The Asymmetric Response Concept (ARC) provides a conceptual framework that allows for testing recovery processes of riverine biota following stressor release. In Phase I, Project A17 challenged the ARC with spatially distributed and time series data on benthic invertebrates from the restored Boye catchment recovering from severe pollution, and from the unrestored but moderately disturbed Kinzig catchment. In the restored Boye catchment, we observed that (i) random starting communities colonise freshly restored streams and are gaining similarity with time since restoration, as in-stream habitats develop; (ii) in the initial phase of recovery, dispersal is a key process, while with time since restoration competition with already established species gains relevance; (iii) water quality issues and extreme hydrological events impede full recovery of restored streams. In the Kinzig catchment, we observed (i) spatially, less-disturbed communities as compared to the Boye that were characterised by higher taxonomic and trait diversity and occurrence of pollution-sensitive taxa; (ii) temporally, improvements in water quality following land-use change resulted in partial recovery of benthic invertebrates in upstream sites; (iii) long-term chemical data explained about 50% of the overall variance in benthic invertebrate community trends; (iv) functions recovered faster than community composition.

In Phase II we will (1) investigate multidecadal trends in benthic invertebrate metacommunity structure at the model catchment scale (Kinzig and Boye/Emscher) during different stages of recovery, and extend our findings to the scale of Germany by (2) examining drivers and pattern of recovery trajectories of benthic invertebrate communities, and by (3) analysing and comparing trajectories of three different riverine organism groups (benthic invertebrates, fish, diatoms). For (1), we expect that due to stressor release metacommunity structure will change with time since restoration with an increased relevance of the local processes environmental filtering and biotic interactions, while dispersal as regional process will decline in relevance. Furthermore, we expect that drivers will fundamentally differ between differently disturbed and restored catchments. This will be tested with unique time series data from the Kinzig and Boye catchments, and the recently restored Emscher main stem that is currently recovering from severe pollution. For benthic invertebrate communities, we further expect (2) predictable differences in recovery patterns and drivers between cases of recovery starting from moderate or severe degradation, and between cases of recovery from different stressor types. This will be tested with a unique array of time series of benthic invertebrates and environmental variables from all over Germany. Finally (3), we expect differential recovery trajectories for diatoms, benthic invertebrates and fish in terms of recovery speed and drivers of recovery, due to difference in the importance of environmental filtering (i.e. tolerances), biotic interactions, and dispersal. This will be tested with time series from all over Germany, leading to the designation of recovery categories and indicator species for these categories. Overall, A17 will be the first to comprehensively analyse and synthesise the effects and drivers of recovery for a wide range of cases and organism groups.

Svenja Gillmann (University of Duisburg-Essen)

Temporal and spatial effects of stressors, biotic interactions and dispersal on riverine benthic invertebrate community variability

Changes in biological communities are mainly driven by stressors (natural and human-induced), biotic interactions and dispersal capacities of the different species. While each of these drivers has been investigated individually, they have never been addressed in concert. To disentangle the role of the three drivers for community variability, this project is focusing on the riverine benthic invertebrates that occur in the Emscher/Boye and Kinzig catchment. During this study it will be investigated how the role of the drivers changes within and between benthic invertebrate communities at near-natural, degraded and restored sites.

Therefore, extensive ecological profiles for all species occurring in the Kinzig and Emscher/Boye catchment will be created, which include niche profiles, comprising habitat preferences and stressor tolerances. By comparing the niche preferences of the different species, biotic interaction profiles will be developed, describing possible biotic interactions such as competition between species. Lastly, the dispersal capacity of the different species will be included in the ecological profiles. Environmental site profiles for each combination of study site and year will be created for both catchments. These will include the respective habitat availability, water quality parameters, time since restoration (if applicable) and distance to recolonization sources. Then, the ecological profiles will be matched to the environmental profiles to identify the niches that have already been occupied in the process of recovery or following fluctuations in environmental variables and along landuse gradients. The resulting data will be used to assess the role of the drivers of community variability in near-natural, differently degraded and restored stream reaches.

Contact: svenja.gillmann@uni-due.de

First Supervisor: Prof. Dr. Daniel Hering (University of Duisburg-Essen, Aquatic Ecology)
Second Supervisor: Prof. Dr. Peter Haase (University Duisburg-Essen, Senckenberg Forschungsinstitut und Naturmuseum)
Mentor: Dr. Mario Sommerhäuser (Emschergenossenschaft und Lippeverband)