Urbanization effects on plankton communities in urban lakes are globally context-dependent

Abstract

Urbanization is one of the main drivers of environmental degradation in continental aquatic ecosystems. Although numerous studies have examined links between urbanization and the structure of aquatic communities, conclusive generalizations about its effects on planktonic communities remain elusive. Drawing on a meta-analysis of 38 studies in urban lakes, we evaluated (i) whether the impacts of urbanization on plankton community attributes (density, biomass, richness, and diversity) are consistent across independent studies (i.e. show a common direction and limited between-study heterogeneity) and (ii) where variation occurs, to identify moderators (e.g. surrounding land use) that may account for between-study differences. We quantified pooled effect sizes using Hedges’ g, meta-regression and subgroup analyses to test moderators, including sampling extent, response descriptors, urbanization measures, and taxonomic group. Between-study heterogeneity was quantified with T2 and I2. The overall effect size did not differ significantly from zero, and heterogeneity was high, indicating context-dependent responses. Among urbanization measures, land use and urban density showed detectable effects, whereas other measures showed no consistent pattern. We call for methodological standardization (particularly in urbanization metrics and spatial extent, plankton response descriptors, and reporting of summary statistics and metadata) to enable generalizations about the biodiversity consequences of urbanization in aquatic ecosystems.