Hillslope and catchment scale soil organic carbon concentration: An assessment of the role of geomorphology and soil erosion in an undisturbed environment

The role of geomorphology in relation to the spatial and temporal distribution of soil carbon is of considerable interest in terms of landscape management and carbon sequestration. Soil carbon plays an important role in soil water holding capacity, soil structure and overall soil health. Soil is also a significant store of terrestrial carbon. This study examines total soil carbon (SC) concentration at the hillslope and catchment scale in the Tin Camp Creek catchment, Arnhem Land, Northern Territory, Australia. The catchment is largely undisturbed by European agriculture or management practices and is located in the monsoonal tropics. Results show that SC concentration along hillslope transects has remained consistent over a number of years and it is strongly related to hillslope position and topographic factors derived from precision surveying and provides a baseline assessment. Poor relationships were found when using a good quality medium resolution digital elevation model to derive topographic factors. This finding demonstrates the need for high resolution survey data for the prediction of total C at the hillslope and catchment scale. There was little difference in SC concentration between years and overall, SC down the hillslope profile varies little temporally suggesting that concentrations are relatively stable in this environment. An assessment of the relationship between SC and soil erosion using 137Cs and erosion pins demonstrates that sediment transport and deposition play little role in the distribution of SC in this environment. Vegetative biomass appears to be the major contributor to SC concentration with vegetative biomass being strongly controlled by topographic factors. While the SC concentration is constant over the study period further sampling is required to assess decadal trends.