Large Catchment Scale Sediment Transport Modelling of SOC Using Environmental Tracers and Remote Sensing

Abstract:

Soil's potential as a carbon sink for atmospheric CO₂ has been widely discussed. Studies of soil organic carbon (SOC) controls, and the subsequent models derived from their findings, have focussed mainly on North American and European regions, and more recently, in regions such as China. In Australia, agricultural practices have led to losses in SOC. This implies that Australian soils have a large potential for increased sequestration of SOC. Building on previous work, here we examine the spatial and temporal variation in soil organic carbon (SOC) and its controlling factors controls across a large catchment of approximately 650 km² in the Upper Hunter Valley, New South Wales, Australia, using data collected from two sampling campaigns, (April 2006 and June-July 2014). The 2006 data represented a period of long-term drought which effectively ended in 2007 with average and above average subsequent rainfall. In 2007 and 2010 there were a series of extreme rainfall events. 137-Cesium and SOC concentrations were obtained from the sampled soils. Remote sensing using Landsat (30m) and MODIS (250m) NDVI was used to determine if catchment SOC could be predicted using both low and high resolution remote sensing. Relationships between SOC and 137-Cesium for both sampling periods were also quantified. Results indicate that, although moderate resolution (250 m) allows for reasonable prediction of the spatial distribution of SOC, the higher resolution (30 m) improved the strength of the SOC-NDVI relationship. Mean 137-Cesium concentrations were observed to show an increase in deposition at the sample sites over the 8 years between samplings. The relationship between SOC and 137-Cesium, as a surrogate for the erosion and deposition of SOC, suggested that sediment transport and deposition influences the distribution of SOC within the catchment. The increase in 137-Cesium also suggests that increased rainfall and extreme storm events, resulting from climate change, may increase the movement of SOC.