Soil erosion and carbon export: A case study in a steep slope grazing landscape

Abstract

Soil organic carbon (SOC) can be transported and deposited along the same pathways as that of soil erosion and deposition. Here soil erosion, deposition and SOC patterns are examined in a steep slope (∼30%) soil mantled environment in south-east Australia using an environmental tracer (137Cs). Multiple surface soil cores were collected and soil depth measured along two transects of similar length and aspect but at different elevation (average 550 and 800 m elevation above sea level). Both transects were located within the same paddock and managed by the same grazing methods. Both transects were found to have a high SOC concentration (∼Upper transect 6% and Lower transect 4%) and were significantly different from each other. SOC decreased moving downslope. Erosion rates for the site was 0.8 and 2.6 t ha−1 yr−1 for the Upper and Lower transects respectively and are probably higher than soil production rates. There were strong and significant positive relationships with SOC and 137Cs (r > 0.77, p < 0.0001). At this site, SOC concentration is related to erosion and deposition patterns. Using erosion rates of 0.8 and 2.6 t ha−1 yr−1 and an average SOC concentration of 5.8 and 3.8% then between 0.05 and 0.10 t ha−1 yr−1 of SOC is exported from the hillslopes which is approximately 2–4% of above ground biomass production (this being a major contributor to soil carbon). Carbon export was similar to that of other south-east Australia sites. The findings demonstrate that SOC can vary significantly in steep slope environments over short length scales highlighting the difficulty of understanding and quantifying geomorphic processes and farm carbon accounting.