Soil organic carbon and soil erosion – understanding change at the large catchment scale

Soil organic carbon (SOC) is a major soil component. However, there is still much to learn regarding its spatial and temporal distribution as well as how SOC moves through the landscape. Of particular interest is how SOC movement is related to soil erosion and deposition. Here we examine the spatial distribution of SOC over two large (562 and 606 km ) catchments in relation to soil erosion and deposition. We found that the spatial distribution of SOC concentration on average is stable (over an eight year period) for the two study catchments. However, differences were found in SOC when concentrations were compared between samples collected in 2006 and 2014. The environmental tracer caesium-137 ( Cs) was used to assess erosion and deposition patterns across the study catchment and a significant relationship was found between SOC change and erosion and deposition at each sample point. That is, locations with an increase in SOC corresponded with an increase in Cs concentration (depositional sites) while locations with a decrease in SOC corresponded with a decrease in Cs concentration (erosional sites). A Monte-Carlo assessment confirmed these results. The driver of the SOC change and soil movement corresponds with the largest rainfall event (since 1969) in the area. The results suggest that SOC can be translocated by significant rainfall events. The findings provide insight into how catchments may respond to stronger and more frequent storm events.