Modeling interplay between regional net ecosystem carbon balance and soil erosion for a crop-pasture region

The balance between erosion-induced soil carbon loss and the reduction in heterotrophic respiration caused by carbon removal in semiarid ecosystems that suffer from severe soil erosion is still largely uncertain. In this paper, we revised and applied a simulation model to analyze responses of ecosystem processes in the crop-pasture belt region of northern China to impacts of soil erosion and climate shift. The revised model includes a new module that calculates runoff-induced soil erosion and soil carbon and nutrient losses. The model was validated against long-term field observations on plant productivity at several sites, and sediment yields of experiments with various vegetation covers and slopes. Simulation with historical climate data without considering erosion showed that the average net primary productivity (NPP), heterotrophic respiration (RHE), agricultural harvest (HAV), and net ecosystem carbon balance (NECB) were 210.1 +/- 26.9, 169.8 +/- 7.7, 35.9 +/- 4.1, and 4.4 +/- 22.5 gCm(-2) a(-1), respectively. In contrast, simulation with soil erosion gave an average erosion-induced loss of soil organic carbon (ECL) of 11.0 +/- 2.8 gC m(-2) a (-1), and decreased average NPP, RHE, and HAV by 3.3 +/- 0.7, 14.5 +/- 0.3, and 0.2 +/- 0.0 gC m(-2) a(-1), respectively. Given NPP maintained by crop fertilization and irrigation for crop fields, the erosion-induced soil carbon loss is thus counterbalanced by the decrease in heterotrophic respiration, resulting in an invariant NECB with respect to soil erosion.