft) below the surface of the water and represents primarily base flow conditions. Routine sampling occurs on a set biweekly schedule at sites along the North Bosque River. A grab sample is not taken during routine monitoring if a site is dry or if the water at a site is pooled and not flowing. During low flow conditions, riffle areas near each sampling site are observed to determine the presence or absence of flow.

Storm samples are collected using automatic sampling equipment consisting of an ISCO 3230 or 4230 bubbler-type flow meter and an ISCO 3700 automatic sampler enclosed in a sheet metal shelter. The flow meter measures the pressure required to force an air bubble through a 3-mm (0.125-in) polypropylene tube (bubbler line) and records this pressure as water level. The flow meters are programmed to record stream water level (stage) and are used to initiate sample retrieval by the automatic samplers when a certain stream level is obtained. Each flow meter is programmed to record water level at five-minute intervals and typically actuates storm sampling when a stream rise of 4-cm (1.5 in) above the bubbler datum is registered. The actuation level was selected by trial and error as the lowest level at which the sampler would actuate for rainfall-runoff events while avoiding undesired actuation from non-rainfall event causes such as wave action. Electrical power is provided to the flow meter and sampler by marine, deep-cycle batteries with recharge provided by solar cells.

Once activated, samplers are programmed to retrieve one-liter sequential samples throughout a storm event following a set sampling sequence. The sampling sequence for North Bosque River sites is (1) an initial sample, (2) three samples taken at one-hour intervals, (3) two samples taken at two-hour intervals, and (4) all remaining samples taken at eight-hour intervals. This sampling sequence allows for more frequent sample collection during the typical rapid hydrograph rise and peak periods following sampler actuation and less frequent sample collection during the longer, receding portion of a storm hydrograph.

To convert the level data recorded by the flow meter to discharge, site specific stage-discharge relationships must be used. For stream sites BO020 and BO040, stage-discharge relationships were developed from manual measurements of flow at various stream levels. Because only a limited number of stage-discharge points were available for site BO020, the flow data for this site were considered of sufficient accuracy to be used in flow weighting of storm event concentrations but of questionable accuracy to be used in determining nutrient loadings. Reliable calculations of loadings are highly dependent upon having accurate flow, whereas, flow-weighted storm event concentrations are generally much less sensitive to inaccuracies in flow. Flow and nutrient loading information for BO020 is, thus, considered provisional in this report. At site BO070, the USGS stage-discharge relationship for station 08094800 was used in conjunction with measured level data to calculate flow. At sites BO090 and BO100, discharge data from corresponding USGS sites 08095000 and 08095200 were obtained for use in this report. Sedimentation problems, particularly during large flow events at USGS site 08095200

21


(Lury, 1997), limit the direct use of the flow information for BO100 in estimating loadings, but the discharge data still provide a good relative indication of storm dynamics at this site.

Routine grab and stormwater samples are analyzed for soluble ammonia-nitrogen, soluble nitrite-nitrogen, soluble nitrate-nitrogen, total Kjeldahl nitrogen, SRP, total phosphorus (TP), and total suspended solids (TSS). As the focus of this report is on in-stream phosphorus transport and transformations, data analyses will focus on SRP, TP, and TSS. General information on the other constituents routinely measured at these sites can be found in TIAER’s semiannual water quality reports (e.g., Pearson and McFarland, 1999). SRP was analyzed using U.S. Environmental Protection Agency (EPA) Method 365.2, TP was analyzed using EPA Method 365.4, and TSS was analyzed using EPA Method 160.2 (EPA, 1983). All sampling and analyses were conducted under EPA or TNRCC approved quality assurance project plans, for example, TIAER (1998).

Bioavailable phosphorus (BAP) was not directly measured for this study but was evaluated as a special study project by TIAER. Preliminary measurements of BAP at sites along the North Bosque River using the iron oxide impregnated strip extraction method (Sharpley et al., 1992) indicate that SRP represents about 90 percent of BAP in this system (R2 = 0.93; BAP = 1.10*SRP – 0.003; n = 75). The bioavailability of P is a critical factor in determining the potential productivity of aquatic systems. BAP refers to the soluble phosphorus fraction and the loosely bound or labile particulate phosphorus fraction that is readily available for the growth of algae or plants. While not a complete measurement of BAP, SRP appears to be a good surrogate of BAP for conditions within the North Bosque River and will be used as such in this report.

In data management, left censored data (values measured below the laboratory method detection limit) were entered into the water quality database as one-half the method detection limit (MDL) as recommended by Gilliom and Helsel (1986) and Ward et al. (1988). MDLs are evaluated about every six months by TIAER’s water quality laboratory. MDL values between November 1995 and July 1998 ranged from 0.003 mg/L to 0.011 mg/L for SRP, from 0.024 mg/L to 0.153 mg/L for TP, and from 3 mg/L to 10 mg/L for TSS.

22

CHAPTER 4

Data Analysis Methods

The monitoring network within the Bosque River watershed has evolved over a number of years as different projects and concerns have directed sampling needs and funding. While routine water quality monitoring by TIAER along the North Bosque River began in April 1991 at sites BO040, BO060, and BO070 (Table 3), routine grab sampling at all eight North Bosque River sites was not initiated until May 1996. Storm sampling began at site BO040 in May 1991 but was not initiated at BO020 until February 1997. To evaluate comparable time periods of data collection between sites, this report focuses primarily on data collected between February 1997 and July 1998 for comparisons between sites for routine grab and storm sampling. Evaluation of inflow volumes and loadings of SRP, TP, and TSS were made for a more extended time period at sites BO040, BO070, and BO090 using data collected between November 1995 and July 1998.

Question 1. Is there spatial variability in P concentrations and P forms at sites on the North Bosque River? Spatial trends in water quality along the North Bosque River for base flow and storm events were evaluated by comparing water quality between sites using a protected least significant difference (LSD) multiple comparison test (Ott, 1984). Routine grab samples were taken on set sampling dates and were screened prior to analysis to remove grab samples taken during elevated flows associated with storm events. Because water quality can vary greatly within a storm event and several samples may be taken within a single event, storm samples were volume-weighted to calculate event-mean concentrations (EMCs). EMCs were calculated by dividing the storm hydrograph into intervals based on the date and time when

Table 3 Monitoring history for sampling sites along the North Bosque River.

Site LocationSample Typea

a. S=storm samples collected with an automatic sample; G=grab samples collected on a biweekly or monthly basis

Date of First Grab

Sample

Date of First Automatic Storm

Sample

BO020 North Bosque River above Stephenville S, G 26-May-94 06-Feb-97

BO040 North Bosque River below Stephenville S, G 04-Apr-91 25-Aug-93

BO060 North Bosque River at Green Creek G 04-Apr-91 NAb

b. NA=not applicable

BO070 North Bosque River at Hico S, G 04-Apr-91 08-May-91

BO080 North Bosque River at Iredell G 07-May-96 NA

BO085 North Bosque River at Meridian G 07-May-96 NA

BO090 North Bosque River at Clifton S, G 26-Sep-95 04-Nov-95

BO100 North Bosque River at Valley Mills S, G 26-Feb-96 05-Apr-96

23


water quality samples were taken using a midpoint rectangular integration method between water quality samples (Stein, 1977). Constant flow was assumed between each five-minute water level measurement to estimate the water volume associated with each water quality sample. EMCs across storm events were used to characterize storm-water quality at each site. Only storm events which activated all five storm-water sampling sites were used to compare storm-water quality between sites (Appendix A). A natural-log transformation was implemented on grab sample constituent concentrations and EMCs prior to statistical analysis based on an evaluation of these data sets using the Shaprio-Wilks test for normality (SAS, 1990) and the Hartley’s F-test for homogeneity of variances (Ott, 1984).

Question 2. Are P concentrations of SRP, PP, and TP correlated to flow conditions? A cross-correlation of flow or storm volume conditions with P and TSS concentrations was conducted to determine if P concentrations were related to flow conditions. This analysis was also used to evaluate the interrelations of the different P forms (SRP, PP, and TP) at upstream to downstream sites. Correlation analyses were conducted using EMCs for storm events and individual base flow samples. Data were evaluated graphically to determine the need for data transformations. For storm events, a natural-log transformation was indicated for both EMCs and storm volume to better linearize these relationships. The use of a natural log transformation does not change the interpretation of the correlation coefficients or the significance of the relationships, although the non-transformed relationships are curvilinear rather than linear (Finkelstein and Levin, 1990).

Question 3. How much of the P load (TP and SRP) in the North Bosque River is transported during base flow versus storm events? To address how much P loading was occurring and in what form (SRP or PP) during base flow versus storm events, flow data were integrated with water quality information. Transport conditions (i.e., storm or base flow) at the five sites with flow information (BO020, BO040, BO070, BO090, and BO100) were evaluated by calculating daily flow volume and loadings using methods similar to those used for calculating EMCs. Storm and grab sample data were included in the integration of daily loadings. Flow volume and mass loadings for each day were classified as storm or base flow using the sampling program as an indicator. If a storm sample was taken on a given day, the volume and mass for that day was classified as storm flow. All days without storm samples were classified as base flow.

Question 4. Is dilution from inflowing tributaries or P transformations responsible for the decrease in SRP concentrations from upstream to downstream sites during storm events? To address the potential for in-stream transformations during storm events, storm concentrations between upstream to downstream sites were compared to concentrations from inflowing tributaries between main stem sites. The objective was to determine if the decrease in SRP concentrations from upstream to downstream sites, noted in several TIAER reports (e.g., McFarland and Hauck, 1999; Pearson and McFarland, 1999), was due to dilution from inflowing tributaries or if P transformations from SRP to PP were occurring. For sites BO040, BO070, and BO090, the time period evaluated included samples collected between November 1995 and January 1997 (Appendix B) and between February 1997 and July 1998 (Appendix A). Inflow loads were not evaluated between sites BO020 and BO040 and sites BO090 and BO100 due to limitations in the flow information at sites BO020 and BO100.

A systematic approach was used to estimate inflow load and volume contributions between sites BO040 and BO070 and sites BO070 and BO090 for storm events. Inflow volumes (equation 1) and loads (equation 2) were estimated for individual storm events as follows:

1) Vb Vd Vu–=

24

Chapter 4 Data Analysis Methods

where:

d = downstream gauging site,

u = upstream gauging site,

Vb = inflow volume between sites u and d,

Vd = the volume of flow at the downstream gauging site, and

Vu = volume of flow at the upstream gauging site.

2)

where:

i = constituent: 1 = SRP, 2 = TP, and 3 = TSS,

Li,b = inflow load of constituent i between sites u and d,

Li,d = load of constituent i at the downstream gauging site, and

Li,u = load of constituent i at the upstream gauging site.

These mass balance equations assume conservation of mass between upstream and downstream sites and that the error in the closure of the mass balance equals zero. That is, the two equations as defined assume that any difference between downstream and upstream conditions is attributable to tributary input and not significantly impacted by in-stream processes, such as channel losses. For river flow, this assumption may be more problematic during base flow than during storm flow. Channel losses (e.g., seepage and evaporation) of flow are typically not great along the North Bosque River during storm events. However, these losses become a more significant proportion of flow as flow decreases. In the mass balance for waterborne constituent loads (equation 2), the assumption of conservation of mass (i.e., conservation of constituents in transport) is expected to be even more problematic than for flow. In fact, a major focus of this study is to determine the accuracy of the assumption of conservation of mass for TP and, especially, SRP.

To test the assumption of conservation of mass during storm events, the average of calculated storm event inflow concentrations was compared to measured storm event inflow concentrations for appropriate tributaries. Between BO040 and BO070, five major tributaries enter the North Bosque River. These are Alarm Creek, Sims Creek, Indian Creek, Green Creek, and Spring Creek (Figure 1). Between BO070 and BO090, three major tributaries enter the North Bosque River. These are Duffau Creek, East Bosque River, and Meridian Creek. If calculated and measured storm event concentrations of SRP for tributary inflow are similar, it could be assumed that dilution is the primary factor causing the decrease in SRP concentrations from upstream to downstream sites and that mass is conserved. If calculated inflow concentrations of SRP are much smaller than measured storm event concentrations, this would indicate that some in-stream transformations of SRP are occurring during transport of storm flow from upstream to downstream sites and that mass as SRP is not conserved.

This comparison was limited to storms in which

3)

Li b, Li d, Li u,–=

Vb Vd⁄ Ab Ad 0.1–⁄( )≥

25


where:

Ab = inflow drainage area between the upstream and downstream gauging sites, and

Ad = the drainage area of the downstream gauging site.

This restriction was applied to ensure that the storms used for comparison had significant tributary inflow contributions.

Question 5. Do transformations of soluble P to PP occur during storm events and/or base flow and what is the magnitude of these transformations if they occur? To evaluate the potential and magnitude for in-stream transformations during base flow and storm events, daily cumulative volumes and loadings were calculated for BO040, BO070, and BO090. Cumulative daily inflow volumes and loads between sites BO040 and BO070 and sites BO070 and BO090 were calculated in a manner similar to that used for storm events (see equations 1 and 2). Cumulative daily volumes and loads were standardized on a per hectare basis for the watershed drainage area represented and plotted over time to highlight periods of loss or gain in loadings of SRP, TP, and TSS. This approach was used to determine if in-stream transformations are apparent during base flow or storm event conditions as would be indicated by decreases in cumulative inflow loadings between upstream and downstream sites.

26

CHAPTER 5

Precipitation Conditions

Spatially and temporally monthly precipitation was quite variable throughout the watershed during the study period (Table 4). The locations of these National Weather Service observer sites can be referenced to the communities on Figure 1.

In comparison to the long-term average for Stephenville and Waco Dam, much of the study period indicated below normal precipitation levels with a few dominating periods of above

Table 4 Total monthly rainfall for selected National Weather Service Observer Stations.

National Weather Service Observer Station

Month Year Stephenville(cm)

Dublin(cm)

Hico(cm)

Cranfills Gap(cm)

Meridian(cm)

Valley Mills (cm)

Waco Dam(cm)

January 1995 2.39 3.10 3.10 4.65 3.66 4.80 a

a. Indicates missing data

February 1.35 2.01 2.51 3.89 2.67 4.39 1.91March 9.75 10.64 7.52 7.16 10.62 11.05 9.32April 5.59 10.03 11.99 15.09 17.73 19.48 19.23May 13.16 17.40 21.41 21.44 21.39 16.05 12.37June 9.75 15.32 10.41 10.64 10.21 8.76 9.40July 21.72 5.66 18.16 6.20 4.32 8.71 5.51August 7.67 17.42 8.79 11.33 28.32 10.80 19.33 September 8.33 14.15 10.80 7.54 12.14 7.01 10.11October 6.55 6.73 0.53 0.15 0.91 0.56 0.81 November 1.57 7.75 3.25 2.31 4.75 2.64 4.34 December 1.75 2.01 2.64 3.96 3.56 5.33 3.23January 1996 1.24 1.40 0.76 1.04 0.08 3.07 2.06February 0.64 0.08 1.02 0.48 0.41 0.00 0.43March 2.87 3.05 3.53 2.46 3.02 6.10 2.95April 6.60 8.05 6.93 8.18 7.14 7.54 6.73May 7.42 13.54 8.08 9.19 2.87 2.95 4.95June 6.93 7.26 8.89 11.53 7.29 4.17 7.90July 7.06 6.48 6.30 8.79 13.34 4.01 7.01August 22.63 34.11 20.37 20.24 20.57 19.35 13.69 September 11.30 6.05 6.58 10.16 21.23 a 9.09October 7.26 8.38 8.18 4.98 8.84 4.14 2.77 November 10.21 9.78 8.23 9.32 10.06 7.54 11.02 December 0.30 0.69 2.08 3.84 4.60 7.19 7.80January 1997 1.04 0.05 2.95 4.93 4.67 a 2.64February 21.08 29.82 25.65 19.56 19.91 a 19.61March 8.36 10.87 8.61 8.20 11.51 a 5.28April 11.33 15.29 14.33 12.57 17.42 a 10.87May 8.76 17.93 11.66 14.73 7.39 a 9.86June 16.31 23.50 19.66 14.27 13.64 a 14.22July 3.40 0.00 0.00 0.18 0.30 a 1.93August 4.42 7.75 2.01 4.75 1.55 a 3.58 September 2.77 2.74 1.68 1.47 1.17 a 3.15October 11.61 7.04 11.91 9.68 14.12 a 6.07 November 1.83 3.25 3.02 3.02 2.44 a 6.63 December 10.59 11.71 10.92 11.89 14.68 17.02 11.23January 1998 5.74 7.21 5.31 4.62 6.22 7.19 11.10February 7.29 11.53 9.07 10.21 9.73 9.63 9.83March 10.80 11.20 16.28 13.16 10.19 10.44 5.36April 0.76 1.91 1.63 3.20 1.40 3.12 4.29May 11.56 9.78 4.11 1.93 3.30 1.27 1.55June 5.92 6.22 4.67 4.50 3.00 4.62 3.43July 3.94 8.26 3.76 1.80 2.26 1.91 1.09Totals 241.86 301.40 244.60 241.33 253.57 nab

b. na indicate not applicable due to missing data

216.51

27


normal precipitation (Figure 3). Rainfall in August 1996 and February 1997 indicated levels well above normal at both the Stephenville and Waco Dam sites. The February 1997 rainfall is of note in that it came as very intense watershed-wide storm events with precipitation of about 5 cm (2 in) or more falling daily on February 6, 12, 19, and 20 followed by more rain on March 2, 1997 (Jones, 1998). While March 1998 does not stand out as strongly as an above normal precipitation month, most of the rainfall in this month occurred on three days, March 14, 15, and 16 (Jones, 1999). During this March 1998 storm event, the upper two-thirds of the watershed received about 10 cm (4 in) and the lower third about 6 cm (2.5 in) of precipitation. These variations in precipitation are largely reflected in the volume of stream flow along the North Bosque River and will be discussed in more detail with the results of the stream water quality analyses.

Figure 3 Monthly precipitation and departure from normal for Stephenville and Waco Dam.Data obtained from National Weather Service observer sites with average monthly precipitation calculated for 1967-1996.

-15

-10

-5

0

5

10

15

20

25

Nov

-95

Jan-

96

Mar

-96

May

-96

Jul-9

6

Sep-

96

Nov

-96

Jan-

97

Mar

-97

May

-97

Jul-9

7

Sep-

97

Nov

-97

Jan-

98

Mar

-98

May

-98

Jul-9

8

Prec

ipita

tion

(cm

)

Stephenville

-15

-10

-5

0

5

10

15

20

25

Nov

-95

Jan-

96

Mar

-96

May

-96

Jul-9

6

Sep-

96

Nov

-96

Jan-

97

Mar

-97

May

-97

Jul-9

7

Sep-

97

Nov

-97

Jan-

98

Mar

-98

May

-98

Jul-9

8

Prec

ipita

tion

(cm

)

Monthly Precipitation Departure from Average

Waco Dam

28

CHAPTER 6

Results and Discussion

Spatial Variability in P Concentrations and FormsIn general, higher phosphorus concentrations were observed at upstream than at downstream sites along the North Bosque River for storm and base flow conditions (Figure 4). The opposite was found for TSS with the highest concentrations occurring at the most downstream sites, BO090 and BO100. Higher concentrations of phosphorus and TSS were also generally observed during storm events than during routine sampling. Only SRP at BO040 showed greater concentrations for routine grab samples than storm events samples.

It is important to note that although grab samples were screened to remove samples taken during storm events, a fairly broad range of flows was still represented for base flow conditions along the river (Table 5). Base flow conditions ranged from trace amounts (less than 0.014 m3/s or 0.5 ft3/s) as a minimum flow rate at BO040 to over 20 m3/s (700 ft3/s) as a maximum flow rate at BO100. The median value for flow at each site probably best represents typical base flow conditions (Table 5).

At site BO040 routine grab samples representing primarily base flow are also greatly influenced by effluent discharge from the Stephenville WWTP. Site BO040 is located about 400 meters below the discharge of the Stephenville WWTP. The median discharge rate of the Stephenville WWTP was 0.07 m3/s (2.5 ft3/s) between February 1997 and July 1998 (Table 6), while the median river flow when routine grab samples were collected was 0.1 m3/s (3.5 ft3/s). This indicates that on a daily average the majority of base flow at BO040 is represented by the Stephenville WWTP discharge. While the effluent from other WWTPs will impact water quality along the North Bosque River to varying degrees, the largest impact occurs at BO040 because of the close proximity of the Stephenville WWTP discharge to BO040 and the relatively large contribution of the effluent discharge to base flow conditions at BO040. For reference, the average daily discharge of each WWTP by month is presented in Appendix C for November 1995 through July 1998.

Table 5 Basic statistics of stream flow associated with routine grab samples. Flow statistics represent data for instrumented sites along North Bosque River collected between February 1997 and July 1998.

Site Mean(m3/s)

Median(m3/s)

Std(m3/s)

Minimum(m3/s)

Maximum(m3/s)

Number of Observations

BO020a

a. Flows at BO020 are considered provisional based on limitations in the development of the rating curve.

0.1 0.1 0.1 Tb

b. Minimum flows below 0.014 m3/s are represented as T or trace flows

0.5 31BO040 0.2 0.1 0.2 T 0.9 35BO070 3.2 2.6 2.1 1.3 10.2 34BO090c

c. Flow at BO090 and BO100 represents provisional data from the USGS.

3.5 1.9 3.6 0.1 11.6 32BO100c 5.5 2.9 5.8 0.4 19.7 32

29


Figure 4 Geometric mean values for SRP, TP, and TSS at sites along the North Bosque River.Samples collected between February 1997 and July 1998. Base flow columns with the same upper case letter and storm columns with the same lower case letter are not significantly different at a probability level of 0.05 according to a test of least significant differences. Storm samples were not collected at sites BO060, BO080, and BO085.

30

Chapter 6 Results and Discussion

To partition TP into its soluble and particulate fractions, SRP was subtracted from TP with the remaining portion representing PP. In the upper reaches of the North Bosque River between sites BO020 and BO070, 38 percent or more of TP is represented by soluble P with the soluble fraction decreasing to about 20 to 26 percent of TP at sites BO090 and BO100 under base and storm flow conditions (Figure 5). This downstream decrease in the fraction of TP represented by soluble P gives an indication of in-stream transformations of SRP to PP and/or a change in the partitioning of TP in the downstream direction with tributary inflows.

The higher proportion of soluble P in the upper portion of the watershed during base flow and storm events reflects the major sources of P to the river. In the upper portion of the watershed (BO070 and above), about 48 percent of the TP loadings are associated with dairy waste application fields (McFarland and Hauck, 1998a). Over 60 percent of the P from dairy

Table 6 Municipal wastewater treatment plant effluent characteristics.Statistics are from data collected between February 1997 through July 1998. SRP, TP, and TSS data represent biweekly effluent samples collected by TIAER, while discharge data represent the monthly average of self-reporting data on file with the TNRCC.

Variable Location Mean Median Std Minimum Maximum n

SRP Stephenville 2.12 1.44 2.33 0.03 13.60 39(mg/L) Hico 3.08 3.21 1.07 0.15 4.83 39

Iredell 2.80 2.87 0.69 0.06 4.61 38Meridian 2.71 2.92 0.99 0.79 4.42 37Clifton 1.80 1.11 2.21 0.01 9.97 39Valley Mills 2.65 2.80 1.12 0.12 4.25 37

TP Stephenville 2.34 1.61 2.56 0.04 15.00 38(mg/L) Hico 3.93 3.37 4.60 0.63 31.20 39


TSS Stephenville 7 5 10 2 48 39(mg/L) Hico 39 5 217 2 1360 39

Iredell 10 5 27 2 173 39Meridian 7 5 5 2 24 37Clifton 17 5 26 2 156 39Valley Mills 5 5 4 2 23 37

Discharge Stephenville 0.079 0.071 0.027 0.054 0.133 18(m3/s) Hico 0.004 0.003 0.002 0.002 0.008 18


31


Figure 5 Percent of TP represented by soluble (SRP) and particulate (PP) forms.Storm samples were not collected at sites BO060, BO080, and BO085.

waste application fields was indicated to be in the soluble form as SRP (McFarland and Hauck, 1998a). At BO040, a notably larger percent of TP is associated with the soluble fraction during base flow than storm events. This larger proportion of SRP at BO040 during base flow is related to the high percent of SRP in relation to TP (about 90 percent) in the Stephenville WWTP discharge (Table 6). In constrast, Neils Creek and Meridian Creek, major tributaries in the lower portion of the watershed, respectively have only 24 and 17 percent of TP as SRP during base flow and 26 and 27 percent of TP as SRP during storm events.

Correlation of Water Quality to Flow Conditions Cross-correlation of base flow samples and storm event mean concentrations were developed for the five-instrumented sites (BO020, BO040, BO070, BO090, and BO100) to evaluate relationships between SRP, PP, TP, TSS, and flow or storm volume (Tables 7-16). Of note is that significant (α=0.05) positive correlations are indicated between storm volume and the concentrations of most P forms and TSS except at BO040. At BO040 (Tables 9 and 10), only TSS indicated a significant relationship with storm volume. The contribution from the Stephenville WWTP most likely confounds the relationship of the phosphorus constituents to storm volume at BO040.

20%22%21%21%38%

63%82%

58%

80%78%79%79%63%

38%18%

42%

0%

20%

40%

60%

80%

100%

BO020 BO040 BO060 BO070 BO080 BO085 BO090 BO100

Bas

e Fl

ow P

arti

tion

ing

22%26%44%

57%47%

78%74%56%

43%53%

0%

20%

40%

60%

80%

100%

BO020 BO040 BO060 BO070 BO080 BO085 BO090 BO100

Stor

m E

vent

Par

titi

onin

g

SRP PP

32


.

Table 7 Cross correlation of flow and concentration data for base flow samples at BO020. ’r’ is the correlation coefficient, ’p’ is the probability value relating to the significance of the correlation, and ’n’ is the number of observations or storm events evaluated. Samples were collected between February 1997 and July 1998.

Site BO020 SRP(mg/L)

PP(mg/L)

TP(mg/L)

TSS(mg/L)

Flow r -0.21 0.05 -0.11 0.37(m3/s) p 0.2751 0.7985 0.5500 0.0448

n 30 29 30 30

SRP r ---- 0.18 0.79 -0.23(mg/L) p ---- 0.3403 0.0001 0.2200

n ---- 30 31 31

PP r ---- ---- 0.74 0.29(mg/L) p ---- ---- 0.0001 0.1194

n ---- ---- 30 30

TP r ---- ---- ---- 0.04(mg/L) p ---- ---- ---- 0.8326

n ---- ---- ---- 31

Table 8 Cross correlation of volume and concentration data for storm events at BO020. ’r’ is the correlation coefficient, ’p’ is the probability value relating to the significance of the correlation, and ’n’ is the number of observations or storm events evaluated. Samples were collected between February 1997 and July 1998.


PP(mg/L)

TP(mg/L)

TSS(mg/L)

ln(Volume) r 0.23 0.56 0.48 0.66(m3) p 0.2641 0.0036 0.0150 0.0003

n 26 25 25 25

ln(SRP) r ---- 0.19 0.80 0.41(mg/L) p ---- 0.3535 0.0001 0.0424

n ---- 25 25 25

ln(PP) r ---- ---- 0.71 0.66(mg/L) p ---- ---- 0.0001 0.0005

n ---- ---- 25 24

ln(TP) r ---- ---- ---- 0.66(mg/L) p ---- ---- ---- 0.0005

n ---- ---- ---- 24

33


Table 9 Cross correlation of flow and concentration data for base flow samples at BO040.’r’ is the correlation coefficient, ’p’ is the probability value relating to the significance of the correlation, and ’n’ is the number of observations or storm events evaluated. Samples were collected between February 1997 and July 1998.


PP(mg/L)

TP(mg/L)

TSS(mg/L)

Flow r -0.25 0.03 -0.24 0.51(m3/s) p 0.1393 0.8630 0.1574 0.0018

n 35 31 35 35

SRP r ---- 0.41 0.98 -0.38(mg/L) p ---- 0.0230 0.0001 0.0259

n ---- 31 35 35

PP r ---- ---- 0.56 0.21(mg/L) p ---- ---- 0.0012 0.2524

n ---- ---- 31 31

TP r ---- ---- ---- -0.33(mg/L) p ---- ---- ---- 0.0512

n ---- ---- ---- 35

Table 10 Cross correlation of volume and concentration data for storm events at BO040.’r’ is the correlation coefficient, ’p’ is the probability value relating to the significance of the correlation, and ’n’ is the number of observations or storm events evaluated. Samples were collected between February 1997 and July 1998.


PP(mg/L)

TP(mg/L)

TSS(mg/L)

ln(Volume) r -0.36 0.33 -0.08 0.72(m3) p 0.0646 0.0945 0.6795 0.0001

n 27 27 27 27

ln(SRP) r ---- 0.06 0.78 -0.21(mg/L) p ---- 0.7600 0.0001 0.2850

n ---- 27 27 27

ln(PP) r ---- ---- 0.65 0.40(mg/L) p ---- ---- 0.0002 0.0386

n ---- ---- 27 27

ln(TP) r ---- ---- ---- 0.06(mg/L) p ---- ---- ---- 0.7698

n ---- ---- ---- 27

34




PP(mg/L)

TP(mg/L)

TSS(mg/L)

Flow r 0.01 0.10 -0.03 0.57(m3/s) p 0.9514 0.5978 0.8539 0.0004

n 34 32 34 34

SRP r ---- 0.20 0.79 0.02(mg/L) p ---- 0.2688 0.0001 0.9254

n ---- 32 34 34

PP r ---- ---- 0.73 0.18(mg/L) p ---- ---- 0.0001 0.3113

n ---- ---- 32 32

TP r ---- ---- ---- 0.11(mg/L) p ---- ---- ---- 0.5500

n ---- ---- ---- 34



PP(mg/L)

TP(mg/L)

TSS(mg/L)

ln(Volume) r 0.41 0.62 0.63 0.84(m3) p 0.0314 0.0004 0.0003 0.0001

n 28 28 28 28

ln(SRP) r ---- 0.27 0.78 0.37(mg/L) p ---- 0.1716 0.0001 0.0530

n ---- 28 28 28

ln(PP) r ---- ---- 0.76 0.72(mg/L) p ---- ---- 0.0001 0.0001

n ---- ---- 28 28

ln(TP) r ---- ---- ---- 0.67(mg/L) p ---- ---- ---- 0.0001

n ---- ---- ---- 28

35




PP(mg/L)

TP(mg/L)

TSS(mg/L)

Flow r -0.03 -0.01 -0.06 0.16(m3/s) p 0.8550 0.9612 0.7508 0.3812

n 32 30 32 32

SRP r ---- 0.41 0.65 0.25(mg/L) p ---- 0.0263 0.0001 0.1657

n ---- 30 32 32

PP r ---- ---- 0.95 0.39(mg/L) p ---- ---- 0.0001 0.0350

n ---- ---- 30 30

TP r ---- ---- ---- 0.39(mg/L) p ---- ---- ---- 0.0273

n ---- ---- ---- 32n ---- ---- ---- 23



PP(mg/L)

TP(mg/L)

TSS(mg/L)

ln(Volume) r 0.53 0.65 0.68 0.84(m3) p 0.0081 0.0006 0.0003 0.0001

n 24 24 24 23

ln(SRP) r ---- 0.44 0.65 0.56(mg/L) p ---- 0.0302 0.0005 0.0056

n ---- 24 24 23

ln(PP) r ---- ---- 0.96 0.83(mg/L) p ---- ---- 0.0001 0.0001

n ---- ---- 24 23

ln(TP) r ---- ---- ---- 0.84(mg/L) p ---- ---- ---- 0.0001

n ---- ---- ---- 23

36


Similarly, for base flow conditions, instantaneous flow (m3/s) was significantly correlated with TSS concentrations at all sites but BO090 and BO100. None of the P forms indicated a significant relationship with flow under base flow conditions. In general, only a weak relationship, if any, was indicated under base flow conditions between TSS and PP or TSS and SRP. During storm events, a fairly strong positive relationship (r = 0.40 to 0.83) was indicated between TSS and PP concentration at all five sites. A positive relationship between TSS and



PP(mg/L)

TP(mg/L)

TSS(mg/L)

Flow r -0.02 0.01 0.02 0.10(m3/s) p 0.9103 0.9602 0.8948 0.5695

n 32 31 32 32

SRP r ---- 0.24 0.47 -0.07(mg/L) p ---- 0.1988 0.0069 0.6841

n ---- 31 32 32

PP r ---- ---- 0.96 0.01(mg/L) p ---- ---- 0.0001 0.9700

n ---- ---- 31 31

TP r ---- ---- ---- -0.01(mg/L) p ---- ---- ---- 0.9419

n ---- ---- ---- 32



PP(mg/L)

TP(mg/L)

TSS(mg/L)

ln(Volume) r 0.45 0.53 0.60 0.75(m3) p 0.0220 0.0070 0.0011 0.0001

n 26 25 26 25

ln(SRP) r ---- 0.303 0.56 0.44(mg/L) p ---- 0.1407 0.0034 0.0290

n ---- 25 26 25

ln(PP) r ---- ---- 0.91 0.75(mg/L) p ---- ---- 0.0001 0.0001

n ---- ---- 25 24

ln(TP) r ---- ---- ---- 0.85(mg/L) p ---- ---- ---- 0.0001

n ---- ---- ---- 25

37


SRP concentrations was also indicated at sites BO020, BO090, and B0100. PP and SRP concentrations showed a weak positive correlation during storm events only at site BO090 (Table 14). At all other sites, the relationship between PP and SRP concentrations for storm events was non-significant. These cross-correlations indicate that SRP concentrations are not necessarily correlated (positively or negatively) with PP concentrations, although both PP and SRP concentrations appear to increase with storm volume in the lower portion of the watershed.

P Loading During Base Flow Versus Storm Events While base flow conditions are important for evaluating critical habitat conditions for aquatic life, the largest loadings of nutrients generally occur under storm conditions. To evaluate flow conditions over the sampling period (February 4, 1997–July 31, 1998), daily flow volume at instrumented sampling sites (BO020, BO040, BO070, BO090, and BO100) on the North Bosque River was categorized as storm flow, base flow, or dry (Table 17).

Dry conditions were assessed when no flow or zero flow was occurring at a site. Base or storm flow conditions were differentiated using the activation and deactivation of the automatic sampler for stormwater sample collection as the indicator for storm flow conditions. All days without storm samples were categorized as base flow if flow was above zero. Base flow conditions were represented about 55 to 64 percent of the time at sites on the North Bosque River, although only 7 to 25 percent of the volume was contributed by base flow (Table 17). Over 75 percent of the total volume between February 4, 1997 and July 31, 1998 was contributed by storm events.

The average flow during the study period was much higher than normal. At BO100, the long-term USGS gauge data indicates an average flow between 1960 and 1995 of 8 m3/s (283 ft3/s), while flows at BO100 between February 4, 1997 and July 31, 1998 averaged 25 m3/s (894 ft3/s). As noted in Figure 3, precipitation during the study period was quite variable with two

Table 17 Flow at North Bosque River sites categorized as storm, base, or dry for February 4, 1997 through July 31, 1998. Dry conditions occurred only at BO020.

Site Flow Type

Days Percent Time

Volume (m3)

PercentVolume

BO020a

a. Flow at BO020 is based on a provisional rating curve.

Storm 192 35.4% 44,700,000 90.7%Base 301 55.4% 4,570,000 9.3%Dry 50 9.2% 0 0.0%

BO040 Storm 206 37.9% 52,700,000 92.6%Base 337 62.1% 4,200,000 7.4%

BO070 Storm 205 37.8% 251,000,000 75.1%Base 338 62.2% 83,300,000 24.9%

BO090 Storm 195 35.9% 757,600,000 86.2%Base 348 64.1% 121,400,000 13.8%

BO100b

b. Flow at BO100 represents an estimate only due to sedimentation problems during large storm events.

Storm 201 37.0% 992,700,000 83.6%Base 342 63.0% 194,700,000 16.4%

38


distinct rainfall periods (February 1997 and February and March 1998) largely impacting storm flow. Flow during the months of February 1997 and February and March 1998 accounts for 46 percent of the cumulative flow between February 4, 1997 and July 31, 1998, emphasizing the large variability in flow over the study period.

Estimated loadings of SRP, TP, and TSS were also categorized in a manner similar to volume as occurring under base or storm flow conditions (Table 18). Volume-weighted mean concentrations were then calculated separately for base and storm flow. Because loadings are determined from concentrations and volumes (both of which are greater during storm flow conditions than base flow conditions), the majority of P loadings occur during storm events. At least 85 percent of the SRP, 88 percent of the TP, and 98 percent of the TSS loadings were associated with storm event flows (Figure 6).

Inflow Impacts During Storm Events The results thus far indicate that the highest concentrations of SRP and TP occur in the upper portion of the North Bosque River (Figure 6). The results also indicate that most of the P loading occurs during storm events and that the majority of SRP loadings occur above site BO070 in the upper third of the watershed (Table 18). These findings lead to several more questions concerning the transport of phosphorus along the North Bosque River. Of most direct interest is the bioavailability of phosphorus for the growth of algae. A distinct decrease in the concentration of SRP (Figure 4) and the proportion of TP represented by SRP (Figure 5) is indicated from upstream to downstream locations along the North Bosque River. A distinct increase in TSS concentrations at more downstream locations within the North Bosque River is also of note (Figure 4 and 6). It is possible that some SRP may be transformed to a sediment bound form, thus, making the SRP loaded in the upper portion of the North Bosque River less bioavailable by the time it reaches Lake Waco. Dilution from contributing tributaries between monitoring sites may also explain the change in SRP concentrations. Does dilution from inflowing tributaries or P transformations better explain the decrease in storm event SRP

Table 18 Estimated loadings by type of flow along the North Bosque Riverfor February 4, 1997 through July 31, 1998. Dry conditions occurred only at BO020.

Site Flow Type Days PO4-P

(kg)

TP(kg)

TSS (kg)

BO020a

a. Loadings at BO020 are based on a provisional rating curve for flow.

Storm 192 20,800 49,200 22,695,000 Base 301 1,400 2,100 87,000 Dry 50 0 0 0

BO040 Storm 206 27,000 52,000 19,145,000 Base 337 3,600 4,500 78,000

BO070 Storm 205 67,300 163,200 126,620,000 Base 338 11,900 22,300 1,279,000

BO090 Storm 195 102,400 471,600 769,433,000 Base 348 6,200 15,900 3,184,000

BO100b

b. Loadings at BO100 represent estimates due to sedimentation problems in measuring flow during large flow events.

Storm 201 121,500 556,000 948,796,000 Base 342 9,800 29,300 17,547,000

39


Figure 6 Volume-weighted mean concentrations and mass loadings as a percent of totalfor SRP, TP and TSS. Base flow represents conditions between February 4, 1997 and July 31, 1998 at sites along the North Bosque River. Percentages above base and storm columns represent the percent of total mass associated with each flow regime.

concentrations from upstream to downstream sites? While the current monitoring data set cannot definitively answer this question, some insight can be gained by evaluating in-stream water quantity and quality for storm events between main stem sampling sites along the North Bosque River compared to storm water contributions from inflowing tributaries between main stem sites.

40


Estimates of the volume and concentration of inflows between sites BO040 and BO070 and sites BO070 and BO090 were evaluated for selected storm events occurring between November 1995 and July 1998 using simple mass balance equations (equations 1 and 2). (The river miles and area between sites BO040 and BO070 and sites BO070 and BO090 are given in Table 19.) The purpose of these calculations was to gain insight into the causes for the downstream decrease observed in SRP and TP concentrations (Figure 4 and 6) and changes in the proportions of SRP and PP during storm events (Figure 5). By evaluating the inflow contribution between sites BO040 and BO070 and sites BO070 and BO090 by storm event, we should be able to determine if dilution from inflow loadings is a major factor in these upstream to downstream changes in water quality by comparing these estimates to storm event concentration information for tributaries between each of the paired sites.

Estimates of inflowing volumes and concentrations between main stem sites were limited to storm events at which the inflow volume represented at least 62 percent of the storm volume at BO070 and 53 percent of the storm volume at BO090 based on equation (3). This volume restriction was applied to ensure that the storms used for comparison had significant tributary inflow contributions. A geometric mean and lower and upper range of the standard deviation was calculated across storm events for inflow concentrations to compare with tributary water quality data.

Between BO040 and BO070 five monitored tributaries enter the North Bosque River—Alarm Creek, Sims Creek, Indian Creek, Green Creek, and Spring Creek (Figure 1). Specific locations of monitoring sites along these tributaries can be referenced in Pearson and McFarland (1999). The monitored drainage area of these five tributaries comprises 55 percent of the drainage area between BO040 and BO070 (Table 20). The aggregated land use above these five tributary monitoring sites is quite similar to the land use for the drainage area between sites BO040 and BO070 with only slight differences between land use categories (Table 20). The aggregated water quality from these five tributaries was, thus, considered representative for the entire drainage area between sites BO040 and BO070.

While some storm monitoring has occurred on each of these five tributaries, the time frame of monitoring does not directly correspond to the evaluation period for this study. By averaging over a time frame representing a number of storm events, the water quality of these tributaries can be generally characterized. Between April 1996 and March 1997, the storm water quality for these five tributaries was characterized using the geometric mean of EMCs based on data from McFarland and Hauck (1998b) and area weighted to estimate an average tributary inflow concentration for storm events (Table 21).

Table 19 Drainage area and river miles between sites BO040 and BO070 and sites BO070 and BO090on the North Bosque River.

Distance Between Sites Along the

North Bosque River

Drainage Area Between

Sites

Percent of Area Between Sites

Location (kilometers) (hectares) (%)

Between BO040 & BO070 34 67,529 72.4

Between BO070 & BO090 72 160,583 63.3

41


Equation 2 was used to calculate individual storm-event inflow concentrations between BO040 and BO070 (Table 22). Area-weighted tributary inflow concentrations (Table 21) were quite similar to estimated geometric mean concentrations (Table 22) for SRP, TP, and TSS in comparing inflow storm contributions between BO040 and BO070. These similarities indicate that during storm events dilution from inflowing tributaries explains much of the change in concentration of SRP, TP, and TSS between sites BO040 and BO070. If SRP were being appreciably lost or transformed to PP, the mass balance calculations in Table 22 should have more consistently given lower concentrations than the tributary values shown in Table 21. The calculated geometric mean concentrations (Table 22) should also have been lower than that monitored for the tributaries (Table 21).

Table 20 Land use of monitored tributaries compared to drainage area between BO040 and BO070.

Site Wood (%)

Range (%)

Pasture (%)

Cropland (%)

Dairy Waste Appl.

Fields (%)

Urban (%)

Barren (%)

Water (%)

Drainage Area

(hectares)

Alarm Creek 19.2 44.8 17.4 7.6 10.1 0.0 0.7 0.3 5,436Green Creek 22.2 49.0 13.3 7.2 6.9 0.7 0.2 0.5 26,165Indian Creek 16.0 49.3 9.5 7.5 17.3 0.0 0.4 0.0 1,820

Sims Creek 20.7 58.5 11.6 2.5 5.9 0.0 0.3 0.4 1,820Spring Creek 30.6 53.6 10.9 4.7 0.0 0.0 0.1 0.1 1,589Aggregated Monitored Inflow Drainage Area 21.7 49.1 13.5 6.9 7.5 0.5 0.3 0.4 36,830

Inflow Area Between Sites BO040 and BO070

23.1 51.8 12.2 5.8 5.5 0.9 0.3 0.4 67,529

Table 21 Storm concentrations for tributaries between sites BO040 and BO070 and area-weighted inflow. Tributary concentrations represent geometric mean values of volume weighted mean concentrations for storm events monitored between April 1996 and March 1997 (McFarland and Hauck, 1998b). The variable ‘n’ represents the number of storm events monitored at each site.

Tributary n SRP (mg/L)

TP(mg/L)

TSS (mg/L)

Alarm Creek 12 0.19 0.52 40Green Creek 10 0.07 0.24 33Indian Creek 18 0.56 0.87 78Sims Creek 20 0.14 0.30 40Spring Creek 17 0.03 0.08 5Area-Weighted Concentration 0.11 0.31 35

42


Between BO070 and BO090, three major tributaries flow into the North Bosque River. These three major tributaries are Duffau Creek, East Bosque River, and Meridian Creek (Figure 1). TIAER has monitored water quality on Duffau and Meridian Creeks (McFarland and Hauck, 1998b; Easterling et al., 1998), while the Brazos River Authority has monitored the East Bosque River (Bothwell, 1994). The land use in drainage areas above monitoring sites on these three tributaries is quite similar to the overall land use for the drainage area between BO070 and BO090, except for the wood and range land use categories (Table 23). The aggregated monitored tributary area represents notably more wood and less range land than the drainage area between BO070 and BO090. When the land area comprised of wood and range is added together, percentages for the monitored tributaries (71 percent wood and range) and the drainage are between BO070 and BO090 (74 percent wood and range) become quite similar. Because the phosphorus losses in runoff from wood and range have previously been show to be quite similar (McFarland and Hauck, 1999), these differences in percent land use were not considered important.

Table 22 Calculated inflow storm volume (equation 1) and concentrations (equation 2)between sites BO040 and BO070.

Site BO040 Site BO070 Inflowing Drainage Area

Begin Date of Storm

Volume (m3)

SRP (mg/L)

TP (mg/L)

TSS (mg/L)

Volume (m3)

SRP (mg/L)

TP (mg/L)

TSS (mg/L)

Volume (m3)

SRP (mg/L)

TP (mg/L)

TSS (mg/L)

Percent of Flow

at BO070

27-Aug-96 1,176,814 0.52 0.99 339 9,165,979 0.13 0.67 504 7,989,165 0.08 0.62 528 0.8731-Aug-96 1,058,181 0.49 0.88 87 7,878,516 0.15 0.46 149 6,820,335 0.10 0.39 159 0.8721-Oct-96 57,669 0.88 1.03 5 199,152 0.13 0.16 8 141,484 -0.18 -0.20 10 0.7127-Oct-96 932,591 0.45 0.77 190 5,728,103 0.20 0.59 373 4,795,512 0.16 0.55 409 0.846-Nov-96 1,539,299 0.37 0.77 220 4,764,511 0.20 0.42 135 3,225,212 0.11 0.25 94 0.68

28-Nov-96 1,719,044 0.59 0.82 78 5,833,544 0.35 0.41 42 4,114,500 0.24 0.24 27 0.716-Feb-97 4,124,171 0.53 0.94 282 12,756,294 0.22 0.56 269 8,632,122 0.08 0.38 263 0.6819-Feb-97 13,919,873 0.49 1.02 467 55,824,776 0.36 0.80 745 41,904,902 0.31 0.72 837 0.752-Mar-97 3,586,087 0.64 0.86 430 18,597,192 0.40 0.65 459 15,011,105 0.34 0.60 466 0.8125-Mar-97 240,448 0.26 0.38 35 1,897,963 0.07 0.11 21 1,657,515 0.04 0.07 19 0.873-Apr-97 3,727,474 0.47 0.80 309 16,206,399 0.23 0.53 282 12,478,925 0.16 0.45 274 0.7725-Apr-97 1,438,018 0.48 1.00 185 7,804,673 0.21 0.41 93 6,366,655 0.15 0.27 72 0.829-May-97 2,780,223 0.55 0.80 394 18,964,925 0.23 0.59 649 16,184,702 0.18 0.55 693 0.8519-May-97 631,914 0.58 1.09 233 3,089,409 0.21 0.44 156 2,457,495 0.11 0.27 137 0.808-Jun-97 1,438,180 0.47 0.94 6 6,388,995 0.21 0.36 12 4,950,815 0.14 0.18 14 0.7722-Jun-97 1,484,512 0.49 0.89 180 25,676,604 0.18 0.51 274 24,192,092 0.16 0.49 280 0.947-Aug-97 122,204 0.47 0.55 46 2,434,188 0.14 0.29 158 2,311,984 0.12 0.27 164 0.956-Oct-97 205,372 1.40 1.61 14 2,260,571 0.28 0.44 5 2,055,199 0.17 0.33 4 0.9123-Oct-97 200,731 1.05 1.58 145 1,595,096 0.38 0.45 20 1,394,364 0.28 0.29 2 0.872-Dec-97 58,471 1.14 2.03 22 674,959 0.18 0.20 3 616,489 0.09 0.03 1 0.917-Dec-97 111,012 0.82 1.09 27 1,298,835 0.72 0.80 6 1,187,823 0.71 0.78 4 0.91

20-Dec-97 588,864 0.71 1.02 124 3,515,440 0.47 0.94 65 2,926,576 0.42 0.92 53 0.834-Jan-98 3,080,625 0.76 1.19 250 8,371,491 0.34 0.73 186 5,290,865 0.10 0.46 149 0.6331-Jan-98 286,327 0.48 0.90 35 2,201,948 0.05 0.31 13 1,915,620 -0.02 0.22 10 0.8720-Feb-98 805,264 0.46 0.95 209 3,562,419 0.19 0.60 190 2,757,155 0.11 0.50 184 0.7725-Feb-98 455,246 0.35 1.17 127 7,258,702 0.17 0.76 528 6,803,456 0.16 0.73 555 0.947-Mar-98 314,445 0.44 0.70 41 3,647,744 0.13 0.24 33 3,333,298 0.10 0.19 32 0.9115-Mar-98 9,785,545 0.41 1.11 514 37,216,358 0.25 0.87 1,000 27,430,813 0.19 0.79 1,173 0.7426-May-98 1,485,199 0.50 1.14 330 4,732,822 0.25 0.82 583 3,247,623 0.13 0.67 698 0.694-Jun-98 53,007 0.67 1.00 62 872,104 0.12 0.32 29 819,098 0.08 0.28 27 0.9410-Jun-98 230,377 0.40 0.76 80 1,946,294 0.20 0.41 24 1,715,917 0.17 0.36 16 0.8812-Jul-98 95,523 1.40 1.70 38 1,112,829 0.03 0.14 4 1,017,307 -0.10 0.00 1 0.91

Geometric Mean 686,252 0.57 0.97 100 4,544,437 0.20 0.44 79 3,726,665 0.15 0.35 64 0.82

Lower Stda 153,872 0.39 0.70 29 1,338,283 0.10 0.26 14 1,127,206 0.08 0.17 8 0.73Upper Stdb 3,060,606 0.84 1.33 349 15,431,646 0.37 0.76 448 12,320,759 0.27 0.73 500 0.92

a. Lower Std represents the exponential of the natural-log transformed mean minus the standard deviation.b. Upper Std represents the exponential of the natural-log transformed mean plus the standard deviation.

43


The water quality information for storm events on these three tributaries was limited (Table 24) but was compared to the calculated inflow contributions between BO070 and BO090 as an indicator of the presence or absence of phosphorus transformations during storm events (Table 25). Values for SRP were comparable, although for TP and TSS, higher concentrations were indicated for calculated inflow concentrations (Table 25) than for area-weighted tributary concentrations (Table 24). These higher TP and TSS concentrations estimated for inflow between BO070 and BO090 indicate that some additional TP and TSS may be coming from sources between sites BO070 and BO090 other than major inflowing tributaries. Stream bank erosion within the North Bosque River between BO070 and BO090 is one potential source. A fair amount of stream bank erosion has been indicated near BO090 following some of the larger storm events. Loadings from cropland fields in the North Bosque River floodplain near BO090 has also been indicated as another potential source (McFarland and Hauck, 1999). Even though some unaccounted TP and TSS loadings appear to be occurring between BO070 and BO090, transformations of SRP to PP are not indicated during storm events. Dilution from inflowing tributaries probably accounts for most of the decrease in SRP concentrations between these two sites.

Table 23 Land use of monitored tributaries compared to drainage area between sites BO070 and BO090

Site Wood (%)

Range (%)

Pasture (%)

Cropland (%)

Dairy Waste

Appl. Fields (%)

Urban (%)

Barren (%)

Water(%)

Drainage Area

(hectares)

Duffau Creek 29.9 31.9 13.7 13.3 7.7 1.8 0.9 0.8 23,243

East Bosque River 24.2 56.8 4.4 10.9 0.0 1.9 0.4 1.4 11,041Meridian Creek 15.9 57.9 12.5 13.3 0.0 0.03 0.0 0.0 47,379Aggregated Monitored Inflow Drainage Area

21.0 50.4 11.8 13.0 2.2 0.9 0.3 0.4 82,204

Inflow Area Between Sites BO070 and BO090

16.8 57.0 12.8 10.3 1.7 1.4 0.3 0.0 160,583

Table 24 Storm concentrations for tributaries between sites BO070 and BO090 and area-weighted inflow.The variable ‘n’ represents the number of storm events or storm samples monitored at each site.

Site n SRP(mg/L)

TP(mg/L)

TSS(mg/L)

Duffau Creeka

a. Values represent the geometric mean of volume weighted event mean concentrations from storm events monitored between April 1996 and March 1997 (McFarland and Hauck, 1998b).

15 0.06 0.29 87East Bosque Riverb

b. Information on the East Bosque River obtained from Bothwell (1994) and represents a composite sample from a June 1993 storm event.

1 0.06 0.18 14Meridian Creekc

c. Storm values from Meridian Creek represent the mean concentration of storm samples collected between January and December 1997 (Easterling et al., 1998).

58 0.02 0.14 49Area-Weighted Concentration 0.04 0.19 55

44


A few qualitative factors support our conclusion that during many storm events on the North Bosque River most of the observed decrease in downstream SRP concentration is the result of dilution from tributary inflow. During storm events, travel times are expected to be relatively fast but will vary greatly with storm event size and location within the watershed. Rough estimates of storm flow velocities indicate travel times of hours between sites BO040 and BO070 and hours to days between sites BO070 and BO090. The uptake of SRP by algae during storm events is probably insignificant due factors such as increased turbidity, scouring of attached algae, dilution of suspended algae, and rapid travel times of storm water. The adsorption of SRP to sediment particles would also most likely be limited during storm events to the creation of a fairly labile pool with soluble P loosely attached to sediment surfaces rather than the creation of a more immobile solid-state of sediment bound phosphorus. Based on P rate kinetics as described by Froelich (1988), the solid-state diffusion of soluble P into the interior of sediment particles usually take days to months, while adsorption of soluble P onto the surface of sediment particles can occur within minutes. SRP contributed from upstream locations within the North Bosque River may be loosely bound to sediment particles by the time it reaches the lower portion of the River, but rate kinetics do not favor the creation of an immobile solid-state of PP. These loosely bound P particles are likely to appear as part of the SRP analysis in analyzing water quality samples, because this loosely bound P is mostly likely associated with very fine clay particles that may pass through the 0.45 µm filter (Droppo et al., 1992; Gippel, 1989). A 0.45 µm filter is used as an operational definition of dissolved or soluble P for laboratory analysis in that it excludes all but some of the finest sediments (EPA, 1983).

Cumulative Daily Volumes and Loadings To evaluate whether transformations of SRP to PP were occurring in the North Bosque River during base flow and storm events and to evaluate the magnitude of these transformations, if they were occurring, cumulative daily volume and loadings were calculated for BO040, BO070, and BO090 from November 1, 1995 through July 31, 1998. Volumes and loadings included both base flow and storm event conditions and were presented as cumulative totals

Table 25 Calculated inflow storm volume (equation 1) and concentrations (equation 2)between sites BO070 and BO090.

Site BO070 Site BO090 Inflowing Drainage Area

Begin Date of Storm

Volume (m3)

SRP (mg/L)

TP (mg/L)

TSS (mg/L)

Volume (m3)

SRP (mg/L)

TP (mg/L)

TSS (mg/L)

Volume (m3)

SRP (mg/L)

TP (mg/L)

TSS (mg/L)

Percent of Flow

at BO090

7-Jun-96 2,961,097 0.18 0.79 517 6,338,116 0.02 0.66 1,320 3,377,019 -0.12 0.55 2,025 0.5327-Aug-96 9,165,979 0.13 0.67 504 27,914,417 0.26 1.33 2,307 18,748,438 0.33 1.65 3,189 0.6731-Aug-96 7,878,516 0.15 0.46 149 17,626,411 0.07 0.34 308 9,747,896 0.00 0.24 437 0.5528-Nov-96 5,833,544 0.35 0.41 42 13,219,272 0.16 0.23 50 7,385,728 0.01 0.10 56 0.566-Feb-97 12,756,294 0.22 0.56 269 52,613,407 0.11 0.52 1,220 39,857,113 0.07 0.50 1,525 0.7619-Feb-97 55,824,776 0.36 0.80 745 172,732,427 0.25 0.95 1,726 116,907,651 0.20 1.02 2,194 0.682-Mar-97 18,597,192 0.40 0.65 459 63,133,334 0.16 0.30 517 44,536,142 0.05 0.16 541 0.7125-Mar-97 1,897,963 0.07 0.11 21 6,118,279 0.04 0.07 14 4,220,316 0.04 0.05 11 0.693-Apr-97 16,206,399 0.23 0.53 282 53,989,014 0.10 0.37 315 37,782,615 0.05 0.30 330 0.7025-Apr-97 7,804,673 0.21 0.41 93 33,642,491 0.07 0.28 246 25,837,818 0.03 0.25 293 0.7723-May-97 2,955,520 0.18 0.19 27 7,201,160 0.09 0.24 34 4,245,640 0.03 0.27 39 0.598-Jun-97 6,388,995 0.21 0.36 12 25,610,066 0.08 0.28 naa 19,221,070 0.04 0.25 na 0.75

20-Feb-98 3,562,419 0.19 0.60 190 10,394,946 0.04 0.55 486 6,832,527 -0.04 0.52 640 0.6625-Feb-98 7,258,702 0.17 0.76 528 18,955,070 0.13 0.64 801 11,696,368 0.10 0.57 970 0.6215-Mar-98 37,216,358 0.25 0.87 1,000 176,362,088 0.09 0.96 1,428 139,145,730 0.05 0.98 1,543 0.79Geometric

Mean 8,391,689 0.20 0.48 169 26,007,496 0.09 0.41 374 17,241,379 0.04 0.35 443 0.66Lower Stdb 3,272,630 0.13 0.27 42 8,804,723 0.05 0.20 78 5,365,170 0.01 0.14 83 0.58Upper Stdc 21,517,997 0.31 0.85 689 76,821,251 0.18 0.86 1,797 55,406,484 0.19 0.87 2,375 0.75

a. ‘na’ indicates that data was not available for estimation.b. Lower Std represents the exponential of the natural-log transformed mean minus the standard deviation.c. Upper Std represents the exponential of the natural-log transformed mean plus the standard deviation.

45


on a per area basis for the drainage area above each site. Inflowing contributions between sites BO040 and BO070 and sites BO070 and BO090 of volumes and loadings were calculated as the difference between upstream and downstream sites. Volumes and loadings were then normalized for the drainage area represented between sites.

In evaluating flow volume per hectare, the area above BO040 indicates the greatest cumulative runoff volume between November 1995 and June 1997, but between July 1997 and July 1998, the area between BO040 and BO070 shows the greatest cumulative volume contribution (Figure 7). The drought conditions during the early portion of the study period (Figure 3) and the constant contributions from the Stephenville WWTP probably explain the greater cumulative runoff at BO040 for November 1995 through June 1997.

Figure 7 Cumulative daily volume of flow for sites and the inflowing area between siteson the North Bosque River.

0

1,000

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46


The cumulative charts clearly indicate that the major flow events during the study period occurred in February and March 1997 and March 1998 with corresponding large increases in the cumulative daily volume (Figure 7). These two major event periods are re-emphasized by observing the time history of daily average flow for sites BO040, BO070, and BO090 (Figure 8).

Figure 8 Daily average flow at sites BO040, BO070 and BO090 on the North Bosque River.

BO040

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47


Cumulative loadings of SRP indicate the greatest total loadings and cumulative loadings per hectare from the drainage area above BO040 (Figure 9). Periods of decrease in cumulative SRP loadings are quite apparent for the intervening area between sites BO040 and BO070 and sites BO070 and BO090 with cumulative loadings dropping below zero and showing a negative slope. These decreases indicate that some upstream loading of SRP is transformed or settled out of the water prior to reaching downstream sites, i.e., SRP is not being transported as a conservative substance (Figure 9).

Figure 9 Cumulative daily loading of SRP for sites and the inflowing area between siteson the North Bosque River.

To a lesser degree than SRP, cumulative loadings of TP for intervening areas also show periods of depletion rather than increasing loads (Figure 10). These periods of decreasing cumulative loads generally correspond with periods of low flow (Figure 8). In comparing inflow loadings of SRP between sites BO040 and BO070 with the daily flow volume at BO070 (Figure 11), negative loadings for intervening areas are clearly associated with periods of low flow.

48


Figure 10 Cumulative daily loading of TP for sites and the inflowing area between siteson the North Bosque River.

Similar correlations of negative loadings and low flow were indicated between sites BO040 and BO070 for TP and between sites BO070 and BO090 for SRP and TP.

Travel times during base flow conditions can be quite long. Upstream base flow may take days to months to travel to downstream locations assuming travel occurs at all. At times the North Bosque River would be intermittent between storm events if not for WWTP discharges. During these dry periods, upstream flow may be used to sustain pools and reach downstream locations with diminshed flows. With these much slower travel times at base flow compared to storm flow, there is a greater opportunity for SRP to be taken up by aquatic plants and algae and the movement of some soluble P into sediment bound P could occur. Passive storage of SRP may also occur as pools within the stream retain water during low flow (e.g., Bencala, 1984). A number of studies have shown that many of the physical, chemical, and biological mechanisms needed to retain and recycle nutrients for maintaining a diverse and productive aquatic ecosystem occur primarily during low flow conditions (e.g., Triska et al., 1984; 1989; Stanley and Hobbie, 1981; Meyer and Likens, 1979). Extensive beds of periphyton (attached

-0.50.00.51.01.52.02.53.03.54.04.5

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Cu

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ve M

ass

of T

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)

BO040 BO070 BO090

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49


Figure 11 Relationship of daily SRP loading for the inflow between sites BO040 and BO070to the daily average flow at BO070.

algae) generally accumulate between storm events in the North Bosque River (TWC, 1991). This periphyton is scoured from the river substrate and transported downstream when storm events generate increased velocity. These mechanisms would account for the depletion of SRP and TP that is shown in the cumulative loading charts for the intervening area between sites (Figure 9 and 10). The depletion of TP during base flow is also probably associated with the settling of sediment bound P with decreasing stream velocities.

Also of note is that by the end of the study period cumulative loadings of SRP in the intervening area between BO070 and BO040 on a per hectare basis are noticeably larger than the cumulative loadings for the area between BO090 and BO070 (Figure 9). In comparison, cumulative loadings for TP are fairly similar for these two portions of the watershed (Figure 10) reconfirming that most of the SRP loading originates from the upper portion of the watershed. The source of the additional TP in the lower portion of the watershed may be associated with additional TSS loading in the lower portion of the watershed from unknown sources or processes (Figure 12).

Because much of the TP is in the particulate form, it is important to also evaluate the dynamics of TSS in evaluating P dynamics. The cumulative loading between BO070 and BO090 for TSS is much greater than for the other two portions of the watershed evaluated (Figure 12). Increasing TSS loading does not appear to come from contributing tributaries between BO070 and BO090 (Table 24); however, stream bank erosion and/or loadings from cropland areas near BO090 are suspected. The geology of the North Bosque River basin is dominated by sandstone in the upper third with a mix of limestone, calcareous marl and sandstone in the lower two-thirds (Abraham, 1998). Fairly low phosphorus levels are associated with these substrates, so without further study, stream bank contributions can only be considered a potential candidate for the increase in TP found at BO090, although substantial stream bank erosion has been noted near BO090, particularly after large storm events.

Movement of TSS and TP from surrounding cropland in the North Bosque River floodplain, particularly in the lower portion of the watershed, is another potential source of the increased TP and TSS during large storm events. A substantial amount of row crop agriculture is apparent in the lower portion of the North Bosque River watershed starting near BO090 (see

50


Figure 12 Cumulative daily loading of TSS for sites and the inflowing area between siteson the North Bosque River.

McFarland and Hauck, 1998a). The P enrichment of soils in these cropland areas, through the incorporation of P fertilizers, may be a significant source of P export to the watershed. The additional TP in the lower portion of the watershed, in part, is also coming from resuspension of PP and detachment of periphyton from the upper portion of the North Bosque during storm events. More detailed studies would be needed to define the amount of P being contributed from each of these sources.

-500

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ha)

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51


As alluded to earlier, the WWTP discharge at Stephenville is expected to have a large impact on the water quality at BO040 due to its location and relative contribution in relation to flow at this site. By subtracting the daily loading estimates for the WWTP discharge from the daily loading at BO040, the contribution of the WWTP can be quantified (Figure 13).

Figure 13 Impact of WWTP discharge on cumulative daily volume and loadings at site BO040.

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52


About 7 percent of the flow volume, 24 percent of the SRP loading and 18 percent of the TP loading at BO040 can be associated with the Stephenville WWTP between November 1995 and July 1998. These contributions correspond closely to source contribution estimates calculated by McFarland and Hauck (1998a) for November 10, 1993 through January 31, 1997. TSS loading from the Stephenville WWTP is minimal (less than 1 percent) for the evaluation period, and thus, not presented. Between BO070 and BO090, wastewater is contributed from the cities of Hico, Iredell, and Meridian. The total flow volume represented by these WWTP contributions over the study period, however, was less than 0.10 percent of the cumulative flow at BO090. WWTP discharges were a fairly minor contributor of phosphorus loadings at BO090 representing about 2 percent of the SRP loading and 0.7 percent of the TP loading assuming no transformations or transport losses.

53


54

CHAPTER 7

Conclusions

With regard to the original five questions set out in this report, the following was determined:

• Is there spatial variability in P concentrations and forms of P represented at sites on the North Bosque River?

¤ Yes. Although overall loadings of SRP and TP increase from upstream to downstream, the highest concentrations of SRP and TP occur in the upper portion of the North Bosque River during base flow and storm events. A much higher proportion of TP as SRP was also indicated at upstream sites compared to downstream sites. TSS responded differently with the highest concentrations occurring at the most downstream sites. Higher concentrations of SRP, TP, and TSS were also generally observed during store events than base flow.

• Are P concentrations of SRP, PP, and total-P correlated to flow conditions?

¤ Yes and No. For storm events, positive relationships between storm volume and the concentrations of P constituents and TSS were indicated at most of the sites evaluated. Site BO040, located below the Stephenville WWTP, was an exception. At BO040, only TSS indicated a significant relationship with storm volume. At base flow, only sites in the upper portion of the watershed indicated a significant relationship of TSS concentration with the rate of flow.

• How much of the P load (TP and SRP) in the North Bosque River is transported during base flow versus storm events?

¤ About 90 percent of TP and SRP is transported along the North Bosque River during storm events versus about 10 percent during base flow conditions.

• Is dilution from inflowing tributaries or P transformations responsible for the decrease in SRP concentrations from upstream to downstream sites during storm events?

¤ Dilution from inflowing tributaries rather than P transformations appears to be responsible for most of the decrease in SRP concentrations that occurs from upstream to downstream locations on the North Bosque River.

• Do transformations of soluble P to particulate P occur during base flow and/or storm events and, if so, what is the magnitude of these transformations?

¤ During base flow conditions some transformations of SRP and losses of TP are evident. The magnitude of these losses or transformations is relatively small compared to the storm transport of P. These base flow losses or transformations are most likely associated with the uptake of SRP by aquatic plant and animals and the settling of particulate attached P during low flow conditions. During storm events, it appears that much of the P lost to the water column at base flow is resuspended and transported along the North Bosque River with increasing stream velocities.

In summary, the highest concentrations of SRP and TP occur in the upper portion of the North Bosque River during base flow and storm events. The overall decrease in SRP and TP concentrations from upstream to downstream sites during storm events may be primarily explained by dilution from contributing tributaries between North Bosque River sites. Under base flow conditions, a number of physical, chemical, and biological mechanisms appear to be

55


working in concert to temporarily retain a small portion of the P transported along the North Bosque River allowing the recycling of SRP to TP and vice versa. Plant and algal (both suspended and attached) uptake, binding with sediment particles, and settling in pools along with dilution probably explain the decrease in SRP concentrations and loadings from upstream to downstream sites during base flow. The P that is retained during base flow will be eventually transport downstream with elevated flows associated with storm events.

Storm events are the dominant transport mechanism within the watershed responsible for 90 percent or more of the TP movement along the North Bosque River. During storm events, decreases in SRP concentrations from upstream to downstream can be attributed to dilution from inflowing tributaries having lower SRP concentrations than the high SRP concentrations in the headwaters. Changes in TP concentrations likewise are primarily attributable during storm events to dilution from inflowing tributaries. A part of the increase in TP concentrations in the lower portion of the watershed near BO090 and BO100 may be associated with increased TSS loadings from the erosion of land used for row crop agriculture near these sites, extensive stream bank erosion during large storm events, and/or contributions from detached periphyton suspended during storm events. More detailed research will be needed to define the relative contribution of each of these sources to the TP loading at BO090 and BO0100.

Cumulative loading charts also indicate that the primary origin of SRP mass and relative contribution by unit area is the upper third of the North Bosque River watershed with the dominant origin of TSS being in the lower two-thirds of the watershed. For TP, the largest mass contribution occurs along the lower two-thirds of the watershed, although the largest per hectare contribution occurs in the upper one-third of the watershed area. In summary, the largest concentrations and loading of SRP occur in the upper third of the North Bosque River watershed, and during storm events, this loading of SRP travels the length of the North Bosque River with few transformations or losses.

56

References

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Bencala, K.E. 1984. Interactions of solutes and streambed sediment. 2. A dynamic analysis of coupled hydrologic and chemical processes that determine solute transport. Water Resources Research 20:1804-1814.

Bothwell, C.P. 1994. Water Quality in Duffau Creek and the East Bosque River: A Comparative Wa-tershed Study. Brazos River Authority, Waco, Texas (May 1994).

Boyd, C.E. 1990. Water Quality in Ponds for Aquaculture. Birmingham Publishing Co., Birmingham, Alabama.

Codd, G.A. 1995. Cyanobacterial toxins: Occurrence, properties and biological significance. Water Science & Technology 32:149-156.

Dallas Morning News, 1997. 1998-99 Texas Almanac and State Industrial Guide. Eds. M. Kingston and M.G. Crawford. Dallas Morning News, Inc., Dallas, Texas.

Dávalos-Lind, L., and Owen T. Lind, 1999. The Algal Growth Potential of and Growth-Limiting Nu-trients in Lake Waco and Its Tributary Waters, Part I (Narrative): A report to Texas Institute for Applied Environmental Research. Limnology Laboratory, Department of Biology, Baylor Univer-sity, Waco, Texas (February 1999).

Droppo, I.G., B.G. Krishnappan, and E.D. Ongley. 1992. Concentration suspended sediment samples by filtration: Effect on primary grain-size distribution. Environmental Science and Technology 26:1655-1662.

EPA, United States Environmental Protection Agency. 1983. Methods for Chemical Analysis of Water and Wastes. Environmental Monitoring and Support Laboratory, Office of Research and Develop-ment, US-EPA, Cincinnati, Ohio. EPA-600/4-79-020, Revised March 1983.

Easterling, N., A. McFarland, and L.Hauck. 1998. Semi-Annual Water Quality Report for the Bosque River Watershed (Monitoring Period: January 1, 1997 – December 31, 1997). Texas Institute for Ap-plied Environmental Research, Tarleton State University, Stephenville, TX, WP 98-04 (July 1998).

Finkelstein, M.O., and B. Levin. 1990. Transformation in Regression Analysis, pp. 437-442. In: Statis-tics for Lawyers, Springer-Verlag, New York.

Froelich, P.H. 1988. Kinetic control of dissolved phosphate in natural rivers and estuaries: A primer on the phosphate buffer mechanism. Limnology & Oceanography 33:649-668.

Gibson, C.E. 1997. The Dynamics of Phosphorus in Freshwater and Marine Environments, pp. 119-136. In: Phosphorus Loss from Soil to Water (H. Tunney, O.T. Carton, P.C. Brookes, and A.E. Johnston, eds). Centre for Agriculture and Bioscience International, New York.

Gilliom, R.J., and D.R. Helsel. 1986. Estimation of distributional parameters for censored trace level water quality data. 1. Estimation techniques. Water Resources Research 22:135-126.

Gippel, C.J. 1989. The use of turbidimeters in suspended sediment research. Hydrobiologia 176:465-480.

Harris, G.P. 1986. Phytophankton Ecology: Structure, Function and Fluctuation. Chapman and Hall, New York.

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Izaguirre, G., C.J. Hwant, S.W. Krasner, and M.J. McGuire. 1982. Geosmin and 2-methlyisoboreol from cyanobacteria in three water supply systems. Applied and Environmental Microbiology 43:708-714.

Jones, T.L. 1999. Meteorological Data for Erath and Northern Hamilton Counties, Texas: January through December 1998. Texas Institute for Applied Environmental Research, Tarleton State Uni-versity, Stephenville, Texas, WP 99-05 (August 1999).

Jones, T.L. 1998. Meteorological Data for Erath and Northern Hamilton Counties, Texas: January through December 1997. Texas Institute for Applied Environmental Research, Tarleton State Uni-versity, Stephenville, Texas, WP 98-03 (August 1998).

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Lurry, D., 1997. USGS, Austin Office, personal communication, October 24, 1997.

Martin, A. and G.D. Cooke. 1994. Health risks in eutrophic water supplies. LakeLine 14:24-26.

Matlock, M.D., and A.D. Rodriguez. 1999. Preliminary Report of Findings: Periphytometer Study on Streams in the Lake Waco/Bosque River Watershed. Prepared for the Texas Institute for Applied Environmental Research, Stephenville, Texas. Dept. Agricultural Engineering, Texas A&M Uni-versity, College Station, Texas (February 1999).

McFarland, A., and L. Hauck. 1999. Existing Nutrient Sources and Contributions to the Bosque River Watershed. Texas Institute for Applied Environmental Research, Tarleton State University, Stephenville, Texas, PR 99-11 (September 1999).

McFarland, A., and L. Hauck. 1998a. Lake Waco/Bosque River Initiative Report: Determining Nutri-ent Contribution by Land Use for the Upper North Bosque River Watershed. Texas Institute for Applied Environmental Research, Tarleton State University, Stephenville, Texas, PR 98-01 (Janu-ary 1998).

McFarland, A., and L. Hauck. 1998b. Stream Water Quality in the Bosque River Watershed: October 1, 1995 through March 15, 1997. Texas Institute for Applied Environmental Research, Tarleton State University, Stephenville, Texas, PR 97-05 (June 1998).

Mulholland, P.J., J.D. Newbold, J.W. Elwood, and J.R. Webster. 1985. Phosphorus spiralling in a woodland stream: Seasonal variations. Ecology 66:1012-1023.

Meyer, J.L., and G.E. Likens. 1979. Transport and transformation of phosphorus in a forest stream ec-osystem. Ecology 60:1255-1269.

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Nelson, D.W., and T.J. Logan. 1983. Chemical Processes and Transport of Phosphorus, pp.65-91. In: Agricultural Management and Water Quality, eds. F.W. Schaller and G.W. Bailey. Iowa State Uni-versity Press, Ames, Iowa.

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Palstrom, N.S., R.E. Carlson, and G.D. Cooke. 1988. Potential links between eutrophication and the formation of carcinogens in drinking water. Lake and Reservoir Management 4:1-15.

Pearson, C., and A. McFarland. 1999. Semi-Annual Water Quality Report for the Bosque River Wa-tershed (Monitoring Period: January 1, 1997 – December 31, 1998). Texas Institute for Applied En-

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Sharpley, A.N., S.J. Smith, O.R. Jones, W.A. Berg, and G.A. Coleman. 1992. Water quality: The trans-port of bioavailable phosphorus in agricultural runoff. Journal of Environmental Quality, 21:30-35.

Stanley, D.W., and J.E. Hobbie. 1981. Nitrogen recycling in a North Carolina coastal river. Limonol-ogy and Oceanography 26:30-42.

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Stevenson, F.J. 1986. The Phosphorus Cycle, pp. 231-284. In: Cycles of Soil: Carbon, Nitrogen, Phos-phorus, Sulfur, Micronutrients. John Wiley & Sons, New York.

TIAER, Texas Institute for Applied Environmental Research. 1998. Quality Assurance Project Plan for the United States Department of Agriculture Bosque River Initiative. TIAER, Tarleton State Uni-versity, Stephenville, Texas.

TNRCC, Texas Natural Resources Conservation Commission. 2000. Two Total maximum Daily Loads for Phosphorus in the North Bosque River for Segments 1226 and 1255. Strategic Assess-ment Division, TMDL Team, TNRCC, Austin, Texas (September 2000).

TNRCC, Texas Natural Resources Conservation Commission. 1999. State of Texas 1999 Clean Water Act Section 303(d) List and Schedule for Development of Total Maximum Daily Loads, Austin, Texas. SFR-58/99.

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Texas Water Commission. 1991. Use Attainability Analysis of North, Middle, and South Bosque Riv-ers Segments 1226 and 1246. Water Quality Standards Unit, Texas Water Commission, Austin, Texas. (2nd Revision August 1991)

Texas Water Commission, and Texas State Soil and Water Conservation Board. 1991. 1990 Update to the Nonpoint Source Water Pollution Assessment Report of the State of Texas. Texas Water Com-mission, Austin, Texas.

Triska, F.J., V.C. Kennedy, R.J. Avanzino, G.W. Aellweger, and K.E. Bencala. 1989. Retention and transport of nutrients in a third-order stream: Channel processes. Ecology 70:1877-1892.

Triska, F.J., J.R. Sedell, K. Cromack, Jr., S.V. Gregory, and F.M. McCorison. 1984. Nitrogen budget for a small coniferous forest stream. Ecological Monographs 54:119-140.

Walker, W.W., Jr. 1983. Significance of eutrophication in water supply reservoirs. Journal of the American Water Works Association 75:38-42.

Ward, R.C., J.C. Loftis, H.P. DeLong, and H.F. Bell. 1988. Groundwater quality: A data analysis pro-tocol. Journal of the Water Pollution Control Federation 60:1938-1945.

59


60

APPENDIX A

Summary of Storm EventsMonitored Between February

1997 and July 1998

Table A–1 Summary of storm events monitored between February 1997 and July 1998at sites along the North Bosque River.

National Weather Observer Sites

Site BeginVolume

(m3)Volume (m3/ha)

Hydr

ogra

ph S

imila

ritya

Huck

abay

Step

henv

ille

Dubl

in

Hico

Cran

fills

Gap

Mer

idia

n

Valle

y Mill

s

Wac

o Da

m

BO020 6-Feb-97 2,948,056 b 136.76 + (cm)BO040 4,124,171 160.47 + 9.98 8.64 11.30 8.28 9.22 9.83 nac 12.93 BO070 12,756,294 136.89 +BO090 52,613,407 207.42 +BO100 79,463,782 b 262.92 +

BO020 19-Feb-97 12,878,194 b 597.41 + (cm)BO040 13,919,873 541.61 + 13.08 12.55 17.12 17.42 10.34 10.11 na 6.73 BO070 55,824,776 599.09 +BO090 172,732,427 680.98 +BO100 222,774,962 b 737.09 +

BO020 2-Mar-97 2,992,432 b 138.82 + (cm)BO040 3,586,087 139.53 + 3.30 4.14 5.08 3.76 3.73 6.43 na 4.60 BO070 18,597,192 199.58 +BO090 63,133,334 248.90 +BO100 86,220,291 b 285.28 +

BO020 25-Mar-97 232,334 b 10.78 + (cm)BO040 240,448 9.36 + 2.01 2.03 2.49 1.40 0.94 1.55 na 1.60 BO070 1,897,963 20.37 xBO090 6,118,279 24.12 xBO100 8,035,887 b 26.59 x

BO020 3-Apr-97 3,326,938 b 154.33 + (cm)BO040 3,727,474 145.03 + 5.82 6.40 8.18 7.70 6.53 8.81 na 5.21 BO070 16,206,399 173.92 +BO090 53,989,014 212.85 +BO100 78,102,220 b 258.42 +

BO020 25-Apr-97 1,208,736 b 56.07 + (cm)BO040 1,438,018 55.95 + 4.70 4.80 7.11 6.55 6.05 7.77 na 5.54 BO070 7,804,673 83.76 xBO090 33,642,491 132.63 -BO100 48,777,542 b 161.39 -

BO020 9-May-97 2,796,216 b 129.71 + (cm)BO040 2,780,223 108.18 + 8.53 5.64 16.51 7.92 9.30 2.46 na 6.40 BO070 18,964,925 203.52 +

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BO090 34,572,433 136.30 xBO100 51,950,314 b 171.89 x

BO020 19-May-97 658,016 b 30.52 + (cm)BO040 631,914 24.59 + 7.62 2.18 0.89 1.63 1.17 0.08 na 0.41 BO070 3,089,409 33.15 +BO090 5,113,353 20.16 +BO100 7,473,858 b 24.73 +

BO020 23-May-97 na b na na (cm)BO040 na na na 0.28 0.43 0.00 1.42 3.66 1.83 na 0.58 BO070 2,955,520 31.72 +BO090 7,201,160 28.39 +BO100 10,777,791 b 35.66 +

BO020 29-May-97 na b na na (cm)BO040 na na na 0.46 0.51 0.53 0.69 0.61 3.02 na 0.53 BO070 na na naBO090 7,944,088 31.32 +BO100 13,270,430 b 43.91 +

BO020 8-Jun-97 1,197,822 b + (cm)BO040 1,438,180 55.96 + 5.79 7.32 10.11 6.22 8.71 8.03 na 7.34 BO070 6,388,995 68.56 +BO090 25,610,066 100.96 +BO100 36,944,928 b 122.24 +

BO020 22-Jun-97 1,168,132 b 54.19 + (cm)BO040 1,484,512 57.76 + 4.95 6.05 9.45 11.40 3.61 4.37 na 5.13 BO070 25,676,604 275.55 +BO090 47,203,769 186.10 xBO100 58,759,190 b 194.42 x

BO020 7-Aug-97 73,760 b 3.42 + (cm)BO040 122,203 4.75 + 4.27 4.37 7.62 2.01 2.03 1.55 na 2.90 BO070 2,434,188 26.12 +BO090 1,463,791 5.77 +BO100 2,139,968 b 7.08 +

BO020 6-Oct-97 66,723 b 3.09 + (cm)BO040 205,372 7.99 + 7.75 7.44 3.81 7.62 9.07 8.00 na 5.61 BO070 2,260,571 24.26 +BO090 928,371 3.66 xBO100 1,294,330 b 4.28 x

BO020 23-Oct-97 52,577 b 2.44 + (cm)BO040 200,731 7.81 + 3.02 4.17 3.23 4.29 0.61 4.67 na 0.38 BO070 1,595,096 17.12 +BO090 2,064,216 8.14 +BO100 2,211,167 b 7.32 +

BO020 2-Dec-97 4,370 b 0.20 + (cm)BO040 58,471 2.28 + 2.01 1.88 1.91 2.16 1.83 2.92 1.98 2.51 BO070 674,959 7.24 +BO090 na na naBO100 333,485 b 1.10 x

BO020 7-Dec-97 46,771 b 2.17 + (cm)BO040 111,012 4.32 + 1.65 2.18 3.68 2.03 1.65 2.06 1.63 1.80 BO070 1,298,835 13.94 +BO090 848,564 3.35 xBO100 697,252 b 2.31 x

Table A–1 Summary of storm events monitored between February 1997 and July 1998at sites along the North Bosque River. (continued)


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Appendix A Summary of Storm Events Monitored Between February 1997 and July 1998

BO020 20-Dec-97 306,391 b 14.21 + (cm)BO040 588,864 22.91 x 5.08 6.53 6.12 0.67 8.41 9.70 13.39 6.86 BO070 3,515,440 37.73 xBO090 6,407,792 25.26 +BO100 12,370,336 b 40.93 +

BO020 4-Jan-98 2,526,665 b 117.21 + (cm)BO040 3,080,625 119.86 + 3.63 5.72 na 4.29 4.50 5.94 10.85 6.22 BO070 8,371,491 89.84 +BO090 10,949,824 43.17 xBO100 15,947,516 b 52.77 x

BO020 31-Jan-98 264,586 b 12.27 + (cm)BO040 286,327 11.14 x 2.74 1.09 2.29 0.91 1.83 2.69 0.00 0.38 BO070 2,201,948 23.63 xBO090 2,339,045 9.22 xBO100 2,583,502 b 8.55 x

BO020 20-Feb-98 470,199 b 21.81 + (cm)BO040 805,264 31.33 + 2.82 2.87 1.09 4.14 3.35 3.99 3.30 3.30 BO070 3,562,419 38.23 +BO090 10,394,946 40.98 +BO100 14,559,990 b 48.17 +

BO020 25-Feb-98 259,033 b 12.02 x (cm)BO040 455,246 17.71 + 0.48 1.22 5.08 2.29 1.07 1.85 1.55 1.78 BO070 7,258,702 77.90 +BO090 18,955,070 74.73 +BO100 23,009,915 b 76.13 +

BO020 7-Mar-98 185,049 b 8.58 x (cm)BO040 314,445 12.23 + 2.36 2.92 8.81 2.41 0.51 2.41 0.64 0.13 BO070 3,647,744 39.15 +BO090 6,050,216 23.85 +BO100 7,215,851 b 23.88 +

BO020 15-Mar-98 8,973,851 b 416.29 + (cm)BO040 9,785,545 380.74 + 10.80 7.75 0.99 12.19 10.77 6.60 6.55 4.24 BO070 37,216,358 399.39 +BO090 176,362,088 695.29 +BO100 196,053,325 b 648.68 +

BO020 20-Apr-98 na b na na (cm)BO040 77,093 3.00 + 0.36 0.69 0.51 0.58 1.02 1.37 1.96 1.12 BO070 na na naBO090 na na naBO100 na b na na

BO020 26-May-98 818,856 b 37.99 + (cm)BO040 1,485,199 57.79 + 3.28 11.56 9.78 4.11 1.91 3.30 1.27 1.55 BO070 4,732,822 50.79 +BO090 3,609,797 14.23 +BO100 4,265,060 b 14.11 +

BO020 4-Jun-98 19,061 b 0.88 + (cm)BO040 53,007 2.06 x 0.08 2.13 0.38 0.28 1.65 2.87 3.56 na BO070 872,104 9.36 x



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BO090 na na naBO100 na b na na

BO020 10-Jun-98 90,894 b 4.22 + (cm)BO040 230,377 8.96 + 3.15 2.57 5.84 4.39 2.84 1.80 3.56 2.46 BO070 1,946,294 20.89 xBO090 na na naBO100 na b na na

BO020 4-Jul-98 na b na na (cm)BO040 na na na 0.30 0.00 5.59 2.54 1.78 2.21 0.00 na BO070 558,486 5.99 +BO090 na na naBO100 na b na na

BO020 12-Jul-98 10,851 b 0.50 + (cm)BO040 95,523 3.72 x 2.26 3.94 2.67 1.22 0.03 0.00 0.20 0.00 BO070 1,112,829 11.94 xBO090 na na naBO100 na b na na

a. Similar symbols indicate similar hydrograph patterns between sites for a storm event based on a visual assessment.b. Flows at BO020 and BO100 are suspect due to limitations in the rating curve or level data at these sites and should

be considered as preliminary values only.c. na indicates not applicable or no measured storm flow or precipitation data.



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APPENDIX B

Summary of Storm EventsMonitored Between November

1995 and January 1997

Table B–1 Summary storm events monitored between November 1995 and January 1997at sites BO040, BO070, and BO090 along the Bosque River.


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BO040 1-Nov-95 409,397 14.33 + (cm)BO070 908,936 9.75 + 3.33 4.75 9.55 1.42 1.09 1.98 0.56 2.11BO090 1,330,955 5.25 x

BO040 17-Dec-95 337,603 11.82 + (cm)BO070 357,168 3.83 + 1.40 1.68 2.01 2.21 3.89 3.15 1.98 2.16BO090 nab na na

BO040 12-Jan-96 338,001 11.83 + (cm)BO070 na na na 1.09 0.97 1.40 0.51 0.91 0.00 2.92 1.17BO090 713,947 2.81 x

BO040 27-Mar-96 328,744 11.51 + (cm)BO070 na na na 3.66 2.51 3.05 1.83 2.34 1.91 1.93 2.11BO090 320,887 1.26 x

BO040 5-Apr-96 890,446 31.17 + (cm)BO070 1,163,868 12.49 + 5.36 5.11 6.35 5.41 6.35 5.74 6.43 5.64BO090 1,602,342 6.31 +

BO040 30-May-96 4,332,684 151.67 + (cm)BO070 2,569,722 27.57 x 16.59 14.05 20.07 16.51 20.37 8.97 13.74 12.70BO090 1,817,209 7.16 -

BO040 7-Jun-96 1,942,931 68.01 + (cm)BO070 2,961,097 31.77 x 4.42 4.67 4.04 4.27 5.56 3.12 2.72 2.26BO090 6,338,116 24.98 x

BO040 11-Jul-96 69,118 2.42 + (cm)BO070 na na na 3.38 2.90 4.32 3.02 4.57 12.32 2.49 5.56BO090 599,887 2.36 x

BO040 8-Aug-96 415,402 14.54 + (cm)

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BO070 141,176 1.51 x 4.47 3.78 9.53 2.24 0.03 2.36 1.09 0.13BO090 na na na

BO040 10-Aug-96 587,212 20.56 + (cm)BO070 1,199,696 12.87 x 2.87 3.84 1.47 2.24 0.89 3.45 0.00 0.84BO090 591,419 2.33 -

BO040 15-Aug-96 2,301,584 80.57 + (cm)BO070 4,037,422 43.31 + 8.66 7.09 10.67 6.05 2.13 6.86 2.69 5.18BO090 2,402,807 9.47 +

BO040 27-Aug-96 1,176,814 41.19 + (cm)BO070 9,165,979 98.33 x 8.92 7.92 12.57 13.82 17.20 9.17 15.57 7.62BO090 27,914,417 110.01 -

BO040 31-Aug-96 1,058,181 37.04 + (cm)BO070 7,878,516 84.52 x 4.42 1.42 0.64 0.33 3.00 9.50 0.00 3.96BO090 17,626,411 69.47 -

BO040 8-Sep-96 333,503 11.67 + (cm)BO070 na na na 1.70 0.84 0.00 0.13 0.00 0.00 0.00 0.00BO090 na na na

BO040 15-Sep-96 5,483,393 191.95 + (cm)BO070 8,809,636 94.51 + 15.14 9.19 5.28 3.58 7.98 11.73 0.00 5.03BO090 11,819,190 46.58 x

BO040 21-Oct-96 57,669 2.02 + (cm)BO070 199,152 2.14 + 1.73 2.51 0.79 2.92 0.51 4.60 0.00 0.61BO090 344,466 1.36 x

BO040 27-Oct-96 932,591 32.65 + (cm)BO070 5,728,103 61.45 x 5.11 4.78 7.24 5.00 4.01 4.24 0.51 1.80BO090 6,974,057 27.48 +

BO040 6-Nov-96 1,539,299 53.88 + (cm)BO070 4,764,511 51.11 + 4.55 3.12 2.92 2.95 2.90 4.93 4.11 3.12BO090 6,739,812 26.56 x

BO040 17-Nov-96 107,059 3.75 + (cm)BO070 na na na 0.13 1.27 1.14 0.89 1.22 0.28 1.09 1.24BO090 2,008,836 7.92 x

BO040 23-Nov-96 1,445,437 50.60 + (cm)BO070 3,327,991 35.70 + 3.66 3.63 1.91 1.91 2.36 1.57 1.78 4.52BO090 4,311,139 16.99 +

BO040 28-Nov-96 1,719,044 60.18 + (cm)BO070 5,833,544 62.58 + 2.54 2.13 3.81 2.49 3.38 3.58 1.93 4.34BO090 13,219,272 52.10 +

a. Similar symbols indicate similar hydrograph patterns between sites for a storm event based on a visual assessment.b. na indicates not applicable or no measured storm flow.

Table B–1 Summary storm events monitored between November 1995 and January 1997at sites BO040, BO070, and BO090 along the Bosque River. (continued)


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APPENDIX C

Average Monthly Discharge fromWWTPs along the North Bosque

River

Table C–1 Average monthly effluent discharge from municipal wastewater treatment plants along the North Bosque River for November 1995 through July 1998. Information obtained from self-reporting data submitted to TNRCC.

Year Month Stephenville Hico Iredell Meridian Clifton Valley Mills

----------------------------------------------------------- (m3/s) ------------------------------------------------------------------

1995 Nov 0.052 0.003 0.001 0.008 0.012 0.0031995 Dec 0.048 0.003 0.001 0.009 0.012 0.0001996 Jan 0.054 0.003 0.001 0.008 0.011 0.0031996 Feb 0.061 0.003 0.001 0.009 0.011 0.0031996 Mar 0.064 0.002 0.001 0.009 0.009 0.0031996 Apr 0.069 0.002 0.001 0.009 0.012 0.0001996 May 0.059 0.002 0.001 0.009 0.012 0.0001996 Jun 0.067 0.002 0.001 0.010 0.012 0.0041996 Jul 0.083 0.002 0.001 0.010 0.012 0.0051996 Aug 0.099 0.003 0.001 0.006 0.014 0.0071996 Sep 0.085 0.002 0.001 0.014 0.014 0.0061996 Oct 0.078 0.002 0.001 0.007 0.013 0.0031996 Nov 0.089 0.002 0.001 0.008 0.014 0.0041996 Dec 0.080 0.002 0.001 0.008 0.014 0.0001997 Jan 0.078 0.003 0.001 0.009 0.014 0.0051997 Feb 0.133 0.007 0.001 0.015 0.012 0.0111997 Mar 0.133 0.008 0.001 0.011 0.028 0.0081997 Apr 0.127 0.007 0.001 0.006 0.026 0.0041997 May 0.086 0.006 0.001 0.006 0.023 0.0041997 Jun 0.078 0.007 0.001 0.008 0.022 0.0061997 Jul 0.070 0.005 0.001 0.006 0.013 0.0031997 Aug 0.057 0.004 0.001 0.005 0.012 0.0041997 Sep 0.055 0.003 0.001 0.005 0.012 0.0051997 Oct 0.074 0.003 0.001 0.006 0.012 0.0041997 Nov 0.055 0.003 0.001 0.004 0.011 0.0041997 Dec 0.060 0.003 0.001 0.006 0.008 0.0051998 Jan 0.069 0.003 0.001 0.007 0.009 0.0051998 Feb 0.093 0.003 0.001 0.009 0.008 0.0051998 Mar 0.097 0.004 0.001 0.009 0.008 0.0041998 Apr 0.072 0.003 0.001 0.006 0.007 0.0021998 May 0.057 0.002 0.002 0.005 0.007 0.0041998 Jun 0.058 0.003 0.001 0.005 0.007 0.0041998 Jul 0.054 0.003 0.001 0.005 0.007 0.004

Mean 0.076 0.003 0.001 0.008 0.013 0.004 Median 0.070 0.003 0.001 0.008 0.012 0.004

Std 0.022 0.002 0.000 0.002 0.005 0.002 Minimum 0.048 0.002 0.001 0.004 0.007 0.000 Maximum 0.133 0.008 0.002 0.015 0.028 0.011

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