Liu, Shuguang (SAIC, USGS National Center for EROS, Sioux Falls, SD, 57198; Phone: 605-594-6168; Email: sliu@usgs.gov)

Spatial and Temporal Patterns of the Contemporary Carbon Sources and Sinks in the Ridge and Valley Ecoregion of the United States

S. Liu *, T.R. Loveland

Quantification of the magnitude, geographic locations, and identifying the major driving forces of the terrestrial carbon sources and sinks are among the major goals of the North American Carbon Program. As part of a project that is designed to quantify the spatial and temporal distributions of the terrestrial carbon sources and sinks in the conterminous United States since 1973, we simulated the carbon dynamics in vegetation and soils in the Ridge and Valley ecoregion of the United States using the General Ensemble Biogeochemical Modeling System (GEMS). Land cover change information was derived from Landsat data acquired in 1973, 1980, 1986, 1992, and 2000 within 40 randomly located 10-km by 10-km sample blocks. Results indicate that urban and forest areas have been increasing, whereas agricultural land has been decreasing since 1973. Forest clear-cutting activity has intensified from 1973 to 2000. Overall, the Ridge and Valley ecoregion has been acting as a carbon sink since 1973. However, the sink strength has declined continuously during the study period owing to forest aging in the northern part of the ecoregion and increased forest clear-cutting activities in the south. Land cover and land use change and climate interannual variability were the primary drivers that determined the spatial and temporal variability of carbon sources and sinks. The relative contributions to the sink from soil organic carbon and harvested materials have increased over time, implying that these components deserve more study in the future