Relative magnitudes and sources of sediment in benchmark watersheds of the Conservation Effects Assessment Project

Sediment is one of the principal pollutrants of surface waters of the United States. Efforts by the USDA to quantify and control sediment erosion have historically focused on fields and upland areas. There is a growing body of evidence in agricultural areas, however, that the locus of sediment erosion has shifted from fields and uplands to channels. This is a critical issue in the Conservation Effects Assessment Project that evaluates the effectiveness of controls on sediment erosion. Rapid geomorphic assessments indicate that channel contributions are significant sources of sediment in the studied watersheds. The relative importance of channel processes are obtained by comparing reference yields for the ecoregion with the respective watershed yields. Annual suspended sediment yields for the Conservation Effects Assessment Project watersheds exceed the median value for stable streams by 243% in lowa, 290% in New York, 630% in Mississippi, and between 2,120% and 7,410% in Oklahoma. Erosion from streambanks is an important process that must be addressed in management strategies aimed at controlling sediment production and delivery.