Biogeochemical Hotspots in Shallow to Bedrock Zones: Sources of Dissolved Organic Carbon (DOC) in the Appalachian Mountain Region of the Eastern USA.

Abstract:

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 near the catchment divide to assess the hypothesis that organic matter in this portion of the catchment is 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 Hubbard Brook Experimental Forest (HBEF), NH, Upper Long Branch Experimental Watershed (UPL), NC and Panthertown Valley (PV), NC. Soils in the HBEF developed in glacial till while the soils in ULB and PV developed in unglaciated residuum. No-tension lysimeters were installed under the base layer of organic horizons in both shallow organic soils and the deeper mineral soils found downslope. Throughfall collectors were installed near sample sites to understand the differences of DOC concentration in coniferous and hardwood forests and inputs into the soil. DOC concentrations were compared to organic horizon thickness and flow regime to determine relationships controlling DOC sources. Shallow soils on top of bedrock had the highest DOC concentrations in the catchment in contrast to throughfall and streamwater chemistry. As shallow soils on bedrock are shown to be hotspots for DOC, future work should focus on the mobilization of metals in these zones due to complexation with organic compounds.