Pond skaters are a common insect in English rivers
HEATH MCDONALD / SCIENCE PHOTO LIBRARY
The diversity of insects and other invertebrates in England’s rivers is better than at any time in the last 30 years, according to an analysis of monitoring data from the Environment Agency. This improvement appears to be related to a reduction in copper and zinc levels in the water.
Andrew Johnson at the UK Center for Ecology & Hydrology and his colleagues analyzed data from samples collected using nets from 1515 sites in England between 1989 and 2018. Each macroinvertebrate — any animal with no backbone that can be seen without a microscope — was identified by what family it belongs to, rather than 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 ecological success story since the [second world] war,” says Johnson.
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 greatest influence on insect diversity. Their preliminary analysis found that reductions in zinc and copper levels were the trends most often associated with an increase in invertebrate diversity.
Metals, including zinc and copper, can affect insect growth and interfere with their reproductive ability. Zinc and copper can accumulate in wastewater from a variety of sources, including soap, meat and shellfish, says Johnson, who reported the findings at the U.S.’s annual meeting. Society for Environmental Toxicology and Chemistry Europe in Dublin, Ireland, on May 1.
He says the improvement in zinc and copper levels in rivers coincided with the privatization of water utilities in England and the introduction of Regulations of the European Union regarding waste waterrequiring companies to remove more pollutants before discharging wastewater into rivers.
Copper and zinc levels also dropped dramatically following the reduction in coal burning in England, Johnson says. “This also stopped acid rain, which can mobilize metals and push them into rivers,” he says.
However, chemical pollution in general appears to be a problem in England’s rivers, and data shows some animals are in decline, including salmon and eels, Johnson says.
Michelle Jackson at the University of Oxford says she has seen an improvement in invertebrate diversity in London’s Thames basin in research currently being peer-reviewed.
Tom Oliver at the University of Reading, UK, notes that a study published last year, which he was involved in, found that the number of freshwater invertebrates in England had increased in recent years. “But there is also substantial variation between locations, with species trends differing significantly 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 to be the reason for the positive trend, but the rate of improvement has slowed over the past four years and it’s unclear what effect this has had on invertebrate biodiversity, he says. “This warrants further investigation into the impact of these recent changes in water quality on freshwater species.”
Subjects:
