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Sedimentation of Prairie Wetlands

Erosion and Sedimentation


Most wetlands in the PPR are surficially closed basins that lack integrated drainage networks (Richardson et al. 1994). Thus, wetland sediment inputs are derived primarily from wind and water erosion of upland soils in catchment and adjacent areas. Tillage has greatly altered the surface hydrologic dynamics of wetland catchments; conventional tillage increases erosion rates and surface runoff relative to grassland landscapes (Gleason 1996; Euliss and Mushet 1996). However, few studies have examined the impact of sedimentation on the majority of functions that prairie wetlands are known to perform. Adomaitis et al. (1967), demonstrated that the aeolian mixture of snow and soil ("snirt") in wetlands surrounded by fields without vegetation accumulated at twice the rate as in wetlands surrounded by fields with vegetation. Similarly, Martin and Hartman (1987) found that the flux of inorganic sediments into wetlands with cultivated catchments occurred at nearly twice the rate of wetlands with native grassland catchments. Organic matter also occurs at significantly greater concentrations in wetland sediments in wetlands with native grassland catchments than in wetlands with cultivated catchments. Dieter (1991) demonstrated that turbidity was highest in tilled (i.e., wetland and catchment areas tilled) that in untilled and partially tilled (i.e., portions of the basin tilled with a buffer strip of vegetation separating the basin and catchment area) wetlands. Similarly, Gleason (1996) and Gleason and Euliss (1996) found that sedimentation rates and the inorganic fraction of sediment entering wetlands were significantly higher in wetlands with cultivated catchments than in wetlands with grassland catchments. There also was more aeolian deposited sediment in wetlands in cultivated catchments than in wetlands with grassland catchments (Gleason and Euliss unpublished data). In the playa wetlands of Texas, Luo et al. (1997) found that wetlands in cultivated watersheds had lost nearly all of their original volume due to filling by sediment, whereas comparable sites in rangeland watersheds lost only about a third of their original volume. A conclusion common to all these studies is that wetlands in agricultural landscapes have shorter topographical lives than wetlands in grassland landscapes.
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