Biodiversity and food web structure in relation to hydrological connectivity in a boreal stream ecosystem

Over the past two decades, hydrological connectivity in river systems has experienced rapid degradation globally. The loss of this connectivity has had adverse effects on aquatic environments. Consequently, biodiversity and food web structure are likely to be strongly associated with hydrological connectivity. Here, we investigated fish, benthic macroinvertebrates, benthic algae, and environmental data (e.g., river width, total phosphorus, and water temperature) were conducted in a river ecosystem in China, with food webs reconstructed using a meta-web approach to identify trophic interactions and assess the ecological cascades resulting from alterations in hydrological connectivity. Our results revealed that enhanced connectivity improved water conditions, such as higher flow rates and better aquatic habitat quality, along with lower water temperature and total phosphorus levels. These changes enhanced biodiversity metrics, including the species richness of fish, macroinvertebrates, and benthic algae communities. As a result, both the diversity (node count and number of intermediate species) and complexity (link number, linkage density, and connectivity) of aquatic food webs increased. Nonetheless, greater complexity in food web structure did not correspond to higher ecosystem functioning, such as improved resource utilization efficiency within the benthic algae community. Our findings suggest intrinsic correlations between hydrological connectivity and food web structures in aquatic ecosystems, thereby enhancing our understanding of ecological cascades in river ecosystems experiencing hydrological connectivity loss.