Catchment-Sensitive Farming: Tackling Diffuse Water Pollution from Agriculture in England —Policies and Drivers - Water and Agriculture: Sustainability, Markets and Policies - page 270

Agricultural sources of DWPA

Significant resources have been committed to understanding the pathways of nutrient
losses from land and the impacts of these nutrients and other pollutants on the water
environment. However, although we have a good understanding of N loss pathways, our
understanding of P loss is still limited. In addition, until recently little was done to
understand the impact of nutrients on the ecology of receiving waters.
Pollutants can either be transported in solution or in suspension, and either in
drainage water moving through the soil or in water moving across the soil. Pathways
differ between pollutants. The mechanism for water movement through soils with little
structure is relatively straightforward: water drains downward through the soil with a
generally uniform wetting front, carrying solutes in the soil profile towards the
groundwater. In more structured soils, such as clays and loams, water generally moves
laterally, either across the surface as 'overland flow' (sometimes called surface runoff) or
through the surface layers via cracks, channels and, ultimately if installed, drains;
collectively known as 'soil water drainage'.
A generalised and simplified summary of pathways and states of solution or
suspension, for the different pollutants are:

Solution Suspension

Overland

NH 4 + , BOD TP, FIO, Sediment

NO 3 -

Subsurface

Both the risk of loss and pollutant pathways vary between farming sectors. Table 3
illustrates the main practices/issues within three representative farming sectors
contributing to diffuse loses of N, P and FIOs in England and Wales.
The most effective on-farm mitigation measures fall into three activity categories —
nutrient management, soil erosion and runoff prevention, and farm landscape and
infrastructure changes. The most effective mitigation measures for tackling N and P
pollution relate to manure management. Soil management measures are shown to be
comparatively less effective (Defra 2005)).

Current and planned policies for tackling DWPA

There are currently a number of policy levers in place for tackling DWPA. The most
significant are the Nitrates Directive and CAP reform.

Nitrates Directive
The Nitrates Directive (91/676/EEC) (see http://europa.eu.int/comm/
environment/water/water-nitrates/index_en.html) is concerned with the protection of
waters against pollution caused by nitrates from agricultural sources. The directive was
adopted by the Commission on 19 December 1991. It seeks to reduce or prevent the
pollution of water caused by the application and storage of inorganic fertiliser and manure
on farmland. It is designed both to safeguard drinking water supplies and to prevent wider
ecological damage in the form of the eutrophication of freshwater and marine waters
generally.