Biodiversity enhances pond ecosystem multifunctionality across Europe.

Small water bodies, such as ponds, are crucial for biodiversity and support multiple ecosystem functions (multifunctionality). Yet, the extent to which their biodiversity contributes to multifunctionality remains largely unexplored. Here we report data from a large-scale, highly standardized, stratified field survey across 206 European ponds, including 2,500 observations of biodiversity (macrophytes, zooplankton, macroinvertebrates and amphibians) and key ecosystem functions and processes, including methane emissions, litter decomposition, carbon sequestration, primary productivity, biomass accumulation and habitat complexity. Our study reveals a positive and significant association between biodiversity and multifunctionality across multiple taxonomic groups of aquatic organisms, with several ecosystem functions strongly linked to zooplankton richness. The biodiversity-ecosystem multifunctionality relationship tended to be more pronounced in arid regions. By contrast, increasing nutrient concentrations associated with intensive cropland (that is, eutrophication) were negatively related to multiple ecosystem functions, underscoring the importance of pond ecological status in supporting multifunctionality. Taken together, our work provides evidence of the importance of biodiversity in maintaining multifunctionality in small standing freshwater bodies. Preserving and restoring pond habitats by reducing nutrient concentrations will sustain key ecosystem functions in the face of multiple drivers of biodiversity loss.