Abstract
AbstractRecent studies have highlighted the importance of understanding ecohydrological drought feedbacks to secure water resources under a changing climate and increasing anthropogenic impacts. In this study, we monitored and modelled feedbacks in the soil–plant‐atmosphere continuum to the European drought summer 2018 and the following 2 years. The physically based, isotope‐aided model EcH2O‐iso was applied to generic vegetation plots (forest and grassland) in the lowland, groundwater‐dominated research catchment Demnitzer Millcreek (NE Germany; 66 km2). We included, inter alia, soil water isotope data in the model calibration and quantified changing “blue” (groundwater recharge) and “green” (evapotranspiration) water fluxes and ages under each land use as the drought progressed. Novel plant xylem isotope data were excluded from calibration but were compared with simulated root uptake signatures in model validation. Results indicated inter‐site differences in the dynamics of soil water storage and fluxes with contrasting water age both during the drought and the subsequent 2 years. Forest vegetation consistently showed a greater moisture stress, more rapid recovery and higher variability in root water uptake depths from a generally younger soil water storage. In contrast, the grassland site, which had more water‐retentive soils, showed higher and older soil water storage and groundwater recharge fluxes. The damped storage and flux dynamics under grassland led to a slower return to younger water ages at depth. Such evidence‐based and quantitative differences in ecohydrological feedbacks to drought stress in contrasting soil‐vegetation units provide important insights into Critical Zone water cycling. This can help inform future progress in the monitoring, modelling and development of climate mitigation strategies in drought‐sensitive lowlands.
Highlights
Sustaining water resources and ecosystem services are complex challenges in the context of accelerating land use and climate change in the Anthropocene (Gleeson et al, 2020)
The severity of impacts from the drought which started in 2018 on green water fluxes was evident in reduced crop yields in the catchment and communicated by local stakeholders engaged in DMC farming and forestry, where crop yields were 40% lower in 2018 and the effects of reduced groundwater are expected to persist for several years (Kannenberg et al, 2019)
The presented study quantified such partitioning in two land use units in a lowland, drought sensitive catchment that is dominated by green water fluxes and where surface water and associated ecosystem services are groundwater dependent
Summary
Sustaining water resources and ecosystem services are complex challenges in the context of accelerating land use and climate change in the Anthropocene (Gleeson et al, 2020). One way forward to address existing knowledge gaps is integrating multiple streams of relevant data into the calibration and validation of process-based ecohydrological models (Fatichi et al, 2016; Guswa et al, 2020) Such models facilitate quantitative estimates of blue and green water fluxes from different soil-vegetation systems. We aim to build on preliminary work by Smith, Tetzlaff, Kleine, et al (2020), to integrate new and extended isotopic data from the subsurface and vegetation into an integrated monitoring and model-based assessment of how prolonged (two subsequent vegetation growing periods) drought affects ecohydrological feedbacks in two contrasting soil-vegetation units. As the study period ended in September 2020, the values allow inter-site comparison rather than inter-annual comparisons
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