Thursday, November 8, 2007 - 8:45 AM
349-2
Watershed-scale Assessment of Soil Carbon with Geographical Information Systems.
Soils represent the largest pool of terrestrial carbon stock and play an important role in the global carbon cycle. In this study we quantified soil organic carbon (SOC) storage across Louisiana’s landscape and assessed factors that affect the SOC spatial distribution in Louisiana’s watersheds. Several geographically-referenced datasets were employed for the large-scale soil carbon assessment. The Soil Geographic Database (STATSGO) was used to aggregate and estimate carbon densities for different soil layers. The National Land Cover Dataset (NLCD) was used to assess the impact of land use on soil carbon density. Terrain attributes and watershed characteristics, such as drainage densities and watershed slopes, were analyzed from the USGS 1:24K Digital Elevation Model (DEM), U.S. Census Bureau Topologically Integrated Geographic Encoding and Referencing (TIGER)/line water features, and Louisiana Department of Environmental Quality (LDEQ) sub-watersheds. The results indicated that soils in Louisiana contained a total of 0.5 Pg (1 pentagram =1 1015g =1 billion metric tons), 0.98 Pg, and 1.4 Pg of organic carbon in their top 30-cm, 100-cm, and the maximum depths, respectively. The historical and current Mississippi river deltaic lobes were the most important areas with highest SOC densities occupied by Entisols soils. Emergent herbaceous wetlands had the highest SOC density among all land cover classes. Grasslands, herbaceous, shrublands, and residential lands in Louisiana had unexpectedly higher SOC densities than forests and crops lands. SOC densities appeared to be positively correlated with drainage density (Pearson correlation coefficient, r=0.61 at watershed scale, r=0.57 at BASIN scale), but was negatively correlated with slope gradient (r=-0.60 at watershed scale, r=-0.83 at BASIN scale). R2 of non-linear regression between SOC densities and average elevations at watershed scale was 0.57 (p<0.0001). R2 of multiple linear regression model among SOC densities, slope ranges, mean slopes and drainage densities at BASIN scale was 0.83 (p=0.0018).
Key words: Soil organic carbon, STATSGO, spatial analysis, land use, Louisiana, landscape, climate change
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