SFB 1439:  Multilevel response to stressor increase and release in stream ecosystems (RESIST)

treams constitute highly dynamic ecosystems and are – worldwide – affected by multiple stress-ors. These stressors often interact in complex, nonlinear ways to impact negatively on biodiversity and ecosystem functions. A mechanistic understanding of the processes underlying degradation and recovery of riverine biota, however, has yet to emerge, but is required to accurately predict stressor effects, their interactions and impacts on biodiversity and ecosystem functioning, and eventually to manage the recovery of degraded freshwater ecosystems. In Phase I, we have published and tested a novel theoretical framework to disentangle mecha-nisms causing stressor interactions during phases of ecosystem degradation and recovery: the ‘Asymmetric Response Concept’ (ARC). As the central tenet of the ARC, the significance of ‘toler-ance’, ‘dispersal’ and ‘biotic interactions’ differs fundamentally between phases of degradation and recovery. We tested three main hypotheses addressing the role of the ARC processes during phases of degradation and recovery, the response of different organism groups to these process-es, and the rates of recovery of community composition and ecosystem functioning. We performed large cooperative experiments with the indoor AquaFlow and the outdoor Ex-Stream mesocosm systems and cooperative field investigations in two catchments, the restored Boye/Emscher catchment and the moderately disturbed Kinzig catchment, and we have tested our hypotheses with statistical and mechanistic models. Main results included that (i) dispersal plays a key role in initial recovery phases of macroorganism communities, and biotic interactions gain rele-vance later, while for microorganisms biotic interactions inhibit recovery; (ii) stressors affecting wa-ter quality impact all organism groups, while stressors affecting hydromorphology have impacts mainly on macroorganisms; (iii) functions recover faster than community composition. Altogether, RESIST has yet published 50 papers, while 20 studies are available as pre-prints. For Phase II, we have refined our Main Hypotheses to include differences between recovery from moderate and severe degradation. ‘Drought’ is included as a focal stressor, from which a complete recovery of the community is required. The suite of experimental systems is complemented by field flumes that will bridge the gap between ExStream mesocosm system and field investigations. We will include the Emscher main stem that was transporting untreated sewage for almost a centu-ry and is recovering from this massive degradation since 2022. We will upscale our results with spa-tially distributed and time series data from all of Germany to test our hypothesis in a more general context. RESIST is run by a well-balanced consortium ensuring the required complementary expertise. RE-SIST is a shining example of how interdisciplinary research is crucial to addressing urgent research questions and societal challenges.

DFG Programme Collaborative Research Centres

• A01 - Microbial key processes and key species during drought and re-wetting of river sediments (Project Head Probst, Alexander )
• A02 - Effects of stressor hierarchies on river microbial communities during degradation and recovery from drought (Project Heads Brauer, Verena ;  Meckenstock, Rainer Udo )
• A03 - Microphytobenthos community recovery: time scales of asymmetric recovery and the modulation of priority effects by stressor severity (Project Head Beszteri, Bánk )
• A06 - Responses of protist communities during degradation and recovery (Project Head Boenigk, Jens )
• A08 - Degradation by and recovery from drought-related stressors of freshwater invertebrate communities (Project Head Leese, Florian )
• A09 - Ecological effects of parasites: their contribution to stress responses of their hosts and their importance for dispersal processes (Project Head Sures, Bernd )
• A10 - The scent of danger – local adaptation of predator-mediated defences and information transfer disruption in multiply-stressed riverine ecosystems (Project Heads Tollrian, Ralph ;  Weiss, Linda Carolin )
• A14 - Modelling degradation and recovery dynamics of environmental stressors during low flow, desiccation and rewetting periods for micro-and mesoscale catchments (Project Head Fohrer, Nicola )
• A15 - The role of biotic interactions in explaining distribution patterns of riverine organisms (Project Head Jähnig, Sonja )
• A16 - Biotic and abiotic drivers of macroinvertebrate dispersal (Project Head Feld, Christian K. )
• A17 - Recovery processes of riverine organism groups (benthic invertebrates, diatoms and fish) from different modes and severities of degradation (Project Heads Haase, Peter Martin ;  Hering, Daniel )
• A18 - Integrating physiological tolerance, biotic interactions, and dispersal ability into (meta)population models (Project Head Le, Ph.D., Thi Thu Yen )
• A19 - Recovery from moderate and severe degradation: ARC theory for the patterns and processes that define full or failed reassembly, and shifts to alternative states (Project Head Vos, Matthijs )
• A20 - Mechanistic modelling of metacommunity dynamics under multiple stressors in stream networks of real and generic catchments (Project Head Schäfer, Ralf B. )
• A21 - Responses of aquatic fungal communities to multiple stressors and consequences for leaf decomposition (Project Head Schreiner, Verena C. )
• A22 - Viral (and host) microdiversity response to multiple stressors in freshwater ecosystems (Project Head Moraru, Ph.D., Cristina )
• A23 - Responses of parasitic protist communities and their effects on their macroinvertebrate hosts under different degradation and recovery conditions (Project Head Rückert, Sonja )
• A24 - Long-term multi-stressor trajectories in Central European rivers (Project Head Flörke, Martina )
• A25 - Effects of stressor increase and release on the functional composition and trophic interactions within food webs (Project Heads Schmidt, Torsten ;  Weitere, Markus )
• MGK - Integrated Research Training Group of RESIST (Project Heads Brauer, Verena ;  Sures, Bernd )
• Z01 - Central administration of the CRC 1439 (Project Head Sures, Bernd )
• Z02 - Maintenance of experimental systems, central field work and central sample analysis (Project Heads Boenigk, Jens ;  Fohrer, Nicola ;  Hering, Daniel ;  Leese, Florian )
• Z03 - Central scientific project: RESIST synthesis (Project Heads Hering, Daniel ;  Jähnig, Sonja ;  Schäfer, Ralf B. )
• ZINF - Data management and integration (Project Heads Beisser, Daniela ;  Moraru, Ph.D., Cristina ;  Probst, Alexander )
• Ö - Public Relation (Project Heads Hering, Daniel ;  Sures, Bernd )

• A04 - The roles of bacteria and fungi for CPOM degradation during stressor increase and release: A metatranscriptomic approach (Project Head Beisser, Daniela )
• A05 - Impairment and recovery of stream ecosystems experiencing multiple stressors: Responses of leaf-associated fungi, microbial activities and litter decomposition (Project Head Gessner, Mark )
• A07 - Degradation and recovery of protistan parasite communities under multiple stressors (Project Heads Beisser, Daniela ;  Boenigk, Jens ;  Dunthorn, Ph.D., Micah ;  Sures, Bernd )
• A11 - Multiple stressor effects on sculpins (Cottus sp.) and related top-down effects on riverine food-webs (Project Head Lampert, Kathrin )
• A12 - Effects of multiple stressors on food web architecture and processes (Project Head Weitere, Markus )
• A13 - Diet-consumer interactions under variable stressor conditions as revealed by stable isotope stud-ies of individual amino acids (Project Heads Jochmann, Maik ;  Schmidt, Torsten )

Applicant Institution Universität Duisburg-Essen

Participating University Christian-Albrechts-Universität zu Kiel; Ruhr-Universität Bochum

Participating Institution Helmholtz-Zentrum für Umweltforschung (UFZ); Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
im Forschungsverbund Berlin e.V.

Spokesperson Professor Dr. Bernd Sures