Soil carbon dynamics in the Big Creek basin, Southern Illinois, USA

Soil organic carbon (SOC) is a biophysical parameter that is acknowledged as the largest storehouse of terrestrial carbon. Recognition of the fact that best management practices can increase SOC in agricultural lands and thereby remove CO2 from the atmosphere has given rise to the possibility of using these potential carbon sinks to offset the emission constraints imposed by climate treaties. Understanding the potential of soils to store carbon however requires comprehension of past and future SOC transformations due to human modifications of the LULC. This knowledge is especially helpful for the prediction of the SOC sequestration potential of the respective land area in question. With these considerations in the background, this research firstly examines the transformations in SOC since the introduction of agriculture (1851) to the present times (2005) in the Big Creek watershed of Southern Illinois. Further, the SOC sequestration potential of 160 land use/cover sequences (includes agricultural rotations) in 272 sub-basins of the same watershed is examined. Lastly, annual changes in total carbon stocks (TCS) and SOC are analyzed from 1999 to 2006 in 272 sub-basins through remote sensing derived LULC data. Three models were used to complete this research. These were; CENTURY an ecosystem model, for SOC computation, SWAT a river basin scale model for demarcation of sub-basins and WEPP a process model for estimating erosion Validation in case of current estimates of SOC was performed by aggregating and comparing CENTURY derived output with SOC estimates given in Soil Survey Geographic Database for the year 2000. The correlation between the simulated and observed SOC estimates was 0.63. The examination of temporal transformations of SOC shows that losses have subsided by 1970's and a recovering trend is visible due to conservational management practices. Presently, annual examination of LULC and management practices show that SOC and TCS are increasing due to predominance of perennial LULC. With respect to future sequestration potential the maximum carbon gain occurs in case of forest, conservation reserve program, pasture, hay LULC and no till agricultural rotation sequences.