The Great Stour Project - River Pollution

Farmland (arable)

Agricultural pollution (the local situation)

There are high concentrations of nitrates in the local groundwater, especially to the north-east of Canterbury (in the Thanet area). This is a Nitrate Vulnerable Zone (NVZ), where pollution levels exceed 50 mg/litre. The EU Drinking Water Directive set this limit for safe nitrate levels in 1980. In 1991, the EU issued another Nitrate Directive which required countries to identify NVZs where excessive nitrate pollution came from agricultural sources. Thanet is one of 68 NVZs in the UK. Locally, farming intensity is not as high as in Thanet, but eutrophication is bad in some of the marsh dykes (Stour Marshes).

Excessive demand for water (farmers are licensed by the Environment Agency to abstract water directly from the river for spray irrigation) can result in low flows, reducing the dilution capacity of the river; this is worse in summer, and particularly in drought years. This is known as a dilution effect, i.e. concentration increases as flow decreases. In wet winters however, prolonged and heavy rainfall may result in organic pollution incidents, with increased runoff from fertilized fields and accidental overflow from slurry pits. This is known as a pumping effect, i.e. concentration increases as flow increases, flushing chemicals off the fields and farmyards. These two responses seem to work in opposite directions, making the evaluation of diffuse pollution quite difficult.

Agricultural pollution (prevention)

The Ministry of Agriculture, Food and Fisheries (MAFF) produced in 1991 a "Code of Good Agricultural Practice" for farmers giving detailed advice on the treating, storing and applying of animal livestock waste, the disposal of dirty water, fertilizers, fuel oil, sheep dip, pesticides, nitrates, disposal of animal carcasses, etc. With EA advice also, local farmers all have to produce a Farm Waste Management Plan to comply with pollution control regulations. Some examples of good practice are:

• reducing ploughing in the autumn
• delaying the ploughing in of crop residues
• reducing the amount of fertilizers, manure and sewage sludge applied
• sowing autumn crops early
• sowing cover crops in winter to avoid bare ground
• careful management of disposal of farm waste

Set-aside regulations will also have the beneficial effect of reducing intensity of farming in the local area, and thus lowering nitrate levels.

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