The Role of Molecular Dissolved Organic Matter (DOM) Composition to Identify Sources and Release of DOM and Trace Elements in Catchments of Drinking Water Reservoirs in Mid-Latitude Mountain Areas – (DOMtrace)A Solid Phase Analytic Pyrolysis (Py-GC-MS, TH

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Evidence of increasing concentrations of dissolved organic matter (DOM) in the surface waters of temperate regions of the Northern Hemisphere is rapidly accumulating. This is largely ascribed to enhanced DOM release from accelerated decay of organic matter from catchment soils, in particular peat deposits, and subsequent DOM transport through streams and rivers into lakes and reservoirs. Besides the importance of DOM for the global carbon cycle and climate projections, "browning" of drinking water reservoirs by DOM brings along many environmental problems and issues related to management, such as declining quality of drinking water, increased expenses on chemicals and increases in heavy metal contamination. Even though DOM quality is one of the key parameters in DOM dynamics, its molecular composition and its relation to land-use, vegetation of the catchment, peat hydrology or heavy metal transport are hardly understood. Moreover, peatlands and forest soils in mountainous areas are often contaminated by heavy metals (Pb, Hg, Zn etc.) and arsenic as a result of centuries of mining activities. We propose research on a drinking water reservoir in the Harz Mountains (Eckertalstausee) and its catchment, where the phenomenon of DOM increase has been recognized for several years now. Even though it is generally assumed that the elevated DOM discharge is associated with peat decomposition, direct evidence of peat as the major DOM and heavy metal source is not available. We propose to monitor the molecular composition of the DOM in the Eckerstausee reservoir, its main tributary, the Ecker stream, and several other streams that drain either peatlands or soils under coniferous forests, for a period of 12 months. We aim to understand the seasonal and spatial variability in DOM load, its sources and its role as a vehicle for trace elements as a function of the molecular DOM composition. Different from other studies DOM composition analyses will focus on solid phase Pyrolyse-GC-MS and Thermally assisted Hydrolysis and Methylation -GC-MS measurements supported by spectroscopic methods and trace element analyses. Hence, this proposal will contribute to filling a gap in our knowledge on the biogeochemical cycle of DOM, more particularly to identify the main suppliers of DOM and trace pollutants to drinking water reservoirs, using the Eckertalstausee as a natural laboratory