Catchment-Sensitive Farming: Tackling Diffuse Water Pollution from Agriculture in England —Policies and Drivers - Water and Agriculture: Sustainability, Markets and Policies - page 266

Nitrogen
For nitrogen (N), agriculture's contribution is roughly 60%, while that of sewage
treatment works (STW) remains at roughly 30% (Defra 2004c). The contribution of point
and diffuse sources of nitrogen to both marine and inland waters in England and Wales
amounted to some 558 ktN/yr. In England and Wales, N levels have increased by about
15% from 287 kt N to 330 kt N, and the estimated inputs from sewage treatment works
(STW) have declined by about 15% — from 216 kt N to 184 kt N (Figure 1). This
decrease has come about primarily as a result of improvements in STW discharges to the
marine environment, undertaken to meet legislative requirements.

Figure 1. Nitrogen sources in England and Wales,
year 2000 nominal (ktN/yr) (from WRc ([2004])

N load (kt/y)

0 50 100 150 200 250 300 350

Agricultural Land
Sewage Treatment Works
Other Land
Direct Industrial
Septic Tanks
Direct Deposition
Combined Storm Overflows

Silt

The highest proportion of suspended solid loadings to rivers derives from diffuse
sources and that in rural catchments this is heavily dominated by agriculturally-derived
soil erosion. However, no national source apportionment is yet available. Where arable
lands are under drained, 50% and more of the silt load that leaves a catchment can be
agriculturally derived. Soil loss by erosion from pastureland can also provide the
dominant source of silt in streams, particularly where under drainage is present and where
poaching of soils has occurred (Defra 2004a).

BOD
Livestock in the UK produce about 2.5 million tonnes of BOD every year. If just 2%
of this were to escape into water it would be equivalent to the total BOD from human
excrement that is discharged via sewage treatment works each year (Defra 2004a).

Faecal Indicator Organisms (FIOs)
Numerous studies (see Defra 2004b) have demonstrated the importance of diffuse
agricultural sources to the faecal loadings at bathing waters. Extensive work in Scotland
has shown the important role that livestock management can play in influencing the
quality of bathing waters. Direct access to watercourses and poor management of
livestock and slurry have all been implicated in high bacterial loads in rivers. The lack of
adequate on-farm storage facilities for manures and slurries was shown to be a major