Project A14

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

Hypothesis 1 ARC 1 ARC 2 Field studies Models Synthesis Nutrient cycling

Project leader

Prof. Dr. Nicola Fohrer

Project Summary

The spatio-temporal dynamics of in-stream environmental variables follow an asymmetric function to catchment management (e.g. degradation and recovery), due to history, storage- and hysteresis effects in the hydrologic system. We aim to (1) investigate and test these effects on in-stream temperature, dissolved oxygen, nitrogen components and salinity (TONS) in relation to hydrology considering that these environmental variables interact, (2) include the asymmetric response and variable interaction in a catchment model to improve the simulation and (3) supply the results to six projects of the CRC (A11, A12, A13 and A15, A16, A17 to enable the depiction of the asymmetric response from changes in the catchment to the impact on organisms. This project investigates the CRC’s Main Hypothesis MH2a in detail, focussing on the assessment of environmental variables and resulting multiple stressor effects instream and at catchment level. This will provide the framework to downscale human activities on the catchment scale to their biota-relevant impact on individual river transects.

The Emscher/Boye and the Kinzig river networks will serve as our main modelling areas. The focus of A14’s CRC-Phase 1 will lie 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 as relevant for the biota and required by the partner projects (Fehler! Verweisquelle konnte nicht gefunden werden.). 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+. The combined field surveys (in the framework of Project Z02) will include continuous observations of TONS as well as drone-based and distributed temperature sensing observations of spatially distributed surface- and riverbed water temperature. Especially water temperature is of importance, since it is a key variable interacting with dissolved oxygen and nitrogen components. This, as well as historically available data, will be used to improve the stressor simulation in SWAT+ in close cooperation with the model developers. This improvement will target spatio-temporal simulation accuracy, the depiction of asymmetric response through implementing hysteretic operators in the algorithms where needed, and interactions of environmental variables in SWAT+. In the data analyses, we will investigate the asymmetric stressor response in both observations and simulations through the comparison of hysteresis indices to test if observed asymmetric response is adequately represented in the models, or if hysteretic operators need to be added or adapted.

Ensuring that the asymmetric response of environmental variables is incorporated into the models will greatly enhance our capabilities to simulate impacts of catchment degradation and recovery. It will also set the prerequisite to transform climate scenarios, management options, as well as past-, current- and restored conditions of streams and connected landscapes into spatio-temporal environmental variables, which will become relevant in later CRC-Phases.