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Using Aquatic Invertebrates to Delineate Seasonal and Temporary Wetlands in the Prairie Pothole Region of North America

Introduction


Wetlands are the only ecosystems regulated on public and private lands in the United States (National Research Council 1995). Thus, methods have been developed to define, identify, and delineate wetlands for regulatory purposes. Current wetland definitions emphasize three major wetland components: water, substrate, and biota. Determining the status of these three characteristics is the basis of current wetland identification and delineation methodologies. Of the three, wetland hydrology (i.e., water) deserves special status because, without the presence of water, neither hydric soils nor wetland biota can develop (National Research Council 1995). However, the presence of wetland hydrology is often the most difficult to measure and determine, so hydric soils and wetland biota are often used to infer wetland hydrology. In the case of wetland biota, this currently means relying exclusively on vegetation, as other biotic indicators have not been developed.

Recent wetland delineation manuals (U.S. Army Corps of Engineers 1987, U.S. Environmental Protection Agency 1988, Federal Interagency Committee for Wetlands Delineation 1989, U.S. Department of Agriculture 1994) rely heavily on hydric soils and hydrophytic vegetation as indicators of wetland hydrology. However, many prairie pothole wetlands lack saturated soil conditions for much of their growing season and are often tilled and planted to an agricultural crop as part of normal farming operations. Due to difficulties in identifying hydric soils on glacial till, prairie pothole wetlands are specifically listed as problem areas in the U.S. Army Corp of Engineers wetland delineation manual (U.S. Army Corps of Engineers 1987). The problem is exacerbated by tillage, especially during drought years when even wetlands with more permanent water regimes become dry and are incorporated into farming plans. In addition to destroying or greatly disturbing indicators of hydric soils, tillage also destroys or severely disturbs hydrophytic vegetation, adding to the difficulties in identifying and delineating these wetlands. Further, the use of herbicides in agricultural fields can exacerbate problems in delineating wetlands based on hydrophytic vegetation.

Due to the problems associated with hydric soils and plant indicators in tilled wetlands, a need exists to identify additional biotic indicators that are unique to wetlands, are easily identifiable, and are not easily destroyed by normal farming activities. Many invertebrates (e.g., water fleas, seed shrimp, clam shrimp, and various species of snails) are restricted to wetlands (Barnes 1968, Clarke 1981) and are specific to particular hydrologic regimes that define wetland classes (Euliss et al. 1999). Further, their remains (e.g., shells, chitinous exoskeletons, resistant eggs) are easily identifiable and persist in wetland substrates even when wetlands are dry. Moreover, these recalcitrant remains are not easily destroyed by mechanical tillage (Euliss and Mushet 1999). Hence, the remains of aquatic invertebrates reflect time-integrated information on wetland hydrology that may be useful to delineate wetlands in the prairie pothole region of North America.

This study is a follow-up to a study we conducted in 1992 and 1993 that demonstrated that invertebrate remains can be used to identify wetlands that are often dry and cultivated (Euliss et al. 2001). However, in the earlier study, we did not assess the potential of invertebrates as a delineation tool. We initiated the current study in 1995 to test the feasibility of using invertebrate remains to delineate the edges of temporary and seasonal wetlands in the prairie pothole region.


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