The Fate of Eroded Soil: Sediment Sinks and Sediment Budgets of Agrarian Landscapes in Southern Minnesota, 1851–1988

Human-induced soil erosion has produced real-world laboratories for studying the fates of eroded soil particles in watersheds all over the world. This article investigates the spatial distribution of historical sediment and the sediment budgets of three of these laboratories in medium-size watersheds of southern Minnesota. Sediment storage is measured in various geomorphic sites or sinks including colluvium, stream-order floodplains, and reservoirs. Two of these watersheds exhibit erosion histories and quantities and patterns of historical alluvium that are comparable with watersheds in Wisconsin's Driftless Area. In these watersheds, the patterns of historical sediment storage are two-tiered, with 47 to 61 percent of all sediment stored in the uplands (in low-order floodplains and colluvium) and 38 to 52 percent stored in the main lower floodplains. In one stream, backwater effects from the Mississippi River cause significantly greater alluviation in the lower floodplain; in another stream, the main floodplain is narrower and alluvial storage is thinner. In both, floodplain width is the major influence on alluvial storage. A third and smaller watershed in central Minnesota reports lower erosion and sedimentation rates and a different pattern of storage; 73 percent of the sediment is stored in colluvium and 27 percent in the lower main floodplain. Based on estimates of soil erosion, historical sediment yields and sediment budgets are estimated for each watershed. Historical sediment yields of about 13 to 36.5 percent are comparable to other estimates for these areas, which means that 63.5 to 87 percent or more of all historically eroded soil still resides within the basins and within 4 to 25 km of original points of detachment. Moreover, in the 137 years of European settlement, 38 to 73 percent of all eroded sediment has travelled no more than 4 km.