RCCZO -- Geomorphology, GIS / Map Data, Soil Biogeochemistry, Topographic Carbon Storage -- Topographic Controls of Soil Organic Carbon -- Reynolds Creek Experimental Watershed -- (2014-2017)

Mountainous terrain defines many dryland regions and results in pronounced variation in soil thickness and soil organic carbon (SOC) stocks that is not currently captured by carbon and global climate models. Here we quantify how total profile SOC varies with topographic morphometry, aspect and curvature, to estimate SOC storage within a 1.8 km2 granite-dominated catchment in Idaho, U.S.A. We show that north-facing soil pits have on average 2.9 times more total SOC per area than the south-facing sites, and convergent soil pits have on average 6.4 times more total SOC per area compared to divergent sites. Curvature explained 91% of variation in total profile SOC at a 3-m resolution when the entire vertical dimension of SOC was determined. Catchment SOC stocks were determined from this curvature-SOC model and showed that SOC below 0.3 m depth accounted for >50% of the catchment total SOC, indicating substantial underestimation of SOC stocks if only sampled at shallower depths. We conclude that processes responsible for carbon sequestration in soils vary spatially at relatively small scales, and they can be described in a deterministic fashion given adequate elevation data.