Projecting Soil Organic Carbon Distribution in Central Chile under Future Climate Scenarios

Soil organic C (SOC) is the largest terrestrial C pool, and it influences diverse soil properties and processes in a landscape. At global scales, SOC is related to climate; as climate changes, we expect that SOC will change at broad scales as well, but how SOC will respond to climate change in diverse environments is complex and highly uncertain. To evaluate the potential impact of predicted changes in temperature and precipitation across central Chile, we first estimated current SOC content using pedon descriptions and environmental variables (temperature, rainfall, land use, topography, soil types, and geology) as predictors. A random forest statistical model was used to predict SOC content by pedon data. Maps were created for six standard depths of the GlobalSoilMap project. Results showed mean SOC of 54 g kg at a depth interval of 0 to 5 cm, 51 g kg at 5 to 15 cm, 42 g kg at 15 to 30 cm, 29 g kg at 30 to 60 cm, 17 g kg at 60 to 100 cm, and 11 g kg at 100 to 200 cm. Model validation, withholding 25% of pedons, showed values of 0.70, 0.73, 0.75, 0.65, 0.56, and 0.29 for six depths, respectively. Two future temperature and precipitation for climate change scenarios, representative concentration pathways RCP4.5 and RCP8.5 from the NASA GISS-E2-R models, were considered in predicting SOC in 2050 and 2080. We found that central Chile would experience a loss of SOC in the depth range of 0 to 30 cm, averaging 9.7% for RCP4.5 and 12.9% for the RCP8.5 scenarios by the year 2050, with additional decreases of 8% in the RCP4.5 scenario and 16.5% under RCP8.5 by 2080.