Sedimentation of Prairie Wetlands

Research Needs

Reduction of Sediment Inputs

Evaluate the effectiveness of alternative agricultural practices to reduce erosion from cropland and Sedimentation of Wetlands. Studies need to simultaneously consider the benefits to both agricultural and conservation communities; scientists from both communities must provide input to make realistic and informed decisions about the management of wetlands within agricultural landscapes. Ideally, studies should be interdisciplinary and have active participants from both agricultural and wetland disciplines to provide a forum for evaluation of agricultural conservation practices. The potential for sedimentation to degrade wetlands is great and the most obvious research need is to evaluate land-use practices that reduce surface runoff and erosion of valuable topsoil. Concerns over soil erosion and its effects on agricultural productivity has resulted in a great body of knowledge on watershed factors (e.g., slope, soils, cover, land-use) that influence erosion and the input of sediment, phosphorus, nitrogen, and agrichemical runoff associated with conventional and conservation tillage practices (Bills and Heimlich 1984; Neely and Baker 1989; Isenee and Sadeghi 1993; Fawcett et al. 1994). These conservation practices certainly reduce soil erosion and runoff, however they have generally been evaluated from an agricultural perspective. Research is now neeeded to evaluate the effectiveness of the various conservation practices to reduce sediment input and thereby maximize the topographic lives of wetlands within the agriculturally-dominated ecosystem of the PPR. Economic incentives may be an important tool to facilitate land-owner acceptance and implementation of conservation practices that target goals of sustained agricultural production and long-term wetland management. Additionally, monitoring programs should be developed to foster the continual improvement of soil conserving practices and ones that enhance the performance or longevity of wetland functions.
Evaluate control measures and siting criteria to reduce sediment input in wetlands. Vegetative buffer strips are frequently used and have been shown to be effective at reducing nonpoint source pollutants, including sediment, from adjacent habitats (Dillaha et al. 1989; Magette et al. 1989; Castelle et al. 1992). However, little research has been conducted on the benefits they may provide to prairie wetlands. The semi-arid PPR undergoes long periods of drought followed by long periods of abundant rainfall. These wet/dry cycles can persist for 10 to 20 years (Duvick and Blasing 1981; Karl and Kascielny 1982; Karl and Riebsame 1984; Diaz 1983, 1986). During periods of severe drought, most wetlands go dry during summer and many remain dry throughout the drought years. Buffer strips established to protect wetlands during a dry cycle may become submerged and ineffective in reducing sediment input in wetlands during the wet cycle (Gleason 1996). Thus, research is needed to identify effective buffer strip widths for wetlands with different catchment morphometrics, soil types, and surrounding agricultural practices. Although substantial amounts of land have been planted to perennial cover as part of the Conservation Reserve Program, studies have not been conducted to evaluate which cover types are most effective in reducing soil erosion under various land use and topographic scenarios.
Effects on Wetland Functions
Evaluate the impacts of increased surface runoff and sedimentation on all wetland functions (e.g., wildlife habitat, groundwater recharge, nutrient cycling, water quality improvement, production). The impact of sediment on all wetland functions has been inadequately studied (Adamus and Brandt 1990). The point at which sediment inputs overload the assimilative capacity of wetlands needs to be identified and management guidelines developed that are based on sound remedial practices that simultaneously consider various interests and needs. Due to the paucity of information, major research gaps exist but a current emphasis seems to be on wildlife and water quality issues. Given the dynamic nature of prairie wetlands, research on sediment impact on wetland functions needs to be conducted and interpreted within a conceptual framework that considers natural hydrologic, chemical, and climatic events that characterize the region.
Wetland Restoration
Evaluation of methods to restore pool depth in silted-in wetlands. Methods to restore drained or nondrained wetlands that are silted in and have lost their original wetland volume need to be evaluated within the context of economics and their postrestoration potential to provide targeted functions. Excavation of sediments and/or increasing the water depth with water control structures may have the same effect of restoring water depth but the economic cost versus gain in wetland functions are not known.

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