Multivariate approaches to assess the drivers of benthic macroinvertebrate communities and biotic indices in a highly urbanized fluvial-estuarine system

Urban estuaries are amongst the most severely altered systems worldwide and undergo a wide range of ecological crises such as habitat destruction, nutrient enrichment and hydrodynamic alterations, resulting in an irreversible loss of biodiversity as well as a further environmental deterioration. Differentiating the main driving forces of multiple stressors is of utmost importance to provide beneficial insights for environmental restoration and management. In the present study, comprehensive investigations and multivariate approaches were performed to reveal the spatio-temporal variations of benthic macroinvertebrate communities and biotic indices and to examine their responses to environmental alterations within a highly urbanized fluvial-estuarine system. The nutrient levels gradually dwindled from urban fluvial sections to estuarine sections, meanwhile, macroinvertebrate community composition and dominant species considerably varied along the estuarine gradient. Overall, environmental parameters, macroinvertebrate communities and biotic indices varied significantly among sections and seasons. Salinity, dissolved oxygen, ammonia, total nitrogen, chemical oxygen demand and total organic carbon significantly explained the spatio-temporal variations of macroinvertebrate communities and biotic indices. Despite some inconsistencies in assessment outcomes, all indices revealed that urban fluvial sections of the Pearl River Estuary were disturbed, more or less severe depending upon the index. Among the tested indices, AMBI, BENTIX and average taxonomic distinctness (Δ+) presented better performance in assessing the ecological quality status and showed high responses to environmental stresses. More importantly, the relative contribution of water parameters vastly overrode sediment parameters in shaping variations of macroinvertebrate communities and biotic indices, demonstrating that anthropogenic activities (e.g., discharge of municipal and industrial sewage) directly altered the benthic community composition and diversity