Large catchment-scale spatiotemporal distribution of soil organic carbon

There are a dearth of studies globally examining soil organic carbon (SOC) at large catchment scales. Here we assess the catchment scale climate and geomorphic controls on SOC. The study was conducted on the east coast of New South Wales, Australia and focussed on a 562 km2 (Krui River) catchment sampled in 2006 and 2015 and a 606 km2 (Merriwa River) catchment sampled in 2015. Both catchments have similar soils, topography and landuse. There was no significant difference in SOC between 2006 and 2014 data sets, indicating that SOC was temporally stable over the intervening 8 years (Krui catchment), despite the seasonal variability in climate such as rainfall. SOC concentration was also shown to have no significant difference between Krui catchment and Merriwa catchment, indicating that SOC is spatially stable for catchments of similar land-use, climate and geomorphology. SOC concentrations from all three data sets were compared to a range of terrain attributes. Similar with other studies, elevation, as a surrogate for orographic rainfall, was found to have the strongest significant control on SOC % at the large catchment scale. Confirmation of the use of elevation as a surrogate for rainfall was made by comparing SOC with rainfall obtained from a network of weather stations across the study sites. Relationships between SOC and other terrain attributes found inconsistent relationships. The findings demonstrate that for catchments with similar soils, topography and climate that SOC can be reliably predicted using simple topographic variables. The methods here provide a robust tool which can be used for SOC assessment at other sites as well as assist in understanding SOC distribution and controls for longer term and regional scales.