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We used the process-based and tracer-aided ecohydrological model EcH2O-iso to assess the effects of vegetation cover on water balance partitioning and associated flux ages under temperate beech forest (F) and grassland (G) in Northern Germany. The model was tuned on the basis of a multi-criteria calibration against an unusually rich measured data set from a long-term monitoring site.. The calibration incorporates metrics of the energy balance, hydrological function and biomass accumulation. It resulted in good efficiency statistics for simulations of surface energy exchange, soil water content, transpiration and biomass production. The model simulations showed that the forest "used" more water than the grassland; from 620mm of average annual precipitation, losses were higher through interception (29% under F, 16% for G) and combined soil evaporation and transpiration (59% F, 47% G). As a result, groundwater recharge was greatly enhanced under grassland at 37% of precipitation compared with 12% for forest. The model allowed us to track the ages of water in the different storage compartments and fluxes. In the shallow soil horizons, the average ages of soil water fluxes and evaporation were similar in both plots (~1.5 month), though transpiration and groundwater recharge were older under forest (~6 months compared with ~ 3 months for transpiration and ~ 12 months compared with ~10 months for GW). Flux tracking with Cl tracers provided independent support for the modelling results, though also highlighted effects of uncertainties in forest partitioning of evaporation and transpiration. This underlines the potential for tracer aided ecohydrological models in land use change studies. By tracking storage – flux – age interactions under different land covers, the effects on water partitioning and age distributions can be quantified and the implications for climate change assessed. Better conceptualisation of soil water mixing processes, and improved calibration data on leaf area index and root distribution appear obvious respective modelling and data needs for improved model results. [ABSTRACT FROM AUTHOR]

Characterising stream water quality and the catchment water balance are effective tools for establishing the response of catchments to changing land management practices. Here we examine the influence of constructed riparian wetlands designed to retain nutrients and alleviate agricultural impacts on water quality. This corresponded to a change to more ecological approaches toward farming and reduced nutrient inputs. Soon after this restoration, re-colonisation by beavers (Castor fiber) greatly extended the wetland areas along the river network. We used long-term (~30 year) water quality and stream discharge data in a 70 km2 rural mixed land use catchment in northern Germany. Weekly samples at 5 nested locations along the river network showed spatio-temporal changes in water quality parameters over the 30 year period, whilst long-term hydrological changes were assessed using groundwater levels and discharge monitoring.Water balance estimates indicate high proportions of evapotranspiration loss (75% of total precipitation) and relatively low groundwater leakance (6% of total precipitation) prior to restoration. Increasing groundwater levels from 2000-2017 and the relatively linear-relationship of the catchment storage to discharge, have resulted in a gradual increase of loss by groundwater leakance (11% of total precipitation) while stream discharge has lost a summer diurnal signal. Long-term changes in stream chemistry occurred at almost all sampling sites. Wetland restoration, aided by increasing beaver populations, resulted in longer transit times and increased long-term DOC concentrations downstream, whilst moderating stream temperatures. Declining electrical conductivity, SO4, Ca+ are consistent with long-term catchment flushing of acidic, atmospheric deposition derived from high industrial air pollution prior to 1990, which may have been be enhanced by S reduction in the wetlands. However, there has not yet been a significant decline in N and P concentrations, reflecting long-term fertilizer use and the resulting reservoirs of nutrients in the catchment soils, groundwater and stream sediments. These long-term trends in stream chemistry and hydrology due to stream restoration and changes in agricultural management practices yield invaluable insights into ecohydrological catchment functioning and evidence base for future planning in relation to long-term climatic changes. [ABSTRACT FROM AUTHOR]

Quantifying the internal flow mechanisms within the critical zone relies heavily on interactions between vegetation usage of soil water; however, the sources and ages of many of the water fluxes remain uncertain. We adapted the StorAge Selection (SAS) function framework to estimate the water residence time of storages and transit times of soil and eco-hydrologic fluxes at multiple soil depths in the Scottish Highlands. The approach was applied to data from two podzolic sites with Calluna vulgaris (Heather) as the dominant plant species, and constrained drainage at one site and freely draining soil at the other site.Rapid movement of young water through the soils occurred at both sites, with the youngest water moving faster during high saturation conditions. This faster movement of younger water resulted in relatively stable water residence times in the soils with depth and time. Estimation of the evaporation source from soil depth resulted in particularly high preference for near surface water (0 – 5 cm soil depth, long-term mean age: 50 – 65 days) with relatively limited temporal variability of the source due to relatively high soil moisture near the surface throughout the study period. The assessment of the root-uptake source with depth revealed more temporal variability, favouring deeper water sources (5 – 15 cm) during drier periods and near surface (0 – 5 cm) during wet periods (long-term mean age: 6 – 15 days older than evaporation). The temporal evaluation of the interaction of hydrologic and ecologic responses greatly aids in understanding how the catchment, soils, and vegetation, will respond to future climactic changes. [ABSTRACT FROM AUTHOR]

Permafrost strongly controls hydrological processes in cold regions, and our understanding of how changes in seasonal and perennial frozen ground disposition and linked storage dynamics affects runoff generation processes remains limited. Storage dynamics and water redistribution are affected by the seasonal variability and spatial heterogeneity of frozen ground, snow accumulation and melt. Stable isotopes are useful to quantify the dynamics of water sources, flow paths and ages, yet few studies have employed isotope data in permafrost-influenced catchments. Here, we applied the model STARR (Spatially distributed Tracer-Aided Rainfall-Runoff model) which facilitates fully distributed simulations of hydrological storage dynamics and runoff process, isotopic composition and water ages. We adapted this model to a subarctic catchment in Yukon Territory, Canada, with a time variable implementation of field capacity to include the influence of thaw dynamics. A multi-criteria calibration based on streamflow, snowpack and isotopes was applied to validate three years of daily data. The integration of isotope data in the spatially distributed model provided the basis to quantify spatio-temporal dynamics of water storages and ages underlying the importance of thaw layer dynamics in mixing and damping the melt signal. By using the model conceptualisation of spatio-temporal variant storages, this study demonstrates the value of tracer-aided modelling to capture thaw layer dynamics and to quantify storage and age dynamics in permafrost environment for the first time. [ABSTRACT FROM AUTHOR]