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Sedimentation of Prairie Pothole Wetlands: The Need for Integrated Research by Agricultural and Wildlife Interests

Potential Impacts to Wetland Ecosystems

Wetland-dependent wildlife values are greatly diminished after wetlands are filled with sediment. At a less catastrophic scale, prairie wetlands in agricultural landscapes receive short spates of sediment input during precipitation events. Sediments alter water quality, primary productivity, and aquatic invertebrates in aquatic ecosystems (Waters 1995). Suspended sediment reduces light penetration and reduces the rate of photosynthesis (Ellis 1936-1 Dieter 1991) and the concomitant fallout of sediment covers substrates critical to the production of periphytic algae and macrophytes. In vitro experiments have shown that sediment depths as little as 0.25 cm can significantly reduce species richness, emergence, and germination of wetland macrophytes (Jurik 1994; Wang 1994). Filling of wetlands also reduces historic water depths and alters the structure of vegetative communities. A common result of wetlands losing water depth from sedimentation is the development of monotypic stands of vegetation (e.g., cattails) that provide little biological diversity and exacerbate problems with farmers because they provide roost sites for blackbirds that depredate sunflowers and other agricultural crops.

Sediment effects on primary production translate into impacts on organisms at higher trophic levels through the aquatic food chain. Aquatic invertebrates are primarily collector-gatherers and grazers that consume periphytic algae associated with detrital food chains and vegetative substrates. Declines in algal production, loss of standing vegetative structure (Krecker 1939; Krull 1970), and covering of organic matter (Murkin 1989) make wetlands less productive of invertebrates through the indirect loss of forage and habitat. Direct effects include covering of invertebrates and their eggs, and clogging of filtering apparatuses. High levels of silt and clay also are toxic to zooplankton and/or reduce feeding rate and assimilation, thus reducing energy available for reproduction (Robinson 1957; McCabe and O'Brien 1983; Newcombe and MacDonald 1991). Aquatic invertebrates play critical roles in wetlands to facilitate nutrient cycling (Merritt et al. 1984) and are required foods for wildlife (Reeder 1951; Krapu 1974a, 1974b; Swanson et al. 1974, 1985; Fritzell et al. 1979; Euliss and Harris 1987).

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