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U.S. Fish & Wildlife Service Status and Trends of Wetlands in the Conterminous United States 1986 to 1997

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Page 1: Status and Trends of Wetlands in the Conterminous United ...mde.state.md.us/programs/Water/WetlandsandWaterways/...1 Status and Trends of Wetlands in the Conterminous United States

U.S. Fish & Wildlife Service

Status and Trends of Wetlands in the Conterminous United States1986 to 1997

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Status and Trends of Wetlands inthe Conterminous United States1986 to 1997

Thomas E. DahlU.S. Fish and Wildlife ServiceBranch of Habitat Assessment555 Lester AvenueOnalaska, Wisconsin 54650

Cover photograph:Lac Qui ParleState WildlifeManagementArea, Minnesota.

Acknowledgments

Many agencies, institutions, andindividuals contributed their time,energy, and expertise to thecompletion of this report, and theauthor would like to thank thefollowing for their contributions:Gregory Allord, Marta Anderson,Elizabeth Ciganovich, Gary Latzke,David McCulloch, Dick Vraga, andvarious personnel from the NationalMapping Division, U.S. GeologicalSurvey; Don Field, NationalOceanic and AtmosphericAdministration; the CooperativeFish and Wildlife Research Unit,South Dakota State University.Staff of several U.S. Fish andWildlife Service offices providedextraordinary input to aspects of thestudy including: Elaine Blok, KevinBon, John Cooper, David Dall, JimDick, Chuck Elliott, Gary Frazier,Ann Haas, Jonathan Hall, GerryJackson, William Knapp, SheilaKratzer, Christine Nolin, DennisPeters, Cathleen Short, MarkSteingraeber, Benjamin Tuggle,Robert Willis, and Rich Young.

Technical review of the manuscriptwas provided by the followingexperts: Kenneth Bierly, OregonWatershed Enhancement Board;Kenneth Burnham, Colorado StateUniversity; Marvin Hubbell, IllinoisDepartment of Natural Resources;J. Henry Sather, ProfessorEmeritus, Western IllinoisUniversity; and Douglas Wilcox,Great Lakes Science Center, U.S.Geological Survey.

Publication design and layout of thereport were done by theCartography and PublishingProgram, U.S. Geological Survey,Madison, Wisconsin.

This report should be cited asfollows:

Dahl, T.E. 2000. Status and trends ofwetlands in the conterminous UnitedStates 1986 to 1997. U.S.Department of the Interior, Fish andWildlife Service, Washington, D.C.82 pp.

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Preface

Photograph: Ashrub wetlandnear Cable,Wisconsin.

The U.S. Fish and Wildlife Service iscommitted to working with others toconserve, protect and enhance fish,wildlife, and plants and theirhabitats for the continuing benefit ofthe American people. Wetlands areamong the most important andecologically unique habitats in ourNation, and they provide societywith many environmental andeconomic benefits.

The Emergency WetlandsResources Act requires the Serviceto update its wetland status andtrends information at ten-yearintervals. Data in this and previousstatus and trends reports provideimportant long-term trendinformation about specific changesand places and the overall status ofwetlands in the United States.Although there are severalprograms in the FederalGovernment that collectenvironmental data, the Service’seffort to monitor wetland trendsprovides the only comprehensiveinformation of that nature availableto a broad range of decision makersand the general public. Data in theService’s wetland status and trendsreports are used at all levels of

government for resource policyestablishment and to assess theefficacy of those policies.

This report presents the mostcomprehensive, technicallyadvanced, and contemporary effortto track wetlands status and trendson a national scale. Its value hasbeen enhanced by the multi-agencyinvolvement in the study’s design, indata collection, and in the peerreview of the findings. There isunprecedented recognition ofwetland issues at all levels ofgovernment and in the privatesector. Some readers will use thisinformation to gain insights on theeffectiveness of wetland protectionmeasures during the past decade;others will look for opportunities tostem wetland losses and restorewetland acreage and functions in acontinuing effort to achieve ourresource conservation objectives. Byassessing our Nation’s progress inattaining wetland policy objectives,this report will serve as animportant tool for conservingwetlands and their ecologicalfunctions and values in the 21st

Century.

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DIRECTOR

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U.S. Customary to Metric

inches (in.) x 25.40 = millimeters (mm)

inches (in.) x 2.54 = centimeters (cm)

feet (ft) x 0.3048 = meters (m)

miles (mi) x 1.609 = kilometers (km)

nautical miles (nmi) x 1.852 = kilometers (km)

square feet (ft2) x 0.0929 = square meters (m2)

square miles (mi2) x 2.590 = square kilometers (km2)

acres (A) x 0.4047 = hectares (ha)

gallons (gal) x 3.785 = liters (L)

cubic feet (ft3) x 0.02831 = cubic meters (m3)

acre-feet (A-ft) x 1233.5 = cubic meters (m3)

ounces (oz) x 28.3495 = grams (g)

pounds (lb) x 0.4536 = kilograms (kg)

short tons (tons) x 0.9072 = metric tons (t)

British Thermal Units (BTU) x 0.2520 = kilocalories (kcal)

Farenheit degrees (F ) 0.5556 (F - 32) = Celsius degrees (C )

Metric to U.S. Customary

millimeters (mm) x 0.03937 = inches (in.)

centimeters (cm) x 0.3937 = inches (in.)

meters (m) x 3.281 = feet (ft)

kilometers (km) x 0.6214 = miles (mi)

square meters (m2) x 10.764 = square feet (ft2)

square kilometers (km2) x 0.3861 = square miles (mi2)

hectares (ha) x 2.471 = acres (A)

liters (L) x 0.2642 = gallons (gal)

cubic meters (m3) x 35.31 = cubic feet (ft3)

cubic meters (m3) x 0.0008110 = acre-feet (A-ft)

milligrams (mg) x 0.00003527 = ounces (oz)

grams (g) x 0.03527 = ounces (oz)

kilograms (kg) x 2.2046 = ounces (oz)

metric tons (t) x 2204.62 = pounds (lb)

metric tons (t) x 1.102 = short tons (tons)

kilocalories (kcal) x 3.968 = British Thermal Units (BTU)

Celsius degrees (C ) 1.8(C ) + 32 = Farenheit degrees (F )

Conversion Table

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Contents

Preface ......................................................................................................................................................................3

Executive Summary ...............................................................................................................................................9

Introduction ...........................................................................................................................................................13

Study Design and Procedures .............................................................................................................................14

Study Area ....................................................................................................................................................14

Wetland Definition and Classification .......................................................................................................15

Study Design ................................................................................................................................................16

Imagery .........................................................................................................................................................18

Field Verification ..........................................................................................................................................19

Technological Advances ...............................................................................................................................19

Quality Control and Quality Assurance ....................................................................................................20

Statistical Sampling and Analysis..............................................................................................................22

Procedural Error and Statistical Error....................................................................................................23

Study Limitations ........................................................................................................................................23

Determination of Wetland Loss and Gains ........................................................................................................25

Results ....................................................................................................................................................................28

National Status of Wetland Resources ......................................................................................................28

Attribution of Wetland Loss .......................................................................................................................28

Intertidal Estuarine and Marine Wetlands ..............................................................................................30

Freshwater Wetlands ...................................................................................................................................32

Freshwater Lakes and Reservoirs ............................................................................................................33

Discussion ..............................................................................................................................................................34

Estuarine and Marine Wetland Resources ...............................................................................................35

Long-Term Trends in Estuarine Wetland Types .....................................................................................44

Freshwater Wetland Resources .................................................................................................................45

Wetland Restoration, Creation and Enhancement..................................................................................63

Differences Between the Fish and Wildlife Service’s Status and Trends andthe National Resources Inventory ............................................................................................................66

Summary ...............................................................................................................................................................69

Literature Cited ....................................................................................................................................................70

Appendix A: Habitat Categories.........................................................................................................................73

Appendix B: Contrasting the Fish and Wildlife Service’s Status and Trends ............................................. 78

Appendix C: Wetland Change from 1986 to 1997 .............................................................................................80

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List of Figures

Figure 1. A 1999 color infrared aerial photograph of the coastal region of Bull Island,South Carolina .......................................................................................................................................................14

Figure 2. The physiographic regions of the conterminous United States. ................................................... 16

Figure 3. Stratification based on physiographic regions and a coastal zone stratum in Georgia .............. 17

Figure 4. Mean dates of imagery used to update wetlands in each of the conterminousUnited States .........................................................................................................................................................18

Figure 5. Sample plots were field verified in parts of 35 States from April 1999 to May 2000 .................. 20

Figure 6. A color-coded digital review plot from coastal New Jersey ........................................................... 21

Figure 7A–D. Wetland area (A) compared to total area of the conterminous United States;(B) percent of estuarine and freshwater types; (C) estuarine cover types; (D) freshwatercover types .............................................................................................................................................................28

Figure 8. Estuarine emergents (salt marsh) near Edisto Island, South Carolina (1995) ........................... 30

Figure 9. Status of marine and estuarine intertidal wetlands in the conterminousUnited States, 1997 ...............................................................................................................................................30

Figure 10. Percent of estuarine and marine wetlands lost to freshwater wetlands, deepwater orupland categories between 1986 and 1997 .........................................................................................................31

Figure 11. Distribution of estuarine emergents (salt marsh) along the Atlantic andGulf coasts, 1997 ....................................................................................................................................................33

Figure 12. Freshwater wetland types in the conterminous United States, 1997 ......................................... 33

Figure 13. Average annual net wetland loss rate over time for the conterminous United States ............. 34

Figure 14. Areas of the Gulf coast where estuarine wetlands were lost to deepwater between 1986and 1997 ..................................................................................................................................................................35

Figure 15. Areas along the Gulf and Atlantic coasts where estuarine wetlands were lost to urbanor rural development between 1986 and 1997 ...................................................................................................37

Figure 16. The broad coastal plain of the southeastern Atlantic supports expansive estuarinewetlands (Coastal South Carolina, 1996) ...........................................................................................................37

Figure 17A and B. Two examples of development in coastal areas ............................................................... 39

Figure 18. Development along the Florida’s Gulf coast beaches ................................................................... 39

Figure 19. Coastal developments encroach on estuarine shrub wetlands (mangroves) alongthe Intracoastal Waterway in Florida ................................................................................................................40

Figure 20. Tidal flats along an estuarine spit in Walkalla County, Florida (1993) ....................................... 41

Figure 21A–C. Color infrared aerial photographs showing changes to coastal features between(A) 1989; (B) 1994; and (C) 1999 ....................................................................................................................42–43

Figure 22A–C. Long-term trends in (A) all intertidal wetlands; (B) estuarine vegetated wetlands;(C) estuarine non-vegetated wetlands, 1950s to 1997 ......................................................................................44

Figure 23. Change in wetlands converted to various land uses between 1986 and 1997 ........................... 46

Figure 24. Freshwater wetlands, by type, that are within or adjacent to agricultural lands, 1997 ........... 47

Figure 25. Color infrared aerial photographs taken in 1989 and 1999 show development(s)proceeding in South Carolina ........................................................................................................................46–47

Figure 26. Gulf and Atlantic coastal counties that experienced wetland losses to uplandsbetween 1986 and 1997 .........................................................................................................................................48

Figure 27. Cumulative loss and conversion of freshwater forested wetlands, 1986 to 1997....................... 49

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List of Tables

Figure 28. A clear-cut of a former freshwater forested wetland in Oklahoma, 2000 .................................. 49

Figure 29. An example of forested wetland loss in Virginia, 1998 ................................................................. 50

Figure 30. This diagram illustrates a drainage technique for forestry production ..................................... 51

Figure 31A–C. Examples of freshwater emergent wetland losses ................................................................ 54

Figure 32. A freshwater emergent wetland in Tennessee (2000) that was being drained and filled ........ 55

Figure 33. Current upland classification of areas where emergent wetlands were lost between1986–97 ...............................................................................................................................................................55

Figure 34. A freshwater emergent wetland within an agricultural field ...................................................... 55

Figure 35. Long-term trends in open water ponds, 1950s to 1997 ................................................................. 56

Figure 36. Freshwater pond types vary dramatically throughout the United States ................................. 57

Figure 37. Contrasting color infrared aerial photographs taken in 1988 and 1999, show new pondscreated as part of a golf course and housing developments ............................................................................ 58

Figure 38. An excavated farm pond in northwestern Iowa, 1999 .................................................................. 59

Figure 39. Catfish farms (ponds) are shown as various shades of blue rectangles on this infraredaerial photograph from Mississippi, 1997 ..........................................................................................................59

Figure 40. Distribution and relative size of freshwater ponds created between 1986 and 1997 ................ 60

Figure 41. A black and white aerial photograph of peat extraction (mining) in Maine, 1996 .................... 61

Figure 42A–C. Long-term trends in selected freshwater wetlands, 1950s to 1997 ..................................... 62

Figure 43. A created wetland created near Orlando, Florida, 1994............................................................... 63

Figure 44. Two oblique photographs showing A) partially drained wetlands prior to restorativeactions, and B) wetland basins with restored hydrology .................................................................................63

Figure 45. Prairie wetlands in the fall of 1999 (South Dakota) have reclaimed some upland area,including the road .................................................................................................................................................64

Figure 46A and B. Color infrared aerial photographs of north-central Florida (A) during droughtconditions in 1989 and (B) during different hydrologic conditions in 1996 ................................................... 65

Figure 47. An example of upland “other” shrub steppe in Montana, 1999. .................................................. 76

Table 1. Wetland, deepwater and upland categories used in this study. The definitions for eachcategory appear in Appendix A ..........................................................................................................................15

Table 2. Change in wetland area for selected wetland and deepwater categories, 1986 to 1997. Thecoefficient of variation (CV) for each entry (expressed as a percentage) is given in parentheses ............ 29

Table 3. Estuarine and marine intertidal wetland area and change 1986 to 1997. The coefficient ofvariation (CV) for each entry (expressed as a percentage) is given in parentheses.................................... 31

Table 4. Estuarine and marine intertidal wetland losses 1986 to 1997. The coefficient of variation (CV)for each entry (expressed as a percentage) is given in parentheses ............................................................. 32

Table 5. Mean size and range of freshwater wetlands as they appeared within the sample unitsin 1997 .....................................................................................................................................................................32

Table 6. Freshwater wetland area and change 1986 to 1997. The coefficient of variation (CV) for eachentry (expressed as a percentage) is given in parentheses .............................................................................45

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ExecutiveSummary

Photograph: Aforested wetlandin the HarrisNeck NationalWildlife Refuge,Georgia.

At the time of European settlement,the area that is now theconterminous United Statescontained an estimated 221 millionacres (89.5 million ha) of wetlands.Over time, wetlands have beendrained, dredged, filled, leveled, andflooded to the extent that less thanhalf of the original wetland acreageremains (Dahl 1990).

The U.S. Fish and Wildlife Service’sfirst wetlands status and trendsreport (Frayer et al. 1983) estimatedthe rate of wetland conversionbetween the mid 1950s and the mid1970s at 458,000 acres (185,400 ha)per year. Those estimates capturedtrends from the period precedingmany efforts to protect and restorewetlands. Society’s views aboutwetlands have changed considerablyand interest in the preservation ofwetlands has increased as the valuesof wetlands have become more fullyunderstood.

Evidence of progress in reducingwetland losses became apparent inthe Service’s updated status andtrends report (Dahl and Johnson1991) covering the mid 1970s to themid 1980s. The estimated rate ofwetland loss had declined to 290,000acres (117,400 ha) per year.

In 1986, the Emergency WetlandsResources Act of 1986 (Public Law99-645) was enacted to promote theconservation of our Nation’swetlands. The Act requires theService to conduct wetland statusand trend studies of the Nation’swetlands at 10-year intervals. Thisreport to the Congress details thestatus and trends of our Nation’swetlands from 1986 to 1997. Itprovides the most recent andcomprehensive estimates of thecurrent status and trends of wetlandhabitats.

An interagency group of statisticiansdeveloped the design for the nationalstatus and trends study. The studydesign consists of 4,375 randomly

selected sample plots. Each plot isfour square miles (2,560 acres or1,040 ha) in area. These plots wereexamined, with the use of recentremotely sensed data in combinationwith field work, to determinewetland change. Twenty-one percentof the plots were field verified, andrigorous quality control measureswere taken to ensure data integrityand quality. Estimates were made ofwetland area by wetland type andchanges over time.

The study incorporated all wetlands,regardless of land ownership, as partof the sampled landscape. Becausewetlands in coastal areas areimportant to a variety of fish andwildlife species, this study includedthem by adding a supplementalsampling stratum along the Atlanticand Gulf coastal fringes.

Determining what caused wetlandloss or gains is an important part ofassessing the effectiveness of policyor management actions. As part ofthis study, the Service worked withother Federal agencies to examineand field test wetland loss and gainattribution categories. Wetlandlosses and gains have been assignedto five general categories: uplandurban development, uplandagriculture, upland silviculture,upland rural development, and othermiscellaneous lands.

National StatusAn estimated 105.5 million acres(42.7 million ha) of wetlandsremained in the conterminousUnited States in 1997. Between 1986and 1997, the net loss of wetlandswas 644,000 acres (260,700 ha). Theannual loss rate during this periodwas 58,500 acres (23,700 ha), whichrepresents an eighty percentreduction in the average annual rateof wetland loss as compared to thelast wetlands status and trendsreport. Various factors have

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contributed to the decline in the lossrate including implementation andenforcement of wetland protectionmeasures and elimination of someincentives for wetland drainage.Public education and outreach aboutthe value and functions of wetlands,private land initiatives, coastalmonitoring and protectionprograms, and wetland restorationand creation actions have also helpedreduce overall wetland losses.

Ninety-five percent of the remainingwetlands were inland freshwaterwetlands. Five percent of theNation’s wetlands were in saltwaterestuarine environments. Freshwaterforested wetlands made up thesingle largest category (50.7 millionacres or 20.5 million ha) of allwetlands in the conterminous UnitedStates.

Estuarine and Marine WetlandsThree categories of estuarine andmarine wetlands were included inthis study: estuarine intertidalemergents such as salt and brackishwater marshes; estuarine shrubssuch as mangroves and other salttolerant woody species; andestuarine and marine intertidal non-vegetated wetlands such as beaches,tidal flats, shoals, sand spits, andbars. These wetlands providevaluable nursery, feeding, breeding,staging, and resting areas for anarray of fishes, shellfish, mammals,and birds. These resources face adual threat from natural stressorssuch as storms, wind and waveerosion, land subsidence, and sealevel rise, and from pressurebrought about by human populationincreases in coastal counties.

An estimated 5.3 million acres (2.2million ha) of marine and estuarineintertidal wetlands made up about 5percent of the total wetland acreagein the conterminous United States.Vegetated estuarine wetlands madeup an estimated 87 percent ofestuarine wetlands. Non-vegetatedestuarine and marine wetlands (seeAppendix A) including beaches, flats,and shoals, made up 13 percent of allintertidal wetlands or 711,000 acres(287,900 ha).

Estuarine and marine wetlandsaccounted for two percent of thetotal loss of all wetlands observed inthis study. Between 1986 and 1997there was a net loss of 10,400 acres(4,200 ha) of estuarine and marine

wetlands; an estimated annual lossof about 1,000 acres (405 ha). Therate of loss for these wetlands wasreduced more than 82 percent fromthe previous decade. This was theresult of various Federal and Stateagencies that have contributed torestoration, protection andmonitoring of coastal areas.

Long-term trends indicate thatestuarine vegetated wetland areadeclined at a much reduced ratefrom earlier decades, and that non-vegetated wetland types haveremained fairly constant over time.

Freshwater WetlandsFreshwater wetlands support avariety of fish and wildlife speciesand contribute to the aesthetic andenvironmental quality in everyState. Millions of Americans usefreshwater wetlands annually forhunting, fishing, bird watching andother outdoor activities.

An estimated 100.2 million acres(40.6 million ha) of freshwaterwetlands of various types remain inthe conterminous United States.There were 50.7 million acres (20.5million ha) of forested wetlands, 25.2million acres (10.2 million ha) offreshwater emergents, and 18.4million acres (7.5 million ha) offreshwater shrub wetlands. Therewere also an estimated 5.5 millionacres (2.2 million ha) of freshwaterponds.

Ninety-eight percent of all lossesrecorded during this study were tofreshwater wetlands. The net loss ofall freshwater wetland types was633,500 acres (256,500 ha).Freshwater forested wetlands andfreshwater emergent marshes eachlost an estimated 1.2 million acres(486,000 ha) between 1986 and 1997.The numeric losses of freshwaterwetlands were partially offset bygains in freshwater shrub wetlands(1.1 million acres or 445,000 ha) andfreshwater ponds (631,000 acres or256,000 ha).

The freshwater shrub category wasthe only vegetated freshwaterwetland type to increase in areabetween 1986 and 1997.

The open water pond categorygained the most area since the1950s. There were 5.5 million acres(2.2 million ha) of open water pondsin 1997. This was more than twice

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the area of open water pondsreported in the mid 1950s.Nationally, the lower MississippiValley and central Floridacontributed substantially to thenumber of larger ponds created byhuman activities. Many of the largerponds in the Mississippi Valley werecreated for aquaculture. Ponds incentral Florida were either waterretention ponds associated withdevelopment or sediment retentionbasins related to surface miningoperations.

The long-term trends in freshwaterwetlands since the 1950s, show thatfreshwater emergent wetlands havedeclined by the greatest percentageof all wetland types with nearly 24percent lost (8 million acres or 3.2million ha). Freshwater forestedwetlands have sustained the greatestoverall loss in area, declining by 10.4million acres (4.2 million ha).

Freshwater Lakes and ReservoirsFreshwater lakes and reservoirs aredeepwater habitats that providerecreation for millions of people.They support inland fisheries andare stopover locations for manymigratory birds.

Between 1986 and 1997, deepwaterlakes and reservoirs exhibited amodest increase in area with a netgain of 116,400 acres (47,100 ha).The rate of lake and reservoircreation declined 43 percent fromthe 1970s to 1980s.

Attribution ofWetland Lossesand GainsThis report indicates that urbandevelopment accounted for 30percent of the loss of wetland toupland land use categories from1986 to 1997; 26 percent of the losswas attributed to agriculture; 23percent to silviculture and 21percent to rural development.

Estuarine and Marine WetlandsThe major factor in estuarine andmarine wetland loss was filling ordraining for development. Together,urban and rural developmentaccounted for 43 percent of theestuarine and marine wetland losses.

Seventy five percent of all estuarineand marine losses occurred inemergent salt marsh wetlands.Emergent salt marshes declined byan estimated 14,450 acres (5,850 ha),a 0.4 percent loss. Fifty-eightpercent of these losses were fromsome form of deepwater intrusioninto the salt marsh. Estuarine shrubwetlands increased slightly with anet gain of about 6,600 acres (2,670ha). Most of this increase was theresult of conversions from otherestuarine wetland types. The loss inestuarine non-vegetated wetlands(flats, bars and shoals) was notstatistically significant (less than 1percent of all estuarine wetlandlosses).

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Yosemite NationalPark, California.

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A freshwaterwetland innorthernWisconsin.

Freshwater WetlandsUrban development accounted for 30percent of the estimated losses inthe freshwater system. Twenty-sixpercent of the loss was attributableto agriculture; 23 percent tosilviculture, and 21 percent to ruraldevelopment. The rate of freshwaterwetland loss on agricultural landsdeclined substantially from theprevious decade. Previously, about1.0 million acres (404,900 ha) werelost to agriculture as opposed to198,000 acres (80,200 ha) during 1986to 1997. However, freshwateremergent wetlands in agriculturalareas, especially those that arepartially drained, continue to be lost.Implementation of the wetlandconservation provisions in the FoodSecurity Act, as amended, andagricultural set-aside and landretirement programs may havecontributed to the reduction inwetland loss rate.

Collectively, 51 percent or 383,300acres (155,200 ha) of all thefreshwater wetlands lost to uplandsresulted from urban expansion orrural development such as theconstruction of buildings, roads,bridges and other infrastructure inwetlands. Freshwater non-tidalwetlands experienced substantialdevelopment pressure just inland

from the coastlines of the UnitedStates.

Freshwater emergent wetlandsexperienced substantial losses ofmore than 1.2 million acres (496,400ha). This was a reduction of 4.7percent. Of the 700,000 acres(283,000 ha) of emergent wetlandslost to upland, an estimated 51percent were on agricultural lands.Another 22 percent were lost todevelopment in urban or ruralsettings, 25 percent to unidentifiedland uses, and 2 percent wereconverted to silviculture.

Substantial inroads were madeduring this study period in curtailingoverall wetland losses and inrestoring or creating wetland area.Progress was also made in reducingthe loss of estuarine wetlands alongour coastlines. The number offorested wetlands converted toagriculture was reduced in areas likethe lower Mississippi alluvial plainand the coastal plain of thesoutheastern United States. Federalprograms such as the conservationprovisions of the Food Security Act,the Fish & Wildlife Service’s coastalprograms and conservationpartnership programs havecontributed to the declining wetlandloss rate.

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Introduction

The mission of the U. S. Fish andWildlife Service is to conserve,protect, and enhance fish, wildlifeand plants and their habitats for thecontinuing benefit of the Americanpeople. The Service has trustresponsibilities for migratory birds,endangered species, anadromousand interjurisdictional fisheries, andsome marine mammals. The Servicealso manages the National WildlifeRefuge System that protects andconserves a myriad of the Nation’swetland habitats.

Wetlands are crucial for manyspecies and they provide benefits topeople. In recent years, publicappreciation of the ecological, socialand economic values of wetlands hasincreased substantially (TheConservation Foundation 1988). Theincreased awareness of how muchwetland acreage has been lost ordamaged since the time of Europeansettlement, and the consequences ofthose losses has led to thedevelopment of many Federal, State,and local wetland protectionprograms and laws. Severallandmark pieces of legislation,Presidential Executive orders, andagency programs have contributedpositively to wetland conservationefforts. There have also beenregional wetland loss studiesconducted that help identifyimportant wetland trends andcontribute to regional managementpriorities.

The Emergency WetlandsResources Act (Public Law 99-645)was enacted to promote theconservation of our Nation’swetlands. Congress recognized thatwetlands are nationally significantresources and that these resourceshave been affected by humanactivities. The Act requires the

Service to conduct wetland statusand trend studies of the Nation’swetlands at 10-year intervals.Earlier reports on wetland statusand trends include Frayer et al.(1983), Tiner (1984), Dahl (1990), andDahl and Johnson (1991).

This report to the Congress detailsthe status and trends of our Nation’swetlands. It covers the period from1986 to 1997, and provides the mostrecent and comprehensive estimatesof the current status of wetland areathroughout the conterminous UnitedStates and the losses or gains tovarious wetland types that haveoccurred during this time.

New technology contributed to theinformation presented in this report.Geospatial analysis capability nowbuilt into the status and trends studyprovided a complete digital databaseto assist in analyzing wetland changeinformation. This information hasimportant resource policyimplications to help managersinterpret the role that wetlands playon the national landscape. It alsoprovided the Service and itspartners with scientific data to helpguide resource managementdecisions on wetland related issuessuch as restoration andenhancement, endangered specieshabitat availability and ecosystemmanagement planning. The datacurrently available provide a half-century record of wetland changebeginning with the first status andtrends report that covered the 1950sto 1970s.

This study provides a quantitativemeasure of the areal extent of allwetlands in the conterminous UnitedStates. The study provides noqualitative assessments of wetlandfunctions.

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Study Design and Procedures

14

Figure 1. A1999 colorinfrared aerialphotograph ofthe coastalregion of BullIsland, SouthCarolina.Wetlandfeatures such assand flats,inter-tidal bars,shoals, andsmall islandswere importantwetlandhabitatsincluded withina coastal zonestratum.(National AerialPhotographyProgram.)

Study AreaThe total land area of theconterminous United States is about1.93 billion acres (0.8 billion ha). Thetopography ranges frommountainous terrain to low reliefcoastal plains and river deltas.Climate and geography influencehabitats that vary from deserts tosubtropical conditions. Althoughwetlands occur in every State andphysiographic region, there areobvious differences in theirabundance between regions.Stratification of the Nation based onthe differences in wetland densitymakes this study an effectivemeasure of wetland resources.

Some Federal inventories stop atcounty boundaries or at a pointcoinciding with the census line forinhabitable land area. Doing so mayexclude offshore wetlands, shallowwater embayments or sounds,shoals, sand bars, tidal flats andreefs (Figure 1). These areimportant fish and wildlife habitats.Consequently, the Service includedwetlands in coastal areas by addinga supplemental sampling stratumalong the Atlantic and Gulf coastalfringes. This zone includes the nearshore areas of the coast with itsbarrier islands, coastal marshes,exposed tidal flats and otheroffshore features not a part of thelandward physiographic zones. Thecoastal zone stratum, as described

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here, included almost 28.2 millionacres (11.4 million ha). At its widestpoint in southern Louisiana, thiszone extended about 92.6 miles (149km) from Lake Pontchartrain to thefurthest extent of estuarine wetlandresources. It was an area wheresaltwater is the overriding influenceon biological systems. The coastalzone in this study was notsynonymous with any State orFederal jurisdictional coastal zonedefinitions. The legal definition of“coastal zone” has been developedfor use in coastal demarcations,planning, regulatory andmanagement activities undertakenby other Federal or State agencies.

Table 1: Wetland, deepwater and uplanAppendix A.

Category

Salt Water Habitats

Marine Subtidal*

Marine Intertidal

Estuarine Subtidal*

Estuarine Intertidal Emergents

Estuarine Intertidal Forested/Shrub

Estuarine Intertidal Unconsolidated Shore

Estuarine Aquatic Bed**

Riverine* (may be tidal or non-tidal)

Freshwater Habitats

Palustrine Forested

Palustrine Shrub

Palustrine Emergents

Palustrine Unconsolidated Shore

Palustrine Unconsolidated Bottom

Palustrine Aquatic Bed

Lacustrine*

Uplands

Agriculture

Urban

Forested Plantations

Rural Development

Other Uplands

* Constitutes deepwater habitat** Technical limitations described in the text

WetlandDefinition andClassificationThe Service uses the Cowardin et al.(1979) definition of wetland. Thisdefinition is the standard for theagency and is the national standardfor wetland mapping, monitoringand data reporting as determined bythe Federal Geographic DataCommittee. This definition has beenused for the present study as well asprevious wetland status and trendsreports. It is a two-part definition asindicated below:

d categories used in this study. The defini

Common Description

Open ocean

Near shore

Open water/bay bottoms

Salt marsh

Mangroves or other estu

Beaches/bars

Submerged or floating es

River systems

Forested swamps

Shrub wetlands

Inland marshes/wet mea

Shore beaches/bars

Open water ponds

Floating aquatic/submer

Lakes and reservoirs

Cropland, pasture, mana

Cities and incorporated d

Planted or intensively m

Non-urban developed ar

Rural uplands not in any

“Wetlands are lands transitionalbetween terrestrial and aquaticsystems where the water table isusually at or near the surface orthe land is covered by shallowwater.

For purposes of thisclassification wetlands must haveone or more of the following threeattributes: (1) at leastperiodically, the land supportspredominantly hydrophytes, (2)the substrate is predominantlyundrained hydric soil, and (3)the substrate is nonsoil and issaturated with water or covered

15

tions for each category appear in

arine shrubs

tuarine vegetation

dows

ged vegetation

ged rangeland

evelopments

anaged forests; silviculture

eas and infrastructure

other category; barren lands

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Coast Ranges

Puget Willamette Lowland

Cascade Klamath Sierra Nevada Ranges

Central Valley of California

Columbia Basin

Blue Mountains

Harney and Owyhee Broken Lands

Basin and Range Area

Northern Rocky Mountains

Snake River Lowland

Middle Rocky Mountains

Wyoming Big Horn Basins

Colorado River Plateaus

Upper Gila Mountains

North Central Lake Swamp Moraine Plain

Upper Missouri Basin Broken Lands

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

12

15

9

10

11

13

14

5

6

7

81

2

3

4

Figure 2. The physiographic regions of thestudy (Source: Hammond 1970).

by shallow water at some timeduring the growing season ofeach year.”

Habitat category definitions aregiven in synoptic form in Table 1.The reader is encouraged to reviewAppendices A and B, which providecomplete definitions of wetlandtypes and land use categories usedin this study as well as a comparisonof wetland definitions and habitattypes that may be treateddifferently by other Federalagencies.

s

Study DesignAn interagency group of statisticiansdeveloped the design for the nationalstatus and trends study. The basic

Dakota Minnesota Drift and Lake Bed Flats

Nebraska Sand Hills

West Central Rolling Hills

Midcontinent Plains and Escarpments

Southwest Wisconsin Hills

Middle Western Upland Plain

Southern Rocky Mountains

Rocky Mountain Piedmont

High Plains

Stockton Balcones Escarpment

17

18

19

20

21

22

23

24

25

26

25

2728

34

36

29

30

15

23

35

26

19

20

1521

22

24

17

18

11

16

conterminous United States. A coastal zone

sampling design and studyobjectives have remained constantfor each wetland status and trendsreport. The study design consists of4,375 randomly selected sampleplots. Each plot is four square miles(2,560 acres or 1,040 ha) in area. Theplots were examined, with the use ofremotely sensed data in combinationwith field work, to determinewetland change. Estimates ofchange in wetlands were made overa specific time period.

To determine changes in wetlandarea, the 48 conterminous Stateswere stratified or divided by Stateboundaries and 35 physiographicsubdivisions described by Hammond(1970) and shown in Figure 2. Topermit even spatial coverage of thesample, the 36 physiographic regionsformed by the Hammond

Ozark Ouachita Highlands

Lower Mississippi Alluvial Plain

East Central Drift and Lake Bed Flats

Eastern Interior Uplands and Basins

Appalachian Highlands

Adirondack New England Highlands

Lower New England

Gulf Atlantic Rolling Plain

Gulf Atlantic Coastal Flats

Coastal Zone

27

28

29

30

31

32

33

34

35

36

34

36

36

31

32

33

26

35

stratum (zone 36) has been added to this

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subdivisions and the coastal zonestratum were intersected with Stateboundaries to form 220 subdivisionsor strata. An example of thisstratification approach and the wayit related to sampling frequency isshown in Figure 3.

In the physiographic stratadescribed above, weighted, stratifiedsample plots were randomlyallocated in proportion to theamount of wetland acreage expectedto occur in each stratum. Eachsample area was a surface plot 2.0miles (3.2 km) on a side or 4 squaremiles of area equaling 2,560 acres(1,036 ha). Plots were initiallyallocated to strata based on the bestinformation available about wetlandarea and variability by strata and ona standard optimal-allocationformula for stratified simple-randomsampling when the study wasinitiated in 1978. Because decliningwetland loss rates require morefinite measurement techniques to

Gulf-Atlantic Rolling

Appalachian Highlands

ensure a high degree of statisticalreliability, the sample size of thisstudy was augmented withadditional sample plots.

For the present study, about 725supplemental sample plots wereadded to parts of Maine, Vermont,New York, Pennsylvania, Ohio, WestVirginia, Kentucky, Tennessee,Nebraska, Kansas, Oklahoma, NewMexico, Arizona, Nevada,Washington, and threephysiographic zones of the northernRocky Mountains and the SnakeRiver Lowlands in Wyoming,Montana, and Idaho. As sample plotlocations were geographicallyreferenced for positional accuracy,some plots were moved to otherstrata based on their true earthcoordinates. In these instances,additional plots were added atrandom in the affected strata toensure a consistent sample size.Wetland changes were determinedby intensive analysis of the imagery,

17

Plain

Gulf-Atlantic Coastal Flats

Coastal Zone

Dry

Wet

—Sample plot location

Figure 3. Statification based onphysiographic regions and a coastalzone stratum in Georgia. The sampleplot density increased in relation towetland area, from drier (AppalachianHighlands) to wetter (Coastal Zone).This stratification scheme has ecologicaland statistical advantages.

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1996199719981999

Arizona

California Colo

Idaho

Montana

Nevada

New Mexico

Oregon

Utah

Washington

Wyoming

Figure 4. Mean dates of imagery used to up

interpretation of wetland types andhydrologic conditions, anddetermination of the changes thatoccurred between the respectivetarget dates. The study wasdesigned to produce estimates oftotal wetland area and changes forthe conterminous United States.

The procedures follow U.S. Fish andWildlife Service (1994a, 1994b). Anadvantage to this design was that itfocused entirely on monitoringwetland change, and it was used tomonitor conversions betweenecologically different wetland types,and measure wetland gains andlosses.

ImageryPrevious studies have used aerialimagery to monitor wetland changesover time (Hefner et al. 1994;Moulton et al. 1997; Dahl 1999; andothers). This study used multiplesources of recent imagery and directon-the-ground observations torecord wetland change information.

Arkansas

radoIllinois

Iowa

Kansas

Louisiana

Minnesota

Mississippi

Missouri

Nebraska

North Dakota

Oklahoma

South Dakota

Texas

Wisconsin

date wetlands in each of the conterminous

An agency decision required the useof imagery with a mean date noolder than 1997. Traditionally, theService relied on aerial photographyavailable from the National AerialPhotography Program (NAPP) formaking wetland change detectionassessments. Although the NAPPimagery still forms a large part ofthe source information, NAPPcoverage dated 1997 or more recent,was not available for all sample plotareas. To achieve complete coverageand meet the target date required,this study used imagery provided byfive Federal agencies, four Stateagencies, and one privateorganization.

The mean imagery date for each ofthe States is shown in Figure 4. WestVirginia and Florida were the twoexceptions that retained meanimagery dates earlier than 1997. Itwas not practicable to update sampleplots to reflect current conditions byusing direct field examination inthese two States because most of theWest Virginia sample plots wereinaccessible and many plots inFlorida contained changes too

Alabama

Connecticut

Delaware

Florida

Georgia

Indiana

Kentucky

Maine

Maryland

Massachusetts

Michigan

New Hampshire

New Jersey

New York

North Carolina

Ohio

Pennsylvania

Rhode Island

South Carolina

Tennnessee

Vermont

Virginia

WestVirginia

United States.

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numerous and extensive toaccurately portray on anything otherthan a recent image base.

Imagery, in the form of aerialphotographs, ranged in scale andtype; most was 1:40,000 scale, colorinfrared. Only the most recent, goodquality imagery was used. In someinstances, customized flights weremade to acquire good qualityphotography.

Early spring and late fall (leaf-off)imagery was usually used. Thedetermination of the extent offorested wetlands can be difficultand there were distinct advantagesto using leaf-off imagery to detectthe extent of forested wetlands.Visual evidence of hydrologicconditions such as saturation,flooding or ponding combined withcollateral data sources such as soilsurveys, topographic maps andwetland maps were used to identifyand delineate the areal extent offorested wetlands. Early spring andlate fall imagery was an importanttool in this process.

The study included all wetlandsregardless of land ownership. Allwetlands 3 acres (1.2 ha) and largercomposed the target population. Theresults indicate that for eachwetland category included, theminimum size represented was lessthan 1.0 acres (0.4 ha). However, notall wetlands less than the target sizecategory were detected. For eachsample plot, the rate of changeamong all wetland types between thetwo dates of imagery was used toestimate the total area of the sampleplot in each wetland type and thechanges in wetland area betweenthese dates. The changes wererecorded in categories that can beconsidered the result of eithernatural change, such as the naturalsuccession of emergent wetlands toshrub wetlands, or human-inducedchange. Areas of the sample plotthat had been identified in previouseras as wetlands but that were nolonger wetlands, were placed intofive land use categories includingagriculture, upland forestedplantations, upland areas of ruraldevelopment, upland urbanlandscapes, and other miscellaneouslands. The outputs from this analysiswere change matrices that providedestimates of wetland area by typeand observed changes over time. Asin past studies, rigorous qualitycontrol inspections were built into

the interpretation, data collectionand analysis processes.

FieldVerificationField verification was completed for912 (21 percent) of the sample plotsdistributed in 35 States (Figure 5).This constituted the largest fieldverification effort undertaken for astatus and trends report.

Field verification addressedquestions regarding imageinterpretation, land use coding andattribution of wetland gains orlosses. Field work was also done as aquality control measure to verifythat plot delineations were correct.Verification involved field visits to across section of wetland types andgeographical settings, and to plotswith different image types, scalesand dates. Field work was used toupdate sample plots based onobservations of on-the-groundconditions. Representatives from sixFederal agencies participated in fieldreconnaissance trips from April 1999through May 2000.

19

TechnologicalAdvancesAdvances in computerizedcartography were used to improvedata quality and geospatial integrity.In past studies, annotated imageswere manually transferred to atopographic base map scale using azoom transfer scope. Areameasurement and changeinformation were obtained from atransfer overlay at 1:24,000 scale byeither scanning or board digitization.That process required humanintervention to retrace lines threetimes: once during the photographicinterpretation process, once duringthe rectification to base map scaleprocess, and finally for areameasurement or board digitizing.

Newer technologies allowed thegeneration of existing digital plotfiles at any scale to overlay directlyonto an image base. The wetlandsinterpreter viewed the new imagerystereoscopically and made changenotations directly on the imageoverlay. The change overlay was

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Arizona

California Col

Idaho

Montana

Nevada

New Mexico

Oregon

Utah

Washington

Wyomin

Figure 5. Sample plots were field verified i

then rescanned. Because the plotinformation was already in aspatially rectified file, any changeinformation could be inserted to thecorrect geospatial position in theplot boundary. Area information wasrecalculated from the new digital fileby use of a geographic informationsystem. This process eliminatedmanual drafting, registered theimage overlays to georeferencedcoordinates, and reduced impreciselines (line pixel width) inherent inolder scanning technologies.

The geospatial analysis capabilitybuilt into this study provided acomplete digital database to betterassist analysis of wetland changeinformation.

Quality Controland QualityAssuranceA quality assurance program isessential for ensuring the validity ofanalytical data (U.S. EPA 1979). TheService has developed andimplemented quality assurancemeasures that provide appropriatemethods to take field measurements,

Arkansas

oradoIllinois

Iowa

Kansas

Minnesota

Missouri

Nebraska

North Dakota

Oklahoma

South Dakota

Texas

g

Louisiana

Mississippi

Wisconsin

n parts of 35 States from April 1999 to May

ensure sample integrity and provideoversight of analyses which includedreporting of procedural andstatistical confidence levels.

The objective of this study was toproduce comprehensive, statisticallyvalid acreage estimates of theNation’s wetlands. Because of thesample based approach, variousquality control and quality assurancemeasures were built into the datacollection, review, analysis andreporting stages. Some of the majorquality control steps were:

Plot Location and PositionalAccuracyStatus and trends sample plots werepermanently fixed georeferencedareas that are revisited periodicallyto monitor land use and cover typechanges. The plot coordinates werepositioned precisely using a systemof redundant backup locators onprints produced from a geographicinformation system, topographicmaps, other maps used for collateralinformation and the aerial imagery.Plot outlines were computergenerated for the correct spatialcoordinates, size and projection. Plotlocations were transferred andregistered onto all work materials.

Connecticut

Delaware

Florida

Indiana

Kentucky

Maine

Maryland

Massachusetts

Michigan

New Hampshire

New Jersey

New York

Ohio

Pennsylvania

Rhode Island

South Carolina

Tennnessee

Vermont

Virginia

WestVirginia

Alabama Georgia

North Carolina

2000.

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Imagery, Base Maps and CollateralDataAerial imagery was the primary datasource, but it was used with reliablecollateral data such as topographicmaps, coastal navigation charts,published soil surveys, publishedwetland maps, and State, local orregional studies. All photographywas cataloged, numbered, tagged,and tracked in a databasemanagement system.

Photo Interpretation Quality ControlReviewDetermination of wetland changecharacteristics from aerial imageryrequires a high level of accuracy inthe identification and classificationof wetlands, deepwater habitats andassociated uplands. Because of thecomplexity and the amount of datato be viewed and processed, accuratewetland interpretation from aerialimagery requires considerableexpertise. A small cadre of highlytrained and experienced wetlandsinterpreters completed the imageanalysis. Wetland image interpretersaveraged 12 years of wetlandsinterpretation and classificationexperience. This ensured highquality, accurate and nationallyconsistent data.

Image interpreters conducted fieldverification exercises to ensureaccurate and consistentinterpretation of imagery and toresolve various interpretationquestions. Quality control field trip

reports and field data sheetsprovided documentation of fieldreconnaissance efforts, generaldescriptions of wetlands and uplandsin an area, descriptions of surfacewater conditions both on theimagery and at the time of fieldwork, and details about the qualityof the source materials used.

Quality control reviews wereconducted by an experienced photointerpreter other than the individualresponsible for the original work.Stereoscopic quality control reviewsof all photo interpretation work wereconducted for each sample plot.These reviews involved checking forerrors of omitted wetlands,identification of false changes (suchas drought or draw-downconditions), classification errors,unlabeled polygon features,incomplete work and agreementwith collateral data sources.Documented proceduralspecifications and conventionsassisted in quality control reviews.This documentation and a completedescription of the techniques used toaccomplish the photo interpretationand change detection process areprovided in various technicalmanuals (U.S. Fish and WildlifeService 1994a; 1994b).

Change Information and Data CaptureColor differential scanning (see“Technological Advances”) of plotchange data eliminated much of themanual cartographic transfer and

21

Figure 6. A color-coded digitalreview plot fromcoastal NewJersey. Theseinterim workproducts wereused as part of thequality controlprocess.

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22

digitizing work of past studies. Thescanning technique was used tocapture changes of plot features,cartographically register the revisedplot information, and determine areameasurement, all in an automatedformat. This minimized inaccuraciesin the process, and it facilitated theuse of interim review plots as anadditional quality control step. Theutility of an interim color-codeddigital review plot to assist with theinspection of polygonal data,classification coding, and spatialintegrity of the data in the plotboundaries is shown in Figure 6.Unlabeled polygons were eliminatedand area measurements becamemore precise by automating the datacapture process.

Quality Assurance of Digital DataFilesAll digital data files were subjectedto rigorous quality controlinspections. Automated checkingmodules incorporated in thegeographic information system(ARC/INFO) were used to correctdigital artifacts including vectordangles, undershoots, overshoots,unclosed polygons, and incorrectlycoded polygons. Additionalcustomized data inspections weremade to ensure that the changesindicated at the image interpretationstage were properly executed.Digital file quality control reviewsalso provided confirmation of plotlocation, stratum assignment, andtotal land or water area sampled.

Database Logic ChecksLogic checking used a series ofcustomized database queriesdesigned to eliminate potentialerrors in plot geophysical addressinformation, attribute coding,improbable change data orimpossible feature classification.

StatisticalSampling andAnalysisThe wetland status and trends studywas based on a scientific probabilitysample of the surface area of the 48conterminous States. The areasampled was about 1.93 billion acres(0.8 billion ha), and the sampling didnot discriminate based on landownership. The study used a

stratified, simple random samplingdesign.

About 754,000 possible sample plotscomprised the total population.Given this population, the samplingdesign was stratified by use of the 36physical subdivisions described inthe “Study Design” section. Thisstratification scheme had ecological,statistical, and practical advantages.This study design was well suited fordetermining wetland acreage trendsbecause the 36 divisions of theUnited States coincide with factorsthat effect wetland distribution andabundance. Once stratified, the landsubdivisions represented very largeareas, and it was desirable, onstatistical-scientific principles, toachieve a more even spatial spreadto the sample plots. The finalstratification, which was based onintersecting physiographic landtypes with state boundaries,guaranteed an improved spatialrandom sample of plots.

Geographic information systemsoftware was used to organize theinformation about the 4,375 randomsample plots. An important designfeature crucial to understanding thetechnical aspects of this study is thata grid of full-sized square plots canbe overlaid on any stratum to definethe population of sampling units forthat stratum. However, at thestratum boundaries some plots were“split” across the boundary andthus, were not a full 2,560 acres(1,036 ha). In sampling theory, plotsize is an auxiliary variable that isknown for all sampled plots andwhose total is known over everystratum. All sampling units (plots) ina stratum were given equal selectionprobabilities regardless of their size.In the data analysis phase, theadjustments were made for varyingplot sizes by use of ratio estimationtheory. For any wetland type, theproportion of its area in the sampleof plots in a stratum was an unbiasedestimator of the unknown proportionof that type in that stratum.

Inference about total wetlandacreage by wetland type or for allwetlands in any stratum began withthe ratio (r) of the relevant totalacreage observed in the sample (Ty),for that stratum divided by the totalarea of the sample (Tx). Thus, y wasmeasured in each sample plot; r =Ty/Tx, and the estimated totalacreage of the relevant wetland typein the stratum was A x r. The sum of

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these estimated totals over all strataprovided the national estimate forthe wetland type in question.

Uncertainty, which was measured assampling variance of an estimate,was estimated based on the variationamong the sample proportions in astratum (the estimation of samplevariation is highly technical and notpresented here). The samplingvariation of the national total wasthe sum of the sampling varianceover all strata. These methods arestandard for ratio estimation inassociation with a stratified randomsampling design (Sarndal et al. 1992;Thompson 1992).

By use of this statistical procedure,the sample plot data were expandedto specific physiographic regions, bywetland type, and statisticalestimates were generated for the 48conterminous States. The reliabilityof each estimate generated isexpressed as the percent coefficientof variation (% C.V.) associated withthat estimate. Percent coefficient ofvariation was expressed as (standarddeviation/mean)x(100). The percentcoefficient of variation indicates thatthere was a 95 percent probabilitythat an estimate was within theindicated percentage range of thetrue value.

Procedural Errorand StatisticalErrorProcedural or measurement errorsare foreign to the notion of statisticalprobability, but they occur in thedata collection phase of any studyand must be considered. Althoughstatistical reliability refers to theability to replicate results, theconcept is conditional on theaccuracy of the measurements. Awell designed statistical study maystill produce erroneous results if theprocedural error is unacceptable.

Procedural error was related to theability to accurately recognize andclassify wetlands both from multiplesources of imagery and on-the-ground evaluations. Types ofprocedural errors were missedwetlands, inclusion of upland aswetland, misclassification ofwetlands, or misinterpretation ofdata collection protocols. Theamount of introduced procedural

error is usually a function of thequality of the data-collectionconventions; the number, variability,training and experience of datacollection personnel; and the rigor ofany quality control or qualityassurance measures. This studyused well established, time-tested,fully documented data collectionconventions (U.S. Fish and WildlifeService 1994a; 1994b). It employed asmall cadre of highly skilled andexperienced personnel for datacollection and processing. Rigorousquality control reviews andredundant inspections wereincorporated into the data collectionand data entry processes to helpreduce the level of procedural error.Estimated procedural error rangedfrom 4 to 6 percent of the true valueswhen all quality assurance measureshad been completed.

StudyLimitationsCertain habitats were excluded fromthis study because of the limitationsof aerial imagery as the primarydata source to detect wetlands. Thiswas consistent with previouswetland status and trends studiesconducted by the Service. Thesehabitats included seagrasses orsubmerged aquatic vegetation thatare found in the intertidal andsubtidal zones of estuaries and nearshore coastal waters (Orth et al.1990). The detection of submergedaquatic vegetation using aerialimagery is difficult without extensivesurface-level observations, tide-stage data, water-clarity data andbecause of surface waves (Fergusonet al. 1993). Because of theserequirements, the majority ofseagrasses were not delineated aspart of this study, and the datapresented in this report are notintended to provide a reliableindicator of the extent of seagrassarea in coastal waters of theconterminous United States. Asupplemental discussion ofseagrasses as estuarine and marinewetland types is provided.

Unlike the broad expanses ofemergent wetlands along the Gulfand Atlantic coasts, the estuarinewetlands of California, Oregon andWashington occur in discontinuouspockets. Their patchy distributionprecludes establishment of a coastal

23

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Freshwaterwetland inWisconson.

stratum as exists for Gulf andAtlantic coast wetlands and nostatistically valid data could beobtained through establishment of acoastal stratum there. Therefore,consistent with past studies, thisstudy did not sample Pacific coastestuarine wetlands such as those inSan Francisco Bay, California; CoosBay, Oregon, or Puget Sound,Washington.

Ephemeral wetlands are notrecognized as a wetland type byCowardin et al. (1979), and were notincluded in this study. These areashave not been included in any of theService’s previous reports.

Wetlands that were farmedperiodically during dry years, butunder normal circumstances supporthydrophytic vegetation (e.g.,seasonally flooded wetlands thatwere periodically farmed for wheatproduction on the Northern GreatPlains) are classified as freshwateremergent wetland in this study.

Emergent andfloatingvegetation.

Effectively drained palustrinewetlands observed in farmproduction were not consideredwetland in the Service’s estimatedbase wetland acreage. For example,throughout the southeastern UnitedStates and in California, rice (Oryzasativa) is planted on drained hydricsoils and on upland soils. When riceis actively being grown, the land wasflooded with water and the areafunctions as a wetland. In yearswhen rice was not grown, the samefields were used to grow other crops(e.g., corn, soybeans, cotton). Anestimated 12 million acres (4.9million ha) of commercial rice landswere identified primarily inCalifornia, Arkansas, Louisiana,Mississippi and Texas. Thesecultivated rice fields were not able tosupport hydrophytic vegetation andbe included as palustrine farmedwetland under the Cowardin et al.(1979) definition. Therefore, theService did not include these landsin the base wetland acreageestimates.

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Determination of Wetland Lossesand Gains

The Fish and Wildlife Service andthe Natural Resources ConservationService both collect data on wetlandchanges. Each agency has adifferent mission and differentlegislative mandates. Both agenciesuse the Cowardin et al. (1979)wetland definition in their respectiveinventories. For programmaticreasons, the Natural ResourcesConservation Service also recordsdata on wetlands as defined by theFood Security Act of 1985 (PL-99-198). The latter represents a subsetof wetlands defined by the Cowardinet al. system. The process ofidentifying or attributing cause forwetland losses or gains has beeninvestigated by both the Service andNatural Resources ConservationService. During 1998 and 1999, theNatural Resources ConservationService and the Service launched aconcerted effort to develop auniform system of definitions toattribute wetland losses and gains totheir causes.

During April and May 1999,cooperative interagency fieldevaluations were conducted to fieldtest the definitions used by theService on its wetland status andtrends plots to attribute wetlandlosses or gains. Field exercisesinvolving the participation of up tofour Federal agencies (Fish andWildlife Service, EnvironmentalProtection Agency, Office ofManagement and Budget andNatural Resources ConservationService) were conducted in Florida,Louisiana and Minnesota. Theseexercises consisted of a carefulreview of determinations made on 89sample plots. Field evaluation ofthese plots resulted in nodisagreement among agencyrepresentatives with how theService attributes wetland losses orgains.

The categories used to determinethe cause of wetland losses and gainsare described below.

25

WapanoccaNational WildlifeRefuge, Arkansas.(M. Caldwell)

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26

AgricultureThe definition of agriculture followsAnderson et al. (1976) and includesland used primarily for theproduction of food and fiber.Agricultural activity may be shownby distinctive geometric field androad patterns on the landscape and/or by tracks produced by livestockor mechanized equipment. Examplesof agricultural land uses includehorticultural crops, row and closegrown crops, hayland, pastureland,native pastures and range land, andfarm infrastructures. Examples ofwhat this study determined to beagricultural land uses are:

Horticultural crops are crops thatinclude orchard fruits (apples,grapefruit, oranges, peaches, pearsand like species). Also included arenuts such as almonds, pecans andwalnuts; vineyards including grapesand hops; bush-fruit such asblueberries; berries such asstrawberries or raspberries; andcommercial flower growing andcutting operations.

Row and close-grown crops includefield and sweet corn, sorghum,soybeans, cotton, peanuts, tobacco,sugar beets, potatoes, other truckvegetables including melons, beets,cabbage, cauliflower, pumpkins,tomatoes, sunflower andwatermelon. Close-grown crops alsoinclude wheat, oats, barley, sod,ryegrass and similar graminoids.

Hayland and pastureland includegrass, legumes, summer fallow, andgrazed native grassland.

Other farmland includesfarmsteads and ranch headquarters,commercial feedlots, greenhouses,hog facilities, nurseries and poultryfacilities.

ForestedPlantationsForested plantations include areas ofplanted and managed forest stands.Planted pines, Christmas tree farms,clear cuts and other managed foreststands such as hardwood forestry,were included in this category.

RuralDevelopmentRural developments occur in sparserural and suburban settings outsidedistinct urban cities and towns. Theyare characterized by non-intensiveland use and sparse building density.Typically, a rural development is across-roads community that has acorner gas station and a conveniencestore which are surrounded bysparse residential housing andagriculture. Scattered suburbancommunities located outside of amajor urban center can also beincluded in this category and someindustrial and commercialcomplexes; isolated transportation,power, and communication facilities;strip mines; quarries; andrecreational areas such as golfcourses. Major highways throughrural development areas were

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included in the rural developmentcategory.

UrbanDevelopmentUrban land consists of areas ofintensive use in which much of theland is covered by structures (highbuilding density). Urbanized areasare cities and towns that provide thegoods and services needed to surviveby modern day standards through acentral business district. Servicessuch as banking, medical and legaloffice buildings, supermarkets, anddepartment stores make up thebusiness center of a city. Commercial

strip developments along maintransportation routes, shoppingcenters, contiguous dense residentialareas, industrial and commercialcomplexes, transportation, powerand communication facilities, cityparks, ball fields and golf courseswere included in the urban category.

Other Land UsesOther Land Use is composed ofuplands not characterized by theprevious categories. Typically theselands would include native prairie,unmanaged or non-patterned uplandforests and scrub lands; and barrenland. Lands in transition may also fitinto this category.

27

A freshwaterwetland along theUpperMississippi RiverbetweenMinnesota andWisconsin. (U.S.Fish and WildlifeService)

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Fccptf

Results

28

Upland 93.5%

A. Total Land Area

Deep1

Wetland5.5%

*Excludes area of the Great Lakes

igure 7 A–D. Wetland area (A)ompared to total area of theonterminous United States; (B)ercentage of estuarine and freshwaterypes; (C) estuarine cover types; (D)reshwater cover types.

Data for the 1986 to 1997 studyperiod are presented in Appendix C,and they are summarized in Table 2.

1 Percentages exceed 100 since somewetlands are adjacent to more than oneupland type.

National Statusof WetlandResourcesAn estimated 105.5 million acres(42.7 million ha) of wetlandsremained in the conterminousUnited States in 1997. Thecoefficient of variation of theNational estimate is 2.8 percent.Between 1986 and 1997, theestimated total net loss of wetlandswas 644,000 acres (260,700 ha). Theestimated annual rate of loss duringthis period was 58,500 acres (23,700ha). The coefficient of variation ofthe loss rate is 36 percent (i.e., theestimated annual loss rate is

B

C. Estuarine Wetlands

water*%

Estuarine5%

Emergents74%

Flats/Beaches13%

Shrubs13%

between 38,000 and 80,000 acres).The annual rate of loss has declined80 percent since the period from themid 1970s to the mid 1980s (Dahland Johnson 1991).

Among the wetlands sampled, 55percent were located in or adjacentto lands classified as other uplands.An additional 31 percent were in oradjacent to agricultural lands; 24percent in or adjacent to silviculture;and 5 percent were in or adjacent tourban areas1.

Ninety-five percent of the remainingwetlands were freshwater wetlands.Five percent were estuarine ormarine wetlands (Figure 7). Amongall freshwater wetlands, freshwater

. Total Wetlands

D. Freshwater Wetlands

Freshwater95%

Forested51%

Emergents25%

Shrubs18%

Ponds6%

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forested wetlands made up thesingle largest category (50.7 millionacres or 20.5 million ha).

Attribution ofWetland LossUsing the study definitions for thecauses of wetland losses and gains,this study determined that urban

Table 2. Change in wetland area for selvariation (CV) for each entry (expressed

Wetland/Deepwater Category

Marine Intertidal

Estuarine Intertidal Non-vegetated1

Estuarine Intertidal Vegetated2

All Intertidal Wetlands

Freshwater Non-vegetated3

Freshwater Vegetated4

Freshwater Emergent

Freshwater Forested

Freshwater Shrub

All Freshwater Wetlands

All Wetlands

Deepwater Habitats

Lacustrine5

Riverine

Estuarine Subtidal

All Deepwater Habitats

All Wetlands and Deepwater Habitats1,2

* Statistically unreliable1 Includes the categories: Estuarine Intertidal 2 Includes the categories: Estuarine Intertidal 3 Includes the categories: Palustrine Aquatic B4 Includes the categories: Palustrine Emergent5 Does not include the Great Lakes.

development accounted for anestimated 30 percent of all wetlandlosses. Estimates for the other losscategories included 26 percent toagriculture, 23 percent tosilivculture, and 21 percent to ruraldevelopment. An estimated 98percent of all wetlands converted toother uses were freshwaterwetlands.

29

ected wetland and deepwater categories, 1986to 1997. The coefficient of as a percentage) is given in parentheses.

Area in thousands of acres

Estimated area,1986

Estimated area,1997

Change,1986–97

Change(in percent)

133.1(19.6)

130.9(19.9)

–2.2(88.5)

–1.7

580.4(10.7)

580.1(10.6)

-0.3 (*)

–0.1

4,623.1(4.0)

4,615.2(4.0)

-7.9(75.1)

–0.2

5,336.6(3.8)

5,326.2(3.8)

–10.4(73.0)

–0.2

5,251.0(4.1)

5,914.3(3.9)

663.3(13.4)

12.6

95,548.1(3.0)

94,251.2(3.0)

–1,296.9(17.1)

–1.4

26,383.3(8.1)

25,157.1(8.4)

–1,226.2(18.2)

–4.6

51,929.6(2.8)

50,728.5(2.8)

1,201.1(23.8)

–2.3

17,235.2(4.2)

18,365.6(4.1)

1,130.4(25.7)

6.6

100,799.1(2.9)

100,165.5(2.9)

633.6(36.5)

–0.6

106,135.7(2.8)

105,491.7(2.8)

–644.0(36.0)

0.6

14,608.9(10.6)

14,725.3(10.5)

116.4(*)

0.8

6,291.1(9.6)

6,255.9(9.4)

–35.2(*)

–0.6

17,637.6(2.2)

17,663.9(2.2)

26.3(95.6)

0.1

38,537.6(4.4)

38,645.1(4.4)

107.5(*)

0.3

144,673.3(2.4)

144,136.8(2.4)

–536.5(30.7)

–0.4

Aquatic Bed and Estuarine Intertidal Unconsolidated Shore.Emergent and Estuarine Intertidal Shrub.ed, Palustrine Unconsolidated Bottom and Palustrine Unconsolidated Shore., Palustrine Forested and Palustrine Shrub.

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30

Non

Figure 8.Estuarineemergents (saltmarsh) nearEdisto Island,South Carolina(1995).(M. Caldwell)

FiinU

IntertidalEstuarine andMarine WetlandsIntertidal wetlands include saltmarshes and salt-tolerant shrubs;non-vegetated wetland such as sandbars, mud flats, and tidally exposedshoals; and shallow watercomponents of the marine systemsuch as sand beaches and shorelines.These wetlands were found in thelow-lying coastal areas that areflooded periodically by tidal waters(Hefner et al. 1994). In 1997, therewere an estimated 5.3 million acres(2.2 million ha) of marine andestuarine intertidal wetlands, thatmade up about 5 percent of the totalwetland acreage in the conterminousUnited States.

Estuarine emergents (Figure 8) andestuarine shrub wetlands (Figure 9)

All Intertidal Wetlands

-vegetated13%

Vegetated87%

gure 9. Status of marine and estuarinetertidal wetlands in the conterminousnited States, 1997.

made up 87 percent of the estuarinewetlands in the conterminous UnitedStates, totaling 4.6 million acres (1.9million ha). Non-vegetated estuarineand marine wetlands, includingbeaches, flats, and shoals, comprised13 percent of all intertidal wetlandsor 711,000 acres (287,900 ha).

The changes that occurred between1986 and 1997 in estuarine andmarine wetlands are shown in Table3. The largest acreage change wasan estimated net loss of 14,500 acres(5,900 ha) of estuarine emergentwetlands. The greatest percentchange was a decline of 1.7 percentof marine intertidal beaches.Estuarine and marine wetlandsaccounted for 2 percent of theoverall wetland losses when all typeswere considered. During the study,estuarine and marine wetland lossestotaled less than 1,000 acres (405 ha)annually. The major factor inestuarine and marine wetland loss

Estuarine Vegetated Wetlands

Emergents85% Shrubs

15%

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Agriculture1%

FreshwaterWetlands

14%

OtherUplands

30%

Deepwater12%

Urban Development

24%

Rural Development

19%

Figure 10. Percent of estuarine andmarine wetlands lost to freshwaterwetlands, deepwater, or uplandcategories between 1986 and 1997.

was development. Urban and ruraldevelopment combined, accountedfor 43 percent of the estuarine andmarine wetland losses (Figure 10).Other upland land uses, whichinvolved fill or spoil deposition,accounted for 30 percent of the loss.The total and annual change inestuarine and marine wetland typesis shown in Table 4.

Seventy five percent of all estuarineand marine losses were in emergentsalt marsh wetlands. The emergentsalt marsh wetlands of the Atlanticand Gulf coast states experiencedlosses due to development as well assaltwater inundation. Thedistribution of these emergent saltmarsh wetlands is shown in Figure11.

Emergent salt marsh wetlandstypically occupy broad expanses ofcoastal lowlands. The mean size ofsalt marsh wetlands on the study

Table 3. Estuarine and marine intertidaleach entry (expressed as a percentage

Wetland Category

Marine Intertidal

Estuarine Unconsolidated Shore

Estuarine Aquatic Bed

Marine and Estuarine Intertidal Non-vegetated1

Estuarine Emergent

Estuarine Shrub

Estuarine Intertidal Vegetated2

Estuarine Subtidal

* Statistically unreliable.1 Includes the categories: Estuarine Unconsoli2 Includes the categories: Estuarine Emergent

plots was 44 acres (18 ha). Overall,the study revealed that estuarinewetlands in urban settings werefairly rare. Approximately 4.8percent of estuarine salt marshwetlands were adjacent to or withinurban areas. The mean size of otherestuarine wetland types was smaller;estuarine shrub wetlands sampledwere 16 acres (7 ha) and estuarinebars, flats and shoals were 12 acres(5 ha).

31

wetland area and change, 1986 to 1997. The coefficient of variation (CV) for ) is given in parentheses.

Area in thousands of acres

Estimated area,1986

Estimated area,1997

Gain or loss,1986–97

Area (as percent) of all intertidal wetland, 1997

133.1(19.6)

130.9(19.9)

–2.2(88.5)

2.5

551.3(10.9)

550.8(10.8)

–0.5 (*)

10.3

29.1(27.1)

29.3(26.9)

0.2(*)

0.6

580.4(10.7)

580.1(10.6)

–0.3(*)

13.4

3,956.9(4.1)

3,942.4(4.1)

–14.5(49.2)

74.0

666.2(12.6)

672.8(12.6)

6.6(76.5)

12.6

4,623.1(4.0)

4,615.2(4.0)

–7.9(75.1)

86.6

Changes in coastal deepwater area, 1986–97

17,637.6(2.2)

17,663.9(2.2)

26.3(95.6)

dated Shore and Estuarine Aquatic Bed.and Estuarine Shrub.

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32

SparseModerateDenseInsufficient data

Figure 11. Distribution of estuarine emergents (salt marsh) along the Atlantic and Gulf coasts, 1997. Sparse distribution is lessthan or equal to 5 percent areal coverage of coastal quadrangles; moderate is 6–20 percent; and dense is greater than 20 percentareal coverage.

Table 4. Estuarine and marine intertidal wetland losses, 1986 to 1997. The coefficient of variation (CV) for each entry (expressed as a percentage) is given in parentheses.

Wetland TypeArea lost,1986–97 (acres)

Annual change (acres)

Losses as percent of

annual intertidal

change

Estuarine Vegetated Wetlands1 –7,830(75)

–712(*)

75

Estuarine and Marine, Non-Vegetated2 –2,590(*)

–236(*)

25

Total Estuarine and Marine Wetland–10,420

(73)–948(*)

100

1 Includes estuarine emergents and estuarine shrub categories.2 Includes estuarine unconsolidated shore, estuarine aquatic bed, and marine intertidal categories.*Statistically unreliable.

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FreshwaterWetlandsFreshwater, or palustrine, wetlandsoccur in every State. They includeforested wetlands, freshwateremergent marshes, shrub wetlands,and freshwater ponds less than 20acres (8 ha).

An estimated 100.2 million acres(40.6 million ha) of freshwaterwetlands of various types remainedin the conterminous United States in1997. There were 50.7 million acres(20.5 million ha) of forestedwetlands, 25.2 million acres (10.2million ha) of freshwater emergents,and 18.4 million acres (7.5 million ha)of freshwater shrub wetlands. Therewere also an estimated 5.5 millionacres (2.2 million ha) of freshwaterponds. The distribution of

Emergent 25%

Shrub 18%

Ponds 6%

Fo

Other FreshwaWetlands

<1%

Table 5. Mean size and range of freshwathe sample units in 1997.

Freshwater Wetland Category

Freshwater forest

Freshwater shrub

Freshwater emergent

Freshwater ponds

Other Freshwater types

1 The upper limit is restricted by the sample plo2 The upper limit reflects the area of ponds conn

freshwater wetland types is shownin Figure 12.

From 1986 to 1997, both freshwaterforested wetlands and freshwateremergent marshes experiencedsubstantial losses of 1.2 million acres(486,000 ha) from each category.These losses in wetland area weresomewhat offset by gains infreshwater shrub wetlands (1.1million acres or 445,000 ha) andfreshwater ponds (631,000 acres or256,000 ha). The estimated net lossof all freshwater wetland types was633,600 acres (256,500 ha) during theperiod of this study. This indicatesthat 98 percent of all wetland lossesin the conterminous United Statesbetween 1986 and 1997 were tofreshwater wetlands.

The mean size of freshwaterwetlands sampled indicated thatfreshwater forested wetlands were

rested 51%

ter

Figure 12. Freshwater wetlandin the conterminous United Sta1997.

ter wetlands as they appeared within

Mean size(acres)

Range (acres)1

21 <1 to 2,560

8 <1 to 2,416

7 <1 to 2,560

1–2 <1 to 1,0002

3–4 <1 to 700

t size and cannot be determined.ected in series.

the largest type (Table 5). The meansize for forested wetlands was 21acres (9 ha). Freshwater shrub andemergent wetlands were 8 acres (3.2ha) and 7 acres (2.8 ha), respectively.The mean size of freshwater pondswas 1–2 acres (0.4–0.8 ha).

FreshwaterLakes andReservoirsDeepwater lakes and reservoirsshowed a modest increase, with a netgain of 116,400 acres (47,100 ha).The rate of lake and reservoircreation declined 43 percent fromthe 1970s to 1980s. The reason forthis decline is not known.

33

typestes,

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Discussion

34

1

2

3

4

5

Acr

es

Figure 13. Average annual net wetlandloss over time for the conterminousUnited States. (Sources: Frayer et al.1983; Dahl and Johnson 1991; thisstudy.)

Dahl and Johnson (1991) estimatedthat 103.2 million acres (41.8 millionha) of wetlands existed in theconterminous United States in 1984.This study produced a revised 1986estimate of 106.1 million acres (43million ha). The adjusted estimate ofwetland area for the mid 1980s waswithin the statistical range of boththe 1991 study and this report.Other factors contributing to thisadjustment were corrections to thewetland data set, and improved datacapture and measurementtechniques.

This study estimated that 105.5million acres (42.7 million ha) ofwetlands were in the conterminousUnited States at the end of 1997.Between 1986 and 1997, a net of

458,000

2

0

00,000

00,000

00,000

00,000

00,000

1950s-1970s 1970s

644,000 acres (260,700 ha) ofwetlands were lost. The wetland lossrate in the United States continuedto decline. The average annual rateof wetland loss decreased by 80percent compared with the rate inthe previous decades (Figure 13).Several factors contributed to thissubstantial decline in the loss rate.Important among them were theapplication and enforcement ofwetland protection measures,elimination of some incentives forwetland drainage, public educationand outreach about the value andfunctions of wetlands, private landinitiatives, coastal monitoring andprotection programs, naturalrestoration due to hydrologic cycles,and wetland restoration and creationactions undertaken by society.

90,000

58,500

-1980s 1980s-1990s

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Estuarine andMarine WetlandResourcesSaltwater intertidal wetlands aredynamic areas of economic andsocial importance. These wetlandsprovide valuable nursery, feeding,breeding, staging and resting areasfor many fishes, shellfish, mammalsand birds. Nearly 45 percent of theNation’s endangered and threatenedspecies are dependent on coastalhabitats (U.S. Fish and WildlifeService 1995). Many species ofshorebirds use exposed estuarinebars and flats as feeding and restingareas. Wading birds use shallowwater salt marshes and tidal poolsfor foraging. Endangered sea turtlesnest along estuarine and marinebeaches and sand spits. Near shorevegetated wetlands provide habitatfor estuarine fish species. Formationof shallow water oyster beds istracked closely as an indicator ofwater quality conditions and theirimportance to commercial fisheries.

Three major categories of estuarineand marine wetlands were includedin this study: estuarine intertidalemergents (salt and brackish watermarshes), estuarine shrubs(mangroves and other salt tolerantwoody species), and estuarine andmarine intertidal non-vegetatedwetlands (beaches, tidal flats, shoals,sand spits and bars). A fourthcategory includes the seagrassesand submerged aquatic vegetation.Because of their importance to fish

EI

and wildlife, a brief discussion ofseagrasses and submerged aquaticvegetation is included in the specialinset section (next page).

Between 1986 and 1997 there was anestimated net loss of 10,400 acres(4,200 ha) of estuarine and marinewetlands. The rate of decline forthese wetlands was reduced morethan 82 percent since the previousdecade (Dahl and Johnson 1991).Enactment of legislation such as theCoastal Wetlands Planning,Protection, and Restoration Act,combined with other Federal andState conservation effortscontributed to this reduction inestuarine and marine wetland losses.

Saltwater intrusion, or the loss ofwetland to open saltwater systems,due to natural and man-inducedactivities, accounted for 12 percentof the estuarine and marine wetlandlosses. The areas along the Gulfcoast where estuarine wetlands werelost to deepwater during this studyare shown in Figure 14. Barras et al.(1994) showed that land loss to openwater is a continuing problem incertain watersheds along theLouisiana coast.

Urban and rural developmentactivities, and the conversion ofwetlands to other upland land uses,accounted for most of the estuarineand marine wetland losses between1986 and 1997. Areas where urbanexpansion and rural developmentresulted in estuarine wetland lossesare shown in Figure 15.

35

Figure 14. Areas of the Gulf coast whereestuarine wetlands were lost todeepwater (shown in blue) between 1986and 1997.

stuarine Wetland Loss to Deepwater Habitatnsufficient Data

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36

Changes to seagrass beds in the CapeLookout, North Carolina, regionbetween 1985 and 1988. For this figure,the change data were superimposed on aconventional aerial photograph taken in1988. This photograph represents anarea approximately five-by-five miles.In addition to aerial photography, towedand hand-held underwater videographyis used as a verification tool. Single-beam acoustics are used in deeper, moreturbid areas. The acoustic sensor toolalso takes bathymetric readings. (NationalOceanic and Atmospheric Administration)

Areas of no seagrass change

Areas of seagrass loss

Areas of seagrass gain

Seagrasses andSubmerged AquaticVegetationSeagrasses or submerged aquaticvegetation are plants that areadapted to living in shallow, subtidalestuarine or marine environments.Seagrasses provide importantenvironmental functions includingstabilizing sediments and adjacentshorelines, serving as nursery areasfor many fish and shellfish, playingan important role in nutrient cycling,and providing cover or habitat forsessile and mobile fauna (Thayer etal. 1984). Seagrasses may also bedirectly consumed by geese,dugongs, manatees, and sea turtles(Zieman 1982; Lanyon et al. 1989).

Seagrasses occur in every coastalState except South Carolina andGeorgia (Fonseca et al. 1998), butthere is no comprehensive nationaldata on the status of seagrassabundance or recent trends. TheNational Oceanic and AtmosphericAdministration (NOAA) is workingto fill some of the data gaps onseagrass habitat trends.

Mapping seagrasses poseschallenges beyond mapping otherwetlands. In order to penetrate the

water column NOAA employsconventional color photographyacquired under specificenvironmental conditions. Propertidal stage, sea state, etc., are crucialto capturing all of the resourcepresent. Additional technologiessuch as videography and acousticsare often necessary for a successfulmapping and monitoring effort.

Changes in AquaticVegetation BedsThese wetlands are subject to rapidchange coincident with stressorssuch as dredging and filling,abnormal water temperaturechanges, input of chemical wastes,increased turbidity and developmentof adjacent uplands and wetlands(Thayer et al. 1984; Ferguson et al.1993).

Information on seagrass distributionhelps state and local officials withpermitting, waterfront planning, andresearch needs. Comparing maps ofthe same area from different yearshelps managers monitor the healthof this resource .

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37

Estuarine Wetland Loss to Urban or Rural Development

Insufficient Data

Figure 15. Areas along the Gulf andAtlantic coasts where estuarinewetlands were lost to urban or ruraldevelopment (shown in orange) between1986 and 1997.

Figure 16. The broad coastal plain of thesoutheastern Atlantic supportsexpansive estuarine wetlands (CoastalSouth Carolina, 1996). (M. Caldwell)

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38

A ditched area inthe Atlanticcoastal plain.

Estuarine Emergent WetlandsThe coastlines of New England andthe Pacific Northwest are typified byhigh energy, rocky headlandspunctuated by small estuarinewetlands, which are mostlyrestricted to protected embayments(Chabreck 1988; Ardito and Finch1998). In contrast, the broad coastalplain of the southeastern Atlanticand Gulf States supports much moreexpansive areas of estuarinewetlands, particularly emergent saltmarsh (Figure 16). Most of thechanges in the estuarine wetlandsoccurred in the southern coastalStates from Virginia to Texas.

Estuarine emergents declined by anestimated 14,450 acres (5,850 ha)between 1986 and 1997, a 0.4 percentloss. Most of this wetland loss (58percent) was caused by open waterintrusion from undeterminedcircumstances. Of the estuarineemergent losses recorded, 58percent were lost to open saltwater,34 percent to uplands, and 8 percentwere converted to other estuarinetypes, primarily shrubs. Sea levelrise, marshland sloughing intodeeper water bays and sounds, andland subsidence may havecontributed to these losses. Theprocesses that cause saltwaterintrusion, whether natural orhuman-induced, are complex, andnot well understood (Sallenger andWilliams 1989). Estuarine marshesin coastal Louisiana haveexperienced these kinds of stressorsover the past several decades(Britsch and Dunbar 1993). In placessuch as Louisiana and the upperTexas Gulf coast, these phenomenainfluenced wetland losses in habitats

other than in the estuarine system(White and Tremblay 1994).Examples of non-estuarine wetlandtypes in coastal drainages subject tosaltwater intrusion included tidally-influenced freshwater marshes andforested or shrub swamps.

The effects of saltwater intrusionare also seen to a lesser extent onareas of the Atlantic coast. InVirginia and North Carolina, someareas were inundated with enoughsaltwater to establish estuarineemergents. This was observed onseveral small tracts of farmland andin several freshwater wetlands.

Although estuarine salt marshwetlands are among the mostecologically productive naturalresources in the United States,about 5,000 acres (2,020 ha) ofestuarine salt marsh wetlands werefilled and developed from 1986 to1997. Urban and rural developmentof houses, roads, and infrastructureaccounted for about 2,300 acres (930ha) of these losses (Figures 17 and18). Other upland land uses in ruralareas filled another 2,700 acres(1,090 ha). Fill accounted for 34percent of the losses in the estuarineemergent wetland category.Development pressure on wetlandsremains intense along the Gulf andAtlantic coasts (Figure 19). ManyFederal agencies are involved in theregulation, protection, andmonitoring of estuarine wetlands,coastal areas, and the species thatinhabit them. Many coastal Statesalso have established coastal zonemanagement plans, growthmanagement plans, and coastalresource agencies.

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39

Figure 17. Two examples of developmentin coastal areas. A) A highway projectresulted in placement of fill in estuarineemergent wetlands in coastal Georgia,1995, and B) an estuarine emergentmarsh was filled for a new developmentin coastal Texas.(B, U.S. Fish and Wildlife Service: J. Dick)

Figure 18.Developmentalong Florida’sGulf coast beaches.

A.

B.

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40

Figure 19. Coastaldevelopmentsencroach onestuarine shrubwetlands(mangroves) alongthe IntracoastalWaterway inFlorida.

Estuarine ShrubsEstuarine wetlands face a dualthreat from natural stressors suchas storms, wind and wave erosion,land subsidence, sea level rise andstressors caused by populationincreases in many coastal counties.These interactions were apparent inan examination of the estuarineshrub wetland trends. The dataindicate that estuarine shrubwetlands increased by 6,600 acres(2,670 ha) during 1986 to 1997.

The increase in area was fromconversion of other estuarinewetland types, predominantlyestuarine emergents and estuarineflats. The data indicate thatestuarine shrubs increased by amuch greater amount (gross changeapproaches 17,000 acres or 6,900 ha),because of conversions fromestuarine emergents and estuarinebars and flats. The gross increasewas tempered by coastal changes asestuarine shrubs died back in someareas and were replaced byemergents, were scoured andremoved by shifting sediments, orbecame inundated by coastal waters.These changes occurred throughoutthe estuarine and marine systems,and they can be attributed to naturalinfluences such as storms, wind andwave erosion. Of the nearly 17,000acres of estuarine shrub wetlands,7,650 acres (3,100 ha) or 45 percentwere converted to other estuarine

and marine wetlands and coastalwaters. Another 39 percentremained as estuarine shrubwetlands, and the remaining 14percent (2450 acres or 990 ha) waslost to some form of development.Urban and rural developmentaccounted for about 1,800 acres (720ha) of these losses (Figure 20). Otherforms of development, includingsome freshwater ponds built aswater traps for seaside golf courses,accounted for the remaining 650acres (260 ha) of loss. These losseswere masked by the conversion ofenough other coastal wetland typesto estuarine shrubs to yield a netgain for this wetland type.

Estuarine shrub wetlands aregeographically restricted to thesouth Atlantic and Gulf coasts; mostare in southern Florida where theyare dominated by mangroves(Rhizophora mangle, Avicenniagerminans, Lagunculariaracemosa). This was an importantconsideration because the increasedextent of estuarine shrub wetlandsmay have resulted from theincreased occurrence of salt tolerantinvasive species. Brazilian pepper(Schinus terebinthifolius) is anaggressive woody shrub originallyfrom South American that is nowfound throughout south and centralFlorida. Brazilian pepper cansurvive hydrologic conditionsranging from coastal mangrove

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wetlands to inland pine forests(McCann et al. 1996). Because thisshrub can out compete native plants,including mangroves growing alongthe edges of estuaries, it is becomingharder to differentiate the estuarineshrub boundary in those areaswhere Brazilian pepper extendsfrom the estuary to the uplands.There may be as many as 700,000acres (283,400 ha) of Brazilianpepper in Florida (Florida Dept. ofEnvironmental Protection 1994).

Beaches, Bars, Flats, and ShoalsThe non-vegetated estuarinewetlands include beaches, bars, flats,and shoals, and a narrow strip ofmarine sand beaches. Thesewetlands experience manyinfluences including coastal storms,erosion, and deposition resultingfrom wave action, inundation fromsea level rise, and artificialmanipulation.

Sand and mud flats are found wheresediments accumulate, and they areoften associated with coastalembayments, spits, barrier islands,or estuaries (Figure 20). Althoughthese areas are not vegetated, theyare important habitat for fishes andshellfish including eastern oysters(Crassostrea virginica), mussels,clams, crabs and grass and sandshrimp. These organisms in turn,

attract shorebirds and wading birds(Whitlatch 1982).

The constant movement of sedimentand water resulting from tidalinfluences, wave action and coastalstorms, makes these wetlandsdynamic. Beaches and shorelineserode, sandbars and shoals form ordisappear, sand spits elongate, andbarrier islands change shape ordisappear (Frankenberg 1995).These changes were the result ofcoastal processes manifested indramatic fashion with the movementof entire barrier islands (Figure21A–C) and were responsible forabout 25 percent of all estuarine andmarine wetland losses observedduring this study. From 1986 to 1997,loss of estuarine non-vegetatedwetlands (flats, bars, and shoals) wasnot statistically significant (less than1 percent of all estuarine wetlandlosses). However, loss of marine non-vegetated wetlands (primarilybeaches and seaward shorelinefeatures) accounted for 2,590 acres(1,050 ha). Coastal erosion andinundation were the primaryreasons for the majority (73 percent)of these losses.

The areas of the coastline thatexhibited the most noticeable changein marine non-vegetated wetlandresources include the southernAtlantic coast and Florida Bay.

41

Figure 20. Tidalflats along anestuarine spit inWalkalla County,Florida (1993).

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42

Figure 21 A–C. Color infrared aerialphotographs showing changes to coastalfeatures between (A) 1989; (B) 1994; and(C) 1999. Vegetated wetlands appearingas mottled green or blue remain fairlyconstant while non-vegetated spits andbars show the result of coastalinfluences (Georgetown, SouthCarolina). Tide stage, sun angle andphotographic emulsion may influencefeature definition. (National AerialPhotography Program)

A. 1989

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43

B. 1994 C. 1999

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44

Figure 22 A–C.Long-termtrends in (A) allestuarineintertidalwetlands; (B)estuarinevegetatedwetlands; (C)estuarine non-vegetatedwetlands, 1950sto 1997.(Source:Frayer et al.1983; Dahl andJohnson 1991;this study.)

Long-termTrends inEstuarineWetland TypesLong-term trends in estuarinewetlands are shown in Figure 22A–C. The areal extent of estuarineintertidal wetland continued todecline through 1997, although therate of decline slowed considerablyfrom earlier periods (Frayer et al.1983; Dahl and Johnson 1991). Theareal extent of estuarine vegetatedwetland declined, but the area ofnon-vegetated wetland typesremained constant.

5,000

5,200

5,400

5,600

5,800

6,000

6,200

Acre

s (in

Tho

usan

ds)

B. Estuarine Vegetated Wetlands

4,200

4,400

4,600

4,800

5,000

5,200

1950s 1970s 1980s 1990s

Acre

s (in

Tho

usan

ds)

C. Estuarine Non-vegetated Wetlands

0

200

400

600

800

1,000

1950s 1970s 1980s 1990s

Acre

s (in

Tho

usan

ds)

A. All Intertidal Wetlands6,000

5,500

5,204 5,195

1950s 1970s 1980s 1990s

4,6154,623

4,854

5,000

580580678

741

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FreshwaterWetlandResourcesNinety-eight percent of all losses(633,600 acres; 256,500 ha) between1986 and 1997 were to freshwaterwetlands. Freshwater forestedwetlands and freshwater emergentwetlands declined 2.3 percent and4.6 percent, respectively. Some ofthese changes were due toconversion from forested oremergent wetland to shrubwetlands, which gained 6.6 percentduring the same time period (Table6). The numerical loss in wetlandarea was masked by a substantialgain in freshwater ponds (13percent), although these were notequivalent habitat types.

Most freshwater wetland losseswere from actions that changedthem to some form of upland landuse. Lands classified as urbanaccounted for 30 percent of thelosses; agriculture 26 percent;upland silivculture 23 percent; andrural development 21 percent(Figure 23). Freshwater wetlands

Table 6. Freshwater wetland area and cas a percentage) is given in parenthese

Wetland Category

Freshwater Emergent

Freshwater Forested

Freshwater Shrub

Freshwater Vegetated Wetlands

Ponds*

Miscellaneous Types

Freshwater Non-vegetated

All Freshwater Wetlands

* Includes the categories: Palustrine Aquatic B

gained about 180,000 acres (72,900ha) from the “other” lands category,primarily from construction offreshwater ponds and wetlandrestoration or creation on landsformerly classified as other uplands.

Forty percent of all freshwaterwetlands sampled were located in oradjacent to agricultural lands(Figure 24). These wetlands arepotentially affected by agriculturalland use practices such as herbicideand pesticide applications, irrigation,livestock watering and waste, soilerosion and deposition.

The rate of freshwater wetland lossto agricultural activities declinedsubstantially from the previousdecade. Between the mid 1970s and1984 about 1.0 million acres (404,900ha) were lost to agriculture (Dahland Johnson 1991), compared to198,000 acres (80,200 ha) lost duringthis study. Implementation of the“Swampbuster” provisions of the1985 Food Security Act (and itssubsequent versions) andagricultural set-aside and landretirement programs are most likelyresponsible for the reduction inwetland losses.

hange, 1986 to 1997. The coefficient of vas.

Area in thousand

Estimated area,1986

Estimated a1997

26,383.3(8.1)

25,157.1(8.4)

51,929.6(2.8)

50,728.5(2.8)

17,235.2(4.2)

18,365.6(4.1)

95,548.1(3.0)

94,251.2(3.0)

4,868.8(4.3)

5,500.1(4.0)

382.2(15.9)

414.2(15.5)

5,251.0(4.1)

5,914.3(3.9)

100,799.1(2.9)

100,165.5(2.9)

ed and Palustrine Unconsolidated Bottom.

Between 1986 and 1997, morefreshwater emergent wetlands werelost to agriculture than either shrubor forested wetlands. During theprevious decade, three times thenumber of shrub and forestedwetlands than freshwater emergentwetlands were cut and drained foragricultural land (Dahl and Johnson1991). This difference suggests thatduring the 1990s there was a declinein the number of forested wetlandsconverted to crop production. Thishelped reduce forested wetlandlosses in regions like the lowerMississippi alluvial plain and thebottomland hardwood wetlands ofthe southeast. The emergentwetlands that continue to be lost aregeographically scattered andgenerally small wetlands; some werealready partially drained by surfaceditches or completely eliminatedthrough intensified use of existingfarmland. Practices such as theimprovement of on-farm drainage,ditch clean-outs, or the eliminationof partially drained wetlands werepermitted under the various FoodSecurity Act revisions. Bernert et al.(1999) observed this trend in theWillamette Valley, Oregon, and

45

riation (CV) for each entry (expressed

s of acres

rea, Change,1986–97

Change(in percent)

–1,226.2(18.2)

–4.6

–1,201.1(23.8)

–2.3

1,130.4(25.7)

6.6

–1,296.9(17.1)

–1.4

631.3(23.4)

13.0

32.0(69.8)

8.4

663.3(13.4)

12.6

-633.6(36.5)

-0.6

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46

Figure 23. Change inconverted to various1986 and 1997.

Figure 25. Color infrared aerialphotographs taken in 1989 and 1999show development(s) proceeding inSouth Carolina. Changes towetlands that have occurred includethe loss of forested and shrubwetlands to upland; the conversionof forested and emeregent wetlandsto open-water impoundments; lossof open water to upland; and theconversion of open water toemergent wetland. (National AerialPhotography Program)

1989

questioned the effectiveness ofcurrent agricultural policy to dealwith wetland loss from intensifieduse of existing farmland.

Five percent of the freshwaterwetlands sampled were located in oradjacent to urban centers and towns.Another 12 percent of freshwaterwetlands were in or adjacent toareas classified as ruraldevelopment.

Collectively, 51 percent or 383,300acres (155,200 ha) of all thefreshwater wetlands lost to uplands

SRural Development 21%

Agriculture 26%

Urba

wetlands land uses between

resulted from urban and ruraldevelopment. Construction ofbuildings, roads, bridges orinfrastructure in wetlands accountedfor these losses. An example of howwetlands were lost to developmentprojects is shown in Figures 25A–B.

Several scenarios could account forwetland losses from development.These involve permitted actionsunder Sections 10 and 404 of theClean Water Act and after-the-factpermits, development allowed undergeneral permit conditions, situationsinvolving non-jurisdictional wetland

ilviculture 23%

n Development 30%

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47

Freshwater Wetland Type

Area

, in

Mill

ions

of A

cres

, With

in o

r Ad

jace

nt to

Agr

icul

tura

l Lan

ds25

20

15

5

10

0

Figure 24. Freshwater wetlands, bytype, that are within or adjacent toagricultural lands, 1997. (Photograph:E. Ciganovich)

1999

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48

Figure 26. Gulf and Atlantic coastal countloss indicates less that 20 acres, medium inwetland lost.

determinations, exemptions, orillegal activities that aresubsequently detected and penaltiesassessed. The area of wetland lossfrom urban and rural development(383,300 acres or 155,200 ha) couldhave been ameliorated by gains infreshwater ponds and lakes (747,700acres or 302,700 ha).

Freshwater non-tidal wetlandsexperienced the greatestdevelopment pressure just inlandfrom the coastlines of the UnitedStates. Wetlands located in coastal

ies that experienced wetland losses to uplandicates 20–150 acres, and a high level of los

watersheds of many coastal countiesare undergoing rapid growth andthey lead in many demographicindicators of development (Culliton1998). These freshwater wetlandswere most susceptible todevelopment from rapid populationgrowth and the demand for housing,transportation infrastructure, andcommercial and recreationalfacilities (Good et al. 1997). Thecoastal counties where there werewetland losses between 1986 and1997 are shown in Figure 26.

Low

Medium

High

ds between 1986 and 1997. Low level ofs indicates greater than 150 acres of

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Freshwater Forested WetlandsThere was more area of freshwaterforested wetlands in the UnitedStates (50.7 million acres or 20.5million ha) than any other wetlandtype. More than 1.2 million acres(485,800 ha) of forested wetlandswere lost between 1986 and 1997.This was the result of the removal of4 million acres (1.6 million ha) offorested wetland from the landscapeand the conversion of 2.8 millionacres (1.1 million ha), primarilyshrubs, returning to the forestedwetland category (Figure 27). Of the4 million acres that underwent somechange, most were converted tofreshwater shrub wetlands bytimber harvesting or otherprocesses that removed the forested

2,825,100

55

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

Are

a, in

Acr

es

Fresh

water Shrub

Fresh

water Emergent

Upland Land U

canopy but retained the wetlandcharacter. Although these areasremain as wetland, the removal ofthe forest canopy can be a radicalalteration of the landscape resultingin changes in hydrology and wildlifevalue (Figure 28).

The loss rate of forested wetlandsdeclined from 6.2 percent in the1970s to the 1980s (Dahl andJohnson 1991), to 2.3 percent in thisstudy. Of the forested wetlands lostto upland land uses, urban and ruraldevelopment (Figure 29) accountedfor the largest amount of the loss.Thirty-three percent or 148,400acres (60,100 ha) were lost to urbanand rural development. Another139,100 acres (56,300 ha) were

49

Figure 27. Cumulative loss andconversion of freshwater forestedwetlands, 1986 to 1997.

Figure 28. A clear-cut of a formerfreshwater forested wetland inOklahoma, 2000. This area representeda conversion within wetland categoriesfrom forest to emergent cover typeswithout a change in area. (U.S. Fish andWildlife Service: J. Dick)

0,800 415,00078,100 27,700

sePonds

Lakes a

nd Rivers

Wetland Conversion

Wetland Loss

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50

Figure 29. Anexample offorested wetlandloss in Virginia,1998. Trees havebeen cleared andthe area filled forbridgeconstruction.

classified as upland agriculture,whereas 23.8 percent or 107,000acres ( 43,300 ha) were converted tomanaged forested plantations.Unidentified land uses wereresponsible for 12 percent (53,400acres or 21,600 ha) of the forestedwetland losses.

An additional 78,100 acres (31,600ha) of forested wetlands wereconverted to freshwater ponds.Conversions to deepwater lakesresulted from human activities byeither creation of newimpoundments or by raising thewater levels on existingimpoundments and thus killing thetrees (Tansey and Cost 1990).Floods, such as those along theMississippi, Ohio, and Missouririvers in the early-to-mid 1990s,reclaimed some forested oxbows andchannels. About 27,700 acres (11,200ha) of forested wetland wereconverted to deepwater habitats.Other conversions may haveresulted from beaver impoundmentof an area and subsequent drowning

of the trees. Seventy-five percent ofthat area was converted to riverinechannels.

Forestry practices have a substantialinfluence on forested wetland areas(Dahl 1999). The availability oftimber used largely for processingpulp and producing paper was thebasis for forestry managementpractices (Kovacik and Winberry1987). Although bottomlandhardwood and other wetland treespecies produce valuable timberproducts, they are fairly slow toregenerate and mature. The averagerotation age of bottomland-cypressforests in the southern UnitedStates is about 65 years (Langdon etal. 1981). Conversely, pinesreplanted in the same areas andintensively managed can attain amuch shorter rotation cycle.Conversion from bottomland forestto managed pine plantationsaccounts for most of the changes inthe freshwater forested category inthe southeastern United States.

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A short harvest rotation can best beachieved by establishing loblollypine (Pinus taeda) plantationscombined with silviculturalmanagement actions (Allen andCampbell 1988). Partial drainagecombined with “bedding” has beenpracticed to initiate seedlingregeneration in wetlands (Figure30). By the mid 1980s, “bedding” wasviewed as essential for the survivaland rapid early growth of pineseedlings on poorly drained soils(Allen and Campbell 1988). Theprocess of partial drainage and“bedding” on hydric soils results insufficient alteration of hydrologicconditions to convert some sites toupland. Other sites planted to pineplantations remain as wetland.

Until the mid 1990s, normalsilvicultural activities, including

earthmoving, planting, seeding,cultivating, minor drainage andharvesting, were exempt fromregulation under Section 404 of theClean Water Act (Welsch et al. 1995).In 1995, the EnvironmentalProtection Agency and the ArmyCorps of Engineers issued guidanceat the Federal level describing “BestManagement Practices” to protectwater quality and hydrologicfunction when establishing pineplantations in wetlands. Thisguidance clarified the circumstancesunder which certain silviculturalactivities were allowed in forestedwetlands and outlined whichmechanical silvicultural sitepreparation activities require apermit under the Clean Water Act(U.S. Environmental ProtectionAgency and Department of theArmy 1995).

51

Figure 30. A drainage technique forforestry production (Source: Tant 1981).In the southeastern United States, goodyields of loblolly pine can be obtained onpoorly drained soils using thesepractices. The photograph shows plantedpine trees with lateral ditches in placeand drainage sufficient to change thehydrology of the area (North Carolina,1995). (Photograph: T. Dahl.)

PRIMARY CANAL (Main)Parallel Ditch

Dirt RoadHoe Drain

1/2-milerow length

The center of each strip is crownedto aid surface-water movement to drainage ditches.

5 to 6 feet200 to300 ft.

2 to 3 ft.

8 to 12 ft.

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DocumentingChanges in LandCoverWith the exception of naturaldisasters, change in the coastal zoneoften occurs one land parcel at atime. Although each action isimportant, the need to evaluatebroad-scale change is needed.

Satellite images combined with sitevisits and aerial photography are thebest means available to documentand characterize the ground cover

Cape Fear, North Carolina, drainage basin. Thisis an unprocessed Landsat Thematic Mappersatellite image from October 31, 1996. Thecomponents of the image are analyzed, categorized,and field checked. The resulting map is an accuratedocumentation of the land cover that existed on thatdate. Comparing maps from different yearsprovides a powerful visual and numericrepresentation of the changes that have occurred.(National Oceanic and Atmospheric Administration).

Sample land cover change map for theCape Fear drainage basin. This imagewas created using satellite data fromOctober 1991 and October 1996 andrepresents an area approximately nine byseven miles. Gray shades indicate areas ofno land cover change. Changes due to clearcutting forestry practices are highlighted inthe colored areas. Processed satelliteimagery such as this was used to documentland cover changes as a result ofhurricanes Bertha and Fran, both of whichhit this area in 1996. (National Oceanic and

Atmospheric Administration.)

Major land cover changes for the entire Cape Fear drainage basin from 1991 to 1996. From the maps and the resulting tables, State and local officials can quickly grasp how an area is changing. This sample table includes information about how many acres have been converted to development and how many acres of forest land have been lost.

Habitat Type 1991 1996 ChangePercent Change

Developed—Low Intensity 44,940 49,775 4,835 10.8

Evergreen Forest 592,644 503,565 –89,079 –15.0

Freshwater Forest 517,528 498,803 –18,725 –3.6

found over large expanses of landand near shore areas. Comparingmaps made with these data from oneyear to the next gives an accuratepicture of how communities and thecoastal zone change over time.

The National Oceanic andAtmospheric Administration(NOAA), working with Federal,State, and local partners, is creatinga national inventory of thisinformation. To see examples of theimagery and a list of ongoing andcompleted projects, see the Web siteat www.csc.noaaa.gov.

Evergreen forest to grassland

Evergreen forest to scrub/shrub

Evergreen forest to bare land

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Freshwater Shrub WetlandsIn 1997, there were an estimated18.4 million acres (7.5 million ha) offreshwater wetlands dominated byshrub species or wetland treespecies less than 20 feet tall (6 m).The mean size of shrub wetlandssampled was 8 acres (3.2 ha). Shrubwetlands were the only vegetatedfreshwater wetland type to exhibitan increase in area between 1986and 1997.

Wetland shrub trends are governedprimarily by changes fromfreshwater forested and freshwateremergent wetlands. During thisstudy, 2.4 million acres (970,000 ha)of shrub wetlands changed toforested wetlands, and 2.8 millionacres (1.1 million ha) changed from

This freshwaterspring supports ashrub wetland insouthernWisconsin.(E. Ciganovich)

forested wetlands to shrub wetlands.Another 1.1 million acres (445,000ha) changed between shrub andfreshwater emergent wetlands.These interactions overshadowed a196,500 acre (79,600 ha) loss touplands and yielded a net gain ofmore than 6 percent in shrubwetlands. It could not be determinedif the increase in shrub wetland fromemergent marsh was the result ofpartial drainage of emergents or dueto other factors. Overall, 22 percentof shrub wetlands underwent eitherhuman induced or natural cover typechanges. Losses of shrub wetlandsto uplands were evenly distributedamong urban and ruraldevelopments, silvicultural activities,and agriculture.

53

Freshwater shrubwetland innorthernWisconsin.

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54

B.

Freshwater Emergent WetlandsFreshwater emergent wetlandsoccur naturally in the heart of theNation’s busiest metropolitan areasor in remote wilderness areas. Thiswetland type was the most easilydestroyed. The mean size offreshwater emergent marshessampled was small (7.2 acres or 2.9ha) and they can be eliminated bysurface ditching, subsurface tiledrains, filling, diverting waterinflows, or otherwise disrupting theconfining layer in the soil (Figure31).

Freshwater emergent wetlandssustained substantial losses from1986 to 1997, declining by more than1.2 million acres (496,400 ha) (4.7percent). More than 700,000 acres(283,000 ha) of emergent wetlandswere lost to upland land uses. Anestimated 51 percent of emergent

Figure 31 Aemergent wemergent mconstructioSouth Dakoother fill mthis emerge1999; (C) shdrainage tifrom this aMinnesota,Service)

A.

C.

wetlands lost were on lands used foragriculture. Another 22 percentwere lost due to development inurban or rural settings, 25 percentto areas manipulated by man butwhere land use was undetermined(Figure 32), and 2 percent were loston lands converted to silviculture(Figure 33).

Freshwater emergent wetland gainsincluded about 190,000 acres (76,900ha) that were reclassified fromfreshwater forested to emergentwetlands. Another 24,000 acres(9,700 ha) were gained from changesthat occurred in the deepwatercategory.

About 36 percent of all freshwateremergent wetlands sampled were inor adjacent to agricultural lands(Figure 34).

–C. Examples of freshwateretland losses: (A) anarsh is being filled forn of a farm service road,ta, 1999; (B) concrete and

aterials are being added tont wetland in Nebraska,allow surface ditches orles have eliminated wetlandsgricultural field in western 1999. (C: U.S. Fish and Wildlife

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55

Agriculture51%

Urban and Rural Development

25%

Miscellaneous Lands25%

Silviculture2%

Figure 33. Current uplandclassification of areas where emergentwetlands were lost between 1986 and1997.

Figure 32. A freshwater emergentwetland in Tennessee (2000) that wasbeing drained and filled. The final landuse is undetermined.

Figure 34. A freshwater emergentwetland within an agricultural field.About 36 percent of all freshwateremergent wetlands sampled were locatedin or next to agriculture. (U.S. Fish andWildlife Service)

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Figure 35. Long-term trends in openwater ponds, 1950s to 1997. (Source:Frayer et al. 1983; Dahl and Johnson1991; this study.)

Freshwater PondsThe area of open water ponds in1999 equaled the area occupied byall estuarine wetlands in theconterminous United States. Theopen water pond category gainedthe most area since the 1950s(Figure 35); there were now 5.5million acres (2.2 million ha) of openwater ponds in 1997. This was morethan twice the area of open waterponds reported in the mid-1950s(Frayer et al. 1983). Similar trendshave been reported by Moulton et al.(1997) who found a doubling infreshwater pond area in coastalTexas between 1955 and 1992.Bernert et al. (1999) also noted thatfreshwater ponds made the largestsingle contribution to wetland gainsin the Willamette Valley of Oregonbetween 1982 and 1994.

This study included freshwaterponds that are functionally andqualitatively different. Pondsincluded beaver ponds, farm ponds,water retention ponds, barrow pits,small open mine pits, dug outs, smallresidential area lakes, water trapson golf courses, fish farms andnatural ponds (Figure 36). All ofthese meet the wetland definitioncriteria of Cowardin et al. (1979).

An estimated 11 percent, by area, ofall freshwater ponds sampled werelocated in or adjacent to urbanareas. Many of these were createdfor runoff and water retention. Somewere recreational or aesthetic, andothers occured naturally in urbansettings. The proliferation of golfcourses in urban and areas of ruraldevelopment has contributed

1950s 1970s

4,393

2,32000

6,000

5,000

4,000

3,000

2,000

Acre

s (in

Tho

usan

ds)

substantially to the number of smallfreshwater ponds (Figure 37).

Forty-four percent of all ponds (byarea) sampled are in or adjacent toagriculture. Many are used directlyfor agricultural purposes such aslivestock watering, waste retention,or as recreational farm ponds(Figure 38).

The creation of larger ponds (i.e.,greater than 5 acres or 2 ha), wasindicative of either aquaculturaldevelopment (e.g., fish farms) orsurface mining operations in certainregions of the country. The increasein the number of commercial fishfarms was evident in the lowerMississippi Valley States ofMississippi, Louisiana, and Arkansas(Figure 39). Nationally, the lowerMississippi Valley and centralFlorida contribute substantially tothe number of new larger pondscreated from 1986 to 1997 (Figure40). These ponds are not anequivalent replacement forvegetated wetlands.

Some freshwater ponds have alsobeen constructed as part ofmitigation, restoration, and wetlandcreation efforts.

Beaver populations have furthercontributed to the increased numberof freshwater ponds throughoutmany regions of the country. Severalstudies have discussed theimportance of beaver populationsand pond building to increasedsurface area of water (Brown et al.1996; McCall et al. 1996).

5,500

1980s 1990s

4,869

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57

Figure 36. Freshewater pond types varydramatically throughout the UnitedStates. Data from this study indicatethat freshwater ponds (unconsolidatedbottom wetlands) have increased.(Middle photograph: G. Latzke)

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Figure 37. Contrasting color infraredaerial photographs taken in 1988 and1999 show new ponds (dark blue orblack) created as part of a golf courseand housing developments (SkidawayIsland, South Carolina). (National AerialPhotography Program.)

1988

1999

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Figure 38. An excavated farm pond innorthwestern Iowa, 1999.

Figure 39. Catfish farms (ponds) areshown as various shades of bluerectangles on this infrared aerialphotograph from Mississippi, 1997.Aquacultural development such as thiscontributed to gains in the freshwaterpond category. (National Aerial PhotographyProgram)

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Small Increase in Large PondsModerate Increase in Large PondsLarge Increase in Large Ponds

Figure 40. Distribution and relative size of freshwater ponds created between 1986 and 1997. Concentrations of large ponds inMississippi, Louisiana, and Arkansas are fish farms. Concentrations of larger ponds in Florida are the result of surfacemining operations or construction of water retention ponds.

A playa wetland,east of Santa Fe,New Mexico.

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Other Freshwater WetlandsFreshwater unconsolidated shoreswere small, non-vegetated wetlandsof about 3.5 acres 1.4 ha), that madeup less than 0.5 percent of allfreshwater wetlands. Between 1986and 1997, freshwater unconsolidatedshores exhibited an 8 percent gain inacreage or about 32,000 acres(13,000 ha). In part, this was due topeat mining operations that removed

Figure 41. A black-and-white aerial photogindicated by a blue dot in the center have haThe accompanying color photograph showsProgram)

the wetland vegetation and exposedthe substrate. Because these areaswere not drained, they remainedwetland, but their classification waschanged from freshwater shrub bogsto freshwater unconsolidated shores(Figure 41). Considered anomalies,these changes were generallyrestricted to northern Minnesotaand Maine.

61

raph of peat extraction (mining) in Maine, 1996. The areasd the surface vegetation removed, but they remain wetland.

the peat surface. (Aerial photograph: National Aerial Photography

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Figure 42 A–C. Long-term trends inselected freshwater wetlands, 1950s to1997; (A) Freshwater forested wetlands;(B) freshwater shrub wetlands; (C)freshwater emergent wetlands. (Source:Frayer et al. 1983; Dahl and Johnson1991; this study.)

A beaver dam has impounded a streamand created this pond in Minnesota.

Long-Term Trends in VegetatedFreshwater Wetland TypesLong-term trends of severalfreshwater classes are shown inFigures 42A–C. Since the 1950s,freshwater emergent wetlands havedeclined by the greatest percentageof any freshwater wetland type;nearly 24 percent have been lost (8million acres or 3.2 million ha).Freshwater forested wetlands havesustained the greatest overall loss inarea, declining by 10.4 million acres(4.2 million ha) since the 1950s. Bothfreshwater forested and emergentwetlands declined at a slower ratesince the mid 1980s.

62,000

60,000

58,000

56,000

54,000

52,000

50,000

Acre

s (in

Tho

usan

ds)

A. Freshwater Forested61,150

55,151

51,93050,729

1950s 1970s 1980s 1990s

20,000

18,000

16,000

14,000

12,000

10,000

8,000

Acre

s (in

Tho

usan

ds)

B. Freshwater Shrubs

11,000

15,50617,235

18,366

1950s 1970s 1980s 1990s

36,000

34,000

32,000

30,000

28,000

26,000

24,000

Acre

s (in

Tho

usan

ds)

C. Freshwater Emergent

33,133

28,440

26,38325,157

1950s 1970s 1980s 1990s

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WetlandRestoration,Creation andEnhancementIn the last several decades there hasbeen considerable emphasis onwetland restoration or rehabilitationactivities. Many worthwhile projects(Figure 43) have been completed byFederal, State, local, and privateorganizations and citizens. Variousagencies and scientists have used in

B.

consistent terminology to describeecological processes and theirresults. For example, “restoration”has often been used to describe thereturn of land area to a formercondition, function, or even theenhancement of condition. Someprojects designed to restorehydrologic function to degradedwetlands have not contributed areagains to the wetland base (Figure44). Direct comparisons of wetlandrestoration estimates from thisstudy with other studies usingdifferent definitions cannot be made.

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Figure 43. A created wetland nearOrlando, Florida, 1994.

Figure 44. Two oblique photographsshowing A) partially drained wetlandsprior to restorative actions, and B)wetland basins with restored hydrology.This example illustrates how wetlandrestoration has taken place with verylittle gain in wetland area. (U. S. Fish &Wildlife Service)

A.

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Between 1987 and 1990, programs torestore wetlands under the 1985Food Security Act added about90,000 acres (36,400 ha) to theNation’s wetland base (Dahl andJohnson 1991). Since that time,additional programs and initiativessuch as the Conservation ReserveProgram and various conservationpartnership programs have beenenacted to create or restore wetlandacreage. This study indicated that,between 1986 and 1997, there was a

net gain of wetland from “other”uplands of about 180,000 acres(72,900 ha).

Because freshwater emergentwetlands can reestablish quicklyunder wet conditions, there issubstantial opportunity forrestoration. However, from 1986 to1997 there was a deficit betweenfreshwater wetland losses and gainsof about 630,000 acres (255,100 ha).This was due to freshwater wetland

Figure 45. Prairie wetlands in the fall of1999 (South Dakota) have reclaimedsome upland area, including the road.This form of natural restorationcontributed acreage to help offset losses.

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losses to urban and ruraldevelopment, agriculture andsilviculture.

More natural forms of restorationhave also contributed to an increasein wetland area. For the first timesince the 1950s, wetland area fromdeepwater habitats increased,mostly from riverine corridors. Thissuggests that the flood events of the1990s may have reclaimed or created

Figure 46 A and B. Color infrared aerialphotographs of north-central Florida (A)1989, during drought conditions and (B)1996, during different hydrologicconditions. (National Aerial Photography Program)

B.

some wetland areas. There was alsoevidence that changing long-termhydrologic cycles might becontributing to the expansion ofsome wetland areas and creating orrestoring others (Figure 45). Thesechanges involving periods of droughtfollowed by above averageprecipitation are oftengeographically specific and cyclical(Figure 46).

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A.

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Differences Between the Fish andWildlife Service’s Status andTrends and the NationalResources Inventory

66

The Emergency WetlandsResources Act of 1986 requires theService to report to Congress, atten-year intervals, on the status andtrends of the Nation’s wetlands.Similarly, the Natural ResourcesConservation Service (NRCS) isrequired by legislation (RuralDevelopment Act of 1972, Soil andWater Resources Conservation Actof 1977, and the Food Security Act of1985 and 1990) to report at intervalsof five years or less on the status ofsoil, water and related resources.The NRCS reports are derived fromthe analysis of data gathered by theNational Resources Inventory(NRI). Data on resource change inboth studies are gathered from theinterpretation of aerial imagerysupplemented with ancillarymaterials.

There are technical differencesbetween the Service and the NRCSregarding how wetland data arecollected, analyzed and reported (seeAppendix B). For example, theService’s wetland status and trendsstudy was designed specifically tosample wetlands and wetlandchange, whereas the NRI is alandscape characterization of allnatural resources of which wetlandsmake up one component. The

Service designed its study to developwetlands trend information for alllands in the conterminous UnitedStates, whereas the NRI collectsdata only on non-Federal rurallands. Definitions, sampling regimes,data handling and analysis routineswere developed independently as thetwo agencies implemented theirprograms over the past two decades.Each program has evolved with theassistance of spatial samplingexperts and resource specialists.Because of these differences,wetland data collected by theService and NRCS are neithercomparable nor interchangeable.

A goal of the Clean Water ActionPlan was to “finalize a plan to useexisting inventory and datacollection systems to support asingle status and trends report bythe Year 2000.” After extensiveefforts, the Department of theInterior and the Department ofAgriculture concluded that it wasinfeasible to combine the Service’snational wetlands status and trendsdata with NRCS data from the NRIfor wetlands on non-Federal rurallands, and produce statisticallyreliable data for a single report onwetlands gains and losses.

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Agency Differencesin EstimatingWetland LossA major difference between theService’s wetland status and trendsstudy and the NRCS’s NRI isillustrated by the following example.A 10 acre (4 ha) parcel of a 160 acre(64.8 ha) dairy farm is made up of 8acres (3.2 ha) of corn and 2 acres (0.8ha) of palustrine emergent wetland.The 10 acre parcel has four wetlandseach 0.5 acres (0.2 ha) in area. Thisparcel is sold to an individual whoconstructs a house, barn and otheroutbuildings. The landowner leavessome of the land in crop productionto feed horses. In constructing thebuildings, the landowner fills in 0.5acre of wetland to build the house,0.5 acre of wetland to build the barn,

A freshwaterwetland nearMadison,Wisconsin.(E. Ciganovich)

and 0.5 acre of wetland to expand afield for pasture for the horses. Inthis situation, the Service wouldrecord the three observed wetlandlosses as: house construction =loss to rural development; barnconstruction = loss to agriculture;pasture expansion = loss toagriculture.

The instructions for the 1997National Resources Inventory(Point Module III, Land Use, P. 11)indicate that this would be anexample of a “rural estate” underthe “Residential” category. Ruralestates are defined as,

A freshwaterwetland inLouisiana.(U.S. Fish and WildlifeService)

“A land use category (underresidential) that includes ruralresidences that are not part of anoperating farm and have nointensive agriculturalenterprises. They may includesmall pastures for livestockgrazing and may have structuressuch as garages or barns, with nospecial use buildings such aspoultry or hog houses or minkranches.”

Rural estates generally have a 10acre size limit. In this example, theNRI would record this as a 10 acreloss to rural development.

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Summary

Wetland along theSt. Louis River innortheasternMinnesota.

This study estimated wetland statusand trends using 4,375 four squaremile sample plots. Twenty onepercent of the plots were fieldverified and rigorous quality controlmeasures were taken to ensure dataintegrity and quality. The findingsindicate that an estimated 105.5million acres (42.7 million ha) ofwetlands remained in theconterminous United States. Theaverage annual net loss of wetlandswas 58,500 acres (23,700 ha), adecline of 80 percent from theprevious decade. This decline in therate of wetland loss was attributedto Federal programs such as theconservation provisions of the FoodSecurity Act, Conservation ReserveProgram, Fish and Wildlife Service’sconservation and restorationpartnership programs,environmental education and otherState sponsored conservationinitiatives.

Estuarine wetlands made up 5percent of the total area of wetlandsfound in the conterminous UnitedStates. Estuarine emergentsdeclined by 14,450 acres (5,850 ha), a0.4 percent loss from 1986 to 1997.Fifty eight percent of the losseswere from some form of deepwaterintrusion into the wetland. Estuarinenon-vegetated intertidal wetlandsdeclined slightly (0.1 percent), butmarine intertidal beaches declined1.7 percent. Marine and estuarinewetland areas accounted for twopercent of the losses.

Between 1986 and 1997, wetlandsdeclined by an estimated 644,000acres (260,700 ha). Ninety-eightpercent of these losses were tofreshwater wetland types. The lossrate of freshwater forested wetlandsdeclined from 6.2 percent betweenthe 1970s to the 1980s, to 2.3 percentin this study. Freshwater emergentwetlands experienced a substantialloss in area, with a net change ofnearly 1.2 million acres (485,800 ha).Shrub wetlands were the onlyvegetated freshwater wetland typethat exhibited an increase in area.

Urban development accounted for 30percent of the wetland losses to

upland; agriculture 26 percent;silviculture 23 percent, and ruraldevelopment 21 percent.

Long-term trends indicate thatfreshwater emergent wetlands havedeclined by the greatest percentageof any freshwater wetland type;nearly 24 percent have been lost.Freshwater forested wetlands havesustained the greatest overall loss inarea, declining by 10.4 million acressince the 1950s.

Open water ponds increased in areaby about 13 percent during thisstudy. There were 5.5 million acres(2.2 million ha) of ponds, more thantwice the area of open water pondsreported in the mid 1950s. Thecreation of large ponds (greater than5 acres or 2 ha), was the result ofaquiculture (fish farms), surfacemining operations or water retentionponds constructed in certain regionsof the country. These ponds were notequivalent replacement forvegetated wetlands.

Among the wetlands sampled, 55percent were located in or adjacentto “other” uplands. An additional 31percent were in or adjacent toagricultural lands; 24 percent in oradjacent to upland silviculture; and 5were in or adjacent to urban uplandareas (percentages exceed 100because some wetlands are adjacentto more than one upland category).

Deepwater lakes and reservoirsexhibited a modest increase in areawith a net gain of 116,400 acres(47,100 ha). The rate of lake andreservoir creation declined 43percent from the previous decade.

There were net gains to wetlandsfrom both inland deepwater habitats(primarily rivers), and from “other”lands. Long-term hydrologic cyclesmight be contributing to theexpansion of some wetland areas andcreating or restoring others. Thereduction in wetland losses coupledwith restoration and creation ofwetland area is helping the Nationapproach its no net loss in wetlandgoal.

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Literature Cited

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Anderson, J.R., E.E. Hardy, J.T. Roachand R.E. Winter. 1976. A land useand land cover classificationsystem for use with remote sensordata. U.S. Geological SurveyProfessional Paper 964. U.S.Geological Survey, Washington,D.C. 28 p.

Barras, J.A., P.E. Bourgeois, and L.R.Handley. 1994. Land loss in coastalLouisiana 1956–90. NationalBiological Survey, NationalWetlands Research Center OpenFile Report 94–01. 4 p. + colorplates.

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Brown, D.J., W.A Hubert, and S.H.Anderson. 1996. Beaver pondscreate wetland habitat for birds inmountains of southeasternWyoming. Wetlands. Vol. 16, No. 2.pp. 127–133.

Charbreck, R.H. 1988. CoastalMarshes—Ecology and wildlifemanagement. Univ. of MinnesotaPress, Minneapolis, MN. 138 p.

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Dahl, T.E. 1990. Wetlands losses in theUnited States 1780s to 1980s.Department of the Interior, U.S.Fish and Wildlife Service,Washington, D.C. 21 p.

Dahl, T.E. and C.E. Johnson. 1991.Status and trends of wetlands inthe conterminous United States,mid-1970s to mid-1980s. U.S.Department of the Interior. U.S.Fish and Wildlife Service,Washington, D.C. 28 p.

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Fonseca, M.S., Kenworthy, W.J. and G.W.Thayer. 1998. Guidelines for theconservation and restoration ofseagrasses in the United Statesand adjacent waters. NOAACoastal Ocean Program DecisionAnalysis Series No. 12, NOAA

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Good, J.W., J.W. Weber, J.W. Charland,J.V. Olson and K.A. Chapin. 1997.State coastal zone managementeffectiveness in protectingestuaries and coastal wetlands: Anational overview. Oregon SeaGrant, Oregon State Univ.,Corvallis, OR. 283 p.

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Appendix A.Definitions of Habitat Categories Used inthis Status and Trends Study

Wetlands1

1Adapted2The U.S.3U.S. Dep

In general terms, wetlands are lands where saturation with water is the dominant factordetermining the nature of soil development and the types of plant and animal communitiesliving in the soil and on its surface. The single feature that most wetlands share is soil orsubstrate that is at least periodically saturated with or covered by water. The water createssevere physiological problems for all plants and animals except those that are adapted for lifein water or in saturated soil.

Wetlands are lands transitional between terrestrial and aquatic systems where the water tableis usually at or near the surface or the land is covered by shallow water. For purposes of thisclassification wetlands must have one or more of the following three attributes: (1) at leastperiodically, the land supports predominantly hydrophytes,2 (2) the substrate is predominantlyundrained hydric soil, 3 and (3) the substrate is non-soil and is saturated with water or coveredby shallow water at some time during the growing season of each year.

The term wetland includes a variety of areas that fall into one of five categories: (1) areas withhydrophytes and hydric soils, such as those commonly known as marshes, swamps, and bogs;(2) areas without hydrophytes but with hydric soils—for example, flats where drasticfluctuation in water level, wave action, turbidity, or high concentration of salts may prevent thegrowth of hydrophytes; (3) areas with hydrophytes but non-hydric soils, such as margins ofimpoundments or excavations where hydrophytes have become established but hydric soilshave not yet developed; (4) areas without soils but with hydrophytes such as the seaweed-covered portions of rocky shores; and (5) wetlands without soil and without hydrophytes, suchas gravel beaches or rocky shores without vegetation.

Marine System

from Cowardin et al. 1 Fish and Wildlife Servartment of Agriculture

The marine system consists of the open ocean overlying the continental shelf andits associated high energy coastline. Marine habitats are exposed to the wavesand currents of the open ocean. Salinities exceed 30 parts per thousand, with littleor no dilution except outside the mouths of estuaries. Shallow coastal indentationsor bays without appreciable freshwater inflow and coasts with exposed rockyislands that provide the mainland with little or no shelter from wind and waves,are also considered part of the marine system because they generally support

typical marine biota.

Estuarine System

The estuarine system consists of deepwater tidalhabitats and adjacent tidal wetland that are usuallysemi-enclosed by land but have open, partly obstructed,or sporadic access to the open ocean, and in which oceanwater is at least occasionally diluted by freshwaterrunoff from the land. The salinity may be periodicallyincreased above that of the open ocean by evaporation.Along some low energy coastlines there is appreciabledilution of sea water. Offshore areas with typicalestuarine plants and animals, such as red mangroves(Rhizophora mangle) and eastern oysters (Crassostrea virginica), are also included in the estuarine system.

73

979.ice has published the list of plant species that occur in wetlands of the United States (Reed 1988). has developed the list of hydric soils for the United States (U.S. Department of Agriculture 1991).

Beach re-establishmentin Florida.

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Marine and Estuarine Subsystems

74

4Although

Subtidal The substrate is continuously submerged by marine or estuarine waters.

Intertidal The substrate is exposed and flooded by tides. Intertidal includes the splash zone of coastalwaters.

Palustrine System

some seagrass beds

The palustrine (freshwater) system includes all non-tidal wetlands dominated bytrees, shrubs, persistent emergents, emergent mosses or lichens, farmed wetlands,and all such wetlands that occur in tidal areas where salinity due to ocean derivedsalts is below 0.5 parts per thousand. It also includes wetlands lacking suchvegetation, but with all of the following four characteristics: (1) area less than 20acres (8 ha); (2) active wave formed or bedrock shoreline features are lacking; (3)water depth in the deepest part of basin less than 6.6 feet (2 meters) at low water;and (4) salinity due to ocean derived salts less than 0.5 parts per thousand.

Classes

Unconsolidated Bottom

may be evident

Unconsolidated bottom includes all wetlands with at least 25 percent coverof particles smaller than stones, and a vegetative cover less than 30 percent.Examples of unconsolidated substrates are: sand, mud, organic material,cobble-gravel.

Aquatic Bed

o

Aquatic beds are dominated by plants that grow principally on or below thesurface of the water for most of the growing season in most years. Examplesinclude seagrass beds4, pondweeds (Potamogeton spp.), wild celery(Vallisneria americana), waterweed (Elodea spp.), and duckweed (Lemnaspp.).

Rocky Shore

n

Rocky shore includes wetland environments characterized by bedrock,stones, or boulders which singly or in combination have an areal cover of 75percent or more and an areal vegetative coverage of less than 30 percent.

Unconsolidated Shore

Unconsolidated shore includes all wetland habitats having twocharacteristics: (1) unconsolidated substrates with less than 75 percentareal cover of stones, boulders or bedrock and; (2) less than 30 percent arealcover of vegetation other than pioneering plants.

Emergent Wetland

Emergent wetlands are characterized by erect, rooted, herbaceoushydrophytes, excluding mosses and lichens. This vegetation is present formost of the growing season in most years. These wetlands are usuallydominated by perennial plants.

Shrub Wetland

Shrub wetlands include areasdominated by woody vegetation lessthan 20 feet (6 meters) tall. Thespecies include true shrubs, youngtrees, and trees or shrubs that aresmall or stunted because ofenvironmental conditions.

Forested Wetland

Forested wetlands are characterizedby woody vegetation that is 20 feet(6 meters) tall or taller.

Palustrine Farmed

Farmed wetlands are wetlands thatmeet the Cowardin et al. definitionwhere the soil surface has beenmechanically or physically alteredfor production of crops, but wherehydrophytes will becomere-established if farming isdiscontinued.

aerial photography, water and climatic conditions often prevent their detection.

A forested wetland in a river bottom inTennessee.

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Deepwater Habitats

Wetlands and deepwater habitats are defined separately because the term wetland has not included deeppermanent water bodies. For the purposes of conducting status and trends studies, riverine and lacustrineare considered deepwater habitats. Elements of marine or estuarine systems can be wetland or deepwater.Palustrine includes only wetland habitats.

Deepwater habitats are permanently flooded land lying below the deepwater boundary of wetlands.Deepwater habitats include environments where surface water is permanent and often deep, so that water,rather than air, is the principal medium within which the dominant organisms live, whether or not they areattached to the substrate. As in wetlands, the dominant plants are hydrophytes; however, the substrates areconsidered non-soil because the water is too deep to support emergent vegetation (U.S. Department ofAgriculture 1975).

Riverine System

The riverine system includes deepwater habitats contained within a channel, with theexception of habitats with water containing ocean derived salts in excess of 0.5 parts perthousand. A channel is “an open conduit either naturally or artificially created whichperiodically or continuously contains moving water, or which forms a connecting link betweentwo bodies of standing water” (Langbein and Iseri 1960).

Lacustrine System

The lacustrine system includes deepwater habitats with all of the following characteristics: (1)situated in a topographic depression or a dammed river channel; (2) lacking trees, shrubs,persistent emergents, emergent mosses or lichens with greater than 30 percent coverage; (3)total area exceeds 20 acres (8 ha). Similar wetland and deepwater habitats totaling less than 20acres may also be included in the Lacustrine System if an active, wave-formed or bedrockshoreline feature makes up all or part of the boundary, or if the water depth in the deepestpart of the basin exceeds 6.6 feet (2 meters) at low water.

75

The Green PeterReservoir, adeepwater habitatin Oregon.

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Uplands

Agriculture5

76

5. Adapted from Anderson

Agricultural land may be defined broadly as land used primarily for production of food andfiber. Agricultural activity is evidenced by distinctive geometric field and road patterns on thelandscape and the traces produced by livestock or mechanized equipment. Examples ofagricultural land use include cropland and pasture; orchards, groves, vineyards, nurseries,cultivated lands, and ornamental horticultural areas including sod farms; confined feedingoperations; and other agricultural land including livestock feed lots, farmsteads includinghouses, support structures (silos) and adjacent yards, barns, poultry sheds, etc.

Urban

Urban land is comprised of areas of intensive use in which much of the land is covered bystructures (high building density). Urbanized areas are cities and towns that provide the goodsand services needed to survive by modern day standards through a central business district.Services such as banking, medical and legal office buildings, supermarkets, and departmentstores make up the business center of a city. Commercial strip developments along maintransportation routes, shopping centers, contiguous dense residential areas, industrial andcommercial complexes, transportation, power and communication facilities, city parks, ballfields and golf courses can also be included in the urban category.

ForestedPlantation

Forested plantations include areas of planted and managed forest stands. Planted pines,

Christmas tree farms, clear cuts, and other managed forest stands, such as hardwood forestryare included in this category.

Forested plantations can be identified by observing the following remote sensing indicators:1) trees planted in rows or blocks; 2) forested blocks growing with uniform crown heights;and 3) logging activity and use patterns.

Figure 47. Anexample of upland“other” shrubsteppe inMontana, 1999.

et al. 1976.

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RuralDevelopment

Rural developments occur in sparse rural and suburban settings outside distinct urban cities

and towns. They are characterized by non-intensive land use and sparse building density.Typically, a rural development is a cross-roads community that has a corner gas station and aconvenience store which are surrounded by sparse residential housing and agriculture.Scattered suburban communities located outside of a major urban center can also be includedin this category as well as some industrial and commercial complexes; isolated transportation,power, and communication facilities; strip mines; quarries; and recreational areas such as golfcourses, etc. Major highways through rural development areas are included in the ruraldevelopment category.

Other Land Use

Other Land Use is composed of uplands not characterized by the previous categories. Typicallythese lands would include native prairie; unmanaged or non-patterned upland forests andscrub lands; and barren land (Figure 47). Lands in transition may also fit into this category.Transitional lands are lands in transition from one land use to another. They generally occur inlarge acreage blocks of 40 acres (16 ha) or more and are characterized by the lack of anyremote sensor information that would enable the interpreter to reliably predict future use. Thetransitional phase occurs when wetlands are drained, ditched, filled, leveled, or the vegetationhas been removed and the area is temporarily bare.

77

A freshwaterwetland inNevada.

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Appendix B.Contrasting the Fish and Wildlife Service’s Statusand Trends with the Natural Resource ConservationService’s National Resources Inventory1

FWS—Status and Trend NRCS—NRI

Methods2

· Stratified random sample of 4,375 4 -square mile plots.

· Includes all lands, Federal and non-Federal.

· Plots are weighted by expected wet-land density.

· Special stratum added to include all coastal wetland resources.

· Probability based random sample of 800,00 points restricted to private lands.

· Principal focus is on commodity crop production.

· 60,000 to 80,000 points in aquatic habi-tats.

· NRI does not sample all coastal wet-lands.

Purpose

· Congressionally mandated by the Emergency Wetlands Resources Act to report on status and trends of wet-lands.

· Focus is entirely on wetlands.· Produces a specific report on status

and trends outlining procedures, defi-nitions, results and statistical validity.

· Congressionally mandated by the Rural Development Act, Soil and Water Conservation Act and Food Security Act.

· Landscape characterization of natural resources of which wetlands are one component.

· Specific purpose is to monitor lands in agricultural production.

· Reports on the status of natural resources with wetlands being one component.

· Produces press releases, informational flyers, news releases, web based sum-maries and articles.

Report Frequency · Ten-year cycle · Five-year cycle

Data Collection

· Aerial imagery used in conjunction with collateral data and field work.

— Soil surveys; — Topographic quads; — NOAA navigation charts; — National Wetlands Inventory

(NWI) maps.· Uses a small cadre of wetland inter-

preters that averaged 12 years experi-ence in wetland identification and classification.

· Soil surveys used as the primary data source.

· Topographic quads, or other base map(s).

· 35mm color or black and white slides· NWI maps..· Uses hundreds of NRCS employees of

many disciplines nationwide for data collection work.

Quality Assurance

· Quality control steps included in vari-ous processes throughout the data col-lection, analysis steps.

· Field verification of 21% of the plots.· Six Federal agencies assisted with field

verification work for the year 2000 sta-tus and trends report.

· Computer generated data verification with up to 2% field verification of all points.

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79

FWS—Status and Trend NRCS—NRI

Technical Differences

• Deepwater Lakes

· Classifies water bodies 20 acres (8.1 ha) or greater as deepwater lakes. Water bodies less than 20 acres are classified as ponds.

· Does not include any persistent emer-gent vegetation in the lacustrine sys-tem (lakes).

· Classifies any water body 6.6 feet (2 m) or deeper as deepwater lakes.

· Includes some emergent vegetation in the lacustrine system (lakes).

• Development· Classifies developed areas into 2 gen-

eral categories; urban and rural.· Classifies developed areas into small

and large based on structure density.

• Forested Wetlands

· Uses leaf-off imagery to identify for-ested wetlands. Bases forested wet-land extent on visible indications of hydrology in conjunction with collat-eral data sources. Some managed pine plantations that have been extensively drained are considered uplands.

· Uses 35 mm slides often taken during the peak of the growing season (leaf-on). Classifies forest cover occurring on hydric soils as wetland. Pine planta-tions on hydric soils are considered forested wetland.

• Ephemeral Wetlands· Ephemeral wetlands are not part of

the Cowardin et al. (1979) classification and thus, are not included.

· Includes wetland types characterized by ephemeral hydrology.

• Wetland Shrubs· Identifies all wetlands with woody veg-

etation 20 feet (6 m) or less as shrub wetlands.

· Identifies tree species less than 20 feet tall as forested wetlands. Shrub spe-cies are identified as shrub wetlands.

• Food Security Act(FSA) Wetlands

· Does not differentiate FSA wetland types.

· Uses the Cowardin et al. definition as well as the FSA definition of wet-lands. FSA differentiates some wet-land and non wetland types to include "farmed wetlands", and "Prior con-verted wetlands" which are non-wet-land for FSA purposes. In addition, Cowardin wetlands may be assigned a cropped covertype if in agricultural production.

1. Also see Shapiro (1995) for a review of the level of consistency among data sets.2. The Service has consulted with leading spatial sampling experts regarding the merging of different sampling schemes and the likelihood of producing a single set of wetland change figures. The consensus from inside and outside the Federal government is that statistically designed sampling approaches, developed independently, such as this study and the NRI cannot be combined to produce statistically reliable data.

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80

Saltwater Habitats

Marine Subtidal

Marine Intertidal

Estuarine Subtidal

Estuarine Aquatic Bed

Estuarine Emergents

Estuarine Forested

Shrub

Estuarine Unconsoli-

dated Shore

Palustrine Aquatic Bed

Palustrine Emergents

Palustrine Forested

19

97

Cla

ss

ific

ati

on

, E

sti

ma

ted

Ac

rea

ge

, a

nd

Pe

rce

nt

Co

effi

cie

nt

of

Va

ria

tio

n

Saltwater Habitats

Marine Subtidal

174250132

126351

2507195

0—

0—

0—

158969

0—

0—

0—

Marine Intertidal

128444

12716420

31667

0—

5896

15278

319244

0—

0—

0—

Estuarine Subtidal

3395

38054

175922912

45395

1528719

47043

2602720

0—

5198

0—

Estuarine Subtidal

0—

0—

0—

2883127

0—

0—

22873

0—

0—

0—

Estuarine Emergents

1095

133959

2361615

0—

39089184

1213933

391225

0—

48543

0—

Estuarine Forested

Shrub

6895

12665

127845

0—

573355

65600113

50944

0—

0—

0—

Estuarine Unconsoli-

dated Shore

40795

43759

1915719

0—

1003918

389144

51433611

0—

5067

0—

Freshwater Habitats

Palustrine Aquatic Bed

0—

0—

0—

0—

0—

0—

0—

21913513

1804431

44452

Palustrine Emergents

0—

0—

794

0—

0—

4896

0—

550449

238750519

36295115

Palustrine Forested

0—

0—

39104

0—

7298

0—

0—

571936

5507479

479673273

Palustrine Shrub

0—

0—

24258

0—

2797

0—

4395

34750

2043099

23657848

Palustrine Unconsoli-

dated Bottom

0—

0—

6661

0—

0—

0—

0—

375230

8640312

294830

Palustrine Unconsoli-date Shore

0—

0—

0—

0—

0—

0—

0—

0—

1145930

8576

Cultivated Rice

0—

0—

0—

0—

0—

0—

0—

0—

1262633

573776

Deepwater Habitats

Lacustrine

0—

0—

1494

0—

0—

0—

0—

105458

11844518

60399

Riverine

0—

0—

0—

0—

0—

0—

0—

0—

6023055

936457

Uplands

Agricultural

0—

0—

13162

0—

28555

0—

0—

398874

16206320

260646

Urban

0—

0—

21453

0—

0—

0—

22178

26193

86846

41100

Upland Forested

Plantation

0—

0—

20495

0—

2495

0—

0—

62172

639444

305443

Upland Rural Development

0—

0—

22286

0—

0—

0—

4196

0—

397239

20199

Other

0—

14676

105226

0—

202652

7969

73036

300657

4593835

735329

Acreage Totals, 1997

174430332

13085520

176639222

2928427

39424684

67278113

55082911

24338612

251571358

507284973

Appendix C.

This table presents estimates of acreage by classification and the number ofacres that changed classification between 1986 and 1997. The rows identifythe 1986 classification. The columns identify the classification and acreage of1997. The number under the acreage estimate for each entry is the percentcoefficient variation for that estimate.

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81

1986 Classification

Freshwater Habitats

Cultivated Rice

Deepwater Habitats Uplands

Palustrine Shrub

Palustrine Unconsoli-

dated Bottom

Palustrine Unconsoli-

dated ShoreLacustrine Riverine Agricultural Urban

Upland Forested

Plantation

Upland Rural Development Other Acreage

Totals, 1986

0—

0—

0—

0—

0—

0—

0—

0—

0—

0—

6894

177049332

Marine Subtidal

0—

0—

0—

0—

0—

0—

0—

0—

0—

2498

93050

13311920

Marine Intertidal

0—

10768

0—

0—

146594

0—

1496

22856

0—

30062

53944

176376442

Estuarine Subtidal

0—

0—

0—

0—

0—

0—

0—

0—

0—

0—

0—

2905927

Estuarine Subtidal

43685

48248

3594

0—

49594

4395

796

159646

0—

85755

254432

39569144

Estuarine Emergents

0—

11856

0—

0—

0—

0—

44270

86451

0—

90957

11689

66616313

Estuarine Forested

Shrub

0—

3362

0—

0—

994

0—

0—

24558

0—

23193

254045

55137711

Estuarine Unconsoli-

dated Shore

708133

557837

5898

44499

8790

20375

132932

21151

0—

54453

55987

25371812

Palustrine Aquatic Bed

94010811

9203813

389434

21302426

14131050

1315263

51673015

11243967

2068949

523733

3401921

263833368

Palustrine Emergents

28250918

7536521

69375

3870760

779249

3000033

14172321

6586516

10982127

8277419

2781719

519295523

Palustrine Forested

143282175

3805115

33761

1956133

928543

1411334

7625620

3709631

7777332

3064921

3309052

172351804

Palustrine Shrub

1433929

43333934

715282

558244

249535

428196

4458132

1246322

39949

2343833

7381674

46151084

Palustrine Unconsoli-

dated Bottom

505578

361623

34804317

1499

7982

4586

181337

719588

5499

207554

265672

38218816

Palustrine Unconsoli-date Shore

3853541

521231

0—

1154297210

126199

0—

1781133

844862

3269046

1331431

424457

1168284810

Cultivated Rice

2837375

554338

2454778

2876245

1438302411

0—

248998

763360

0—

619342

220964

1460888811

Lacustrine

11999246

414787

12385

20677

0—

60837679

255979

2217100

0—

132685

719665

629112810

Riverine

3592146

37187013

796435

70302529

4497840

3950168

Agricultural

1498

900116

59653

0—

200972

337102

Urban

444037

2345716

148880

7998

717259

8085

Upland Forested

Plantation

115371

2386839

390093

15289

848146

205062

Upland Rural Development

1686538

26485113

1533836

540535

11537775

6834451

Other

183656204

52567304

41416815

1255793210

1472532011

62559169

Acreage Totals, 1997

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82

All photographs were taken by TomDahl, U.S. Fish and Wildlife Service,unless otherwise noted.

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U.S. Department of the Interior U.S. Fish & Wildlife Service

http://www.fws.gov/

December 2000