BIOGEOCHEMICAL HOTSPOTS IN SHALLOW TO BEDROCK ZONES: SOURCES OF DISSOLVED ORGANIC CARBON (DOC) IN THE APPALACHIAN MOUNTAIN REGION OF THE EASTERN USA

Sources of dissolved organic carbon (DOC) to headwater streams are important in understanding carbon delivery and metal mobilization to downstream ecosystems. We investigated DOC sources in shallow soils on top of bedrock in the northern and southern Appalachian region to test the hypothesis that organic matter in this portion of the catchment is a hotspot for DOC generation and a significant contributor of DOC to streamwater. In order to examine this hypothesis in the Appalachian mountain region of the eastern USA, we instrumented catchments at the Hubbard Brook Experimental Forest (HBEF) in North Woodstock, NH, and the Wolf Creek watershed (WC) in Cullowhee, NC. Soils in the HBEF developed in glacial till while the soils in WC developed in unglaciated residuum. Zero-tension lysimeters were installed under the base layer of organic horizons in both shallow organic soils over bedrock and the deeper mineral soils (>20cm) found within the catchment. Throughfall collectors were installed near sample sites to understand the differences of DOC concentration in coniferous forests, hardwood forests, and their inputs to the soil. DOC concentrations were compared to organic horizon thickness and DOC concentrations to determine relationships controlling DOC sources. Shallow soils on top of bedrock had the highest DOC concentrations in the HBEF catchment in contrast to the WC watershed. As shallow soils on bedrock are shown to be hotspots for DOC at HBEF but not WC, future work should focus on why these differences exist between watersheds. Another important focus should be the investigation on metal mobilization in these zones due to complexation with organic compounds.