Nitrogen loading in freshwater ecosystems: impacts on benthic communities and sediment nutrient dynamics in shallow lakes

Nitrogen (N) loading in aquatic ecosystems has increased globally due to intensive fertilizer use, giving rise to widespread environmental concerns. While the effects of excessive N on pelagic communities (e.g., phytoplankton) are relatively well-documented, its impacts on benthic communities, critical for maintaining lake ecosystem health and mediating pelagic-benthic interactions, have received comparatively less attention. Here, we provide an overview of the responses of benthic communities (macroinvertebrates, submerged macrophytes, and periphyton) to increased N loading and the effects of N on sediment phosphorus (P) release, a key process maintaining eutrophication, particularly in shallow lakes. High N loading generally reduces benthic biodiversity while favoring tolerant species, thereby simplifying the structure and function of benthic food webs, and can promote P release from sediments exacerbating eutrophication. Furthermore, N enrichment alters biotic interactions among benthic communities (e.g., promoting periphyton growth which may shade macrophytes), and enhance bioturbation by macroinvertebrates (e.g., Oligochaetes and midge larvae) which may increase sediment P mobilization. Global warming amplifies N-driven benthic processes, and although warmer temperatures may increase the use of nutrients by benthic organisms due to higher metabolic rates, they also intensify stressor effects like ammonium toxicity. We highlight the urgent need for incorporating benthic responses in eutrophication management strategies, not least in the context of climate changes.