Abstract: The Demnitzer Millcreek catchment (DMC), is a 66 km2 long‐term experimental catchment located 50 km SE of Berlin. Monitoring over the past 30 years has focused on hydrological and biogeochemical changes associated with de‐intensification of farming and riparian restoration in the low‐lying landscape dominated by rain‐fed farming and forestry. However, the hydrological function of the catchment, which is closely linked to nutrient fluxes and highly sensitive to climatic variability, is still poorly understood. In the last 3 years, a prolonged drought period with below‐average rainfall and above‐average temperatures has resulted in marked hydrological change. This caused low soil moisture storage in the growing season, agricultural yield losses, reduced groundwater recharge, and intermittent streamflows in parts of an increasingly disconnected channel network. This paper focuses on a two‐year long isotope study that sought to understand how different parts of the catchment affect ecohydrological partitioning, hydrological connectivity and streamflow generation during drought conditions. The work has shown the critical importance of groundwater storage in sustaining flows, basic in‐stream ecosystem services and the dominant influence of vegetation on groundwater recharge. Recharge was much lower and occurred during a shorter window of time in winter under forests compared to grasslands. Conversely, groundwater recharge was locally enhanced by the restoration of riparian wetlands and storage‐dependent water losses from the stream to the subsurface. The isotopic variability displayed complex emerging spatio‐temporal patterns of stream connectivity and flow duration during droughts that may have implications for in‐stream solute transport and future ecohydrological interactions between landscapes and riverscapes. Given climate projections for drier and warmer summers, reduced and increasingly intermittent streamflows are very likely not just in the study region, but in similar lowland areas across Europe. An integrated land and water management strategy will be essential to sustaining catchment ecosystem services in such catchment systems in future.
The authors are grateful to all colleagues involved in the sample collection and infrastructure installation in the DMC (in particular H. Dämpfling, J. Freymüller, H. Wang, S. Jordan, A. Douinot, A. Wieland, N. Weiß, L. Kuhlemann, C. Marx, L. Lachmann and W. Lehmann). We thank D. Dubbert for support with the extensive isotope analysis, as well as Department 6 of the IGB (in particular T. Rossoll) for help with the sampling, measurement equipment and insights to the long‐term catchment infrastructure and background. We are thankful for trustful collaboration with B. Bösel and technical support by the WLV furthermore access to their well (Wasser und Landschaftspflegeverband Untere Spree)
- ecohydrological partitioning
- intermittent streams
- research catchment
- stable isotopes