Bacteria are the main players for important ecosystem functions such as nutrient cycling and DOC degradation in aquatic ecosystems.

We discovered that flow velocity is a key driver for stream microbiomes, outcompeting the effects of other stressors. After recovery, however, some stressed river microbiomes did not return to their unexposed composition, highlighting the importance of stressor legacy effects (Stach et al. 2024).

Fungal heterotrophs, together with bacteria, dominate microbial decomposer communities, which degrade coarse particulate organic matter (CPOM).

Our experiments aimed to test the hypothesis that litter decomposition would be least efficient at recently restored sites.  However, decomposition dynamics was independent of the time elapsed since restoration and mainly explained by land use, pH, and chloride concentrations. That suggests extremely rapid recovery of ecosystem functioning or persisting functional impairment across the stream network (David et al. 2024).

Protists include autotrophic organisms such as diatoms, which are essential components of the biofilm and the main primary producers in streams, and heterotrophic organisms, which feed mainly on bacteria.

The response of heterotrophic nanoflagellates to salinity and temperature differs between taxa and this difference is more pronounced for temperature. Diatom species responded with a bell-shaped growth curve to temperature changes, while their growth tended to decrease with increasing electrical conductivity. The taxon-specific responses result in a shift in community composition. The turnover of differently adapted cryptic species with similar feeding preferences and predator-prey interactions may stabilise microbial food webs facing environmental change (Boden et al. 2023).

Benthic invertebrates are a large and diverse organism group colonising all riverine bottom habitats and feeding on a great variety of food sources.

In our field studies, we observed an increasing similarity of benthic invertebrate communities with time since restoration in the Boye catchment, indicating a random starting community that is increasingly streamlined with the development of environmental conditions. In slightly disturbed systems traits reflected recovery processes better than community compositon (Gillmann et al. 2023).

Parasites are a diverse and widespread group occurring in many aquatic hosts. They can have single or multiple host life cycles and can affect the host response to multiple stressors and recovery processes (Prati et al. 2022).

We showed that diversity and abundance of microsporidians are not related to the state of degradation, and that parasite diversity is not related to the diversity of macroinvertebrates. Apparently, there are still other factors preventing the further development of parasite communities. In our experiments, carbon-based isotope analysis of amino acids revealed parasite (cestode) nutrient assimilation closely linked to the liver metabolism of the fish host (three-spined stickleback). The results further suggested increased (immune-) metabolic activities due to parasitic infection (Hesse et al. 2023).