Biogeochemical Hotspots as DOC Sources

Hello,
My name is Kyle Corcoran and I am currently a rising senior at Western Carolina University studying Geology with a focus in Hydrology.

Background Information

Below is a conceptual model showing the distribution of soil groups along a representative hillslope located at Hubbard Brook Experimental Forest. The vertical arrows in the diagram below show a typical podzol for the region where the first layers of the solum (surface and subsurface soil layers that undergo the same soil forming processes) are the Organic (O horizon) and A horizons followed by the E horizon where organic acids leach the soil layer of iron and manganese. The Bhs horizon layer that forms under the E is more organic rich than the Bs horizon which is typically richer in metals causing the soil to be redder in coloration. The C horizon (parent material) is typically made up of glacial till and is found below the B horizon. In shallow bedrock areas however, the same soil horizons form differently. This soil forming process occurs because bedrock can commonly cause water to flow laterally due to its impervious nature. The flow of water over the bedrock causes the soil horizons to be deposited downslope of each other rather than vertically which is indicated by the horizontal arrows.

Bailey et al. 2014. Geoderma 226-227 (2014) 279-289.10.1016/j.geoderma.2014.02.017

Initial evidence in recent studies suggest that shallow bedrock areas containing shallow soil layers on top are biogeochemical hotspots. The highest Dissolved Organic Carbon (DOC) concentrations in groundwater have been found to be in the O and E horizons observed near shallow soils on top of shallow bedrock outcrops [Zimmer et al.,2013]. This evidence suggests that these shallow bedrock areas are potential sources of DOC.

REU Project

For my REU project I am focusing on shallow bedrock areas which are suspected to be a source of DOC. I plan to test throughfall in multiple watersheds containing different species of vegetation to have a better understanding of the DOC input in each watershed in relation to the concentration of DOC observed in shallow soil water after storm events. Soil water in the bedrock areas will be collected using no tension lysimeters that were installed on top of bedrock at the base of the shallow soil layers. Soil water samples will be analyzed for DOC, total ions, spectral slope and DOM quality.