Tracer-aided ecohydrological modeling from headwaters to mesoscale catchments: integrated impacts of agricultural activities, landscape gradients and droughts

Abstract:

Ecohydrological modeling can explicitly quantify the partitioning of “blue” and “green” water fluxes. Constraining models using tracers can provide a more realistic representation of ecohydrological functioning (i.e., water flow paths, storage dynamics and ages), including the effects of environmental changes resulting from natural and anthropogenic impacts. Moreover, in the domain of process-based modeling, fully-distributed models have been shown to be advantageous in terms of efficiently capturing the high heterogeneity of natural and anthropogenic controls, and provide a means of linking modeling efforts with multiple data sources at different scales.

We revised the advanced fully distributed, process-based ecohydrological model (EcH₂O-iso model) for the intensively monitored TERENO - Bode catchment (central Germany, ca. 3300 km²), which exhibits high gradients of hydroclimate, geology and landscape characteristics, as well as associated gradients of anthropogenic impacts. The catchment also experienced prolonged drought conditions in recent years (2017-2019). Cross-scale investigations of the potential impacts on ecohydorlogical functioning were set-up from the upland, agricultural headwater (Schäfertal, 1.44 km²) to the mesoscale catchment (Selke, 456 km²). Rich data sets (incl. isotopes monitoring network, long-term, high-frequency hydrometeorological records, and detailed management practices) were collected and integrated for multi-criteria calibrations. Preliminary results showed that (1) isotope data effectively constrained the model uncertainty through tracer simulations, (2) ecohydrological fluxes and water ages showed strong spatial and temporal variability, and (3) the prolonged drought has strong seasonal impacts on the catchment scale ecohydrological fluxes and surface water ages. This study revealed insights into catchment ecohydrological functioning in terms of flux-stroage-age interactions across spatial scales under the changing natural and anthropogenic conditions. This has implications for improved targeting of future monitoring and management of ecohydrologically sensitive areas and periods.