River biodiversity increased by reduced metal pollution
There has been no significant improvement to biodiversity since early 2000s.
A new study has linked an increase in freshwater biodiversity in the 1990s to a reduction in zinc and copper pollution in England’s rivers.
Researchers say that this is likely due to the decline of coal burning and heavy industry during this time.
The UK Centre for Ecology and Hydrology (UKCEH) uses population counts of invertebrate species to evaluate the ecological health of the river. Through this they are able to assess the river’s biodiversity, as well as considering how pollution might be impacting the river’s ecosystem.
Using Environment Agency data, UKCEH had observed a significant increase in species richness in the 1990s and in the early 2000s. However, they have reported no significant improvement since then.
The UKCEH’s latest study, funded by the Natural Environment Research Council, sought to investigate the reasons behind these changes.
A team of scientists, led by UKCEH, implemented statistical modelling to investigate the chemical and physical factors that might be involved. This included data on temperature, river flow and landscape.
The data consisted of 65,000 individual observations on pollutant measurements and invertebrates from 1,457 sites between 1989 and 2018.
An analysis of the data highlighted how effluent sewage impacted concentrations of ammonia and organic matter, and how this then impacted river wildlife. However, it was the correlation between invertebrate diversity with zinc and copper which was strongest.
Researchers theorise that a reduction in coal burning in the 1980s could be linked to a reduction of metal pollution in England’s rivers. Coal burning is a major source of atmospheric metals pollution, which then ends up in rivers through acid rain.
The decline in heavy industry has also been associated with improved biodiversity in the 1990s. UKCEH says the industry was also responsible for metal pollution, as well as leaking polluted sewage through treated and untreated effluent.
The reduced production of domestic products containing zinc and copper may also have resulted in less metal pollution in the sewage.
Andrew Johnson, an environmental research scientist at UKCEH, said: “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.
“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.”
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