Agricultural Pollution Control

A major cause of pollution in surface water comes from excessive levels of phosphorus and fine sediment (silt) arising from agricultural activities. Phosphorus, derived from eroded sediment, newly applied manure, fertiliser and cut vegetation, enters surface waters in land run-off following heavy rain. Intensive farming practices, in particular, have led to increased erosion of soils into surface waters.

High phosphorus levels can lead to accelerated plant growth, resulting in a range of effects including loss of submerged plants and oxygen depletion that are collectively termed eutrophication. High levels of silt can reduce water visibility (decreasing the amount of light available to submerged plants), smother river and lake sediments and their dependent flora and fauna, and limit the use of the water for drinking and recreational purposes.

Under the Water Framework Directive (WFD), management of water sources is based on river basins and individual bodies of water, which require integrated management to control point (specific) and diffuse (varied) sources of pollution. In particular, strategies which control phosphorus and silt from diffuse sources are required to meet targets of the WFD and other European Directives (such as the EC Habitats and Species Directive), wider international commitments and national obligations.

The researchers suggest that such strategies should be implemented at catchment-wide scales. Accurate assessment of the impact of local and dispersed sources of phosphorus and silt should be combined with the development of targeted initiatives that evaluate the most effective management practices, and meet environmental objectives.

A further recommendation is that modelling should be a key component of catchment management systems. This technique allows the assessment of management actions that are difficult to quantify through environmental monitoring; linking the catchment-scale evaluation of pollution sources with the effects of management changes implemented at farm scale.

In addition to using integrated catchment management to limit the loss of phosphorus and silt from farmland, the strategy also benefits other catchment objectives, including better flood risk management, increased water reserves in times of drought and wetland habitat restoration.