Impact of Soil Erosion On Soil Carbon Dynamics at the Landscape Scale.

Soil organic carbon can vary greatly within topographically complex landscapes. In uncultivated landscapes this variability is largely a result of the impact of hydrology on biomass production and decomposition. In cultivated landscapes soil erosion can cause considerable redistribution of soil and, with it, soil organic matter. It can expose in some areas subsoil that is poor in organic carbon, and it can bury soil in other areas topsoil that is rich in organic carbon. Accurate assessments of the rate of soil organic carbon redistribution within cultivated landscapes are not available. This represents a major gap in our understanding of carbon sequestration at the landscape scale.

This objective of this study was to assess the impact of soil erosion on soil carbon at a field site near Cyrus, Minnesota. Samples were collect in 1999 and again in 2007 from two, perpendicular transects. These samples were analyzed at the University of Manitoba for ¹³⁷Cs. The repeated sampling for ¹³⁷Cs provided highly accurate estimated of soil erosion over the 8-year interval with losses exceeding 100 t ha yr^-1. Samples were analyzed for soil organic carbon and inorganic carbon at the USDA-ARS in Morris, Minnesota. The surface and profile soil organic carbon data and the surface inorganic carbon data were correlated against the rates of soil erosion to assess the impact of soil erosion on soil carbon. These data were also compared against model data for water and tillage erosion to assess the relative contribution of these erosion processes to the changes in soil carbon. Geostatistical analyses of the soil carbon and soil erosion data were examined to further assess the relationship between soil carbon and soil erosion. Soil erosion at this field site has had a measurable and statistically significant impact on the soil carbon within the short period of 8 years.