Linking pollution to biodiversity and ecosystem multifunctionality across benthic-pelagic habitats of a large eutrophic lake: A whole-ecosystem perspective

Biodiversity loss is often an important driver of the deterioration of ecosystem functioning in freshwater ecosystems. However, it is far from clear how multiple ecosystem functions (i.e., ecosystem multifunctionality, EMF) relate to biodiversity across the benthic-pelagic habitats of entire ecosystems or how environmental stress such as eutrophication and heavy metals enrichment might regulate the biodiversity-EMF relationships. Here, we explored the biodiversity and EMF across benthic-pelagic habitats of the large eutrophic Lake Taihu in China, and further examined abiotic factors underlying the spatial variations in EMF and its relationships with biodiversity. In our results, EMF consistently showed positive relationships to the biodiversity of multiple taxonomic groups, such as benthic bacteria, bacterioplankton and phytoplankton. Both sediment heavy metals and total phosphorus significantly explained the spatial variations in the EMF, whereas the former were more important than the latter. Further, sediment heavy metals mediated EMF through the diversity of benthic bacteria and bacterioplankton, while nutrients such as phosphorus in both the sediments and overlaying water altered EMF via phytoplankton diversity. This indicates the importance of pollution in regulating the relationships between biodiversity and EMF in freshwater environments. Our findings provide evidence that freshwater biodiversity loss among phytoplankton and bacteria will likely weaken ecosystem functioning. Our results further suggest that abiotic factors such as heavy metals, beyond nutrient enrichment, may provide relatively earlier signals of impaired ecosystem functioning during eutrophication process.