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Sedimentation of Prairie Wetlands

Introduction

The prairie pothole region (PPR) occurs in a topographic, hydrologic, and land use setting that exacerbates the accumulation and retention of sediments in wetlands. Sediment retention by wetlands is often described as a water quality benefit (e.g., Botto and Patrick 1978; Kuenzler 1990). However, excessive sediment input from erosion of agricultural soils has potential to severely impact PPR wetlands; sediment is the major pollutant of wetlands, lakes, rivers, and estuaries in the United States (Baker 1992; USEPA 1995). Wetlands in the PPR are embedded within an agricultural lanscape where cultivation of wetland catchment areas (i.e., the area that contributes surface runoff to the wetland basin) has greatly altered surface runoff dynamics and hydrologic inputs to groundwater. Grasslands that once protected prairie soils from erosion and moderated surface runoff have been converted to cropland. Consequently, wetlands in agricultural fields receive significantly more surface runoff containing sediment than occured prior to agricultural conversion (Grue et al. 1986; Neely and Baker 1989; Euliss and Mushet 1996; Gleason 1996).

The impact of suspended sediment and sedimentation on fish and aquatic life has been investigated in riverine systems (Newcombe and MacDonald 1991; Waters 1995), but few studies have adressed impacts of sedimentation in wetland ecosystems. Sedimentation impacts include increased turbidity that reduces the depth of the photic zone and increases sediment fallout which may cover primary producers and invertebrates. Excessive sediment input thus potentially alters aquatic food webs as well as basic wetland functions related to water quality improvement, nutrient cycling, and other biogenic processes that transform and sequester pollutants. Moreover, erosional sediment can fill wetlands either as a single catastrophic event or gradually; basins totally filled with sediment provide no natural wetland functions of benefit to society.

The primary source of sediments in prairie wetlands is wind and water erosion from agricultural fields (Gleason 1996). Agricultural research is replete with information on soil erosion and the detrimental effects of soil loss on agricultural production (e.g., Wischmeier and Smith 1978; Bills and Heimlich 1984; Lane and Nearing 1989; Moldenhauer and Black 1994). Agricultural research also has been instrumental in developing and implementing conservation practices on private lands that reduce soil erosion, maintain productivity of croplands, and improve soil and water quality (Cook 1988; Moldenhauer and Black 1994). However, the benefits of such consequences of implementing those conservation practices on most wetland functions have not been evaluated. Future research needs to examine the impact of sedimentation from an interdisciplinary platform. Integration of agricultural and wetland interests and expertise is critical to development of such research programs (Gleason and Euliss 1997).

This manuscript is a review of sedimentation in PPR wetlands. Its purpose is to (1) present an overview of sedimentation and identify potential impacts on wetland functions, (2) identify management strategies that reduce sediment inputs, and (3) highlight research needs of prairie wetlands relative to soil conservation issues.

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