A study of river water quality during one of the UK’s wettest ever winters has shown a massive increase in agricultural pollution – giving a glimpse of the problems farmers will face as the climate changes.

Pollutants washing from farmland within the upper catchment of Devon’s River Taw increased dramatically during the winter of 2019/20, with the amount of soil washed off arable fields showing a twenty-fold increase on average.

Large pulses of such sediment pollution harm both aquatic wildlife and drinking water quality, and the study’s climate modelling predicts that the weather pattern responsible will be more common in the future.

The report by Rothamsted Research also found that levels of nitrate, another major aquatic pollutant arising from fertiliser use, increased by four times during the wet winter from recently converted arable land.

Hydrologist Professor Adie Collins, who leads Rothamsted’s research in this area, said: “These changes in autumn and winter rainfall are elevating run-off and the water pollution problems arising from modern farming. Sadly, current on-farm mitigation strategies, including those subsidised by agri-environment schemes, aren’t working very well.”

Read more: SEPA targets Ayr South farms on water quality

February 2020 was the wettest February on record for the UK, with the overall winter – December, January, February - ranked as the fifth wettest on record since 1862. Research suggests that this sort of weather pattern will become more common in the future, with the most extreme rain days occurring even more often than they did in February 2020.

“Pollution from intensive farming generates environmental damage with resultant costs such as those for drinking water treatment to remove nutrients and sediment,” said Professor Collins. “Elevated pollution driven by extreme wet-weather increases such problems considerably.

“Compared to the period 1981 to 2010, the 19/20 winter had nearly 20% more rainfall, with about 209 mm falling in February 2020 – which is more than 133% more than the climatic baseline.”