The first phase of A14 primarily dealt with the analysis and modelling of high-resolution streamflow and environmental variables at the catchment scale. A14 focussed on novel simulation methods for anthropogenic water structures and stream temperature with SWAT+. We designed and applied new methods for Distributed Temperature Sensing (DTS) in gravel-bed rivers to measure river-bed temperature. We additionally developed and provided SWAT+ models for RESIST’s research areas, the Boye, including the extension to the Rotbach, and Kinzig catchments, based on high-resolution climate and land-use data. In the Kinzig, the integration of high-resolution land management data and the source code adaptations to more realistically simulate water structures improved the process representation and thus the hydrological simulation significantly. This new approach was also tested in the Boye model, where a high number of anthropogenic flow modifications was represented with the new decision table features of SWAT+. We improved the United States Geological Survey’s (USGS) EflowStats package to enable the calculation of tailored species-relevant hydrological indicators (Blodgett et al., 2023). The SWAT+ models and indicators were used by five other projects that led to six joint publications with A14. In addition, a comprehensive German-wide dataset of high-frequency water quality and discharge time series was collected. Based on this dataset, A14 investigated and revealed asymmetric responses, hysteresis, and concentration-discharge relationships between water quality parameters and streamflow which represents important information to improve the simulation of export processes. The data, methods, and models developed by A14 in Phase I laid a strong foundation for Phase II.

Phase II will focus the analysis of stressor interactions to climate change related stressors and will address the increasing temperatures and extended low flow, desiccation and rewetting periods that have been highly intensified since 2018 and that are projected to further intensify in the future. A14 will therefore be the first project modelling primary and secondary stressor interactions in two catchments with diverse anthropogenic impacts in varying degrees of pollution and hydrological impairment. It will focus on the Boye/Emscher and Kinzig catchments, whereby the Boye model will be extended to the whole Emscher system to allow the investigation of the recovery process of the formerly heavily polluted main stem. The extension to the Emscher is of particular interest to A14 in Phase II to study the recovery of hydrological and water quality processes, allow a more in-depth comparison with the equally sized Kinzig catchment, include a higher variety of streams from more natural to anthropogenically influenced sections that a are subject to increased low flow periods, desiccation and rewetting. In addition, a rich database for building hydrological models is available for the Emscher system from EGLV. With these analyses, project A14 contributes to testing Main Hypothesis (MH) 1.1 and will provide detailed process knowledge and environmental data on event-based (short-term) and chronical (long-term) stressors focussing on low flow, desiccation, and rewetting periods on different time scales. It will focus on the analysis and simulation of the central stressors within RESIST such as temperature and salinity in addition to water fluxes and oxygen content. This involves the analysis of event-based and long-term low flow, desiccation and rewetting cycles using spatially and temporally aligned soil moisture and streamflow data with the RESIST stressors, as well as the assessment of long-term air temperature increases and soil moisture changes on water temperature, oxygen, and salinity. Supported by this analysis, high-resolution low flow, desiccation, and rewetting processes will be simulated in the new model version SWAT+ gwflow, which became recently available and is expected to simulate groundwater-surface water interaction and low flow processes more realistically. Results will be compared with observations of low flow, desiccation and rewetting events collected within field work conducted within Phase II. The source code improvements of water temperature and water structures developed in Phase I will be transferred to SWAT+ gwflow model to simulate the RESIST stressors with a focus on low flow, desiccation and rewetting conditions. A14 will exclusively work on the catchment scale and investigate processes down to the river reach-, and field scale, which is a clear differentiation to the large-scale modelling of A24. A14 will continue its strong collaboration within RESIST and provide crucial data and model outputs to various projects. Based on the improved model outputs, ecohydrological indicators will be generated to describe hydrological stressors and environmental variables, focusing on low flow periods, desiccation and rewetting. These indicators will be used by collaborating subprojects in Species Distribution Models (SDMs) and meta-community models to simulate ecological degradation and recovery as well as species occurrences.

Kristin Peters (Kiel University)

Spatio-temporal dynamics of environmental variables, stressors and their interactions on the instream- and catchment scale

Streams constitute highly dynamic ecosystems and are – worldwide – affected by multiple stressors resulting from anthropogenic water and land uses. These stressors often interact in complex, nonlinear ways and impact biodiversity and ecosystem functions negatively. The A14 subproject of RESIST aims to understand spatio-temporal dynamics of in-stream environmental variables that follow an asymmetric function to catchment management, due to history, storage- and hysteresis effects in the hydrologic system. The focus lies on assessing, understanding and simulating the baseline conditions, asymmetric responses and variable interactions in the connected catchment- and stream system on a high spatio-temporal resolution.

This will be accomplished through field surveys, data analyses and improving the simulation of the ecohydrological and physicochemical environmental variables in the catchment model SWAT+. Especially water temperature is of importance since it is a key variable interacting with dissolved oxygen and nitrogen components. The combined field surveys therefore include continuous observations of environmental variables as well as drone-based and distributed temperature sensing observations of high-resolution surface- and river bed water temperature.

Contact: kpeters@hydrology.uni-kiel.de

First Supervisor: Prof. Dr. Nicola Fohrer (Kiel University, Hydrology and Water Management)
Second Supervisor: Prof. Dr. Sonja Jähnig (Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Ecosystem Research)
Mentor: Dr. Jens Kiesel (STONE Environmental)