SENSITIVITY OF THE US CORN-BELT TO CLIMATE-CHANGE AND ELEVATED CO2 .2. SOIL-EROSION AND ORGANIC-CARBON

Climate models indicate that increasing atmospheric concentrations of carbon dioxide and other greenhouse gases could alter climate globally . The EPIC (Erosion/Productivity Impact Calculator) model was used to examine the sensitivity of soil erosion (wind, water) and soil organic carbon (SOC) (15 cm and 1 m depth) across the US corn belt to changes in temperature (+2 degrees C), precipitation (+/-10%, +/-20%), wind s peed (+/-10%, +/-20%), and atmospheric CO2 concentration (350, 625 ppm v). One-hundred-year simulations were run for each of 100 sites under 36 climate/CO2 regimes. The 100-year regionally aggregated mean water erosion rates increased linearly with precipitation, whereas the wind erosion rates decreased and total erosion rates increased by 15-18%. T otal erosion increased with increased temperature. Increasing CO2 from 350 to 625 ppmv (with temperature increased by 2 degrees C and mean w ind speed held constant) had no effect on water erosion, despite incre ases in annual total and peak runoff; this was attributed to increased vegetation cover. Wind erosion decreased by 4-11% under increased CO2 . Wind erosion was very sensitive to mean wind speed, increasing four- fold and decreasing 10-fold for a 20% increase or decrease in mean win d speed, respectively. This was attributed to a threshold effect. SOC to 1 m decreased 4.8 Mg-C ha(-1) from an initial value of 18.1 Mg-C ha (-1) during the 100-year baseline simulation. About 50% of this loss ( 2.3 Mg-C ha(-1)) was due to transport off-site by soil erosion. SOC in the top 15 cm decreased 0.8 Mg-C ha(-1) from an initial value of 4.9 Mg-C ha(-1). Increased temperature and precipitation accelerated these losses of SOC, whereas increased CO2 slowed the losses. Copyright (C) 1996 Published by Elsevier Science Ltd