Hydrological Controls of DOC in Runoff in a forested Watershed in Germany

Dissolved organic carbon (DOC) plays a crucial role in the global carbon cycle and directly influences water quality and mobility/toxicity of metals. Its concentration is rising in large areas throughout the northern hemisphere with unforeseeable implications for ecosystems. Recent studies have postulated temperature increase and reduction of atmospheric S deposition as dominant drivers of the DOC increase. Here we evaluate long term monitoring data (1989 - 2008) on DOC and runoff chemistry in a forested watershed. We relate the dynamics of DOC to the hydrological regime and to hydrochemical parameters. Additionally, we will use this data set to validate existing models for the prediction of DOC concentrations. The Lehstenbach catchment is located in the south eastern part of Germany. Annual precipitation averages 1150 mm and mean annual temperature is 5.3°C. The watershed size is 4.5 km2 and its elevation ranges from 877 to 695 m a.s.l. A large fraction of the watershed area (about 30%) is occupied by hydromorphic fen soils, which have predominantly formed in the riparian zones that are characterized by very shallow water tables. In the Lehstenbach catchment distinct flow path changes have been documented: under high precipitation, near surface flow determines runoff chemistry and presumably results in high DOC concentrations; under base flow conditions runoff derives from groundwater with low DOC concentrations. Hence changes in the hydrological regime will affect the DOC loadings in catchment runoff. This study is conducted within the framework of the ”Complex Terrain and Ecological Heterogeneity” (TERRECO) program at the University of Bayreuth, Germany.