Isotope tracing of critical zone processes for catchment scale water cycling

Abstract:

Here, we used stable water isotopes to improve ecohydrological process understanding in the long-term, mixed-landuse research catchment Demnitz Millcreek (66 km²) near Berlin, Germany. In addition to hydroclimatic monitoring, we documented spatial and temporal isotopic variation from plot to catchment scale across the critical zone in precipitation, throughfall, bulk soil water, vegetation, groundwater, and streams. During the study period, the low relief landscape experienced unusual dry periods resulting in decreasing groundwater levels and an ephemeral-to-intermittent drainage network locally running dry. This was followed by a partial winter replenishment of catchment groundwater storage. These conditions represent anticipated climate change conditions in this region. Tracing the modifications of the precipitation isotopic input signal through the critical zone enabled us to assess water cycling through the critical zone at the catchment scale and to quantify young water fractions of different water cycle components. Our results indicate the importance of groundwater storages for maintaining discharge in such landscapes and differences in groundwater recharge characteristics between soil/landuse units. The surface connectivity of the anthropogenically altered stream network was highly dynamic with implications for stream water ages and in-stream transport. We further saw some resilience of oak transpiration dynamics towards the drought 2018. Further modeling on the plot scale gave preliminary quantities of ecohydrological fluxes in the soil-plant atmosphere continuum. Our findings highlight the importance of vegetation on mediating ecohydrological fluxes in such drought sensitive lowland catchments. This research aims to better understand and manage such ecosystems under climate change conditions.