Intermittency affects the self-purification capacity of headwater streams by changing the viability of biofilms and, thus, the intensity of biogeochemical processes in the benthic and the hyporheic zone. The main objective of the project is to investigate the effects of intermittency on the self-purification capacity of gravel bed streams in temperate climate zones. We are investigating the effects of drying and re-wetting on biofilm communities and on the organic carbon and nutrient cycling in the hyporheic zone via experimental flumes specifically designed for this purpose. The flumes are 5 m long, 0.6 m wide, and 1.2 m deep and are filled with gravel up to a depth of 80 cm. Inlets and outlets at different sediment depths allow us to lower the water level in the flumes until only a residual flow in the bottom sediment layer is left, thus simulating partial desiccation common for temperate regions. Experiments will deal with the effects of drought conditions (e.g., drought duration, drought frequency, and speed of re-wetting) and sediment composition (e.g. proportion of fine sediments, POM content) on the resistance and the resilience of hyporheic communities and processes under pristine and slightly nutrient-enriched conditions.