Abstract
Abstract. In drought-sensitive lowland catchments, ecohydrological feedbacks to climatic anomalies can give valuable insights into ecosystem functioning in the context of alarming climate change projections. However, the dynamic influences of vegetation on spatio-temporal processes in water cycling in the critical zone of catchments are not yet fully understood. We used water stable isotopes to investigate the impacts of the 2018 drought on dominant soil–vegetation units of the mixed land use Demnitz Millcreek (DMC, north-eastern Germany) catchment (66 km2). The isotope sampling was carried out in conjunction with hydroclimatic, soil, groundwater, and vegetation monitoring. Drying soils, falling groundwater levels, cessation of streamflow, and reduced crop yields demonstrated the failure of catchment water storage to support “blue” (groundwater recharge and stream discharge) and “green” (evapotranspiration) water fluxes. We further conducted monthly bulk soil water isotope sampling to assess the spatio-temporal dynamics of water soil storage under forest and grassland vegetation. Forest soils were drier than the grassland, mainly due to higher interception and transpiration losses. However, the forest soils also had more freely draining shallow layers and were dominated by rapid young (age <2 months) water fluxes after rainfall events. The grassland soils were more retentive and dominated by older water (age >2 months), though the lack of deep percolation produced water ages >1 year under forest. We found the displacement of any “drought signal” within the soil profile limited to the isotopic signatures and no displacement or “memory effect” in d-excess over the monthly time step, indicating rapid mixing of new rainfall. Our findings suggest that contrasting soil–vegetation communities have distinct impacts on ecohydrological partitioning and water ages in the sub-surface. Such insights will be invaluable for developing sustainable land management strategies appropriate to water availability and building resilience to climate change.
Highlights
Climate change provides an urgent impetus for an improved understanding of ecohydrological interactions in areas where water is limited (Wang et al, 2012)
This study focuses on the Demnitz Millcreek catchment (DMC) long-term monitoring site, a mixed land use catchment located south-east of Berlin in Brandenburg, Germany
We found short-term monthly Standardized Precipitation Index (SPI) values ranged from −2.1 (February 2018) to 1.1 (January 2018)
Summary
Climate change provides an urgent impetus for an improved understanding of ecohydrological interactions in areas where water is limited (Wang et al, 2012). Complementary to hydroclimatic monitoring, stable isotopes as environmental tracers can provide insights into ecohydrological processes in the “critical zone” (Grant and Dietrich, 2017) They have been used to investigate evaporation (Allison and Barnes, 1983; Barnes and Allison, 1988), groundwater recharge (Koeniger et al, 2016), weathering influence on flow paths (Bullen and Kendall, 1998), as well as water ages (Tetzlaff et al, 2014; Sprenger et al, 2019b), plant water uptake (Rothfuss and Javaux, 2017), and the partitioning of evapotranspiration (Kool et al, 2014; Xiao et al, 2018). 3. discuss the implications of ecohydrological processes for the response times and recovery of hydrological stores in the DMC by combined use of hydroclimatic and isotope data
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