Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 322

from urban areas and highways, while sediment, nutrient and pesticide loads are most
troublesome in agricultural runoff and subsurface flows. Novotny et al. (1999) have
stressed that heavy salt usage and receiving water loads during winter from munici-
palities and roads are serious water quality problems in the snowbelt areas of North
America and Europe. In addition to salt (sodium and calcium chloride), winter salt-
laden snowmelt also contains complex cyanide (an anticaking additive to salt) that
may break down to toxic hydrogen cyanide and several toxic compounds.
According to Ferrier et al. (2004), a useful way of thinking of diffuse pollution is
that it is the often individually minor but collectively significant source in a watershed
(see Figure 10.3).
Tackling diffuse water pollution promptly and vigorously is a crucial requirement
of the European Water Framework Directive (WFD, 2000) prescribing an integrated
river basin management for Europe. Clean Air for Europe (CAFE, 2001), Groundwater
Directive (2003), Thematic Strategy for Soil Protection (2002), Common Agricultural
Policy (2003), Sewage Sludge Directive (1986), Nitrate Directive (1991), the Imple-
mentation of Nitrate Directive (2002) and the Landfill Directive (1999) all require the
appropriate management of diffuse pollution in Europe.
The main characteristics of diffusely polluting substances are that they cannot be
easily traced back to a single or definite source, or their reduction cannot be solved or
is not feasible to be solved locally i.e., air pollution from heating or water pollution
from runoff waters and treated wastewaters, and therefore they need watershed-scale,
regional or global measures (Figure 10.3).
According to the scale the pollution transport from diffuse sources affects
the environment, we distinguish global-scale and watershed-scale diffuse pollution
(Figure 10.3).
Diffuse pollution endangers air, surface water systems and soil by causing:

- Excessive concentrations of airborne contaminants such as CO 2 ,SO x ,NO x ,PM

and volatile organic contaminants which result in unacceptable air quality in big
cities, global warming, acid rain, etc.;

- Increased nutrient levels in lakes, rivers, ponds and ditches as well as in seas and

oceans causing eutrophication;

- Pesticides, biocides and other emerging pollutants in freshwater endangering

humans and the ecosystem;

- Deterioration and endangering conditions of agricultural soils;

- Damage to wildlife.

Around 80% of marine pollution comes from land-based sources and more than
50% of nitrogen entering the marine environment derives from agriculture. Studies
by the UK government agency English Nature (EN) and the UK Environment Agency
show that over half of the most important marine wildlife sites are at risk through
eutrophication in the UK. According to EN estimates, at present 60% of freshwater
sites of special scientific interest (SSSIs) are in unfavorable condition, including 57%
of river SSSIs, partly as a result of diffuse pollution impact. Furthermore, EN has
identified 100 priority sites where diffuse pollution is thought to be the primary cause
of damage only in the UK.