Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 363

The most severe water quality changes caused by excessive applications of agricul-
tural chemicals have occurred in Central Europe, the Netherlands, the United Kingdom
and some parts of North America (Campbell et al., 2004). The current pattern in
Europe is rather different. Some countries and regions in the EU have nutrient surplus,
while others are affected by undersupply. In the Central and Eastern European (CEE)
countries economic changes in the 1990s caused a significant drop in fertilizer use.
The previous significant soil nutrient surplus has been depleted by the extraction of
these reserves leading to a temporary decrease in fertilizer use for some years. Slight
improvement has been achieved over the last few years. Nutrient undersupply is a
serious problem resulting in increasingly low yields and causing agronomic problems
(Csathó & Radimszky, 2009). In contrast, rural regions with intensive livestock farm-
ing import high amounts of nutrients through forage (e.g., Benelux, England, Northern
Italy and Normandy) creating a nutrient surplus. Past and recent activities are respon-
sible for eutrophication of the aquatic environment throughout Europe, leaving water
bodies at risk of not reaching targets set by the Water Framework Directive (WFD,
2000).
5.2 Measures to reduce diffuse pollution from agriculture
Water pollution such as sewage and industrial effluent is normally easy to monitor as
it generally arises from a single source. Pollution is usually controllable by a system of
legally enforceable discharge consents (e.g., effluent limits which have been set by ref-
erence to environmental quality standards, or EQSs). Such an approach is not feasible
in the case of agriculturally derived diffuse pollutants due to their special appearance.
There is no source to monitor because the sources of pollutants are rarely well defined
and the pathways of movement are frequently poorly understood. Because the mea-
surements are not available, models become increasingly useful at the watershed scale
to quantify emissions and loads reaching the aquatic environment. Risk assessment
tools can identify key source and transport processes which control nutrient loss at the
field scale. They recognize that small areas may contribute disproportionately large
amounts of nutrients and, by ranking “vulnerability to damage and loss,'' mitigation
can be targeted to those areas at the highest risk. The problem is that there are concerns
surrounding uncertainty and a lack of fully validated and spatial distributed models
affecting assessments of transport methods in particular (Cherry et al., 2008).
Similar to the problems associated with measuring and modeling diffuse pollution,
applicability of load reduction measures is also limited. Well-defined EQSs are often
not available which could act as a yardstick (D'Arcy & Frost, 2001). The best man-
agement practice (BMP) to solve agricultural diffuse pollution problems does not seek
to set numerical quality targets for individual farmers to meet. Rather, it sets forth
a series of good practices which the farmer is encouraged to adopt (Campbell et al.,
2004). BMPs as measures and activities to control the diffuse water pollution have
become a cornerstone of watershed management plans. Numerous BMPs reducing the
diffuse emissions and loads have been published (Novotny, 2003; Zanou et al., 2003;
Campbell et al., 2004; Delgado & Scalenghe, 2008). Interventions have two main
groups: source and delivery control.
Source control includes minimizing the introduction of pollutants into the environ-
ment and preventing their mobilization. Legislation is widely applied with the intention