Diffuse urban pollution impacts on river ecosystems

A review

Abstract

Rivers and streams within urban settlements provide many ecosystem services, including water and food supply. However, increasing urbanization across landscapes worldwide has led to the degradation of river ecosystems. In the coming years, anthropogenic pressure upon urban rivers is expected to intensify because of increased population in cities. Nevertheless, the knowledge about current impacts of urban-related pressures on river ecosystems is fragmented, particularly regarding diffuse urban pollution. We reviewed scientific literature focused on the impacts of urban diffuse pollution on riverine ecosystems to identify potential knowledge gaps on the temporal and spatial distribution of the studies, as well as the abiotic factors used to characterise diffuse urban pollution. We also identified the taxonomic groups and ecosystem functions most commonly employed to characterise the impacts of diffuse urban pollution on river ecosystems. Our dataset comprised 63 studies published between 2000-2020, covering all inhabited continents, major ecosystem functions, and taxonomic groups. We found that ca. 70% of the studies were biased towards countries of the Global North. Macroinvertebrates were the taxonomic group most frequently employed to address diffuse-pollution impacts on urban rivers (53.97% of the studies). The most frequently addressed ecosystem functions were nutrient cycling (36.51% of the studies) and organic matter decomposition (31.75% of the studies), followed by river metabolism (30.16% of the studies). Finally, we found that only 46.03% studies simultaneously addressed biodiversity and ecosystem functions. Our findings highlight the need to urgently address the impacts of urbanization in river ecosystems from the Global South, improve the knowledge about their impacts on microorganisms and their associated functions, and specifically address how urbanization alters the relationship between biodiversity and ecosystem functioning in urban rivers. Our results aim to open the path to further research improving our ecological understanding and wise management of urban river ecosystems.