Causes of pollution
SLURRY FROM COW HERDS
Causes include overflowing stores, contaminated drains, broken seals, burst sluices and general mismanagement of slurry spreading around surface waters. Huwel Manley at Natural Resources Wales says the intensification of dairy herds – prompted by spikes in milk prices – has made matters worse, with more cattle producing more slurry that must be stored in infrastructure that has not been enlarged or updated to hold it. “Slurry is very damaging, it’s quickly broken down by bacteria and spreads phosphates in rivers and damages the ecology,” says Angling Trust’s Mark Lloyd. “The good farmers are as frustrated as we are. Others are struggling, they would like to do the right thing but face big capital investments.”
PESTICIDES AND POULTRY POO
During wet weather, these can be washed into rivers. High levels of phosphates and nitrates create algae that smothers river beds. Free-range poultry is an increasing problem – chickens compact the grass on which they forage, hardening the surface. Their faeces, containing high levels of phosphates, is easily washed away by rain.
Pesticides cause problems for water companies. Dr Jodie Rettino at Severn Trent Water says: “We shut down works on a number of occasions because pesticides get into reservoirs. If we get three or four pesticides at a high peak, our treatment processes don’t work so well. Clean-up costs at a single water treatment works for pesticides can be around £4m a year.”
SEDIMENT
Topsoil can be washed off land into rivers during bad weather. Ploughing of grasslands and the inappropriate choice and positioning of crops, such as maize (which has risen from 8,000ha to 180,000ha in just 10 years) and potatoes is a significant cause, along with poor drainage. Inappropriate crop planting in upland areas – maize, wheat and stubble turnip on steep slopes – has caused landslips that clog up river courses. Overgrazing by sheep on hills also leads to soil being washed away. “The soil smothers the gravel on the river bed and fills the gaps between stones where fish lay their eggs,” says Angling Trust’s Mark Lloyd. “That also stops eggs of all kinds of insects hatching.”