Status and Trends of 

Prairie Wetlands in the 

United States 1997 to 2009

U.S. Fish & Wildlife Service 

Status and Trends of Prairie Wetlands 

in the United States 1997 to 2009

T. E. Dahl

U.S. Fish and Wildlife Service 

Washington, D.C.
Early spring meltwater attracts geese to this temporary wetland, Kulm Wetland Management District, ND.
 iii

This report should be cited as:

Dahl, T.E. 2014. Status and trends of prairie wetlands in the United States 1997 to 2009.

U.S. Department of the Interior; Fish and Wildlife Service, Ecological Services, 

Washington, D.C. (67 pages).

The author would like to acknowledge the technical contributions of the following people 

from the National Standards and Support Team, U.S. Fish and Wildlife Service in 

Madison, WI: Mitchell T. Bergeson, Geographic Information Systems Specialist; Andrew Cruz, 

Information Technology Specialist; Rusty K. Griffin, Physical Scientist; and Jane Harner, 

Geospatial Information Analyst. All have made significant contributions to the collection, 

field verification and analysis of the data for this report. 

The Cooperative Fish and Wildlife Research Unit, South Dakota State University, 

Brookings, SD conducted the image analysis for this study. 

Subject matter peer review of this report was provided by Dr. Rex Johnson, Habitat and 

Population Evaluation Team, U.S. Fish and Wildlife Service, Wildlife Research Station, 

Boone, IA; Jorge Coppen, North American Waterfowl Management Plan Coordinator, 

Office of Migratory Bird Management, U.S. Fish and Wildlife Service, Laurel, MD; 

Myra Price, U.S. Environmental Protection Agency, Office of Wetlands, Washington, D.C.; 

Michael Watmough, Canadian Wildlife Service, Prairie & Northern Region, Environment 

Canada; Robb Macleod, Ducks Unlimited, Great Lakes and Atlantic Regional Office, 

Ann Arbor, MI; Dr. John M. Coluccy, Director of Conservation Planning, Ducks Unlimited, 

Great Lakes and Atlantic Regional Office, Ann Arbor, MI; Dr. Bill O. Wilen, National Wetland 

Inventory, U.S. Fish and Wildlife Service, Arlington, VA; and Dr. Jonathan Phinney, Chief, 

Branch of Geospatial Mapping and Technical Support, Ecological Services, U.S. Fish and 

Wildlife Service, Arlington, VA. 

Field verification work and editorial assistance were provided by Sydney Nick, U.S. Geological 

Survey, Wisconsin Water Science Center. Further editorial review, report layout and printing 

were provided by the U.S. Geological Survey, Science Publishing Network. 

Cooperative funding for this study was provided by the Prairie Pothole Joint Venture, with 

special acknowledgement to Casey Stemler, Prairie Pothole Joint Venture Coordinator, U.S. 

Fish and Wildlife Service, Denver, CO; and Kevin Doherty, Science Coordinator, Bismarck, ND. 

Ecological Services of the U.S. Fish and Wildlife Service has supported this study with funding 

and logistical help. Many individuals from the U.S. Fish and Wildlife Service’s Headquarters 

Office have been involved, but specific recognition is due to the following: Gary Frazer, 

Assistant Director, Ecological Services; Paul Souza, Deputy Assistant Director, Ecological 

Services, Martha Balis-Larson, Chief, Division of Technical Support and Jo Ann Mills of the 

Branch of Geospatial Mapping and Technical Support.

Acknowledgments
iv

Conversion Table

U.S. Customary to Metric

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

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

feet (ft) x 0.30 = meters (m)

miles (mi) x 1.61 = kilometers (km)

square feet (ft2) x 0.09 = square meters (m2)

square miles (mi2) x 2.59 = square kilometers (km2)

acres (A) x 0.40 = hectares (ha)

Farenheit degrees (FE) 0.5556 = Celsius degrees (CE)

(FE-32)

Metric to U.S. Customary

millimeters (mm) x 0.04 = = inches (in.)

centimeters (cm) x 0.39 = inches (in.)

meters (m) x 3.28 = feet (ft)

kilometers (km) x 0.62 = miles (mi)

square meters 

(m2)

x 10.76 = square feet (ft2)

square kilometers 

(km2)

x 0.39 = square miles (mi2)

hectares (ha) x 2.47 = acres (A)

General Disclaimer

The use of trade, product, industry, or firm names or products in this report is for informative 

purposes only and does not constitute an endorsement by any agency of the U.S. Government.
Contents

Acknowledgments.....................................................................................................................iii

Executive Summary.................................................................................................................. 1

Introduction................................................................................................................................ 3

The Prairie Pothole Region of the United States ................................................................ 6

Procedures ............................................................................................................................... 12

Study Area and Sampling Design ................................................................................. 12

Habitat Definitions .......................................................................................................... 14

Study Limitations .................................................................................................................... 17

Results....................................................................................................................................... 18

Status of Prairie Wetlands, 2009.................................................................................... 18

Trends in Wetlands 1997 to 2009.................................................................................... 24

Changes in Grassland Area, 1997 to 2009..................................................................... 30

Discussion.................................................................................................................................. 32

Changes in Wetland Extent in the Prairie Pothole Region....................................... 32

Trends Affecting Wetland Changes in the PPR.......................................................... 34

Changes in Hydrology and Climate .............................................................................. 37

The Effects of Development and Agriculture ............................................................. 40

Wetland Restoration........................................................................................................ 46

Federal Wetland Protection Mechanisms in the Prairie Pothole Region ............... 48

Trends in Grassland Habitat.......................................................................................... 50

Summary ................................................................................................................................... 55

References................................................................................................................................. 56 

Appendix: Definitions of Habitat Categories Used in This

Status and Trends Study .............................................................................................63

 v
vi

Figures

1. Aerial image of numerous wetland basins, Day County, SD, circa 2010 ............ 6

2. An emergent wetland in the Prairie Pothole Region of North Dakota. 

Semi-permanently flooded to temporarily flooded zones represent 

different hydrologic regimes reflecting water permanence within a 

single depressional basin ........................................................................................... 7

3. The Prairie Pothole Region is renowned for waterfowl production. Mallards, 

pictured here, are a common species that use prairie pothole wetlands............ 9

4. Wetlands in the Prairie Pothole Region support many species of 

wildlife including the Sandhill Crane....................................................................... 9

5. The Ringed-neck Pheasant has become a popular bird for hunters and 

wildlife enthusiasts ..................................................................................................... 9

6. Historic wetland drainage in the Prairie Pothole Region of 

Iowa and Minnesota, circa 1950 .............................................................................. 11

7. The U.S. Prairie Pothole Region boundary as used in this study..................... 13

8. A single wetland basin in the Prairie Pothole Region may contain 

different zones reflecting hydrologic gradients depending on the 

persistence of surface water ................................................................................... 17

9. Estimated wetland area (acres) by type as found in this study in the 

U.S. Prairie Pothole Region, 2009.......................................................................... 18

10. Estimated wetland area in the U.S. Prairie Pothole Region, 2009................... 19

11. A depressional pothole basin with forest canopy in the 

prairie region of Minnesota ..................................................................................... 20

12. Relative wetland density based on wetland area in the 

U.S. Prairie Pothole Region, 2009.......................................................................... 21

13. Wetland basin numbers for all wetland classification types in the 

U.S. Prairie Pothole Region, 2009.......................................................................... 23

14. Attribution of gains (blue), losses (red) and conversions (yellow) of 

emergent wetlands in the U.S. Prairie Pothole Region to other upland 

land-use, wetland or deepwater types, 1997 to 2009 ........................................... 26

15. Emergent wetland gains (blue) and losses (red) in the 

Prairie Pothole Region, 1997 to 2009 ..................................................................... 27

16. Gains (blue) and losses (red) in wetland basin number for each 

state in the U.S. Prairie Pothole Region, 1997 to 2009 ....................................... 27

17. Loss or conversion in area of emergent wetland hydrologic types 

and ponds in each of the states in the U.S. Prairie Pothole 

Region, 1997 to 2009 ................................................................................................. 28

18. Wetland basin gains (green) and losses (red) in upland grassland area 

within the U.S. Prairie Pothole Region, by state, 1997 to 2009......................... 30

19. Trends showing percentage of area for the primary wetland and water 

body types in the U.S. Prairie Pothole Region from 1983 to 2009 .................... 33

20. This photograph shows a temporarily flooded wetland in a 

wheat field in late summer ...................................................................................... 33

21. Attribution of changes to emergent wetlands in the U.S. Prairie 

Pothole Region, 1997 to 2009................................................................................... 34

22. Areas exhibiting changes in wetland hydrologic indicators, wetland loss 

or wetland gain in the U.S. Prairie Pothole Region, 1997 to 2009..................... 35

23. Between 1997 and 2009 drier wetland types (shorter hydroperiod) 

declined as wetter types increased in area.................................................................36

24. The Palmer Drought Severity Index (Palmer 1965) is a meteorological 

drought index used to assess the severity of dry or wet conditions ................. 37
25. Overflow basins have merged across a road crossing in North Dakota........... 38

26. An example of wetland drainage into a larger wetland/water complex,

Kingsbury County, SD, circa 2010.......................................................................... 39

27. Filling a wetland for urban development near Devils Lake, ND...................... 40

28. The effects of drift from chemical applications to this farm field impact 

this emergent wetland in the prairie region of North Dakota as evident 

by the discoloration of the remaining vegetation ................................................ 41

29. A farmed wetland in North Dakota’s Prairie Pothole Region with remnant 

wetland vegetation in the center portion of the basin ........................................ 42

30. A historic wetland basin in Iowa (effectively drained by subsurface tile) 

has been flooded by recent rain storms and holds ephemeral surface water 

that will persist for only a few days under normal conditions ........................... 43

31. The density of breeding duck pairs in the spring is inversely related to 

wetland size where size increases with water permanence ............................... 45

32. A temporary wetland as part of a conservation easement on former 

agricultural land in Minnesota’s prairie region, 2009 .......................................... 47

33. Increased water levels in some areas of the U.S. Prairie Pothole Region 

have reclaimed some wetland shallow lake basins .............................................. 49

34. Density of upland grassland in the U.S. Prairie Pothole Region, 2009 ............ 50

35. Soil erosion and sedimentation can adversely affect wetlands as seen 

in this photograph from the prairie region in Minnesota.................................... 51

36. Upland grassland adjacent to wetlands provides valuable habitat for 

waterfowl and other wildlife in the U.S. Prairie Pothole Region 

(Mclean County, ND).................................................................................................52

37. Wetlands without grassland buffers are subject to additional 

environmental stressors and potentially provide less suitable habitat............ 53

Tables

1. Historic wetland extent and trends of wetlands in the 

Prairie Pothole Region of the United States........................................................ 10 

2. Area of the U.S. Prairie Pothole Region with number of sample 

plots and area sampled as part of this study ........................................................ 13

3. Emergent wetland types used to describe herbaceous prairie 

wetland basins in this study.................................................................................... 15

4. Wetland, deepwater and upland classifications used in this study.................... 16

5. Estimated area and change for all wetland and deepwater habitat 

types in the U.S. Prairie Pothole Region, 1997 to 2009 ...................................... 19

6. Wetland and lake basin numbers, change, mean size and density for 

portions of the states in the U.S. Prairie Pothole Region, 1997 to 2009........... 22

7. Estimates of emergent wetland areal extent and basin number by type 

for the U.S. Prairie Pothole Region, 2009............................................................. 23

8. Wetland basin number by wetland type for each of the states 

in the U.S. Prairie Pothole Region, 2009............................................................... 24

9. Change in wetland, deepwater habitats and grassland area 

in the U.S. Prairie Pothole Region, 1997 to 2009 ................................................. 25

 vii
A seasonally flooded wetland basin (foreground) and a larger semi-permanently flooded wetland (background).
 1

Executive Summary

The number of wetland/water basins1 in the PPR was 

determined using a geospatial model to calculate spatial 

dominance of basin area by water regime type. There 

were an estimated 2,624,990 wetland/water basins in 

the PPR. Temporarily flooded emergent wetland basins 

were the most numerous, composing almost half of all 

emergent wetland basins in the PPR. An estimated 

41.7 percent of emergent basins were seasonally flooded, 

6 percent were semi-permanently flooded and farmed wetlands made up an estimated 2.4 percent of the emergent 

wetland basins in 2009. There were very few (0.2 percent) 

saturated emergent wetland areas in the PPR.

The maximum density of wetland was 148 basins 

per mi2 (57 basins/km2) in portions of North Dakota. 

Wetland/water basins averaged from 30 per mi2

(12 basins/km2) in North Dakota to 4 and 5 basins per 

mi2 (1–2 basins/km2) in Iowa and Minnesota. The mean 

number of wetland/water basins found in the PPR in 

2009 was 17.4 basins per mi2 (6.7 basins/km2). The mean 

size of these basins was 3.2 acres (1.3 ha).

Wetlands as a percentage of surface area in the PPR 

were most abundant in North Dakota, making up 

9 percent of the surface area in the prairie region of 

that state in 2009. South Dakota was similar with 

8.5 percent of the land area identified as wetland. 

Minnesota had 6.7 percent wetland by area, Iowa 

2.7 percent and wetlands were the least common in 

Montana with 1.9 percent of the land area as wetland.

An estimated 94 percent of wetlands were located 

within or adjacent to agricultural lands or grassland. 

Less than 1 percent were within or adjacent to urban 

or developed areas and about 5 percent were within or 

adjacent to other types of uplands or river corridors. 

Between 1997 and 2009, total wetland area declined by 

an estimated 74,340 acres (30,100 ha) or 1.1 percent in 

the PPR. This represents an average annual net loss 

of 6,200 acres (2,510 ha). However, emergent wetlands 

(emergent marshes and farmed wetlands) declined by 

an estimated 95,340 acres (38,600 ha). Shrub wetlands 

also declined by 46,080 acres (18,660 ha). Forested 

wetlands increased in area (61,280 acres or 24,810 ha) 

ameliorating some of the loss of emergent marsh and 

shrub wetland area. Open water ponds also increased 

in area by 5,800 acres (2,350 ha) over the 12 year 

period. 

1

Basin numbers include wetland and lake (deepwater) basin types.

This study examined recent trends in wetland extent 

and habitat type throughout the Prairie Pothole Region 

(PPR) in the United States. Wetland trends were measured by the examination of high resolution imagery for 

755 randomly selected sample plots covering the prairie 

regions of Montana, North Dakota, South Dakota, 

Minnesota and Iowa. The analysis of this imagery in 

combination with field verification provided a scientific 

basis for estimations of wetland extent, type and distribution that had occurred between 1997 and 2009. 

This information provides a quantitative measure of the 

areal extent of all wetlands, regardless of ownership, in 

the PPR. Wetlands were defined using biological criteria and standardized nomenclature for the classification 

of wetland types. Recently acquired remotely sensed 

imagery was used as the principle means to assess 

wetland change with a number of geoprocessing and 

quality control measures implemented to ensure data 

completeness and accuracy. The spatial sample design 

involved randomized sampling of geospatial information 

on 4 mi2 (10.4 km2) plots. This was a well-established 

procedure that provided a practical, scientific approach 

for measuring wetland area extent (status) and change 

rates (trends). Statistical estimates provided regionally 

specific status and change information as well as estimates by wetland type. Important procedural enhancements to this study of the PPR included the addition 

of wetland and water basin morphology, hydrologic 

descriptors and the addition of an upland grassland 

category to track changes in grassland area. Field 

verification was completed for 205 (27 percent) of the 

sample plots during 2010 to 2013. 

This report provides data regarding trends in wetland 

extent and type; however, it does not draw conclusions 

regarding the quality or condition of prairie wetlands.

Results from this study indicated that there were an 

estimated 6,427,350 acres (2,602,165 ha ± 4.3 percent) 

of wetlands in the PPR in 2009. Emergent wetlands 

made up about 87.7 percent of the total wetland area 

and 93 percent of all wetland basins in the PPR. Wetlands classified with woody vegetation (wetland forest 

or shrubs collectively) composed 8.3 percent of the 

surface area and open water ponds 4 percent. By area, 

seasonally flooded emergent marshes had the greatest area with 2,313,650 acres (936,700 ha) followed by 

semi-permanently flooded marshes with 1,945,460 acres 

(787,636 ha) and temporarily flooded wetland with 

1,187,700 acres (480,850 ha). 
2 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Minnesota sustained the largest loss of emergent 

wetland area between 1997 and 2009. South Dakota 

was the only state to exhibit gains in emergent 

wetland area.

Because most wetlands and water basins in the PPR 

are hydrologically closed systems, they are sensitive 

to climate variability and can exhibit dramatic changes 

in water levels, size and distribution on the landscape. 

Over the course of this study, high water conditions 

affected 40 percent of the emergent wetlands. Semipermanently flooded wetlands, open water ponds and 

deepwater lakes increased in area, often at the expense 

of vegetated wetland area.

Emergent wetlands lost to upland land uses (agriculture and development) between 1997 and 2009 

accounted for 39 percent of all losses. Small-sized 

farmed and temporary wetlands experienced substantial losses. Farmed wetlands were very vulnerable to 

drainage for agricultural crop production because they 

were usually small, in close proximity to existing farm 

field operations and could be easily drained, usually 

without penalty under existing regulations. Temporarily flooded and farmed wetland basins were lost to 

agriculture even during periods of abnormally high 

water conditions. 

Between 1997 and 2009 wetland/water basins declined 

by over 107,177 or 4 percent. Wetland basin numbers 

declined in every state in the PPR with the exception 

of Montana, where there was a small gain in wetland 

basins of less than 1 percent.

Ninety-six percent of the basins lost were temporarily flooded emergent and farmed wetlands as these 

basin types declined by 7.8 percent. The mean size of 

the basins lost was 0.85 acres (0.3 ha). An estimated 

49 percent of the wetlands lost between 1997 and 2009 

were geospatially isolated wetlands2

. 

The restoration of wetland and grassland in the PPR 

has been a priority for resource management agencies 

at the federal and state level for some time. Because 

the drainage of prairie pothole wetlands typically 

2

Geospatially isolated wetlands are those areas not having a direct 

connection to other water bodies via channel or navigable water. Isolated 

wetlands were determined by a geospatial data model developed to identify wetlands not connected to or within a 100 ft. (30 m.) buffer distance 

ters (rivers, streams or permanent lakes).

involves a single outlet ditch or tile drain to put land 

into agricultural production, the potential for restoration is much greater than if the lands were developed as 

part of urban areas. Between 1997 and 2009, an estimated 87,690 acres (35,500 ha) of emergent wetland was 

restored from agricultural lands. These restored wetlands averaged 5.8 acres (2.4 ha) and were seasonally or 

semi-permanently flooded areas.

The results of these wetland restoration efforts were 

overshadowed by the loss of 125,400 acres (50,770 ha) of 

emergent wetland converted to upland agriculture. The 

deficit, represented by a loss of 37,770 acres (15,270 ha), 

indicated that the no-net-loss of wetland policy goal had 

not yet been reached in this region. 

Grassland occupied approximately 21.1 million acres 

(8.6 million ha) in the PPR in 2009 (± 4.2 percent). There 

was a 3:1 ratio of grassland to wetland region-wide. 

However, grassland was not evenly distributed and was 

sparse in the prairie regions of Minnesota and Iowa. 

Between 1997 and 2009, grassland area declined by 

an estimated 568,040 acres (229,980 ha) or 2.6 percent. 

Grassland area declined by 805,000 acres (325,910 ha) 

in the western prairie states of Montana, North Dakota 

and South Dakota. Minnesota and Iowa gained grassland 

area (236,960 acres or 95,935 ha) over the period of this 

study. Ninety-five percent of the area lost from grassland was reclassified as agriculture. 

Grasslands in the PPR have the ability to directly 

impact up to 32 percent of the remaining wetlands that 

were either within or directly adjacent to grassland 

areas. The elimination of grassland may not result in 

direct wetland loss but can influence wetland condition 

and landscape function by increasing sedimentation, runoff of chemicals or nutrients, or by otherwise reducing 

or eliminating surrounding habitat suitability. It is likely 

that grassland to cropland conversion will increase if 

agricultural commodity prices continue to follow recent 

trends.

Changes in wetland extent and type between 1997 and 

2009 were the result of cumulative impacts related 

to ecological change; changes in climate that altered 

hydrology (e.g. flooding); anthropogenic changes such as 

draining, ditching or filling wetlands; or a combination of 

these influences. Evidence from this study indicates that 

some wetland basins have become wetter. However, the 

duration and sustainability of this trend is unclear. 
Introduction 3

Introduction

The U.S. Fish and Wildlife Service (USFWS) has been 

entrusted with legal authorities and responsibilities for 

fish and wildlife conservation including the management of fish and wildlife populations; conserving endangered and threatened species, inter-jurisdictional fish 

and migratory birds; managing an extensive conservation land base composed of over 560 National Wildlife 

Refuges; and collaborating in carrying out conservation 

activities under international conventions, treaties and 

agreements. The USFWS communicates information 

essential for public awareness and understanding of the 

importance of fish and wildlife resources and changes 

reflecting environmental conditions that will ultimately 

affect the welfare of people. 

Wetlands are transitional from true aquatic habitats 

to dry land (upland) and as a result, their abundance, 

type and condition are directly reflected in the health 

and abundance of many species. In addition to providing habitat for a variety of animal and plant species, 

wetlands of the Prairie Pothole Region (PPR) perform 

a number of other environmental services. Depending 

on their location, type and size, wetlands can attenuate floodwaters, recharge ground water, provide water 

and forage for livestock and support biodiversity. The 

ecological condition of many of the remaining wetlands 

in the PPR have been affected by land use changes 

including encroachment of development and farming 

practices, alteration of hydrology via drainage, introduction of invasive species, fragmentation of habitat 

and reduced diversity in wetland complexes.

Continued pressures on wetland resources require 

effective monitoring efforts at temporal and spatial 

scales useful for detecting significant change that leads 

to effective wetland conservation efforts. Probabilistic 

Restored wetland in northwest Iowa. (Photo courtesy of NRCS.)
4

sampling to periodically measure wetland area extent 

(status) and change rates (trends) are an effective 

means to gather information regarding wetland 

resources. Resource managers, researchers and policy 

makers have come to rely on statistically based sampling strategies to capture recent wetlands status and 

trends information.

Monitoring of wetland resources has been widely 

considered essential for identifying changes in wetland 

community types and spatial extent and guiding additional research or management actions. The USFWS 

has produced a series of reports on wetland status and 

trends that provide information on wetland extent and 

types in various parts of the country. These provide 

resource managers useful data to inform decisions on 

wetland-related issues such as establishing restoration 

and habitat enhancement priorities, assessing habitat 

availability, identifying possible changes from climatic 

conditions and implementing strategic ecosystem 

management actions.

Conservation efforts in the PPR reflect USFWS 

participation with other partner organizations in 

international management plans and treaties including 

the North American Waterfowl Management Plan 

(NAWMP 2012). This plan calls attention to the 

continuing loss of key wetland and related habitats 

needed to sustain waterfowl populations at desired 

levels and identifies the PPR as crucial to the longterm viability of breeding waterfowl habitat in North 

America (Beyersbergen et al. 2004). Federal, state, 

local and tribal agencies as well as private organizations play key roles in slowing and reversing the 

trend of habitat loss by protecting and restoring wetland and grassland habitats throughout this region. 

Understanding the relationships between extent and 

types of wetlands and waterbird and waterfowl density 

and distribution is essential to population monitoring 

and management (Niemuth and Solberg 2003). Over 

the past 30 years the scientific community has developed various ecological models that assist biologists 

and resource managers in identifying land and water 

resources necessary for supporting various ecological functions and services, including requirements for 

maintaining migratory bird populations. Many of these 

models depend on geospatial data that reflect contemporary land-use information to assess landscape-level 

conditions. This study contributes to those efforts by 

tracking and quantifying wetland losses, restoration or 

creation actions and providing a measureable element

to gauge management actions, assess progress in 

achieving federal policy objectives and provide further information crucial to understanding the wetland 

resources of the PPR. 

This report presents the latest status information on 

the extent, type and trends of wetland resources in 

the PPR and provides estimates of losses or gains3

that occurred between 1997 and 2009. The information 

presented provides data on the areal extent of wetland 

types, both past and present, to help prioritize conservation planning efforts for wetland resources and contribute additional information to facilitate strategy and 

policy development. This study does not assess wetland 

condition or other qualitative changes to wetlands in 

the PPR.

3

Wetland loss or gain as used in this report is defined as a decline or 

increase in wetland area.

This study was supported by the Prairie Pothole Joint Venture 

and Ecological Services of the U.S. Fish and Wildlife Service. 

Cooperative efforts for field operations were also provided by the 

U.S. Environmental Protection Agency, Office of Wetlands, 

Washington, D.C.
McIntosh County, ND, spring 2014.
The Prairie Pothole Region of the United States 

The glaciated prairie region is an area of about 

300,000 mi2 (777,000 km2) located in the central 

portion of the North American Continent (Smith et al.

1964). In the United States, this region encompasses 

an area of about 150,930 mi2 (390,910 km2) and extends 

from central Iowa north to the Canadian border and 

includes portions of the states of Iowa, Minnesota, 

North Dakota, South Dakota and Montana. The region 

is characterized by glacial or post-glacial derived 

depressions or basins resulting from the retreat of the 

Laurentide ice sheet of the Wisconsin Glacial Episode 

(Johnson et al. 2008). As a result, there are numerous 

small landscape depressions left behind as the glaciers 

receded from this part of the continent. These landscape depressions, termed “potholes,” collect rainfall 

and snowmelt, forming small shallow wetlands and 

ponds (Figure 1). 

Figure 1. Aerial image of numerous wetland basins, Day County, SD, circa 2010. 

6 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

The PPR is a grassland ecoregion of regional and 

global importance for migratory birds and other fauna 

(Blann et al. 2009). The North American prairie as it 

existed prior to European settlement was dominated 

by grasses, and a scarcity of shrubs and trees except 

along river or stream corridors (Weaver 1954). By the 

late 1990s less than 1 percent of the historic native 

tall-grass prairie and less than 30 percent of the native 

mixed-grass prairie remained (Samson et al. 1998; 

Wright and Wimberly 2013). Grasslands are considered one of North America’s most endangered ecosystems (Beyersbergen et al. 2004; Hoekstra et al. 2005). 

Upland grassland in the PPR provides a range of ecological benefits including trapping of sediment; slowing 

of water runoff; and a source of food, nesting cover and 

habitat corridors for many wildlife species. 
Today, agriculture is the primary land use in the 

PPR (Gleason et al. 2008; Johnson and Higgins 1997). 

Cropland currently makes up about 69 million acres 

(27.9 million ha) or 71 percent of the 96.6 million acres 

in the PPR of the United States (Rashford et al. 2010). 

Small grain and other row crop farming along with 

grazing of livestock strongly influence the landscape 

and have a profound effect on wetland communities. 

Wheat, corn, soybeans, barley, hay, sunflowers, flax 

and cattle make up some of the agricultural products 

produced in the PPR of the United States. 

In the PPR, wetlands include an array of temporary, 

seasonal and semi-permanently flooded marshes, 

sloughs, and swales as well as larger, more permanent 

water bodies and relatively few shrub and wooded wetlands. Most prairie wetlands receive water from either 

precipitation in the form of direct rainfall, meltwater 

from snow, runoff from the surrounding watershed 

or, to a lesser extent, groundwater discharge. Many 

prairie potholes form more-or-less concentric bands of 

wetland vegetation around the deepest portion of the 

basin (Kantrud et al. 1989). These wetland vegetation 

zones orient themselves from the area where water 

persists the longest to the periphery where water is 

less permanent (Figure 2). Each of these zones reflect 

differences in the persistence of inundation, types of 

plants, soil and water chemistry. However, it is common for this zonation to be patchy, degraded or missing 

altogether.

Various wetland classification schemes have been 

developed for wetlands, ponds and lakes in the prairie 

region of the United States (Stewart and Kantrud 1971; 

Cowardin and Johnson 1973; Hubbard 1988). A number 

of these methodologies classify prairie wetlands using 

water permanence (hydroperiod) as a descriptor for 

categorizing these habitats.

Figure 2. An emergent wetland in the Prairie Pothole Region of North Dakota. Semi-permanently flooded to temporarily 

flooded zones represent different hydrologic regimes reflecting water permanence within a single depressional basin. 

Temporary Wetland

Seasonal Wetland

Semi-permanent Wetland

The Prairie Pothole Region of the United States7
8 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Historically, throughout the PPR the average annual 

precipitation has always been less than the average 

annual rate of evaporation (Winter 1989). The amount 

and timing of precipitation affects the duration and 

depth of water in prairie pothole wetlands on a seasonal or annual basis, and changes in snowfall, rainfall, 

soil moisture, frost, temperature and winds can cause 

dramatic fluctuations in surface water conditions and 

alter the number of ponded prairie wetlands at irregular intervals. There has been a strong tendency for 

many pothole wetlands to become dry late in the growing season. Smith et al. (1964) estimated that in any 

given year as many as one third of the prairie pothole 

wetlands will dry up between May and July. Cowardin et al. (1988) assumed that only 26 percent of the 

temporarily flooded wetland basins, 51 percent of the 

seasonal and 72 percent of the semi-permanent basins 

may hold water in an average year. 

This cyclical pattern of flooding and drying greatly 

influences wetland ecology in the PPR as it is possible 

for an intact wetland basin to exhibit different hydrologic traits along a continuum depending on precipitation from year to year or even season to season. For 

example, during extended wet periods, some wetland 

basins classified as temporarily flooded can take on the 

characteristics of seasonally flooded (hierarchically 

wetter) wetlands. The opposite may apply in dry years 

as semi-permanently flooded wetlands may be the only 

basins with surface water and resemble seasonal or 

even temporarily flooded wetlands in both appearance 

and function (Johnson et al. 2008). These dynamics, 

compounded by anthropogenic alterations (i.e. drainage or redirection of water) and potential long-term 

climatic changes, complicate efforts to categorize wetlands in the PPR by type.

Variations in the hydrology of prairie wetlands also 

make their biological characterization challenging 

(Euliss and Mushell 2011) as plant community composition and extent change to reflect current water 

conditions. 

Nationally, waterfowl are the most economically important wildlife using prairie pothole wetlands (Figure 

3). At least 15 duck species nest in the prairie region 

(Niering 1985) and an estimated 70 to 80 percent of the 

production of Mallard (Anas platyrhynchos), Northern 

Pintail (A. acuta), Canvasback (Aythya valisineria) 

and Redhead (A. americana) are concentrated in the 

PPR of North America (Smith et al. 1964; Munro 1967). 

Wetlands are the cornerstone that support these species as well as other populations of North American 

waterbirds including Franklin’s Gull (Leucophaeus 

pipixcan), Western Grebe (Aechmophorus occidentalis), American Bittern (Botaurus lentiginosus), Sora 

(Porzana carolina), Black Tern (Chlidonias niger), 

American White Pelican (Pelecanus erythrorhynchos) 

and Sandhill Crane (Grus canadensis) (Figure 4). 

Prairie pothole wetlands are also extremely important 

to other forms of wildlife. There are over 300 animal 

species known to use wetlands in the PPR (Peterson 

et al. 1985; Fritzell 1989; USGAO 2007; Herman and 

Johnson 2008). Many game species such as Ring-necked 

Pheasants (Phasianus colchicus) and White-tailed 

Deer (Odocoilius virginianus) use pothole wetlands 

extensively for habitat cover (Figure 5). Additionally, 

various state and federally endangered species such 

as the Whooping Crane (Grus americana), Piping 

Plover (Charadrius melodus) and Interior Least Tern 

(Sterna antillarum) use these wetlands as habitat or 

for forage. Shorebirds such as Long-billed Dowitchers 

(Limnodromus scolopaceus), Stilt Sandpipers (Calidris himantopus) and Wilson Phalaropes (Phalaropus 

tricolor) utilize prairie wetlands as staging or stopover 

sites and seek out wet mud flats and shallow water 

areas during migration (Skagen and Knopf 1994; 

Skagen and Thompson 2013).

This report provides a comprehensive, scientifically 

sound assessment on the status of these wetland 

resources that has not been summarized for this region 

as a whole. 

Figure 3. (Right, top). The Prairie Pothole Region is 

renowned for waterfowl production. Mallards, pictured here, 

are a common species that use prairie pothole wetlands.

Figure 5. (Right, center). The Ringed-neck Pheasant has 

become a popular bird for hunters and wildlife enthusiasts. 

The availability of cover during winter months is important 

for the health and survival rate of pheasants in the upper 

Midwest. In agricultural landscapes, pockets of wetland 

grasses and sedges provide vegetative cover and may be all 

that is available during the winter season. 

Figure 4. (Right, bottom). Wetlands in the Prairie Pothole 

Region support many species of wildlife including the 

Sandhill Crane, Logan County, ND.

10 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Historically, wetlands probably covered about 

16 to 18 percent of the landscape in the tall-grass and 

mixed-grass prairie regions in the states of North 

Dakota, South Dakota, Minnesota and Iowa (Table 1). 

During the past century, prairie wetlands have been 

extensively drained and in some areas only isolated 

tracts of wetland habitat remain. Drainage for agriculture during the years preceding the 1980s was pervasive as tile and open-ditch drains eliminated large 

numbers of wetland basins and converted lands to 

crop production (Figure 6). 

Since the mid-1980s and implementation of conservation provisions contained in successive Farm Bill legislations4

, wetland drainage attributed to agricultural 

practices has markedly declined nationally (Dahl 2000). 

Federal policies such as the “Swampbuster” provision 

4

Food Security Act of 1985; Food and Agriculture Trade Act of 1990; 

Agriculture Improvement and Reform Act of 1996; Food, Conservation 

and Energy Act of 2008.

reduced or eliminated incentives and other mechanisms 

that made the destruction of wetlands in the prairies 

technically and economically feasible (Dahl and Allord 

1996). Other conservation programs such as the North 

American Wetland Conservation Act, Wetland Reserve 

Program, Conservation Reserve Program, land retirement programs and those programs that encourage 

wetland restoration or creation and promote grassland 

reestablishment have also contributed to wetland conservation efforts. 

Regionalized studies of wetland status that summarize wetland inventory data or report on more recent 

changes have been conducted (Johnson et al. 1997; 

Oslund et al. 2010; Johnston 2013), but comprehensive 

wetland trends for the Prairie Pothole Region as a 

whole have been lacking. 

Table 1. Historic extent and trends of wetlands in the Prairie Pothole Region of the United States. Estimates from circa 1850 to 

the mid-1980s.

State

Estimated Wetland 

Area (acres)

Circa 1850

Estimated Wetland 

Area (acres)

Circa 1980s

Change

(percent) References

North Dakota 4.9 million 2.5 million -49% Natural Resources 

Conservation Service, 

wet soils of North Dakota 

(drained and undrained1) 

unpublished; Dahl 1990

South Dakota 2.7 million 2.1 million -32% Natural Resources 

Conservation Service, Huron, SD, unpublished data); 

Johnson et al. 1997

Minnesota 7 million 1.4 million -80% Redelfs 1980

Iowa 3.4 million 30,000–35,000 -90% Bishop et al. 1998; Bishop 

2006; Miller et al. 2009

Montana Estimates not 

available

— — —

Prairie Pothole 

Region

16.6–17 million 6 million -60 to 65% —

1

Cowardin et al. (1979) utilized the term “undrained hydric soils” to differentiate soils that had not been effectively drained and still maintained 

wetland hydrology.
11

Figure 6. (Top and bottom). Historic wetland drainage in the Prairie Pothole Region of Iowa and Minnesota, circa 1950.
12 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Procedures 

Study Area and Sampling Design

Various researchers (Kantrud and Stewart 1977; van 

der Valk 1989; Omernik 1995; Prairie Pothole Joint 

Venture 2003; Beyersbergen et al. 2004; Gleason et 

al. 2008) have provided slightly different iterations of 

the geographical boundary of the PPR in the United 

States. This study used a boundary for the PPR as 

defined by Bird Conservation Region 115 (North 

American Bird Conservation Initiative 1999). This 

physiographic area approximated the extent of the 

PPR in the United States and, as part of this study, 

was truncated at the South Dakota border and 

Missouri River in Montana (Figure 7). The area 

included a portion of the Lake Agassiz Plain Ecoregion 

in northwestern Minnesota that is a distinct ecotone 

consisting of aspen parkland and usually considered 

to be transitional between prairie and boreal forest 

(Stewart and Kantrud 1971). It has also been expanded 

to include portions of Montana north of theMissouri 

River, an area that usually has not been associated with 

the glaciated “pothole” region of the tall and mixed 

grass prairie. This study area was intersected with the 

state boundaries to divide the region into five state 

sub-regions for reporting purposes. 

The sample-based surveys and monitoring methods 

used in this study have been an effective means to 

gather information regarding wetland resource types 

(Johnson et al. 1999). Olsen et al. (1999) have described 

the conceptual relationships among the key elements 

in a probabilistic sampling survey design, and the 

USFWS has used a scientific probability sample of 

the surface area of the conterminous United States to 

produce wetland status and change estimates for wetland monitoring studies that document spatial changes 

on the landscape (Dahl 2011). These studies have used 

specialized knowledge of wetland habitats, classification

and ecological change processes and have been conducted specifically to monitor the nation’s wetland area 

using a single, consistent definition and study protocol.

This study builds on those scientific foundations for 

measuring wetland area extent (status) and change 

rates (trends) in the PPR of the United States. The 

study determined wetland type, areal extent and 

change using a statistically stratified, simple random 

sampling design. The foundations and scientific principles underlying such surveys are well developed and 

5

Bird Conservation Region 11 is one of 37 physiographic regions defined 

by the North American Bird Conservation Initiative as a geographic unit 

for planning and implementation of bird conservation efforts.

have been applied to formulating national resource 

estimates as well as conducting regional assessments 

of wetland extent (Moulton et al. 1997; Dahl 1999; 2005; 

2011; Dahl and Stedman 2013). These techniques have 

been used to monitor conversions between ecologically 

different wetland types, as well as to quantify wetland 

area gains and losses. Important enhancements specific 

to this study of the PPR included the addition of basin 

morphology, hydrologic descriptors and an upland 

grassland category to track changes in grassland area.

A total of 755 4 mi2 plots (2,560 acres or 1,036 ha) were 

sampled in this study6. To ensure spatial balance and 

improve precision of estimates, plots from the National 

Wetlands Status and Trends study (242) were augmented with randomly selected sample plots (106) 

from the operational breeding waterfowl population 

and habitat survey7, and supplemental plots (407) were 

randomly selected specific to this study to intensify the 

sample. The entire study area included 96,596,863 acres 

(39,108,041 ha). The distribution of sample plots by 

state is shown in Table 2.

Documentation of wetland change relied primarily on 

observable physical or spectral characteristics evident 

on high resolution imagery, in conjunction with collateral data, to make decisions regarding wetland extent 

and classification.8 Wetlands were identified based on 

vegetation, visible hydrology and physical geography. 

Delineations on the sample plots reflected ecological 

change or changes in land use that influenced the size, 

distribution or classification of wetland habitats. The 

heterogeneity of cover types (delineation of cover type 

within a basin) was retained in the data allowing for 

aggregation of that information for analysis. Specific 

procedures used for image interpretation of wetlands 

followed protocols used for national level wetlands 

status and trends studies and have been described by 

Dahl and Bergeson (2009). However, for this study 

the minimum target size for wetlands included was 

reduced to 0.2 acres (0.08 ha)9

. Actual results indicated 

6

Plots split by the study area or by state boundaries were less than 

2,560 acres. 

7

A 4 mi2 plot sampling design to assess landscape changes in habitat on 

waterfowl populations for the USFWS–National Wildlife Refuge System 

(Loesch et al. 2012).

8

Analysis of imagery was supplemented with field work and ground 

observations.

9

Smaller wetlands were detected and included in the study, but it cannot be determined that all wetlands less than 0.2 acres were detected.
Montana

Wyoming

North

Dakota

Nebraska

Minnesota

Iowa

South

Dakota

Procedures13

Figure 7. The U.S. Prairie Pothole Region boundary as used in this study. The area shown in green includes 

96.6 million acres (39.1 million ha) in portions of five states.

that for each wetland category included in the study, 

the minimum size represented was less than 0.2 acres 

(0.08 ha). 

Wetland, deepwater, and upland habitat changes 

were determined by intensive analysis of the high 

resolution aerial imagery, determination of wetland 

types and identification of the changes that occurred 

between the respective target dates. The mean 

dates of the aerial imagery used to determine wetland trends were 1997 and 2009, with the difference 

being an average of 12 years. Changes were recorded 

in areal extent or type of wetland observed on the 

sample plots between 1997 and 2009. 

Ground verification of features on the aerial imagery was done for portions of 205 sample plots (27.2 

percent) from 2010 to 2013. Verification involved site 

visits to a variety of wetland types and geographical settings. Field verification addressed questions 

regarding image interpretation, land use coding and 

attribution of wetland gains or losses. Field work was 

also performed as one of the quality control measures 

to verify that plot information was accurate. 

To reflect reliability each statistical estimate generated 

is accompanied by a coefficient of variation expressed 

as a percentage. The wetland area estimates produced 

for this study included all wetlands regardless of land 

ownership. The results represent the latest wetland 

monitoring information specific to the PPR of the United 

States that included portions of Montana, North Dakota, 

South Dakota, Minnesota and Iowa. 

Table 2. Area of the U.S. Prairie Pothole Region with number 

of sample plots and area sampled as part of this study.

State Area (acres) Number of 

Sample Plots

Montana 18,111,122 85

North Dakota 31,638,333 269

South Dakota 21,992,065 190

Minnesota 17,299,763 156

Iowa 7,555,580 55

Total—Prairie 

Pothole Region

96,596,863 755
14 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Habitat Definitions

During the mid-1970s USFWS began work on a biological definition of wetland and standardized nomenclature for the classification of wetland types. This system 

described by Cowardin et al. (1979), was adopted as a 

standard by USFWS and subsequently became a Federal Geographic Data Committee (FGDC) Standard 

for mapping, monitoring and reporting on wetlands 

(FGDC 1996). This institutionalization of a biological 

definition and classification system has facilitated its 

use in numerous federal applications and has provided 

consistency and continuity by defining the biological 

extent of wetlands and common descriptors for wetland 

types. It is a two-part definition as indicated below:

Wetlands are lands transitional between 

terrestrial and aquatic systems where the 

water table is usually at or near the surface 

or the land is covered by shallow water. 

For purposes of this classification wetlands 

must have one or more of the following three 

attributes: (1) at least periodically, the land 

supports predominantly hydrophytes, 

(2) the substrate is predominantly undrained 

hydric soil, and (3) the substrate is nonsoil 

and is saturated with water or covered by 

shallow water at some time during the 

growing season of each year.

Cowardin et al. (1979) and other researchers (Gosselink 

and Turner 1978; Mitsch and Gosselink 1993) recognized that hydrology was universally regarded as the 

most basic feature of wetlands and that hydrology, not 

the presence of vegetation, determines the existence 

of wetland (Cowardin and Golet 1995). For this reason, 

in areas that lack vegetation or soils (e.g. sand or rock 

beaches bars, and shorelines) hydrology determines 

that these areas are wetlands. In practice, three indicators—hydrophytic vegetation, undrained hydric soil, 

and wetland hydrology; two indicators—hydrophytic 

vegetation and wetland hydrology or undrained hydric 

soil and wetland hydrology; or a single indicator—wetland hydrology, respectively, may be used to identify 

wetland based on the conditions at any particular site 

(FGDC 2013).

The majority of all depressional prairie wetlands are 

in the palustrine system as defined by Cowardin et al.

(1979). Class-level descriptors indicated dominant vegetation or substrate types and water regime designations provide indicators of the duration of flooding or 

ponding of water in these areas. 

Because prairie pothole wetlands are dominated by 

several principal wetland basin types (emergent marsh 

with various water regime indicators), these wetlands 

have been the primary focus of prairie wetland conservation and management efforts. Five types of emergent 

wetland basins were characterized using water regimes 

based on the Cowardin et al. (1979) classification system

(Table 3). The assessment of these wetland types composes an essential part of this study. Table 4 provides a 

synopsis of all wetland types found in the prairies and as 

used in this study. Complete definitions of wetland types 

and upland categories used in this study are provided in 

the Appendix.

The use of water regimes to distinguish between wetland types in the prairies is based on a spatial dominance 

concept where an entire basin, spatially dominated 

by a particular hydrologic type, may be described as 

temporarily, seasonally, semi-permanently flooded, etc. 

However, distinct zones within a single basin may be 

described by using several different water regimes to 

indicate heterogeneity of habitat types and hydrologic 

gradients (Figure 8). While this delineation approach is 

often used to impart more information about wetland 

habitats, it confounds efforts to accurately and consistently characterize wetlands by a single basin type. 

Because of this limitation, basin number determined by 

a single descriptive hydrologic type has been an important metric used to assess wetland resources in the PPR, 

especially for waterfowl management purposes (Stewart 

and Kantrud 1971) and wetland restoration work (Galatwoistsch and van der Valk 1994). A number of researchers have used the deepest part of the wetland basin to 

describe the basin type by hydrology and go on to summarize basin numbers by that single basin type (Johnson 

and Higgins 1997; Johnson et al. 1999; Reynolds et al.

2006; Niemuth et al. 2010).

For this study a geoprocessing model was developed 

to classify wetland basins by hydrologic characteristics 

(water regime) by considering both the areal extent of 

the expected duration of surface water persistence as 

well as the spatial dominance of the basin zones represented by different hydrologic conditions. A “basin” 

for the purposes of this study is defined as a wetland on 

the landscape that may contain different but contiguous 

hydrologic zones. 
Procedures

15

Table 3. Emergent wetland types used to describe herbaceous prairie wetland basins in this study.

Common Descriptors Hydrologic Regime Habitat Description

Farmed wetland Temporarily flooded

Farmed wetlands are wetlands that have been tilled for 

agriculture but are not actively drained and will retain their wetland characteristics if farming is discontinued. Under drier conditions these wetlands may be 

tilled and planted for crop production, but in wetter 

years they return as shallow emergent marshes. 

Temporarily flooded 

emergent marsh; 

temporary ponds; 

low wet prairie

Temporarily flooded

Temporarily flooded emergent wetlands typically 

outnumbered all other wetlands in the PPR. They 

occur in shallow depressions that fill with rain or 

snow-melt early in the spring and retain water 

for short periods (2−4 weeks) during the growing 

season. Although variable in numbers, depending 

on rainfall conditions, these wetlands are extremely 

important to waterfowl. There is generally little 

vegetation that remains to identify temporary 

wetlands if they are planted to cropland.

Saturated emergent 

wetland; wet meadow; 

prairie fen

Saturated

Saturated wetlands are dominated by grasses and 

sedges that may be grazed or left fallow. Saturated 

emergent wetlands are characterized by poorly 

drained soils where the water table is at or very 

near the land surface. They are isolated pockets of 

low prairie, prairie fens or streamside swales and 

are most common in portions of Minnesota where 

a transition to aspen parklands begins at the PPR 

periphery.

Seasonally flooded 

emergent marsh; 

shallow marsh; 

seasonal ponds

Seasonally flooded

Seasonally flooded emergent wetlands are commonly 

referred to as shallow marshes. The soils are 

normally waterlogged during the growing season 

and surface water will persist for extended periods 

(30−90 days). Seasonal wetlands will usually lack 

appreciable standing water during the late summer 

months (July and August). These wetlands are 

subject to cropping and are often tilled later in the 

growing season. During dry years standing water 

may be absent.

Semi-permanently 

flooded emergent 

wetland; deep marsh; 

semi-permanent ponds

Semi-permanently 

flooded

These emergent wetlands are typified by the 

persistence of surface water throughout the growing 

season in most years. During years of normal 

precipitation, water is deep enough to support a 

variety of wildlife species including waterfowl and 

Muskrats (Ondatra zibethicus). Semi-permanent 

marshes will lack standing water in drought years 

and may be cropped or hayed.
16 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Table 4. Wetland, deepwater and upland classifications used in this study.

Freshwater Habitats Common Description

Palustrine forested Forested wetlands

Palustrine shrub Shrub wetlands

Palustrine emergents Marshes/sloughs/wet meadows

Palustrine unconsolidated bottom Open water ponds

Palustrine farmed Farmed wetlands

Lacustrine1 Lakes and reservoirs

Riverine1 River and stream channels

Upland Habitats Common Description

Agriculture Row-crop agriculture, farmsteads and supporting 

infrastructure

Urban Cities and incorporated developments

Rural development Non-urban developed areas and infrastructure

Other uplands Undeveloped, rural uplands not in any other category 

(i.e. barren lands, gravel pits)

Grasslands Native prairie, hay land, planted grasses, fallow fields, 

pasture, rangeland

Water Regimes Applicable to Wetland 

and Deepwater Habitats Common Description

Temporarily flooded Temporary ponds, low prairie wetland

Saturated Wet meadows, prairie fens, aspen parkland wetland

Seasonally flooded Seasonal ponds, shallow marsh

Semi-permanently flooded Semi-permanent ponds, dugout ponds, deep marsh

Intermittently exposed Alkali lakes, shallow lakes, deep marsh/open water

Permanently flooded Open water lakes, perennial rivers

1

Constitutes deepwater habitat.

Ephemeral waters10, which are not recognized as a wetland type, and certain types of “farmed wetlands” as 

defined by the Food Security Act11 were not included in 

this study because they do not meet the Cowardin et al. 

(1979) definition. 

10This refers to temporary surface water and should not be confused 

with ephemeral (temporary) wetlands.

11For purposes of administration of the Farm Bill legislation, some 

areas are identified as “prior converted” wetlands. These areas may or 

may not be wetland under the Cowardin et al. definition.

Wetlands and deepwater habitats are defined separately by Cowardin et al. (1979) because the term “wetland” does not include deep, permanent water bodies. 

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 in which the dominant 

organisms live, whether or not they are attached to the 

substrate. For the purposes of conducting status and 

trends work, all lacustrine (lake) and riverine (river) 

waters were considered deepwater habitats.
Figure 8. A single wetland basin in the Prairie Pothole Region may contain different zones reflecting hydrologic gradients 

depending on the persistence of surface water.

Temporarily flooded

Seasonally flooded

Semi-permanently flooded

Permanently flooded

Procedures17

Upland categories included lands not meeting the 

definition of either wetland or deepwater habitats. 

An abbreviated upland classification system patterned after the land classification scheme described 

by Anderson et al. (1976) was used to describe generalized upland land-use categories. For this study, an 

additional upland category of “grassland” was added. 

Different grass cover types are often difficult to 

distinguish using remotely sensed imagery (Wright 

and Wimberly 2013); consequently the grassland 

category included a broad range of grassland types 

including minimally managed or native grasslands, 

extensively managed hay land (i.e. alfalfa), pasture 

or rangeland, Conservation Reserve Program lands 

in perennial grass cover and fallow or retired cropland in grass. The definition of grassland as used in 

this study was similar to the description of grassland 

types used by the U.S. Department of Agriculture 

(Claassen et al. 2011).

Study Limitations

The identification and delineation of wetland habitats through image analysis formed the foundation 

for deriving the wetland status and trends data 

results reported here. Because of the limitations 

of aerial imagery as the primary data source to 

detect some wetlands, certain wetland types were 

excluded from the study. These limitations included 

the inability to detect some small (fractional acre) 

wetland areas and to accurately detect or monitor 

submerged aquatic vegetation. 
18 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Results

Status of Prairie Wetlands, 2009

In 2009, there were an estimated 6,427,350 acres 

(2,602,166 ha) of wetland in the PPR of the United 

States (±4.3 percent). The population of wetlands in 

the PPR represents 5.8 percent of the total area of 

wetlands found in the conterminous United States in 

2009. There were also an estimated 1,843,220 acres 

(746,240 ha) of deepwater lakes and rivers in the 

prairie region in 2009. 

In 2009, wetland accounted for 6.7 percent of the total 

surface area of the U.S. PPR. This is slightly higher 

than the national average of 5.5 percent found in the 

conterminous United States. Emergent marshes comprised about 87 percent of the total wetland area and 

93 percent of all wetland basins in the PPR. Wetlands 

classified with woody vegetation (wetland forest and 

shrubs collectively) composed 8.3 percent of the surface 

area and open water ponds 4 percent. Wetland area by 

vegetated type for the PPR is shown in Figure 9.

The estimated area for all wetland and deepwater 

habitats in the U.S. PPR is shown in Table 5. 

The distribution of wetland area by state in the PPR 

is shown in Figure 10. By area, wetlands were most 

common in North Dakota, making up 9 percent of the 

surface area in the PPR of that state. South Dakota 

was similar with 8.5 percent of the land area in the 

prairie region having been wetland in 2009. Minnesota 

had 6.7 percent wetland by area, Iowa 2.7 percent, 

and wetlands were the least common in Montana with 

1.9 percent of the land area classified as wetland in the 

prairie portions of the state.

The majority of forested and shrub wetlands 

(82.9 percent) were located in Minnesota as part of 

the transitional region from prairie to parkland/forest. 

Depressional wetland basins dominated by trees or 

shrubs (Figure 11) were scarce outside of this transition zone or as part of river or stream corridors.

An estimated 94 percent of wetland was within or 

adjacent to agricultural lands or grassland. Less than 

1 percent was within or adjacent to urban or developed 

areas, and about 5 percent was within or adjacent to 

other types of uplands or river corridors. 

Figure 9. Estimated wetland area (acres) by type as found in this study in the U.S. Prairie Pothole Region, 2009.

5,587,702

(86.9%)

292,884

(4.6%)

256,695

(4.0%) 238,473

(3.7%) 51,593

(<1%) Ponds

Farmed Wetland

Shrub Wetland

Forested Wetland

Emergent Wetland
Results

19

Table 5. Estimated area and change for all wetland and deepwater habitat types in the U.S. Prairie 

Pothole Region, 1997 to 2009. (The Coefficient of Variation [CV] for each estimate is given in parentheses.)

Habitat Type Area 1997 

(acres)

Area 2009 

(acres)

Change Area 

(acres)

Change as 

Percentage

Shrub wetland 284,553

(31.4)

238,473

(29.6)

-46,080

(93.4)

-16.2

Emergent 

wetland1

5,734,634

(3.7)

5,639,295

(3.8)

-95,339

(44.4)

-1.7

Forested wetland 231,606

(19.2)

292,884

(20.9)

61,277

(65.8)

26.5

Open water 

wetlands

250,895

(6.9)

256,695

(6.4)

5,800

(*)

2.3

All wetland 6,501,688

(4.2)

6,427,350

(4.3)

-74,340

(58.2)

-1.1

Lakes 1,656,989

(13.3)

1,712,502

(12.9)

55,513

(34.9)

3.4

Rivers 128,362

(14.1)

130,720

(14)

2,359

(66.2)

1.8

All deepwater 1,785,351

(12.3)

1,843,222

(12)

57,871

(33.6)

3.2

Total wetland 

and deepwater

8,287,039 8,270,572 -16,467 -0.2

1

Includes emergent and farmed wetland categories.

*

Statistically unreliable. 

Figure 10. Estimated wetland area in the U.S. Prairie Pothole Region, 2009. (Percentage shown is the land 

area of the Prairie Pothole Region that is wetland in each state.)

1,163,650

(6.70%)

2,847,680

(9.00%)

343,330

(1.9%)

201,890

1,870,790 (2.70%)

(8.50%)

North Dakota

Montana

South Dakota

Minnesota

Iowa
Figure 11. A depressional pothole basin with forest canopy in the Prairie Pothole Region of Minnesota. Pothole wetlands with 

woody vegetation (forest and shrubs) make up about 8 percent of the total area of wetland in the U.S. Prairie Pothole Region.

20 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

There were an estimated 21.1 million acres of grassland in the PPR in 2009. This represented a 3:1 ratio of 

grassland to wetland region-wide.

Wetlands were not distributed evenly across the PPR. 

The current wetland distribution is influenced by 

topography, hydrology and past conversions of wetland 

to other land uses. The relative wetland density by 

area in the PPR is shown in Figure 12.

In determining wetland/water basin number and type, 

this study utilized a geospatial model to account for 

spatial dominance of basin area by water regime type12. 

For example, a 10 acre (4 ha) basin containing 9 acres 

(3.6 ha) of seasonally flooded wetland with a 1 acre 

(0.4 ha) semi-permanently flooded portion would have 

been classified as a semi-permanently flooded basin by 

the protocols used in previous studies (Johnson and 

12Basin calculations excluded some wetlands within or connected to 

river or stream channels. Examples include gravel outwashes, sand bars 

and hydrologically connected oxbows.

Higgins 1997; Kahara et al. 2009), whereas this study 

recognized spatial dominance as a crucial factor in 

basin classification and categorized this type of wetland 

as a seasonally flooded basin. 

Wetland density based on basin type was determined 

on a per unit basis and was calculated using the 

equation: 

By using this method, wetlands and water bodies were 

distributed in 2,624,990 distinct basins throughout 

the PPR in 2009. An estimated 88 percent of these 

basins by count were geospatially isolated13. The 

13Geospatially isolated wetlands are those areas not having a direct 

connection to other water bodies or wetland complexes via channel or 

navigable water. Isolated wetlands were determined by a geospatial 

data model developed to identify wetlands not connected to or within a 

100 ft. (30 m.) buffer distance of navigable waters (rivers, streams, 

wetland complexes or permanent lakes). 

Density = Total basin number

Total landscape area
Utah

Wyoming

Drier Areas

Wetter Areas

Montana

Wyoming

North

Dakota

Nebraska

Minnesota

Iowa

South

Dakota

Results21

Figure 12. Relative wetland density based on wetland area in the U.S. Prairie Pothole Region, 2009. Wetlands were not 

distributed evenly across the prairie region. (Drier regions may have no wetland whereas wetter areas may contain up to 100+ 

wetland basins per square mile.) Current density and distribution has been influenced by topography, hydrology and past 

conversions of wetland to other land uses.
22 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

maximum density of wetland was 148 basins per mi2

(57 basins/km2) in portions of North Dakota. There was 

considerable variation in the density of wetlands across 

the landscape of the PPR. Wetland and water basins 

averaged from 30 per mi2 (12 basins/km2) in North 

Dakota to 4 and 5 basins per mi2 (1−2 basins/km2) in 

Iowa and Minnesota (Table 6). The mean number of 

wetland and water basins found in the PPR in 2009 was 

17.4 basins per mi2 (6.7 basins/km2). The mean basin size 

by state ranged from 2.1 acres (0.9 ha) in Montana to 

12.3 acres (5 ha) in Minnesota. The mean size wetland/

water basin in the PPR was 3.2 acres (1.3 ha) in 2009.

Wetland/water basins14 declined by over 107,177 or 

4 percent between 1997 and 2009.

Because wetland basin types in the PPR are dominated 

by emergent marshes (emergent wetlands made up 

93 percent of all wetland basins in the PPR in 2009), 

wetland resources have been described by using hydrologic characteristics (water regimes indicating flooding 

or ponding duration) to differentiate wetland type. The 

distribution of these emergent wetland types in 2009 is 

shown in Table 7.

14Basin numbers include wetland and lake (deepwater) basin types.

Temporarily flooded emergent wetlands were the most 

numerous type, composing almost half of all emergent 

wetland basins in the PPR. An estimated 41.7 percent 

of emergent basins were seasonally flooded, 6 percent 

were semi-permanently flooded and farmed wetlands 

made up an estimated 2.4 percent of all emergent wetland basins in 2009. There were very few (0.2 percent) 

saturated emergent wetland basins in the PPR.

By area, seasonally flooded emergent marshes had 

the greatest area with 2,313,660 acres (936,705 ha) 

followed by semi-permanently flooded marshes with 

1,945,460 acres (787,637 ha) and temporarily flooded 

wetland with 1,187,700 acres (480,850 ha). Collectively, 

temporarily flooded and seasonally flooded emergent 

wetland basins made up 85 percent of the total number 

of wetland basins (all wetland types) in the PPR and 

55 percent of the total wetland area.

The remaining other wetland/water body types 

that are not classified as emergent marshes include 

forested, shrub wetlands, open water ponds and 

lake basins. Pond numbers make up an estimated 

4.6 percent of the basin numbers. Shrub and forested 

wetlands were each about 1 percent and lake basins 

were less than 0.5 percent by basin number. All of the 

basin types and estimates sampled in this study are 

shown in Figure 13.

Table 6. Wetland and lake basin numbers, change, mean size and density for portions of the states in the U.S. Prairie Pothole 

Region, 1997 to 2009.

State Basin No. 

1997

Basin No. 

20091

Change in 

Basin No. 

1997–2009

Change

(percent)

Mean Basin 

Size 2009 

(acres)

Basin No. per 

Square Mile 

2009

Montana 199,754 201,312 1,558 0.8% 2.1 7

North Dakota 1,550,497 1,498,716 -51,781 -3.3% 2.5 30

South Dakota 774,568 752,943 -21,625 -2.8% 3.1 22

Minnesota 156,650 128,330 -28,320 -18.1% 12.3 5

Iowa 50,699 43,689 -7,010 -13.8% 5.8 4

U.S. Prairie 

Pothole Region

2,732,167 2,624,990 -110,718 -4% 3.2 17.4

1

Includes all wetland lake basins not directly associated with river channels.
Results

23

Table 7. Estimates of emergent wetland areal extent and basin number by type for the U.S. Prairie Pothole Region, 2009. 

(The Coefficient of Variation [CV] for the area estimate is given in parentheses.)

Emergent 

Wetland Type

Area 

in 2009 

(acres)

Area of 

Emergents

(percent)

Number 

of Basins

Mean Size 

(acres)

Basin 

Type

(percent)

Change 

in Basin 

No. 1997 to 

2009

Emergent-Temporary 1,187,700

(6.2)

21.1% 1,213,970 0.98 49.7% -102,574

Emergent-Seasonal 2,313,660

(4.2)

41% 1,019,940 2.26 41.7% -16,010

EmergentSemi-permanent1,945,460

7.1)

34.5% 147,040 13.23 6% 8,920

Farmed Wetland 51,590

(11.4)

0.9% 57,830 0.89 2.4% -9,072

Emergent-Saturated 140,8801

(42.2)

2.5% 6,010 23.45 0.2% -1,212

All Emergent 

Wetland Types 

5,639,295 100% 2,444,790 2.31 100% -119,948

1

Eighty eight percent of saturated emergent wetland area was in located in Minnesota. Many saturated wetland areas may not conform to “pothole” basin configuration but can occur as swales, meanders or fens.

Figure 13. Wetland basin numbers for all wetland classification types in the U.S. Prairie Pothole Region, 2009. 

1,213,967

1,019,940

147,036

121,342

57,827

6,008

22,815

27,897

Ponds

Farmed Wetland

Saturated Emergent 

Forested Wetland

Shrub Wetland

Semi-permanent Emergent 

Temporary Emergent

Seasonal Emergent
24 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Wetland basin distribution by type within the PPR 

states is shown in Table 8. The basin number for each 

wetland/water body type for states in the PPR indicates that North Dakota had the highest number of 

temporary emergent basins. Minnesota had the highest number of saturated emergent, shrub and forested 

wetland basins.

Table 8. Wetland basin number by wetland type for each of the states in the U.S. Prairie Pothole Region, 2009.

State Farmed 

Wetland

Temporary 

Emergent

Saturated 

Emergent

Seasonal 

Emergent

SemiPermanent 

Emergent

Ponds Shrub 

Wetland

Forested 

Wetland Lakes

Montana 0 96,729 2,105 66,872 6,569 25,667 2,358 420 590

North Dakota 29,991 677,163 906 661,099 80,053 34,776 8,445 3,160 3,125

South Dakota 11,591 398,386 295 250,220 43,101 40,465 2,069 4,750 2,068

Minnesota 12,671 26,875 2,701 31,632 12,971 13,227 14,827 11,448 1,978

Iowa 3,576 14,813 0 10,117 4,342 7,208 199 3,037 397

Trends in Wetlands 1997 to 2009

Between 1997 and 2009, total wetland area in the PPR 

declined by an estimated 74,340 acres (30,100 ha) or 

1.1 percent. This was an average annual net loss of 

6,200 acres (2,510 ha). However, emergent wetlands 

(emergent marshes and farmed wetlands) declined by 

an estimated 95,340 acres (36,250 ha) or 7,950 acres 

(3,020 ha) per year. Shrub wetlands also declined by 

46,080 acres (18,660 ha). Forested wetlands increased 

in area (61,280 acres or 24,810 ha), ameliorating some of 

the losses of emergent marsh and shrub wetland area. 

Open water ponds also increased in area by 5,800 acres 

(2,350 ha) over this 12 year period. Table 9 summarizes 

the changes in wetlands and deepwater habitats 

between 1997 and 2009.

Emergent wetlands (including farmed wetlands) 

declined by an estimated 1.7 percent between 1997 

and 2009. The largest percentage of the changes 

in area to emergent wetland was attributed to an 

increase in deepwater habitat. An estimated 40 percent 

(40,550 acres or 16,420 ha) of emergent wetland area 

was lost or converted to deepwater lake systems 

or open water ponds (Figure 14). An additional 

39,050 acres (15,810 ha) were lost to upland land uses 

(agriculture and development). All of the net wetland 

losses to agriculture were farmed wetlands or temporarily flooded wetlands.
Results

25

Table 9. Change in wetland, deepwater habitats and grassland area in the U.S. Prairie Pothole Region, 1997 to 2009. 

(The Coefficient of Variation [CV] for each estimate is given in parentheses.)

Habitat Type Area in 1997 

(acres)

Area in 2009 

(acres)

Change in 

Area 1997–2009 

(acres)

Change 

1997–2009

(percent)

Area of All PPR 

Wetland 2009

(percent)

Farmed wetland 96,900

(15.7)

51,590

(11.4)

-45,310

(30.1)

-46.8% 0.8%

Emergent—temporary 1,275,175

(5.9)

1,187,700

(6.2)

-87,480

(15.3)

-6.9% 18.5%

Emergent—saturated 156,700

(40.6)

140,880

(42.2)

-15,820

(45.5)

-10.1% 2.2%

Emergent—seasonal 2,304,090

(3.9)

2,313,660

(4.2)

9,570

(*)

0.4% 36%

Emergent—semi-permanent1,901,770

(7.2)

1,945,460

(7.1)

43,700

(63)

2.3% 30.3%

All emergent wetland 5,734,634

(3.7)

5,638,695

(3.8)

-95,339

(44.4)

-1.7% 87.7%

Open water ponds 250,895

(6.9)

256,695

(6.4)

5,800

(*)

2.3% 4%

Shrub—temporary 20,590

(23)

23,760

(21.9)

3,160

(52.7)

15.4% 0.4%

Shrub—saturated 161,180

(40.6)

115.480

(38.4)

-45,700

(92.9)

-28.4% 1.8%

Shrub—seasonal 102,780

(59.6)

99,240

(54.6)

-3,540

(*)

-3.5% 1.5%

All shrub wetland 284,550

(31.4)

238,470

(29.6)

-46,080

(93.4)

-16.2% 3.7%

Forested—temporary 95,290

(19)

97,570

(18.3)

2,280

(*)

2.4% 1.5%

Forested—saturated 77,900

(43.7)

130,970

(41)

53,080

(74.7)

68.1% 2%

Forested—seasonal 58,420

(23.1)

64,340

(28.3)

5,920

(*)

10.1% 1%

All forested wetland 231,610

(19.2)

292,880

(20.9)

61,280

(65.8)

26.5% 4.5%

All wetland types 6,501,688

(4.2)

6,427,350

(4.3)

-74,340

(58.2)

-1.1% 100%

Lakes 1,656,990

(13.3)

1,712,500

(12.9)

55,510

(34.9)

3.4% —

Rivers 128,362

(14)

130,720

(14.1)

2,360

(66.2)

1.8% —

Upland grassland 21,689,400

(4.1)

21,121,360

(4.2)

-568,040

(27.2)

-2.6% —

*

Statistically unreliable.
26 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

The mean size of wetland lost between 1997 and 2009 

as measured by this study was 0.85 acre (0.3 ha). An 

estimated 49 percent of the wetlands lost between 1997 

and 2009 were geospatially isolated wetlands15.

Minnesota sustained the largest loss of emergent 

wetland area between 1997 and 2009. South Dakota 

was the only state to exhibit gains in emergent wetland 

area (Figure 15).

The number of wetland and open water basins (including lake basins) in the PPR declined between 1997 

and 2009 by 107,177 or 4 percent. This was an average 

annual loss of 8,931 basins. 

15Geospatially isolated wetlands are those areas not having a direct 

connection to other water bodies via channel or navigable water. 

Isolated wetlands were determined by a geospatial data model developed 

to identify wetlands not connected to or within a 100 ft. (30 m.) buffer 

distance of navigable waters (rivers, streams or permanent lakes).

Ninety-six percent of the basins lost were temporarily 

flooded emergent wetlands as temporary basin numbers declined by 7.8 percent. Semi-permanent wetlands 

increased by 8,920 basins or 6.5 percent.

Overall, wetland basins declined in every state in the 

PPR with the exception of Montana, which experienced 

a gain in wetland basins of <1 percent. While North 

Dakota lost the largest number of wetland basins 

(51,780), Minnesota sustained the largest percentage 

loss of remaining wetland basins, declining by over 

18 percent. Iowa lost 14 percent of the remaining basin 

numbers, and both North and South Dakota each lost 

about 3 percent. Changes in basin number by state are 

shown in Figure 16.

All states except South Dakota experienced net losses in 

emergent wetland area. South Dakota had a net gain of 

an estimated 19,170 acres (7,760 ha). Emergent wetland 

changes are shown for each state in Figure 17 A–E. 

Figure 14. Attribution of gains (blue), losses (red) and conversions (yellow) of emergent wetlands in the U.S. 

Prairie Pothole Region to other upland land-use, wetland or deepwater types, 1997 to 2009.

5,000

-45,000

-40,000

-35,000

-30,000

-25,000

-20,000

-15,000

-10,000

-5,000

0

Acres

Ponds

Development

Grassland

Other Uplands

Agriculture

Woody 

Wetlands

Deepwater
Results

27

Figure 15. Emergent wetland gains (blue) and losses (red) in the U.S. Prairie Pothole Region, 1997 to 2009.

-100,000

-40,000

-80,000

-60,000

-20,000

20,000

0

Acres

Minnesota

Montana

North Dakota

South Dakota Iowa 

Figure 16. Wetland basin gains (blue) and losses (red) for each state in the U.S. Prairie Pothole Region, 1997 to 2009.

-60,000

-30,000

-50,000

-40,000

-20,000

10,000

0

Acres

-10,000

Minnesota

Montana

North Dakota

Iowa 

South Dakota
28 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Figure 17 A–E. Loss or conversion in area of emergent wetland hydrologic types 

and ponds in each of the states in the U.S. Prairie Pothole Region, 1997 to 2009.

A

4,000

Acres

3,000

2,000

1,000

-1,000

-2,000

-3,000

-4,000

0

Montana

B

Acres

5,000

-25,000

0

-15,000

-20,000

-10,000

-5,000

10,000

15,000

20,000

25,000

North Dakota

Farmed Wetland

Temporary Wetland

Saturated Wetland

Seasonal Wetland

Semi-permanent Wetland

Ponds
Results

29

C

Acres

-30,0000

-20,000

-10,000

10,000

20,000

30,000

South Dakota

D

Acres

5,000

-5,000

-40,0000

-30,000

-35,000

-25,000

-20,000

-10,000

-15,000

10,000

Minnesota

E

Acres

-20,0000

-15,000

-10,000

5,000

10,000

15,000

-5,000

Iowa
30 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Changes in Grassland Area, 1997 to 2009

Grassland occupied approximately 21,121,360 acres 

(8,551,158 ha) in the PPR in 2009 (±4.2 percent). 

Between 1997 and 2009, grassland declined overall by 

an estimated 568,040 acres (229,980 ha) or 2.6 percent. 

Ninety-five percent of the area lost from grassland 

was reclassified as agriculture. Another 4.8 percent 

of grassland was lost to development and a fractional 

percentage went to open water ponds and lakes. 

There was a small gain in upland grassland area from 

“other” uplands most likely, from planted grasses on 

managed conservation lands. 

Grassland area declined by 805,000 acres (325,910 ha) 

in the western prairie states of Montana, North Dakota 

and South Dakota. Minnesota and Iowa gained grassland area (236,960 acres or 95,935 ha) over the period 

of this study (Figure 18).

Figure 18. Gains (green) and losses (red) in upland grassland area within the U.S. Prairie Pothole Region, by state, 

1997 to 2009.

-600,000

-300,000

-500,000

-400,000

-200,000

100,000

0

Acres

-100,000

-700,000

200,000 Minnesota

Montana

North Dakota

Iowa 

South Dakota

This study estimated that region-wide the grassland to 

wetland ratio was 3:1 in 2009. An estimated 32 percent of all remaining wetlands in the PPR are within 

or directly adjacent to upland grasslands16. Montana 

had the highest ratio of grassland to wetland at 24:1. 

By contrast, the prairie region of Minnesota has more 

wetland than grassland with an estimated grassland 

to wetland ratio of 0.7:1. North Dakota, South Dakota 

and Iowa have similar ratios of 2.3:1; 2.7:1 and 2.5:1, 

respectively. 

16This was determined by geospatial analysis. The distance to grassland 

from wetlands other than those within or adjacent to grassland was 

undetermined.
Wetlands among the managed mixed-grass prairie of North Dakota.
32 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Discussion

Changes in Wetland Extent in the Prairie Pothole Region

The surface area that comprises the PPR represents 

about 4.8 percent of total surface area of the conterminous United States. This region is often discussed as an 

area of high ecological importance principally for migratory birds, waterfowl production and as an area continuing to experience wetland losses that directly affect the 

regional ecology. Past studies (Dahl 1990; Johnson et 

al. 1997; van der Valk and Pederson 2003) indicate that 

this region supported between 16.6 to 17 million acres 

(6.7 to 6.9 million ha) of wetland prior to settlement in 

the 1800s. The results of this study indicate that there 

were 6.4 million acres (2.6 million ha) of wetland 

remaining in 2009, a decline of 61 percent. 

From the period between 1997 and 2009, wetlands losses 

continued throughout the PPR. The average annual net 

loss of wetland was estimated to have been 6,200 acres 

(2,510 ha) over this 12 year time span. This rate of loss 

represents a disproportional amount of the total net 

wetland loss for the nation, estimated to have been 

13,800 acres (5,590 ha) between 2004 and 2009 (Dahl 

2011). Findings from this study support those conclusions as the PPR experienced a net loss of 74,340 acres 

(30,100 ha) between 1997 and 2009. 

Between 1997 and 2009, wetland area in the PPR 

declined by an estimated 1.1 percent. The number of 

wetland basins also declined over that period by 107,177. 

Small farmed wetlands and temporary wetlands experienced substantial losses. Conversely, semi-permanently 

flooded wetlands, open water ponds and deepwater 

lakes increased in area. In the PPR, temporary wetland area declined in all states between 1997 and 2009, 

whereas semi-permanent wetland area increased in all 

states with the exception of Minnesota. The remaining 

wetlands of the PPR were fewer in number and many 

exhibited changes in hydroperiod toward wetter conditions. When data from this study were compared to 

National Wetlands Inventory data (circa 1983—USFWS 

2014) the mean size of the remaining wetland population 

had increased from 2.1 acres (0.9 ha) in 1983 to 3.2 acres 

(1.3 ha) in 2009. This reflects the loss of many small wetlands over time. Figure 19 shows a longer term trend in 

wetland area for the primary wetland and water body 

types in the PPR. 

Emergent wetlands declined in the number of basins 

(119,948 or 4.7 percent) and area (95,340 acres [38,600 ha] 

or 1.7 percent) between 1997 and 2009. Of the principal 

emergent wetland types in the PPR, temporarily 

flooded emergent basins (including farmed wetland 

basins) declined in number by 8.1 percent and in area by 

9.7 percent. Seasonally flooded emergent basins declined

in number by 1.6 percent but increased in total area by 

0.4 percent. Semi-permanently flooded emergent basins 

increased both in number (6.5 percent) and area (2.3 percent). This difference between wetland gains and losses 

of basin numbers and wetland area was also observed by 

Kahara et al. (2009) in study areas in South Dakota. They 

hypothesized that some smaller wetland basins either 

merged together or merged with larger wetter basins, 

thus reducing basin number but increasing wetland area. 

In this study, an estimated 40 percent of the emergent 

wetland losses resulted from the expansion of deep, more 

permanent water areas.

Ninety-six percent of the wetland basins lost were classified

as temporary emergent wetlands. Gains in semi-permanent 

emergent wetland basins, open water ponds and lake basins 

offset some of the overall decline in basin numbers.

The size distribution of emergent marshes by hydrologic 

type indicated that temporary basins were most numerous, making up almost 50 percent of all emergent wetland 

basins in 2009 (Figure 20). Forty two percent were seasonally flooded basins. Although temporary emergent wetland 

basins were found to be the most numerous by basin type, 

these basins contained less area than either seasonal or 

semi-permanently flooded emergent wetlands. They were 

smaller in size, averaging 0.98 acres (0.4 ha) per temporary 

basin. Past wetlands studies in the PPR have also characterized wetland size with most wetland basins being small 

<1.2 acres (<0.5 ha) in area (Cowardin et al. 1981; Kantrud 

et al. 1989). 

The maximum density of wetland and water basins found 

in this study of 148 per mi2 (57/km2

) occurred in portions of 

North Dakota. This number exceeds past estimates of 

100 basins per mi2 (40/km2) reported by Kantrud et al.

(1989). Other estimates of wetland density for portions 

of the PPR17 have indicated an average 83 wetlands per 

mi2 or 32 wetlands per km2 (Zohrer 2001; USGAO 2007). 

This study estimated the mean wetland density by state 

in the PPR and found a range from a high of 30 wetland 

basins per mi2 (12 basins/km2) in North Dakota to 4 and 

5 basins per mi2 (1−2 basins/km2) in Iowa and Minnesota. 

The overall basin density for the PPR in this study was 

17.4 basins per mi2 (7 basins/km2) with an overall decline of 

4 percent in the total number of wetland and water basins 

in the PPR between 1997 and 2009. Minnesota experienced 

a loss of over 18 percent of the remaining wetland basins 

between 1997 and 2009. 

17Some studies estimated wetland density for only portions of the PPR and 

for different eras. 
Figure 20. This photograph shows a temporarily flooded wetland in a wheat field in late summer. 

Almost half of all emergent wetland basins in the U.S. Prairie Pothole Region are temporary 

wetlands.

Discussion33

Figure 19. Trends showing percentage of area for the primary wetland and water body types in the 

U.S. Prairie Pothole Region from 1983 to 2009. Temporary wetlands (including farmed wetlands) and 

seasonal wetland area have declined while semi-permanent wetland, open water ponds and deepwater 

lakes have increased in area. (Source: USFWS National Wetlands Inventory data; this study.)

35

30

25

20

15

10

5

0

Temporary Wetland

Seasonal Wetland

Semi-permanent Wetland

Ponds

Lakes

Area (percent)

2009

Circa 1983

1997
34 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Trends Affecting Wetland Changes in the PPR

In the U.S. PPR, wetland trends were driven by stressors 

on emergent wetlands. There were two primary factors 

influencing emergent wetlands observed in this study: The 

first involved climatic changes that effectively changed 

the hydrologic characteristics of wetlands by making some 

basins wetter and in some cases (i.e. semi-permanent 

wetlands) increasing wetland area. The second factor was 

the loss of wetland area due to drainage for agricultural 

production. Both of these processes exhibit nuances and 

complexities associated with how they interact at the landscape level in the PPR. 

In a simplistic analysis, increased water levels affected 

40 percent of the emergent wetlands by changing their 

hydroperiod to a wetter condition. Of the total emergent 

wetland area that experienced changes in hydroperiod, 

cover type or land use, 39 percent were lost to upland, 

primarily via conversion to agriculture (Figure 21). 

Figure 22 shows areas where wetland losses and gains 

occurred in the PPR between 1997 and 2009.

Figure 21. Attribution of changes to emergent wetlands in the 

U.S. Prairie Pothole Region, 1997 to 2009. Emergent wetland area 

declined by an estimated 95,340 acres (38,600 ha). Forty percent 

of the emergent wetland area was changed to deepwater lakes or 

ponds, 39 percent was lost to upland land uses and 21 percent was 

converted to other types of wetland.

40%

Open Water

Lakes/Ponds

21%

Other

Wetlands

39%

Uplands
Figure 22. Areas exhibiting changes in wetland hydrologic indicators, wetland loss or wetland gain in the U.S. Prairie Pothole 

Region, 1997 to 2009.

Montana

Wyoming

North

Dakota

Nebraska

Minnesota

Iowa

South

Dakota

Drier

Wetter

No Net Change

Discussion35
36 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Changes in Hydrology and Climate 

Most PPR wetlands and water basins are hydrologically closed systems, are sensitive to climate variability 

(Liu 2011) and demonstrate dramatic changes in water 

levels, size and distribution on the landscape. Longterm climate change in the PPR has the potential to 

alter temperature, precipitation amounts and patterns, 

length of the growing season and possibly timing and 

location of routes for migratory birds, all of which could 

result in changes to this regional ecosystem. Climatic 

changes may pose especially difficult challenges in the 

prairie regions of Iowa and Minnesota where a large 

majority of wetlands have already been effectively 

drained (Johnson et al. 2010).

Cyclical natural drawdowns in water levels due to 

unstable climatic conditions in the PPR are an important part of the “marsh cycle” (Weller 1981; van der 

Valk 1989; 2005). When surface water levels are low or 

non-existent (dry cycle), wetlands are in a drawdown 

stage allowing emergent or pioneer plant species to 

germinate. As precipitation cycles change to wetter 

conditions, increasing water levels selectively eliminate 

some of the less water-tolerant species and promote 

the growth of hydrophytes. At the high water portion 

of this cycle, prolonged inundation can kill the emergent vegetation and the wetland becomes dominated 

by open water. These wet and dry periods can persist 

for 10 to 20 years (Diaz 1986) and on a recurring cycle. 

An important issue in understanding the role of 

climate and climate change in the PPR involves distinctions between “normal” cyclical patterns of flooding and drought from longer term climatic changes 

that have the ability to alter wetland characteristics 

and landscape-level functions.

Precipitation (climate) plays a major role in what 

type(s) and how many wetlands are on the landscape 

in the PPR (Figure 23). However, wetland changes as 

determined from this study resulted from cumulative 

actions that changed wetland area, number and type 

that occurred between 1997 and 2009. Those impacts 

can be related to ecological change; changes in 

climate such as altered hydrology (e.g. flooding); 

anthropogenic changes such as draining, ditching or 

filling wetlands; or a combination these influences. 

Figure 23. Between 1997 and 2009 drier wetland types (shorter hydroperiod) declined as wetter types increased in area.

2,000,000

1,000,000

1997

2009

Semi-permanent

Wetland

Temporary

Wetland

Seasonal Wetland

Ponds and Lakes

Dry

Acres

Wet
Discussion

37

The Palmer Drought Severity Index (PDSI; Palmer 

1965) has been strongly correlated to water levels and 

wetland hydrologic status (Euliss and Mushet 2011; 

Johnston 2013) and is a good indicator of regional water 

conditions. By using this information, it was determined 

that the PPR was in a period of above average precipitation between the years covered by this study (Figure 

24) and portions of the region may be experiencing 

the wettest period in the past 130 years (Winter and 

Rosenberry 1998; Loesch et al. 2012; Johnston 2013). 

Prolonged periods of high water produce more lake-like 

conditions that can eliminate emergent wetland vegetation in basins that tend to hold water throughout the 

growing season or along the periphery of some pond/

lake margins (Figure 25). Water can also overflow from 

one basin to another, thereby creating new surface 

water connections. These high water conditions influence the areal extent and type (hydroperiod) of wetlands. It is not clear whether these periods of high 

water reflect cyclical fluctuations in precipitation or 

are indicative of longer-term climate change (Niemuth 

et al. 2010). Tying wetland gain, loss or change to a 

definitive cause does not always have a clear linkage, 

and in many cases there is no distinguishing between 

multiple drivers of change(s) that influence wetland 

resources. Consequently, it is difficult to quantify 

some of the changes associated with any specific factor 

affecting wetlands such as climate. 

Although climatic conditions are suspect in accounting for some wetlands merging with larger/wetter 

wetland basins as hydrology has shifted from a more 

temporary/seasonal status to semi-permanent or 

even lake-like conditions, wetland drainage practices 

may also contribute to this trend. Some wetlands are 

drained into other wetlands (Figure 26) or water bodies and increase the hydrologic connections that exist 

between basins as water is shunted off the landscape, 

forming more permanently flooded areas (McAllister et 

al. 2000). This study did not differentiate wetland loss/

gain or change explicitly due to climate in cases where 

anthropogenic factors (i.e. drainage) also strongly 

influenced some changes in wetland hydrology. For 

example, by using remote sensing it is difficult to 

Figure 24. The Palmer Drought Severity Index (Palmer 1965) is a meteorological drought index used to assess the severity 

of dry or wet conditions. The average PDSI values for all 25 climatic zones covering the U.S. Prairie Pothole Region between 

1995 and 2010 are shown here. Values above zero indicate periods of wet conditions and values below zero indicate periods of 

dry conditions.

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

-3

-2

-1

0

1

2

3

4

5

6

7
38 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Figure 25. Overflow basins have merged across a road crossing in North Dakota. These emergent wetland basins had become 

open water and increased in size due to prolonged periods of high water. The depth of the water prohibited the growth of 

emergent or aquatic vegetation.

distinguish between some wetland restoration projects 

(reflooding land) from other areas where wetland has 

been reestablished via wet climatic conditions (deluge 

or prolonged high water). 

Recent projections of regional climate change (Johnson et al. 2005; 2010) indicate prairie wetlands could 

potentially become drier with shorter hydroperiods for 

seasonal and semi-permanent wetlands in the western 

and central portions of the PPR. Those studies proposed that waterfowl management interests should 

consider shifting conservation efforts east and north, 

concluding that the areas in Minnesota and Iowa would 

provide more suitable waterfowl habitat under future 

climate projections. While there are many management considerations and constraints in this alternative 

approach (Loesch et al. 2012), there would also seem 

to be substantial social, economic and logistical challenges in this strategic shift in waterfowl management. 

Based on historical land-use patterns and recent wetland 

trend information, there may be insufficient wetland 

resources remaining in the prairie regions of those states 

to attract moderate to high numbers of breeding hens 

to successfully maintain waterfowl populations. In areas 

such as the Agassiz Lake Plain along the North Dakota/

South Dakota border, very few wetlands remain and 

this area would require extensive and costly wetland 

restoration efforts (Niemuth et al. 2009). This situation 

would also apply to other areas in Minnesota and Iowa 

where prairie wetlands have been extensively drained, 

and although topographic depressions (former wetland 

basins) remain, they lack wetland hydrology.
Discussion

39

Figure 26. An example of wetland drainage into a larger wetland/water complex, Kingsbury County, SD, circa 2010. The red 

arrows show areas of former wetland that are being drained for agriculture. Dark gray and black tones are indications of wet 

soils as surface water is being removed. This type of drainage not only eliminates some wetland area but changes the hydrology 

of the wetland basin receiving the water being shunted off the landscape.

Climate change models are predictive tools that forecast potential changes into the future. These hypothetical trends may not correspond directly to observed 

changes. Evidence from this study as well as other 

recent studies (Solberg et al. 2008; Niemuth et al. 2010) 

indicates that some wetland basins in the PPR have 

become wetter; however, the duration and sustainability of this trend is unclear and will depend on additional 

information that will help distinguish between cyclical 

weather patterns versus longer term climate change. 

Due to natural variability of precipitation trends in 

the PPR, shorter term studies such as this (<15 years) 

may not reflect long-term climate trends and should 

not be used to support or dispute arguments regarding climatic changes or draw conclusions beyond the 

intended use.

Climate change should be viewed as a potential source 

of environmental variability (Nichols et al. 2011) that, 

along with other stressors, undoubtedly contribute to 

the overall landscape-level changes that influence wetland distribution and characteristics in the PPR.
The Effects of Development and Agriculture

Wetland losses to development between 1997 and 

2009 included 1,420 acres (575 ha) lost to urban and 

suburban development (Figure 27) and accounted for 

an estimated 5 percent of the wetland lost to uplands 

over the course of this study.

Loss of wetlands to agriculture accounted for about 

95 percent of the wetland area lost to uplands between 

1997 and 2009. The impacts of agriculture on wetlands 

in the PPR vary. Threats to the ecological integrity of 

wetlands related to agricultural practices can result in 

direct habitat loss from wetland drainage or indirect 

effects (Figure 28) such as pesticide-induced loss of 

invertebrate populations in wetlands and water bodies 

(Beyersbergen et al. 2004). 

Farmed wetlands are wetlands that have been tilled 

for agriculture but retain their wetland characteristics. For example, it was not uncommon in the prairie 

region for some shallow, temporary wetlands to be 

dry in certain years, depending on the amount of snow 

cover and early spring precipitation. Under these drier 

conditions, wetlands may be tilled and planted for crop 

production, but in wetter years return as shallow emergent marshes. Because of the wet and dry cycles experienced in the prairies, many wetlands have a history of 

being intermittently cropped (Figure 29). Reynolds 

et al. (2006) assumed that small wetlands (<1 acre or 

0.4 ha) that were temporarily or seasonally flooded 

could be farmed in most years and were the most likely 

wetland type to be drained and converted to cropland. 

Figure 27. Filling a wetland for urban development near Devils Lake, ND. Development such as this accounted for 5 percent of 

all wetland losses between 1997 and 2009.

40 Status and Trends of Prairie Wetlands in the United States 1997 to 2009
Figure 28. The effects of drift from chemical applications to this farm field impact this emergent wetland in the prairie region 

of North Dakota as evident by the discoloration of the remaining vegetation. Grue et al. (1989) noted this impact to wetlands in 

agricultural fields as the effects of land use on wetlands can be varied.

Discussion41
Figure 29. A farmed wetland in North Dakota’s Prairie Pothole Region with remnant wetland vegetation in the center portion 

of the basin. Drier conditions allowed this wetland to be tilled, but because this basin is not artificially drained, the area should 

return to wetland if farming is discontinued.

42 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

The losses of wetland to agriculture between 1997 and 

2009 focused on the conversion of farmed wetlands and 

small temporarily flooded emergent wetland basins. 

Net losses attributed to agriculture involved these 

wetland types. In a period of high water, temporarily 

flooded and farmed wetlands would also experience 

prolonged periods of ponded water, making farming 

without artificial drainage difficult. In Iowa, some 

effectively drained former wetland basins were holding 

ephemeral water during the growing season (Figure 

30). However, high water conditions may not always 

result in increases in wetland area, because these 

conditions have the potential to stimulate additional 

drainage in efforts to remove water, especially in small 

temporary basins that have an established history of 

farming. This drainage can be done effectively and 

without penalty under existing regulations and the 

costs may be off-set by higher crop prices.

This study found that between 1997 and 2009 farmed 

wetlands declined by an estimated 45,310 acres (18,340 ha). 

An estimated 6,175 acres (2,500 ha) or 13.6 percent of 

these areas were converted to other wetland types, 

primarily seasonal or semi-permanent marshes, either 

by way of abandonment of farming practices, wetland 

restoration efforts or as a result of wetter climatic conditions. The majority of farmed wetlands (86.4 percent) 

that were no longer considered to be wetland were 

converted to upland agriculture. The loss of farmed 

wetland to upland agriculture was determined by the 

loss by wetland hydrology (i.e. drainage via ditching, 

tile drains or land leveling [fill] in some cases). These 

farmed wetlands are very vulnerable to drainage 

because they are usually small, in close proximity to 

existing farm field operations and can be easily drained, 

usually without penalty under existing regulations. 
Figure 30. A historic wetland basin in Iowa (effectively drained by subsurface tile) has been flooded by recent rain storms 

and holds ephemeral surface water that will persist for only a few days under normal conditions. 

Discussion43

The loss or degradation of these wetlands is deleterious 

to shorebird utilization for feeding in shallow water or 

exposed mudflats that support aquatic invertebrates.

Recently there has been renewed interest and 

increased installation of subsurface tile drainage 

systems that effectively drained some wetlands in 

this region (Blann et al. 2009). Subsurface tile drainage systems have been popular with some landowners for removing surface waters and wetlands in both 

southwestern Minnesota and Iowa, and this trend has 

extended into portions of the Dakotas. In portions of 

the prairie region, pattern tile drainage systems are 

being installed to replace aging networks of tile drains 

and to further facilitate drainage in agricultural fields. 

In some areas, these drainage networks are so extensive they have effectively altered regional hydrology 

(Galatowitsch and van der Valk 1994; Dahl 2011) and 

may have ramifications for the success of any future 

wetland restoration projects that attempt to reestablish hydrologic connectivity to wetland complexes. 

It is evident that small, temporary and seasonal 

wetland basins contribute substantially to the overall 

make-up of the wetland resource base in the PPR. 

Temporary wetlands are a major component of the 

wetland ecosystem both in terms of function and area, 

comprising an estimated 49 percent of all remaining wetland basins in 2009, and losses of temporary 

and farmed wetland area approached 133,000 acres 

(53,700 ha) between 1997 and 2009. The loss of these 

temporarily flooded wetlands is important, and 

although they are typically smaller in size than other 

wetlands, they determine the carrying capacity of a 
44 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

PPR landscape. Because these wetlands are 

disproportionally used by breeding waterfowl, their 

disappearance can disrupt habitat connectivity and 

reduce diversity (Beyersbergen et al. 2004). 

Researchers have found that a variety of wetland types 

and sizes is essential to sustain waterfowl populations as well as other ecological processes, and the 

importance of small, temporary basins to waterfowl in 

the PPR has been well documented (Batt et al. 1989; 

Swanson and Duebbert 1989). Johnson and Hubbard 

(1998) have shown that the density of ducks during the 

breeding season is inversely related to wetland size 

as seen in Figure 31. Early in the spring female ducks 

feed at temporarily flooded wetlands to satisfy protein demands for egg production (Krapu and Swanson 

1975). As breeding pairs isolate themselves to establish territories, they use seasonally flooded wetlands 

and require more space (generally larger wetlands) to 

maintain a degree of isolation for courting and breeding (Murkin and Caldwell 2000). Later in the season 

duck broods tend to move to deeper marshes and ponds 

ringed with emergent vegetation and more persistent 

water conditions (Flake and Vohs 1979). Thus, wetland 

complexes, made up of wetlands of various sizes and 

types, support greater species richness compared to 

single, isolated basins (Naugle et al. 1999). 

The interrelationship between different wetland 

types and uplands that form habitat complexes supports other birds and animals (Skagen and Knopf 1994; 

Leibowitz and Vining 2003). For example, migrating 

shorebirds are influenced by the regional location and 

availability of such wetland complexes.

Temporarily flooded wetland basins are particularly 

important as components of these larger wetland clusters or complexes. However, because these wetlands 

are typically small basins (<1 acre or 0.4 ha) that are 

only temporarily flooded early in the growling season, 

they tend to be more vulnerable to agricultural activities (Bartzen et al. 2010). 

Temporarily flooded and farmed wetland basins were 

lost to agriculture even during periods of abnormally 

high precipitation. The prairie region of Minnesota 

experienced the highest loss and conversion rate of 

emergent wetland, totaling 74 percent of all emergent 

wetland changes measured in the PPR between 1997 

and 2009. An estimated 36 percent were lost to deepwater lakes, 34 percent to agriculture, 23 percent were 

converted to forest or shrub wetlands, 4.5 percent to 

open water ponds and 2.5 percent were lost to other 

types of upland development.

A number of studies have shown that agricultural 

drainage continues to be one of the greatest threats to 

wetlands in the PPR (van der Valk and Pederson 2003; 

USGAO 2007; Blann et al. 2009; Johnston 2013). The 

continuing emphasis on increased crop production for 

biofuels places additional pressure on wetland conversion to agriculture in the PPR (Fargione et al. 2009; 

Johnston 2013). Drainage can have multiple impacts on 

wetland complexes by decreasing the area of wetland 

as well as decreasing the spatial and temporal frequency of surface water connections formed between 

basins during periods of high water (Leibowitz and 

Vining 2003). Wetland drainage may also lead to flooding downstream as water is quickly moved off from the 

landscape and into streams, channels or other drainage 

systems. 

Despite these deleterious effects, the majority of emergent wetland restoration or creation in the PPR stems 

from conservation programs on agricultural lands or 

agricultural land management approaches. Conservation provisions as part of the Farm Bill legislation have 

deterred some wetland drainage for crop production in 

the Dakotas, but have not totally eliminated wetland 

losses to agriculture (Johnston 2013). Studies indicate 

that considerable wetland gains (upwards of 59 percent 

of wetland restoration or creation) by area occurred on 

agricultural lands between 1997 and 2007 (U.S. Department of Agriculture 2010).

Background photo, right, Northern Shovelers (Anas clypeata) on 

a prairie wetland.
0

0.2

0.4

0.6

0.8

1.2

1.0

Temporary 

Wetland

Wetland Type

Seasonal 

Wetland

Semi-permanent 

Wetland

Permanent 

Water

Smaller Larger

Duck Pairs

per Wetland Acre

45

Figure 31. The density of breeding duck pairs in the spring is inversely related to wetland size where size 

increases with water permanence. (Adapted from Johnson and Hubbard 1998.)
46 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Wetland Restoration

The objective of most wetland restorations is to 

mitigate some of the past loss of wetland habitat. 

Cumulative wetland losses, due primarily to drainage 

for agriculture, have altered the landscape patterns 

and hydrology of the remaining wetlands in the PPR. 

Portions of this region have transitioned from areas of 

wetland clusters consisting of diverse wetland types 

and sizes to fewer, more isolated and more permanent 

wetlands and water bodies (Krapu et al. 2004; Bann et 

al. 2009). Given this extensive wetland drainage, it is 

unrealistic to restore wetlands in the PPR to mirror 

their historic extent or spatial distribution. Restored 

wetlands are usually more isolated because there are 

relatively few of them and they are not normally part 

of wetland complexes (Galatowitsch and van der Valk 

1994). As a consequence, at the landscape level, areas 

that have restored wetland(s) are very different from 

pre-settlement conditions.

Because losses of prairie pothole wetlands typically 

involve water drainage via a single outlet ditch or the 

tile drain, the potential for restoration on agricultural 

lands is much higher than if the lands were developed 

as part of urban areas or the basins were filled and 

leveled. 

This study found an estimated 87,690 acres (35,500 ha) 

of emergent wetland reestablished from agricultural 

lands between 1997 and 2009. However, pressures to 

put lands into agricultural production outdistanced 

area gains. Wetland restoration or creation actions 

were overshadowed by losses of 125,400 acres (50,770 ha) 

of emergent wetland resulting in a net loss of 37,700 acres 

(15,270 ha) attributed to agriculture over the 12 year 

period of this study. 

There has been considerable wetland restoration activity in the PPR since the passage of the Food Security 

Act in 1985 (Galatowitsch and van der Valk 1994; 

Bishop 2006). The restoration of wetland and grassland 

in the PPR has been a priority for resource management agencies in both the U.S. Department of the 

Interior and U.S. Department of Agriculture for some 

time (Gleason et al. 2008). The USFWS has developed 

goals in collaboration with conservation and land-use agencies for restoring an additional 682,000 acres (276,110 ha) 

of wetland in the PPR (USGAO 2007). Some states 

have also undertaken efforts to restore prairie landscapes. For example, the Iowa Department of Natural 

Resources has placed major emphasis on land acquisition in the PPR of Iowa and has identified potential 

wetland complexes, targeted land acquisition priorities 

and restored wetland and upland habitats (Zohrer 2001; 

Bishop 2006). Substantial state funding in Minnesota is 

also contributing to wetland and prairie restoration in 

the PPR region of that state (MNDNR 1997). 

Although there is no comprehensive accounting of all 

restoration actions, regional studies such as reported 

by Galatowitsch and van der Valk (1996), have provided 

information about restoration numbers and characteristics. These studies indicated wetland restorations in 

the PPR are usually small areas (less than 10 acres or 

4 ha), and they have tended to have wetter hydroperiods (seasonally or semi-permanently flooded). In this 

study, wetlands reestablished from agricultural lands 

(Figure 32) averaged 5.8 acres or 2.4 ha. Temporary 

wetlands have been under-represented in restoration projects compared to their historic number and 

extent (Galatowitsch and van der Valk 1996), and that 

trend has continued over the period of this study as 

the majority of restorations were seasonal and semipermanent wetlands. 

Wetland restoration programs at the state and federal 

level have become more common as federal policy has 

shifted away from regulation to an incentive-based 

approach to reduce wetland losses and promote conservation and/or restoration of wetland areas (Dahl 2011). 

The federal resource agencies supporting wetland 

restoration work consider regional and programmatic 

priorities, available funding and technical limitations 

and depend largely on willing landowner participation. 

These programs have realized successes in increasing 

the area of wetland restored or created on a national 

level (Dahl 2006), but since current estimates of wetland area losses in the PPR outdistance wetland gains, 

a no-net-loss goal for this region has yet to be achieved. 

Despite ongoing efforts to restore wetland habitats in 

the PPR, current land-use trends and market forces 

continue to encourage wetland drainage and point to 

continued habitat losses in this region (USGAO 2007). 
Figure 32. A temporary wetland as part of a conservation easement on former agricultural land in Minnesota’s prairie 

region, 2009. This wetland reestablished naturally once farming was discontinued.

Discussion47
48 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

Federal Wetland Protection Mechanisms in the Prairie Pothole Region

The Federal Government has a multi-faceted role in 

the protection of prairie wetland resources. This role 

includes mechanisms for wetland regulation (including 

mitigation of losses), incentive programs for conservation, land acquisition and conservation easement 

programs. 

Section 404 of the Clean Water Act (CWA) established 

a permit program to regulate the discharge of dredged 

or fill material into the waters of the United States, 

including wetlands. CWA Section 404(f) exempts from 

regulation discharges associated with certain specified activities, provided the discharges do not convert 

an area of waters of the United States to a new use, 

and do not impair the flow or circulation of waters of 

the United States or reduce the reach of waters of 

the United States. For example, a permit is generally 

not needed for discharges of dredged or fill material 

associated with normal farming, ranching and forestry 

activities, such as plowing, cultivating, minor drainage 

and harvesting for the production of food, fiber and 

forest products or upland soil and water conservation 

practices. This exemption pertains to normal farming 

and harvesting activities that are part of established, 

ongoing farming or forestry operations.

Federal legislation to reduce wetland destruction 

under the CWA has been subject to various interpretations as to its ability to include or exclude prairie 

pothole wetlands (Johnson and Higgins 1997; van der 

Valk and Pederson 2003). Supreme Court decisions 

regarding the exclusion of some “isolated” wetlands 

have further ramifications. This study estimated that 

88 percent of wetlands and water bodies in the PPR are 

geospatially isolated from navigable waters, streams, 

larger wetland complexes or river systems. Following 

a Supreme Court decision in 2001 relating to federal 

jurisdiction over wetlands (SWANCC18), van der Valk 

and Pederson (2003) concluded that the majority of 

wetlands in the PPR were no longer considered waters 

of the United States and thus not afforded federal protection under the CWA. More recently, Johnston (2013) 

recognized that federal permits are not required under 

the CWA for agricultural uses of isolated wetlands and 

consequently many wetland losses to row crops have 

gone unrecognized by federal regulatory agencies in 

North and South Dakota. 

18Solid Waste Management Agencies of Northern Cook County v. 

United States Army Corps of Engineers [531 U.S. 159 - SWANCC].

In an agreement reached between the principle federal 

agencies, the U.S. Army Corps of Engineers delegated 

the lead for identifying wetlands on agricultural 

lands to the U.S. Department of Agriculture–Natural 

Resources Conservation Service for purposes of implementing the Swampbuster program19 (U.S. EPA 2013). 

Under the Swampbuster provision of the 1985 and subsequent Farm Bill legislation, wetlands with an established history of cropping prior to 1985 are termed 

“converted” or “prior converted” croplands, are not 

considered waters of the United States and are exempt 

from regulation under Section 404 of the CWA. Prior 

converted croplands are also exempt from the wetland 

conservation (Swampbuster) provisions. In the PPR, 

where the transitory nature of surface water allows 

even some of the deepest emergent marshes to dry 

sufficiently and have an established history of cropping, 

there are very few prairie wetlands on private lands 

that appear to have any federal protection status either 

through CWA (because they are likely to be considered 

“isolated”) or through other exemptions in the Farm 

Bill legislation (because of past cropping practices). The 

lack of federal protection may also exclude areas that 

have recently become more permanent water features 

on the landscape as a result of hydrologic changes 

(Figure 33) as well as other “isolated” wetlands that 

have been restored. Other mechanisms for conserving 

PPR wetland resources that are especially important 

are the conservation provisions of Farm Bill legislation that include agricultural incentive programs 

linked to wetland conservation, such as the Conservation Reserve Program or Agricultural Conservation 

Easement Programs20. Federal wetland acquisition 

and easement programs in the PPR also have added 

importance. 

To this end, the USFWS acquires wetlands and related 

areas either by outright purchase (fee title) of land 

or through the purchase of conservation easements. 

Areas purchased in fee title are owned by the USFWS 

and are usually open to wildlife-oriented public use. 

Wetlands with conservation easements remain under 

control of the private landowner, but draining, leveling 

or filling of wetlands is prohibited under terms of the 

agreement. The objectives of the USFWS in acquiring 

lands in the PPR are to preserve wetland functions 

19NRCS wetland determinations may not be valid for determining 

Clean Water Act jurisdiction on a specific site.

20The Agricultural Act of 2014 established the Agricultural 

Conservation Easement Program.
Figure 33. Increased water levels in some areas of the U.S. Prairie Pothole Region have reclaimed some wetland shallow 

lake basins. However, because of established land-use practices, federal regulations likely will not accommodate extending 

protection status to these areas. North Dakota, 2013.

Discussion49

(i.e. waterfowl habitat) and eliminate the threat of future 

drainage of properties of high resource value. Ideally, 

land acquisition programs in the PPR should seek to 

protect or restore features that represent the natural 

size, type and distribution of wetland basins historically found on the prairie landscape. However, this is 

not always possible given the extent of past drainage 

and wetland loss and changes in size, type and distribution of wetlands from historic patterns to simply what 

remains. Land acquisition for conservation purposes is 

often on a willing seller basis. Consequently the most 

desirable or the most threatened wetland areas may 

not be available for purchase.

Restored wetlands that are smaller, isolated basins are 

not protected by current legislation in many jurisdictions (Blann et al. 2009) unless they are part of a 

contractual easement agreement or land acquisition 

from a resource agency/organization. As an example, 

the USFWS had acquired perpetual, limited interest 

easements on 543,000 acres (219,840 ha) of wetland as 

of 2012 (USFWS 2012). U.S. Fish and Wildlife Service 

easement wetlands account for about 8.5 percent of the 

remaining wetland area in the PPR. Approximately 

70 percent of the remaining prairie wetlands are in 

private ownership and largely unprotected by federal 

mechanisms.
Trends in Grassland Habitat

Because of the important relationship between upland 

grasslands and wetlands in the PPR, examination of 

recent changes in grassland area helps to understand 

landscape-level impacts and trends. In this study, 

grasslands were generalized to include an array of 

lands that produce legumes, forbs or grasses20. There is 

inherently some overlap between grassland as defined 

in this study with agricultural lands. For example, 

agricultural fields planted to alfalfa as a crop rotation 

practice or fallow fields are still agricultural lands that 

produce “grass.” The juxtaposition and extent of these 

lands complement wetlands monitoring efforts in the 

PPR.

20This study was not intended to be an authoritative source regarding 

upland land use characteristics or extent. Other monitoring efforts such 

as the Natural Resources Inventory (NRI) conducted by the Natural 

Resources Conservation Service provide more complete data on farmland 

and land-use categories for non-federal, rural lands. 

This study estimated that grassland occupied about 

21.1 million acres (8.6 million ha) or 22 percent of the 

land area in the PPR in 2009. The density of grassland 

in the PPR as found in this study is shown in Figure 34.

Net losses of grassland between 1997 and 2009 totaled 

568,040 acres (229,980 ha) or 2.6 percent of the grassland area. The annual rate of loss of grassland area 

was estimated at 0.2 percent. An estimated 95 percent 

of the grassland area lost between 1997 and 2009 was 

attributed to agricultural operations, primarily crop 

production. Development (urban and rural construction) accounted for the loss of 4 percent of the grassland area. About 1 percent was lost to open water 

habitats such as lakes, rivers or ponds and less than 

1 percent was converted to wetland.

Figure 34. Density of upland grassland in the U.S. Prairie Pothole Region, 2009.

Montana

Wyoming

North

Dakota

Nebraska

Minnesota

Iowa

South

Dakota

Low

High

50 Status and Trends of Prairie Wetlands in the United States 1997 to 2009
Grassland buffers around wetlands can have important 

beneficial effects on wetland water quality and increase 

the suitability of habitat for wetland-dependent wildlife. Euliss et al. (1999) noted that increased siltation, 

contamination from agricultural chemicals, altered 

hydrology and habitat fragmentation resulting from 

wetland drainage and the conversion of native grasslands to agriculture impacted wetland systems. Tilling 

the upland directly adjacent to wetlands can increase 

sediment inputs to PPR wetlands by several orders 

of magnitude (Gleason and Euliss 1998) and grassland 

buffers adjacent to wetlands and streams have been 

shown to greatly reduce sedimentation and improve 

water quality (Figure 35).

Both wetland and grassland habitats are also essential 

for maintaining waterfowl populations at current levels 

(Loesch et al. 2012). Various strategies relating to the 

conservation of grasslands to support bird populations 

have emphasized the importance of landscape-level 

interactions between wetland and interconnected 

uplands in order to sustain healthy bird populations. 

Upland grasslands connected or in close proximity to 

wetlands are crucial for nesting waterfowl and a variety of other birds and wildlife species (Figure 36). The 

USFWS’s National Wildlife Refuge System and the 

Partners for Fish and Wildlife Program have restored 

some of the historic grasslands in the PPR in efforts 

to expand grassland habitats (Johnson et al. 2010), and 

many wildlife managers have made the protection and 

restoration of grassland cover a priority for lands managed for waterfowl production throughout the PPR 

(Reynolds et al. 2006; Pardieck and Sauer 2007). 

Figure 35. Soil erosion and sedimentation can adversely affect wetlands as seen in this photograph from the prairie region 

in Minnesota. Grassland buffers help reduce these impacts.

Discussion51
Figure 36. Upland grassland adjacent to wetlands provides valuable habitat for waterfowl and other wildlife in the 

U.S. Prairie Pothole Region (Mclean County, ND).

52 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

In the past, the conversion of grasslands to agriculture 

in the central portion of the United States has significantly influenced declines in some bird populations 

(Peterjohn and Sauer 1999; Murphy 2003; Johnson et 

al. 2010). Over time, grassland area has diminished 

substantially in the PPR and recent evidence suggests 

that grasslands continue to be lost with many potential 

ecological consequences (Rashford et al. 2010; Claassen et al. 2011; Wright and Wimberly 2013). A number 

of studies (Johnson 1996; Mac et al. 1998; Stephens et 

al. 2008; Fargione et al. 2009; Johnson et al. 2010) have 

pointed to declines in grassland area as an indicator of 

an alarming land-use trend in the PPR.

This study found that any land-use change to the 

remaining grasslands in the PPR has the ability to 

directly impact up to 32 percent of the remaining 

wetlands that are either surrounded by or directly 

adjacent to grassland areas. The elimination of grass 

may not result in direct wetland loss but certainly 

can influence wetland condition and landscape function by increasing sedimentation, runoff of chemicals 

or nutrients, or by otherwise reducing or eliminating 

surrounding habitat suitability (Figure 37). Based on 

economic analysis, Rashford et al. (2010) predicted that 

grassland to cropland conversion will increase if agricultural commodity prices continue to follow recent trends.

Concern about the effect of federal agricultural programs on grassland to cropland conversion has been 

growing over the past number of years. In a recent 

study, agricultural producers in the Northern Plains 

states were more likely to convert grassland to cropland or retain land in crops rather than return it to 

grass (Claassen et al. 2011), likely due to high commodity prices for corn and soybeans resulting from demand 

for biofuel production (Wright and Wimberly 2013). 

The role of federal crop insurance and disaster relief 

programs may also mitigate the risk of crop failure due 

to flooding or drought as some marginal lands are put 

into crop production (Faber et al. 2012). In Minnesota, 

researchers have found a high proportion of grassland 

conversion on lands with excess wetness that will likely 

lead to additional drainage (Wright and Wimberly 2013). 
Figure 37. Wetlands without grassland buffers are subject to additional environmental stressors and potentially provide 

less suitable habitat than wetlands with grassland buffers.

Discussion53

Contributing to this trend has been a reduction in the 

number of acres enrolled in agricultural conservation 

programs. Targeting the conservation or restoration of 

native prairie and promoting the expansion of upland 

grasslands found in conjunction with wetlands are 

important mechanisms for increasing upland-nesting 

waterfowl habitat. Some federal programs important 

for grassland conservation and restoration include the 

Conservation Reserve Program (CRP), which pays 

farmers to establish and maintain grassland (or trees) 

on former cropland based on a rental payment over 

a fixed time period. This program was designed to 

increase wildlife habitat and help improve water quality by limiting nutrient runoff and sedimentation. The 

CRP has been a major factor in returning croplands to 

grass in the prairie region. However, when crop prices 

are high or payments are available for farmers to produce crops, this can encourage grassland to cropland 

conversion and work at cross purposes with conservation programs such as CRP. In 2007 and 2008 the area 

of lands enrolled in the CRP shrank as higher prices 

for corn and soybeans resulted in more land being used 

for crop production (Miller 2008). In 2007 alone, CRP 

acreage in North Dakota declined by 12.4 percent 

(Wilson 2008) as incentives for corn production for 

biofuels resulted in additional acreage put into row 

crop agriculture. 

While the interaction between grassland and row crop 

agriculture is the primary cause for land use change in 

the PPR, some grassland was also lost to non-agricultural land uses. An estimated 27,310 acres (11,060 ha) 

were developed as a result of expanding urban areas 

and infrastructure in the PPR between 1997 and 2009. 

Loss of grassland habitat has also been reported owing 

to planting trees and suppression of grazing and fire in 

the prairie region (Bakker 2003; Quamen 2007).

55

Summary

Past wetland drainage in the PPR has been extensive 

and has altered the landscape and hydrology considerably. This long-term trend continues to change the 

complexion of prairie wetlands from one of diverse 

wetland sizes and types to fewer wetland basins 

characterized by longer hydroperiods. Prolonged high 

water conditions may be contributing to this situation 

as many small wetland basins that flooded and dried 

on an intermittent basis move toward becoming larger, 

more permanent wetland/water basins.

The losses of wetland to agriculture between 1997 

and 2009 were due to the conversion of farmed wetlands and small temporarily flooded emergent wetland 

basins. In some areas, these agricultural drainage 

networks are so extensive they have effectively altered 

regional hydrology and may have ramifications for the 

success of any future wetland restoration projects that 

attempt to reestablish hydrologic connectivity to wetland complexes. Additional wetland losses and impacts 

are still a concern due to these cumulative effects and 

other changes to wetland hydrology exhibited in this 

region. Geospatially isolated wetland basins in the 

PPR are generally not likely to be protected by current federal regulatory or legislative jurisdiction. This 

places added importance on conservation measures 

that target agricultural program incentives to conserve 

wetland resources.

There has always been a close correlation between 

declines in waterfowl population numbers and the 

decline in wetland area in the PPR. In the United 

States the amount and quality of waterfowl habitat 

decreased substantially up until the early 1980s as 

wetland drainage, regionally dry conditions and the 

loss of grassland adversely affected the amount and 

quality of habitat. The continued loss and degradation 

of waterfowl habitat is one of the most serious threats 

facing waterfowl populations today. The loss of grassland in the PPR is particularly disturbing because this 

has been shown to seriously reduce bird populations, 

influence sedimentation rates and impair water quality 

in remaining wetlands and surface waters. Grassland 

conversion to other land uses will further reduce wildlife diversity across this region and have other environmental effects. 

Climate change, along with other stressors, undoubtedly contribute to the overall landscape-level changes 

that influence wetland distribution and characteristics 

in the PPR. However, there are often multiple drivers 

of change and linking wetland changes to a definitive 

cause such as climate may not be straightforward. 

Despite efforts to conserve and restore wetlands in the 

PPR, these resources continue to decline in number, 

diversity and extent. This puts the future of wetlands 

and prairie ecosystems in general in flux, depending 

upon climatic shifts in temperature and precipitation 

with the compounding influences of anthropogenic 

alterations to local and regional land use and hydrology. 

A prairie pothole wetland with a mix of emergent and aquatic 

bed vegetation in an agricultural landscape, North Dakota.
56 Status and Trends of Prairie Wetlands in the United States 1997 to 2009

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63

Appendix 

Definitions of Habitat Categories Used in This Status and Trends Study

Wetlands22

In general terms, wetlands are lands where saturation with water is the dominant factor

determining the nature of soil development and the types of plant and animal communities 

living in the soil and on its surface. The single feature that most wetlands share is soil or

substrate that is at least periodically saturated with or covered by water. The water creates 

severe physiological problems for all plants and animals except those that are adapted for life 

in water or in saturated soil.

Wetlands are lands transitional between terrestrial and aquatic systems where the 

water table is usually at or near the surface or the land is covered by shallow water. 

For purposes of this classification wetlands must have one or more of the following 

three attributes: (1) at least periodically, the land supports predominantly 

hydrophytes23, (2) the substrate is predominantly undrained hydric soil24, and 

(3) the substrate is non-soil and is saturated with water or covered by 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 with

hydrophytes 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 drastic

fluctuation in water level, wave action, turbidity, or high concentration of salts may prevent the

growth of hydrophytes; (3) areas with hydrophytes but non-hydric soils, such as margins of 

impoundments or excavations where hydrophytes have become established but hydric soils 

have not yet developed; (4) areas without soils but with hydrophytes such as the seaweedcovered portions of rocky shores; and (5) wetlands without soil and without hydrophytes, such 

as gravel beaches or rocky shores without vegetation.

Palustrine System The Palustrine (freshwater) System includes all non-tidal wetlands dominated by

trees, shrubs, persistent emergents, emergent mosses or lichens, farmed wetlands,

and all such wetlands that occur in tidal areas where salinity due to ocean-derived

salts is below 0.5 parts per thousand. It also includes wetlands lacking such

vegetation, but with all of the following four characteristics: (1) area less than

20 acres (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. 

Wetland Classes

Emergent Wetland Emergent Wetlands are characterized by erect, rooted, herbaceous

hydrophytes, excluding mosses and lichens. This vegetation is present for

most of the growing season in most years. These wetlands are usually

dominated by perennial plants.

22Adapted from Cowardin et al. 1979.

23Lichvar and Kartesz 2009.

24U.S. Department of Agriculture, Natural Resources Conservation Service maintains the list of hydric soils for the United States

(U.S. Department of Agriculture, NRCS 2010).

Appendix

65

Shrub Wetland Shrub Wetlands include areas dominated by woody vegetation less than 20 feet 

(6 meters) tall. The species include true shrubs, young trees, and trees or shrubs 

that are small or stunted because of environmental conditions. 

Forested Wetland Forested Wetlands are characterized by woody vegetation that is 20 feet (6 meters) 

tall or taller.

Farmed Wetland Farmed Wetlands are wetlands that meet the Cowardin et al. (1979) definition 

where the soil surface had been mechanically or physically altered for production 

of crops, but where hydrophytes would become reestablished if farming were 

discontinued. Farmed Wetlands lack artificial drainage systems that would 

effectively eliminate wetland hydrology.

Ponds Open water, unconsolidated bottom, less than 20 acres (8.0 ha). 

Deepwater Habitats

Wetlands and deepwater habitats are defined separately because the term wetland does not include deep,

permanent water bodies. For conducting status and trends studies, riverine and lacustrine are

considered deepwater habitats. Elements of marine or estuarine systems can be wetland or deepwater.

Palustrine includes only wetland habitats.

Deepwater habitats were permanently flooded land lying below the deepwater boundary of wetlands and

included environments where surface water was permanent and often deep, so that water, rather than air,

was the principal medium within which the dominant organisms lived, whether or not they were

attached to the substrate. As in wetlands, the dominant plants were hydrophytes; however, the substrates

were considered non-soil because the water is too deep to support emergent vegetation

(U.S. Department of Agriculture 1975).

Riverine System The Riverine System included deepwater habitats contained within a channel, with the

exception of habitats with water containing ocean derived salts in excess of 0.5 parts per

thousand. A channel was “an open conduit either naturally or artificially created which

periodically or continuously contains moving water, or which forms a connecting link 

between two bodies of standing water” (Langbein and Iseri 1960).

Lacustrine System The Lacustrine System included 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). 

Appendix 67

Uplands

Agriculture25 Agricultural land was defined broadly as land used primarily for production of food and

fiber. Agricultural activity was evidenced by distinctive geometric field and road 

patterns on the landscape and the traces produced by livestock or mechanized 

equipment. Examples of agricultural land use included cropland; orchards, groves, 

vineyards, nurseries, cultivated lands, confined feeding operations; and other agricultural 

land inclusive of livestock feed lots and farmsteads (including houses, support structures 

(silos) and adjacent yards, barns, poultry sheds, etc.).

Urban Urban land was comprised of areas of intensive use in which much of the land

was covered by structures (high building density). Urbanized areas were cities and 

towns that provide the goods and services needed to survive by modern-day standards

through a central business district. Services such as banking, medical, legal office

buildings, supermarkets, and department stores made up the business portion of urban

areas. Commercial strip developments along main transportation routes, shopping 

centers, contiguous dense residential areas, industrial and commercial complexes, 

transportation, power and communication facilities, city parks, ball fields and golf courses 

were also included in the urban category.

Rural 

Development Rural Developments occurred in sparse rural and suburban settings outside distinct

urban cities and towns and were 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 a convenience store that are surrounded by sparse residential

housing and agriculture. Scattered suburban communities located outside of a major

urban center were also included in this category as well as some industrial and 

commercial complexes; isolated transportation, power, and communication facilities; 

strip mines; quarries; and recreational areas.

Other Land Use Other Land Use was composed of uplands not characterized by the previous categories.

Typically these lands included unmanaged or non-patterned upland forests and scrub

lands and barren land. Lands in transition were also included in this category. 

Transitional lands were lands characterized by the lack of any remote sensor information 

that would enable the analyst to reliably predict future use. The transitional phase 

occurred when wetlands were drained, ditched, filled, leveled, or the vegetation had been 

removed and the area was temporarily bare

Grassland Upland Grassland was developed as a generalized category to include an array of lands that

produce legumes, forbs or grasses. This included a broad range of grassland areas such 

as minimally managed or native grasslands, extensively managed hay land (including 

alfalfa), pasture or rangeland, Conservation Reserve Program lands in perennial grass 

cover and fallow or retired cropland in grass. The definition of Grassland as used in this 

study is similar to the description of grassland types used by the U.S. Department of 

Agriculture (Claassen et al. 2011).

25

Adapted from Anderson et al. 1976.

All photos, unless 

otherwise noted, were 

provided courtesy of the 

U.S. Fish and Wildlife Service, 

with special thanks to Krista 

Lundgren and Tom Koemer.

Front cover, a prairie pothole 

wetland surrounded by wheat 

and grassland, North Dakota. 

Title page, bulrush (Scirpus 

spp.) near the end of the 

growing season. Inner back 

cover, mallards at sunset in 

Lacreek NWR.

Graphic services provided

by the Columbus Publishing 

Service Center, Science 

Publishing Network, 

U.S. Geological Survey.
U.S. Department of the Interior

Fish and Wildlife Service

http://www.fws.gov

June 2014