Spatial Variability of Soil Carbon and Post-Settlement Alluvium in the Glaciated Landscape of Minnesota.

Whether human-induced erosion and deposition due to agriculture since the European settlement has led soil to a net carbon sink or source is still being debated. Understanding the spatial distributions of soil carbon and post-settlement alluvium (PSA) over the landscape will improve scientific understanding of the Earth system responses to anthropogenic changes of land use, needed to predict the soil carbon budget. The goal of this project is to document the spatial variations of PSA and soil carbon on the glaciated till landscape of Minnesota. We hypothesize that effects of human-induced erosion in this region for the past 170 years is a redistribution of soil down slopes to the wetter and depressional wetlands that have buried and preserved carbon from decomposition to the atmosphere. By explicitly considering the three dimensional distribution of PSA and depressional soils, we are able to predict the effect of PSA on landscape carbon dynamics. The objectives of this project are 1) to observe and to measure locations and depths of PSA and soil carbon on all hillslope positions over the glacial till landscape at the Lake Rebecca Park Reserve in East-Central Minnesota, 2) to map the spatial distribution of PSA and soil carbon, and 3) to determine the spatial correlations of the soil characteristics with terrain attributes including slope, plane and profile curvatures, and upslope contributing areas.  Soil profile observations and soil sampling will be undertaken at topographic gradient-stratified transects of the field site hillslopes in the summer 2010. The PSA distributions and organic carbon contents of surface and subsurface soil horizons will be mapped in three-dimensions using the geographic information system (GIS). The terrain attributes will be constructed from the digital elevation model (DEM), and the relationships between soil carbon, PSA and the terrain attributes will be spatially analyzed. Preliminary results indicated that PSA are likely located on footslopes and wetlands where the surface becomes flat compared to their upper slopes, and soil carbon contents are more concentrated at such locations as well as where the profile curvature is concave.