Adas A+

Diffuse pollution costs the water industry an estimated £250m a year. Traditionally companies have relied upon end-of-pipe technologies to remove the pollutants from the water, but as these technologies are capital-intensive and unsustainable in the long term, many companies are now looking at alternative solutions to the problem.

Diffuse pollutants in the water cycle originate from a number of different sources, making them difficult, but not impossible, to regulate. In addition to the water quality challenges they present to water companies, and the significant cost which will be passed on to the consumer for water treatment, diffuse pollutants also have an impact on the ecological, aesthetic and economic aspects of water resources.

Agriculture is the single biggest cause of diffuse pollution, releasing a wide variety of substances into water systems. These include: nutrients from over application of fertilisers and manure; faecal and other pathogens from livestock; soil particles from arable and livestock farming; pesticides and veterinary medicines, as well as organic wastes that are poorly stored or disposed of and spread to land. While all of these substances are fundamental elements of a farmer’s business, all can have significant effects on wildlife and water quality.

Currently the vast majority of water companies use treatment plants to remove pollutants from water. However, there is now a need for diffuse pollution to be tackled at source as it is becoming increasingly clear that end-of-pipe technologies are not sustainable in the long term. As well producing a significant amount of carbon, such technologies can be ineffective at critical times such as spraying periods, as pollutant levels in the water may exceed treatment capacity. Furthermore, traditional treatment methodologies are proving to be less effective at treating certain pesticides, including metaldehyde, a widely used molluscicide most commonly found in slug pellets, and the herbicide clopyralid.

Rather than treating the symptom of the problem, catchment management systems involve using mitigation methods which attempt to prevent the pollutants from entering the water system in the first place. Key to this approach is collaboration with the agricultural community in order to raise awareness of the problem and of the methods that can be employed to tackle it.

Many of the mitigating methods for reducing pollution from point sources are relatively simple to implement. In the case of pesticides, this could include analysing where they are kept, prepared and made ready for spraying and use on crops. By avoiding spillages, carefully managing empty containers, ensuring equipment is cleaned in the right place, locating pesticide handling areas in a dedicated place and storing sprayers undercover, farmers can help to prevent many pollutants from entering the water system. Biobeds are another simple solution which farmers can implement to reduce the spread of pesticide pollution. These rectangular lined pits are filled with a mixture of topsoil, peat free compost and straw, and then turfed over and placed near the sprayer filling/wash-down area to minimise point source pollution. The biobed filters out pesticides and uses enhanced microbial activity to break them down.

Diffuse sources are harder to mitigate and key is an understanding of the different pollutants, the effects they have and the ways in which they are mobilised into the water system. Careful planning can help to reduce the likelihood of pollutants spreading. Practically, farmers can use methods which make a direct contribution to the levels of pesticides released into the environment. For example, low drift technology allows spraying to be carefully directed into specific areas which helps to prevent pesticides from entering nearby surface water.

Surface run-off is a major cause of diffuse pollution, particularly in periods following prolonged or heavy rain-fall. Soil management can go some way to mitigating against the effects by identifying problem areas and then carrying out appropriate remedial action. Beetle banks, for example - strips of grass or perennial plants in fields used to foster and give cover for ...