Abstract
AbstractThe 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.
Highlights
Global climate change and population growth are increasing pressure on agricultural landscapes, threatening food and water security in many lowland catchments
Water stable isotopes were used to supplement existing data in a longterm research catchment to enhance our understanding of ecohydrological function and catchment-scale connectivity
Our sampling over 2 years coincidentally captured catchment responses to drought conditions
Summary
Global climate change and population growth are increasing pressure on agricultural landscapes, threatening food and water security in many lowland catchments. We report an investigation that sought to up-scale insights from these initial plot-scale studies (Kleine et al, 2020; Smith et al, 2020b), through catchment-scale isotope monitoring of precipitation, soil water, groundwater and stream water over a >2-year period. This complemented and leveraged data from an existing, longer term hydrometric infrastructure. To assess for spatial variations in the isotopic composition of precipitation inputs, weekly rainfall samples were collected at four locations (from July 2018) along the stream network from rain gauges (Figure 1e; Marxdorfer St., Bruch Mill, Demnitz Mill, Berkenbrück). This simple method allowed estimating the soil storage as volumetric percentage from the total (1000 mm) soil profile for inter site comparison
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