Metal Pollution Reduction Linked to Increased Biodiversity in English Rivers, Study Finds

It stands to reason that if you reduce the amount of pollution in an environment, the organisms there will thrive. Now, a study confirms that is happening in rivers in England. According to the research, reducing the amount of metal pollutants like zinc and copper in English rivers led to an increase in the aquatic biodiversity of macroinvertebrates.

As coal and heavy industry have declined, related river pollution also cleared up, allowing more invertebrates to thrive, the study published in Environmental Science & Technology found.

A team led by the UK Centre for Ecology & Hydrology (UKCEH) analyzed over 65,000 observations 1,457 sites from 1989 to 2018 found in the UK Environmental Agency’s data.

In their findings, reduction in metal pollutants had the biggest impact on invertebrate biodiversity, although other pollution reduction, such as sewage, also impacted the variety of invertebrate species. According to the findings, zinc levels below 14 micrograms per liter and copper levels below 3.3 micrograms per liter led to the biggest improvements in species richness.

The authors estimated that metal pollutants and sewage may have declined for multiple reasons, including reduced coal dependence, which would lead to a decline in acid rain that contribute to metal pollution in waterways. Some of the ammonia, organic matter, and other pollutant declines could also be attributed to the 1991 European Urban Wastewater Treatment Directive and improved agricultural practices, according to the study.

With strong evidence that zinc & copper concentrations have the biggest influence on invertebrate species richness, efforts to increase freshwater biodiversity are unlikely to bear fruit without further reductions in these metals, lead author Prof Andrew Johnson said 🔗 www.ceh.ac.uk/press/biodiv…

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— UK Centre for Ecology & Hydrology (UKCEH) (@ukceh.bsky.social) February 18, 2025 at 8:09 AM

“There is a widespread desire by the public to improve water quality and biodiversity in our rivers but the problem for policymakers is what steps would be most likely to achieve results,” Andrew Johnson, lead author of the study and environmental research scientist at UKCEH, said in a statement. “Our study provides strong evidence that concentrations of zinc and copper have the biggest influence on invertebrate species richness, so future attempts to increase freshwater biodiversity are unlikely to bear fruit without further reductions in these metals.”

The study determined that while river biodiversity improved in the 1980s and 1990s with reduced metal pollution, the species richness has mostly plateaued since 2000, and the authors cited other research that has shown similar trends across North America and Europe.

The authors wrote that more research is needed to determine what urban land cover pollutants most impact biodiversity of invertebrates, and that runoff from urban areas could still contribute to higher levels of zinc and carbon pollution that may not be detected in routine river sampling. Further, the study found that higher levels of metal pollution continue to exist downstream from former mines.

These factors will need to be considered for environmental protection efforts, as the UK’s Department for Environment Food and Rural Affairs (Defra) has set a target to reduce the length of rivers impacted by metal pollutants from mines by half by 2038.

“The way priority chemicals are currently identified for action, ensuring aquatic wildlife may be better protected, could be described as ‘top-down,’” the authors concluded in the study.

“Here, we used a ‘bottom-up’ approach, relying on a statistical analysis of large wildlife and stressor field data sets (consistent monitoring by regulatory agencies being critical to this approach) to identify factors that are most closely associated with biodiversity. We suggest that this approach has considerable merit and at the very least can act as a sense check on the traditional approach.”