The research was funded by the Scottish Executive and led by Professor David Kay of the University of Wales, Aberystwyth, who has studied microbial threats to bathing water and shellfish for more than 20 years.
The EU introduced mandatory microbiological standards for bathing waters in a 1976 Directive. After making a very slow start and twice being taken to the European Court, the UK’s compliance has at last improved (ENDS Report 382, p 21 ).
A revised Directive, agreed in 2005 and effective from 2015, will be more challenging. Indeed, the Environment Department (DEFRA) thinks up to a quarter of English and Welsh bathing waters may be at risk of failure (ENDS Report 370, p 45 ).
In the past, efforts have focused on sewage treatment works but most of the obvious improvements have been made and the emphasis is shifting to agricultural sources and storm sewer overflows.
The study shows that the use of slurry and manure to fertilise fields, and allowing livestock access to streams, can result in surprisingly high concentrations of faecal coliforms in catchments that might otherwise seem pristine. Streams draining through a dairy farming area near Newport in Pembrokeshire, for example, have coliform concentrations comparable to sewage overflows from storm tanks and sewer systems.
Professor Kay believes agriculture is the critical factor in around 50% of UK catchments - particularly those in the west where livestock farming predominates. And agricultural sources are particularly important after storms, which stir up river sediments and cause dramatic dips in bathing water quality.
His team assessed drainage measures at seven farms in the Brighouse Bay catchment in Dumfries and Galloway, southwest Scotland, and fenced off around 35% of the riverbanks. The fences prevented livestock entering and fouling the river, and created a buffer zone to filter runoff.
Brighouse Bay has a poor compliance record with bathing water standards and would be rated as "poor quality" under the EU’s new four-tier classification introduced by the 2005 revised Directive.
The study’s results are rather confused because the team did not have time to collect a proper set of control measurements before the improvements began. But comparison with a neighbouring catchment suggests that fencing caused a significant decrease in faecal coliforms and a 66-81% decrease during periods of peak flow.
However, samples taken around the bay during a storm showed that, even with the fencing in place, the water breached the current mandatory standards.
Professor Kay thinks this may be because the sampling was carried out only a few months after the improvements were made. He expects the fencing to become more effective as vegetation in the buffer zone recovers and the team will be revisiting the catchment this summer to take new measurements.
The study also suggests that the restoration or construction of wetlands might provide extra protection.
A separate study carried out for DEFRA five years ago warned that meeting the highest EU bathing water standards after their revision would be expensive, perhaps costing farmers £7 billion over 25 years (ENDS Report 330, p 13 ).
According to Professor Kay, the solution lies in recent reforms to the EU common agricultural policy which allow a greater proportion of subsidies to be awarded on the basis of environmental improvements. So far, the UK’s emphasis has been on animal husbandry and farm management, he says, but farming’s effects on the water environment should be given more attention.