Interactions of stressors affecting environmental variables

Very often, stressors do not act directly on organisms but modify the intensity of secondary stressors, which eventually affect biota. It is therefore crucial to better understand the interactions between stressors and we have evaluated that matter within RESIST.

To gain a more complete overview of interactions between stressors, we collected an unprecedented dataset composed of 72 high-frequency, sub-hourly continuous time series across Germany. With these, we calculated the share of events in nine hysteresis classes for eight water quality parameters. Particularly water temperature, oxygen, pH, ammonium, turbidity and chlorophyll are subject to increasing concentrations (enrichment) as discharge events unfold. These variables also exhibit a slow response, indicated by the occurrence of the concentration peaks usually after the discharge peak. The environmental variables nitrate and conductivity, on the other hand, tend to be governed more by dilution effects.

We also developed a mechanistic model for predicting the concentration of oxygen dissolved in water, in which the influence of temperature and salinity on the processes that influence dissolved oxygen dynamics is considered. The model considered, besides phytoplankton, also macrophytes and periphyton, which represents a step forward.

Our studies on interactions between stressors support parts of RESIST’s Main Hypothesis MH1, i.e. that primary stressors lead to secondary stressors that may impact organisms.