Thriving rivers significantly contribute to biodiversity and human health. As ecosystems, rivers provide services across the four categories defined by the Millennium Ecosystem Assessment: provisioning (potable water and fisheries), regulating (flood attenuation, water infiltration), supporting (riparian habitats), and cultural (recreation, aesthetics). Balancing current uses against rivers’ capacity to maintain or supply resources into the future poses management challenges, as the amount of change that rivers can accommodate seems to be rapidly diminishing. This loss of capacity becomes more apparent when it comes to processing chemical pollution.
Since the EU Water Framework Directive came into force in 2000 to ensure water protection, only 14% of English rivers have achieved good ecological status, and none show good chemical status. The Environment Agency considers agricultural run-off, sewage discharges, and run-off from urban areas and transport infrastructure as the main drivers for not achieving good chemical status. These emissions alter water quality in rivers by discharging a combination of nutrients, synthetic chemicals, plastics, and fine sediments that originate at both point (e.g. combined sewer overflows) and diffuse (e.g. fertiliser spreading) sources.
Overview
Because of chemical pollution, no clean bill of health has been given to any English river. Improving water quality, therefore, should become a priority, as reflected in the report of the House of Commons Environmental Audit Committee on Water quality in rivers (2022). Hence, the main challenges ahead are to: 1) study the occurrence, transport, and fate of pollutants and assess how climate and catchment dynamics influence point and diffuse discharges into rivers; 2) investigate how rivers process chemical mixtures and their potentially detrimental effect on ecosystem services; and 3) propose management and mitigation strategies oriented to improve the capacity of rivers to absorb pollution without compromising their basic function and structure.
Tackling these issues demands an interdisciplinary approach to deepening scientific insight into the processes by which multiple pressures affect the freshwater quality and river ecosystems. Pressures include pollution (chemicals, nutrients, and sediments), physical modifications (hydromorphology), climate change, and abstraction. Research needs to elucidate whether synergies between multiple pressures aggravate impacts on the freshwater environment. It should also consider the influence of climate change on the hydrological cycle, particularly on water quantity and temperature, along with increasing abstraction demands. These pressures, in turn, combine with pollution diffuse and point sources to cause a cascade of impacts on freshwater quality and ecosystems.
