Insects thrive in English rivers after metal pollution drops

The diversity of insects and other invertebrates in England’s rivers is better than at any time in the past 30 years, according to an analysis of Environment Agency monitoring data. This improvement seems to be linked to a decrease in copper and zinc levels in the water.

Andre Johnson at the UK Center for Ecology & Hydrology and colleagues analyzed data from samples collected using nets at 1,515 sites in England between 1989 and 2018. Every macroinvertebrate – any animal without a backbone that can be seen without a microscope – has been identified by which family it belongs rather than to a particular species.

The results show that the diversity of invertebrate families in English rivers has steadily increased over the past 30 years in both urban and rural rivers. “You could say that our rivers are our greatest environmental achievement since the [second world] war,” Johnson says.

The researchers looked at 45 different variables, including chemical levels and physical factors such as temperature, and used a model to determine which had the biggest influence on insect diversity. Their preliminary analysis revealed that reductions in zinc and copper levels were the trends most frequently linked to increases in invertebrate diversity.

Metals, including zinc and copper, can affect insect growth and interfere with their ability to reproduce. Zinc and copper can build up in wastewater from a variety of sources, such as soaps, meat and shellfish, says Johnson, who reported the findings at the annual meeting of the Society of Environmental Toxicology and Chemistry Europe in Dublin, Ireland, on May 1.

He says the improvement in zinc and copper levels in rivers has coincided with the privatization of water companies in England and the introduction of European Union Wastewater Regulationswhich required companies to remove more contaminants before discharging wastewater into rivers.

Copper and zinc levels have also dropped dramatically following the decline in coal burning in England, Johnson says. “It also stopped acid rain, which can mobilize metals and push them into rivers,” he says.

However, chemical pollution in general seems to be a problem in English riversand the data shows some animals are in decline, including salmon and eels, Johnson says.

Michele Jackson at the University of Oxford says she has seen an improvement in invertebrate diversity in London’s Thames catchment in research that is currently peer-reviewed.

Tom Olivier at the University of Reading, UK, notes that a study published last year, in which he participated, found that the number of freshwater invertebrates in England had increased in recent years. “But there is also substantial variation from place to place, with species trends differing markedly between rivers and regions,” he says. “This means that high-resolution monitoring, both in space and time, is essential to track the responses of our freshwater biodiversity.”

Improvements in water quality are likely the reason for this positive trend, but the rate of improvement has slowed over the past four years and it is unclear what effect this has had on invertebrate biodiversity, says- he. “This warrants further investigation into the impact of these recent changes in water quality on freshwater species.”