Project Leader: Prof. Dr. Doerthe Tetzlaff (IGB Leibniz Institute of Freshwater Ecology and Inland Fisheries)

C1 will use and assess the value of stable water isotope data in conjunction with other environmental variables (e.g. data on C dynamics (from project B1); ecosystem-atmosphere fluxes (from B2); 13C and soil physical characteristics (from B5, S2); root and vegetation dynamics (from A1, B4, C2, C3, S3) obtained spatially distributed at plot – peatland – landscape scales within WETSCAPES2.0. Stable water isotopes can be used as “fingerprints” of water allowing to quantify sources and pathways of water but also estimating the ages of different waters. Water age is an important metric of hydrological functioning in terms of response and recovery times after climatic perturbations. The passage of conservative, environmental tracers (e.g., water isotopes, chloride, tritium) through the landscape allows quantifying the dampening of precipitation input signals by internal mixing processes and connections between different spatial units, including deeper groundwater. This provides estimates of the storage water volumes needed to damp the tracer input signal, and thus, quantifies total storage dynamics in landscapes (which is usually only derived from soil moisture dynamics). When isotopes are integrated into so-called isotope-aided models, new insights into mechanisms of water cycling and total storage dynamics are possible, e.g. on heterogeneous vertical and lateral flows of soil water, fluctuations in groundwater recharge, preferential uptake of soil water held under different tensions and at different (rooting) depths by plants for transpiration, storage connectivity, etc. So far, such integrated investigation and analysis of hydrological dynamics has not been done in rewetted fens. The objectives of C1 are to (i) fundamentally advance and test the capacity of process-based, tracer-aided, ecohydrological modeling frameworks and thus, to (ii) investigate the hydrological functioning of rewetted fens from the plot scale (ca. 10*10m²) up to the landscape scale (ca. 100km2) in terms of spatial patterns and temporal dynamics of water storage, pathways and release. To achieve this, C1 will (1) use water isotope data measured across spatial scales and from different waters from different fen landscape compartments to drive a process-based, tracer-aided ecohydrological model; (2) develop new modules and codes to incorporate fen specific ecohydrological processes and test different data streams in multi-criteria model calibration and uncertainty assessment to improve the quantification of ecohydrological partitioning of rewetted fens (i.e. water storage versus release); and (3) assess how such model improvements aid upscaling of ecohydrological fluxes and storage from the plot to the landscape scale. C1 will further use forcing data (remote sensing data on vegetation dynamics, data on local climate) from C4, C5 and parametrization of GHG fluxes from A7 and CO2  fluxes from C5 to improve model parametrisation in terms of vegetation dynamics. C1 will also feed into and be closely linked with S4 as the tracer-aided model used and enhanced in C1 will be one of the models used in S4. Thus, C1 will play an essential integrating role in WETSCAPES2.0 through data-driven, process-based modeling of water cycling, storage dynamics and pathways in restored fens across different spatial and temporal scales. C1 will contribute quantifications of spatio-temporal dynamics of water storage, sources, pathways and ages (which provide important hydrological indices of the timescales of water cycling and resilience to perturbation) up to the landscape-scale.