Spatio-temporal variation of water soluble organic carbon in an intermittent catchment (Hesse, Germany)

The terrestrial carbon cycle is a well researched topic, but for this we basically assume a perennial water flow, which transports the organic carbon along terrestrial flow pathways from the soils to the fluvial network. Climate change will accelerate hydrological processes within water basins and lead to more intermittent catchments, where internal water fluxes will be interrupted and subsurface water flow pathways disturbed due to dry periods. From this perspective, the question arises, what is the impact of an intermittent catchment in the low mountain range on water-soluble carbon transport in the headwaters? To meet this question soil samples were taken seasonally including snowmelt events both in an intermittent and a perennial catchment of a headwater stream over a period of one year. A total number about 700 soil samples were collected in five field campaigns. A transect-based system was used to sample the slopes along the upper slope, middle slope and lower slope. The sample points were chosen to cover all catchment slopes and also the exposures. In the laboratory, the following indicators were determined with the help of a TOC analyser (Shimadzu), C/N analyser (Elementar), photometer (Thermo Fischer) and fluorescence spectrometer (Shimadzu): DOC (WSOC), TOC, SUVA₂₅₄, spectral slopes, BIX, FI and freshness index. The analysis of the comprehensive dataset aimed to build a bridge between the clear changes in the individual events and the annual course and to show how changes, such as the dry fall in the intermittent catchment, 'first flush' effects during heavy rainfall events and new carbon input in autumn through leaf fall impact the spatial and temporal variability of WSOC, which indicates changing of subsurface transport pathways. Preliminary results indicate that indices and total dissolved carbon in the intermittent catchment show differences (factor 0.9) compared to the perennial catchment.