Iowa
Wetlands and
Riparian
Areas
Conservation
Plan
Info:
Wetlands
and
Riparian Areas
Status
of
Iowa Wetlands
Types of Wetlands
Wildlife biologists and other wetland scientists have devised a number of systems to classify wetlands and their ecosystems. Any such system involves artificially dividing what is really a continuum; hence, some wetlands will seem to fall between categories and may be judged differently by different systems or scientists. Systems that have been used to describe Iowa wetlands primarily reflect conditions in glaciated midwestern states, and depend largely on characterization of vegetation, water depth, and hydroperiod. The current national standard for classifying wetlands is the Cowardin system, which reflects a more complex and comprehensive understanding of wetland ecology than earlier approaches to classification. The Cowardin system is "hierarchical," meaning it is structured around a combination of ecological, biological, hydrological, and substrate characteristics that permit its use across the United States. The system can even take into consideration different broad categories of human influence. This system is the basis for the National Wetlands Inventory (NWI).
Riparian areas include areas of streamside vegetation along any perennial or intermittent stream, including the streambank and adjoining floodplain or bottomland, which are typically distinguishable from upland areas in terms of vegetation, soils, topography, or other landscape characteristics. Underneath these areas of periodic inundation caused by the outflow of rivers and streams are alluvial aquifers. Iowa's geologic history has greatly influenced the characteristics of streams and associated riparian wetlands. Streams in the geologically young glaciated region of north-central Iowa are widely spaced and slowly meander through flat terrain with black topsoil. In the geologically older and steeper landscapes of southern and western Iowa, streams are more numerous and closer together. In northeast Iowa's Paleozoic Plateau or "Driftless Area," where the landscape has weathered longer than any other part of the state, rock ledges and cliffs border relatively cool, steep streams flowing over gravel bottoms (Iowa Association of Naturalists, 1993b). Human activity has also greatly influenced Iowa's riparian areas, and this influence continues. The dramatic changes in the character of the state's streams and rivers from damming and channelizing exemplify this.
Past and present estimates of wetlands and riparian areas vary widely, depending on the source and its purpose. It is estimated that in the late- 1700s to early- 1800s, the state had from 4 to 6 million acres of wetlands. USDA inventories of Iowa showed 930,000 acres of wetlands in 1906 and 368,000 acres in 1922. Approximately 138,000 acres of water habitat were thought to have existed in 1955. Though estimates differ, all agree that wetlands and riparian areas have had a dramatic net decrease in size and number.
Soil survey data indicate that the area of palustrine wetlands in north-central Iowa in the mid- 1800s was in the range of 11 to 30 times the current area. An estimate of the reduction in wetland area in the 29 counties of the Des Moines Lobe compared results from hydric soils data with the USDA National Resources Inventory (NRI) and U.S. Fish and Wildlife Service National Wetlands Inventory (NWI). For the Des Moines Lobe region, the reduction in area has been in the range of 91.1 percent to 96.5 percent.
In a national report to Congress, "Wetlands: Losses in the United States 1780s to 1980s," the estimates given for Iowa indicate a loss of wetland area of 89 percent, from 4.0 million acres in the 1780s to 421,900 acres in the 1980s. In the study, only two states showed a higher percentage loss than Iowa (Ohio: 90 percent, California: 91 percent). The national average loss was 53 percent (Dahl, 1990).
Two other often-quoted sources give the acres of Iowa's existing wetlands as considerably fewer. An article by Bishop (1981) in the Proceedings of the Iowa Academy of Sciences reported a loss of 95 percent of the state's natural wetlands, and showed just, over 26,400 acres of natural and artificial marsh still existing. The book Iowa's Natural Heritage (1982) puts the amount of wetlands in Iowa at approximately 110,000 acres in the 1970s, which included marshes, "sloughs, lakes, and riverine wetlands." It may be that the above estimates do not adequately account for all of Iowa's wetland types, especially wet prairies and fens.
According to the U.S. Geological Survey, the amount of wetlands existing in Iowa in 1997 is estimated to be about 1.2 percent of the state's surface area, compared to about 11 percent 200 years ago. Efforts are underway by state and federal agencies to develop up-to-date state inventories based on refinements in National Wetlands Inventory data. There are ongoing controversies over the amount of wetlands, and the relative losses versus gains. There are several reasons why estimates do not agree on acreage amounts. Even over short time-frames, acreage amounts change due to cultural and natural processes such as drainage and weather. There are also a variety of methods and data sources for quantifying wetlands and riparian areas. Then, there are a variety of definitions of wetlands and riparian areas -- different purposes for wetland inventories can lead to different inventory criteria and resulting estimates.
It is widely agreed, however, that national policies to protect wetlands have helped slow the rate of loss, and restoration programs are slowly reintegrating wetlands restorations back into the landscape. Iowa wetland and riparian wetland restorations that have occurred as a result of federal programs have included more t 78,000 acres enrolled in USDA Natural Resources Conservation Service (NRCS) programs, and another 10,000 acres through the FWS Partners for Wildlife Program.
The NWI is a relatively recent inventory of U.S wetlands by the FWS. The wetland amounts reported by the NWI are based on interpretations of aerial photographs, and do not consider whether areas interpreted as wetlands are regulated. In Iowa, the NWI mapped a total of 577,429 acres of vegetated wetlands; 289,356 acres of pond, lake and reservoir habitats; and 97,405 acres of river and stream habitats.
In preparing NWI data, the FWS adapted and used the Cowardin system. Though it is based on a non-regulatory definition, the Cowardin System is very similar to the major regulatory definitions. In the past 20 years that NWI maps have been produced, experience and increasing knowledge in wetland and soil science, and hydrology have led to changes in NWI mapping procedures. The minimum size wetland on NWI maps is generally one to three acres. Very narrow wetlands in river corridors, forested wetlands, and wetlands cultivated at the time of mapping are generally not depicted. What this means is that the NWI is designed to err on the side of omission. If an NWI map indicates the presence of a wetland in a given area, it is highly likely that a wetland is there. If the NWI does not indicate a wetland, one is usually not there, but the maps omit many small and drier-end wetlands and others that are difficult to photointerpret.
The NWI is officially recognized as a national wetlands mapping tool. The advantages to using the NWI include that the data cover the entire state, are relatively recent, are inclusive of a variety of wetlands and riparian types, are available in digital form, and are relatively well documented and detailed. However, the NWI also has limitations that are typical of many similar large geographic information databases. These limitations include that each wetland was photographed only once and the photos were taken over a 6-year period (1980-1985) -- data collection, verification, digitizing, and documentation has occurred over 17 years and is still continuing. In addition, the photos were taken during normal to slightly above normal precipitation conditions, there are uncertain boundaries in relatively flat landscapes, and some non-regulatory wetlands are included. Because of such limitations, the resultant summary information alone should not be used for local decision-making or regulatory purposes.
There are several things to remember about using wetlands classifications. Some wetlands may not clearly fit into specific types because of an infinite variety of local conditions, and local conditions may change over time. Some changes, such as water fluctuations, are cyclical and can be predicted, based on annual precipitation or drought cycles, while others, for example flood-related scouring or deposition, are catastrophic and can't be predicted. Changes such as reduction in depth or species diversity depend on wildlife activity, human activity, and management. Finally, there are natural processes that can create or fill wetlands, but typically when such changes occur today, they have been greatly accelerated by human activity.
The following information is USDA Wetlands Programs statistics as of September 15, 1998. For more information contact: Leroy Brown (515) 284-6655, USDA NRCS.
Top States restoring wetlands under USCA federal programs:
Number of Contracts:
|
Iowa |
642 |
|
Missouri |
473 |
|
South Dakota |
322 |
|
New York |
293 |
|
Louisiana |
252 |
|
Wisconsin |
243 |
|
Minnesota |
204 |
Number of acres (appx):
|
Louisiana |
101,000+ |
|
Iowa |
75,000+ |
|
Missouri |
75,000+ |
|
Minnesota |
66,000+ |
|
Arkansas |
60,000+ |
Summary of Iowa's wetland restoration program:
|
WRP/EWRP/EWP |
Number |
Acres |
|
Application accepted |
733 |
78,474 |
|
Permanent |
701 |
75,259 |
|
30-year easement |
30 |
2,918 |
|
Cost share only |
2 |
297 |
|
Of those accepted |
||
|
Restoration complete |
406 |
34,291 |
|
Easements recorded restoration not complete |
229 |
31,439 |
|
Easement in progress |
98 |
12,744 |
|
Applications not funded |
252 |
19,260 |
|
WRP |
203 |
15,013 |
|
EWP |
49 |
4,247 |