Aberystwyth University scientists have warned that flooding could worsen unless liming practices on uplands are maintained.

Published in the journal Science of the Total Environment, the new research shows that if steep improved pastures are allowed to become acidic, earthworm populations will decline, so reducing the capacity of the land to infiltrate and store rainfall.

In the second half of the 20th century large areas of the UK uplands were converted to more productive pasture to increase livestock production, encouraged by government incentives. This practice was particularly extensive in Wales.

A key component of pasture improvement was making soil less acidic, commonly through the application of ground limestone. Liming of acid soils increases earthworm activity, which means the land can soak up more rainwater. Withdrawal of support for maintenance liming, along with economic and practical constraints, has led to less liming, which is needed to counter soil acidity in the UK, particularly in upland soils.

Dr John Scullion from Aberystwyth University’s Department of Life Sciences led the study in collaboration with the Environment Systems Ltd Consultancy.

He said: “We are seeing more frequent intense rainfall events due to climate change with a resulting increase in flood risk. Previous research into land use impacts on flood risk has focussed on soil compaction and afforestation. Here we demonstrate that soil acidification may represent a further risk factor.”

He added: “In the past farmers received payments for regularly liming of their land to improve its agronomic potential. The cessation of such grants and pressure on farming economics has meant that liming has become less prevalent, particularly on the steeper slopes in the Welsh uplands, but also elsewhere in the UK and Europe. Some fields used in the present study had not been limed for 30 years with limited earthworm populations and poor water infiltration.

“Our research highlights that on previously improved grasslands, targeted liming to promote healthy earthworm populations may be a practical tool that farmers can use to contribute towards this important flooding ecosystem service.

"We need to better understand the role of steep sloping grasslands in upland catchments and their management in mitigating flood risks.

"Further work is needed to quantify any impacts of reduced infiltration and storage of rainfall in soils on river flow rates. Also, there is a need to assess the extent and catchment distributions of liming deficits particularly in Wales.”