1 Agricultural pollution – the problems.
14.04 The potential for modern agriculture to cause pollution is attributable largely to the by-products generated by intensive livestock and arable production – notably silage effluent, slurry, and nitrates.
Silage effluent is 200 times as polluting if released into surface waters than raw untreated sewage, and cattle slurry can be up to 100 times as polluting. The potential of silage effluent to cause major environmental damage cannot be underestimated; it has a Biochemical Oxygen Demand (BOD) of 30,000–80,000 mg/litre, compared with a BOD of 300–400 mg/litre for raw domestic sewage.8 Its potential for removing oxygen from waters into which it is released is therefore very considerably more and its uncontrolled or accidental release (even in small quantities) will inevitably cause major damage to fish stocks and river eco-systems.14.05 Agriculture is a significant source of recorded pollution incidents involving rivers and watercourses in the UK, although the number of pollution incidents attributable to farming, as a proportion of the total number of all incidents reported, is relatively small. Between 1991 and 2000 there was a 50% increase in the number of substantiated pollution incident involving farms. At the same time, however, there was a big reduction in the number of serious (that is, Category 19) incidents. Nevertheless, agriculture remains a significant source of water pollution. In 1985 there were 3,510 substantiated pollution incidents involving agriculture, a figure that had risen to 4,560 incidents in 2000. In the same period recorded category 1 incidents involving agriculture fell from 572 in 1985 to just 21 in 2000.10 The latest statistics from the Environment Agency show that farming caused 12 major (Category 1) incidents in 2006, a slight improvement over 2005 when 19 serious farming incidents were recorded. In the case of water pollution, dairy farming was the source of the largest number of incidents: out of a total of 65 Category 1 and 2 incidents involving serious pollution of water sources in 2006, 31 were attributable to dairy farming, as were 6 of the 12 most serious (ie Category 1) incidents.11