Citation. Cheng, H. H.; Bell, J. C.; Molina, J. A. E.; Reece, C.; Bliss, N. 1993. Assessing the potential impact of global climate changes on soils as sinks or sources of CO₂ in the terrestrial carbon cycle. Final report on project NAG 5-1846 to NASA.   [1018  LTERCC]

Abstract. The specter of climate change has raised many questions regarding the interaction of terrestrial systems on atmospheric carbon (C) under conditions of climate change. The soil is a major repository of C in terrestrial systems and could act as either a sink or a source for atmospheric C and either ameliorate or accelerate increases in atmospheric C. The spatial complexity of soils properties complicates efforts to predict temporal changes in soil organic carbon (SOC) in response to environmental stresses. The purpose of this research was to investigate an approach to consider both spatial and temporal variability of SOC under different scenarios of climate change. Three study sites in different physiographic regions of Minnesota were chosen to compare spatial and temporal changes in SOC both with the local landscapes and among the physiographic regions. Within local landscapes, SOC in the surface mineral soil horizons ranged from 1,260 to 15,824 g m^-2 for sandy glacial outwash soils as Cedar Creek, 4,415 to 9,905 g m^-2 for medium-textured glacial till soils at Lamberton, and 6,832 to 9,576 g m^-2 for fine- and medium textured laustrine soils at Crookston. Similar ranges were found for estimates of SOC at 15-cm and 100-cm depths. The average rates of SOC storage in the surface soil horizons across the landscape were estimated at 3,275 g m^-2 for Cedar Creek, 6,264 g m^-2 for Lamberton, and 7,558 g m^-2 for Crookston. The total amount of C stored in Minnesota soils was estimated at 4423 Tg of C from the State Soil Geographic (STATSGO) database, although this estimate is probably low since only the surface soil horizons were considered for many soils, including organic deposits. Temporal changes in SOC for gradual deviations of temperature and precipitation from historical patterns over a 50-year time period were simulated for all soils in the three landscapes using a SOC dynamics model (CENTURY). The simulations indicated that soils within the same landscape may have different responses to climate change. Soils in well-drained portions of the landscape were more sensitive a decrease in precipitation than were poorly or very-poorly drained soils. From a regional perspective, sandy soils with low moisture retention capacities were more sensitive to decreases in SOC from a drop in primary productivity. Mean temperature increases of 3°C and 5°C resulted in simulated decreases of SOC, with varying magnitudes depending on soil conditions. While the magnitude of simulated changes of SOC is dubious due to the uncertainties and assumptions associated with the SOC dynamics model, the model simulations indicate that SOC transformation processes and plant productivity will respond differently to changing climates within the same landscape and among different physiographic regions.