Northern Prairie Wildlife Research Center
Although incomplete, we have a better understanding of the indirect impact sediment exerts on water quality through its influence on hydrophytes, organic exchange substrates, and microbial populations. Reduction of light available for photosynthesis due to turbidity and the burial of macrophyte seed banks are obviously negative impacts of excessive sediment entering wetlands from adjacent fields. Aquatic macrophytes and algae are important in the uptake, short-term storage, and cycling of nutrients in wetlands; negative impacts on plants from sediments may alter water quality functions. Increased input of allochthonous inorganic matter to wetlands (Martin and Hartman 1987; Gleason 1996) would reduce the availablity of organic exchange surfaces important for sorption of contaminants, especially on the thin aerobic zone at the soil-water interface. While the impact of sedimentation on microbes has not been studied (Adamus and Brandt 1990), sediment fallout may cover microbes, or organic matter needed for microbial processes, or alter redox profiles important in the performance of water quality processes. Finally, the ability of wetlands to remove and retain sediments is a basic concept of improved water quality, but many PPR wetlands are closed systems that can totally fill with sediments and hence lose their capacity to function properly. The trade off between the importance of sediment removal as a water quality benefit and maintaining the topographic life of wetland basins clearly needs to be integrated into management strategies of wetlands.