There are many reasons why we would want our waters to be unpolluted. Perhaps the most obvious benefit to people is the provision of drinking water. The clean, safe water you receive from your tap has travelled a long journey before it reaches your house. Before it reaches the water treatment plant, it may have made its way downstream from a river which bends and snakes through a wide and varied landscape. Any rainfall within the catchment is likely to eventually reach the river, but not before crossing terrain which may include urban areas, arable fields or livestock farms, picking up pesticides, fertilisers and other pollutants on the way. The purpose of the treatment plant is to remove these pollutants making the water safe to drink, but this can be a costly process taking a lot of time and energy. It is far more effective to ensure these pollutants do not reach the watercourse in the first place.
Farms can put in place a variety of measures to ensure they do not contribute to the problem, including reducing the amount of fertilisers or pesticides they apply in sensitive areas, managing livestock in a way that prevents erosion and creating buffer strips of rough grassland. In arable fields, ploughing should been done across the slope rather than up the slope where possible, and a cover crop can be provided to prevent the soil being exposed outside of the growing period. Semi-natural habitat which is allowed to grow in key areas can filter out pollution before it has the chance to reach the watercourse.
Improving the water quality of rivers has many other benefits, not least of all to wildlife. As well as the obvious detrimental effect of pesticides, high nutrient input to a watercourse can create eutrophic conditions which are toxic to fish and other wildlife. Clean, healthy, unpolluted rivers are able to support a diverse, thriving ecosystem from tiny invertebrates (such as caddisflies and stoneflies) up to large fish and birds (such as Salmon, Dippers and Kingfishers).
Another aspect of water quality, particularly relevant to Cornwall, is the condition of our bathing waters. This has obvious implications for the health of locals and tourists alike, with knock-on economic effects.
When assessing water quality, we considered three aspects:
- The ability of a site to filter or contribute to the pollution of a watercourse
- The significance of water quality to the watercourse (i.e. what is downstream?)
- The water quality of the watercourse the site feeds into, where such data exists
The highest scoring sites will make a positive contribution to the quality of drinking water or other sensitive areas directly downstream. A low-scoring site may not necessarily be detrimental; it may simply mean that there are little to no sensitive areas downstream which would benefit from improved water quality.