Pelagic-benthic coupling of the microbial food web modifies nutrient cycles along a cascade-dammed river

Cascade dams disrupt the river continuum, altering hydrology, biodiversity and nutrient flux. Describing the diversity of multi-trophic microbiota and assessing microbial contributions to the ecosystem processes are prerequisites for the restoration of these aquatic systems. This study investigated the microbial food web structure along a cascade-dammed river, paying special attention to the multi-trophic relationships and the potential role of pelagic-benthic coupling in nutrient cycles. Our results revealed the discontinuity in bacterial and eukaryotic community composition, functional group proportion, as well as alpha-diversity due to fragmentation by damming. The high microbial dissimilarity along the river, with the total multi-trophic beta-diversity was 0.84, was almost completely caused by species replacement. Synchronization among trophic levels suggests potential interactions of the pelagic and the benthic groups, of which the beta-diversities were primarily influenced by geographic and environmental factors, respectively. Dam-induced environmental variations, especially hydrological and nutrient variables, potentially influence the microbial food web via both top-down and bottom-up forces. We proposed that the cycles of carbon, nitrogen and phosphorus are influenced by multi-trophic groups through autotrophic and heterotrophic processes, predator-prey relationships, as well as the release of nutrients mainly by microfauna. Our results advance the notion that pelagic-benthic trophic coupling may intensify the accumulation of organic carbon, ammonium and inorganic phosphorus, thereby changing the biogeochemical patterns along river systems. As a consequence, researchers should pay more attention to the multi-trophic studies when assessing the environmental impacts, and to provide the necessary guidance for the ecological conservation and restoration of the dam-regulated systems. (C) Higher Education Press 2021

Automated summary

Cascade dams disrupt the river continuum, affecting hydrology, biodiversity, and nutrient cycles. This study reveals the discontinuity in microbial community composition and diversity caused by damming. The potential interactions between pelagic and benthic groups and dam-induced environmental variations influence the microbial food web. The findings suggest that pelagic-benthic trophic coupling may change the biogeochemical patterns in river systems.