Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 362

5 ASSESSMENT AND MANAGEMENT OF DIFFUSE SOURCES
FROM AGRICULTURE

A. Clement
5.1 General characterization of agricultural diffuse pollution
Watershed-scale agriculture is one of the largest sources of diffuse pollution. It emerges
over a wide geographical area and is dependent on what happens on the surface of
the land. Although individually minor, such pollution on a watershed scale can be
significant considering the cumulative effect which these separate discharges can have
on the environment.
Diffuse pollution from agriculture can be categorized as follows:

- Increased soil erosion and soil loss;

- Chemical pollution by fertilizers and pesticides;

- Irrigation return flow; and

- Pollution from animal husbandry (Campbell et al., 2004).

In addition, we have to mention the agrotechnologies endangering air with CO 2 ,
ammonia and methane:

- Rice cultivation producing large amounts of methane;

- Stubble burning releasing greenhouse gases into the atmosphere;

- Livestock farming is the main source of ammonia emission into the air;

- Farming cattle and other ruminants are responsible for methane production.

Activities such as plowing, seedbed preparation, crop spraying, fertilizer spreading
and applying slurry may contribute to diffuse pollution. Runoff from farm roads and
yards are all potential sources of pollution. There is, therefore, a wide range of potential
contaminants which are associated with farming practices and which can harm the
environment: soil particles, nutrients, nitrogen and phosphorus; pesticides and other
potentially toxic chemicals, pathogens, for example, bacteria from livestock slurries
and manure spread on land and runoff associated with intensive grazing practices;
gases such as ammonia.
Until the 1950s, most farming, even in Europe and the US, was carried out on
smaller family farms that used organic fertilizers. Their waste production was easily
assimilated by soils and receiving water bodies. Since the 1950s there has been a world-
wide shift to larger monocultural, intensively operated farm units. Farm yields have
increased dramatically. However, to sustain increasing yields and productivity, farms
were using large quantities of chemical fertilizers and pesticides (Campbell et al., 2004).
The pursuit of maximizing crop yields and the low cost of these fertilizers has led to
their excessive use, without considering that excess nutrients are not utilized by the
plants and ultimately pollute the water. Livestock production is mainly dangerous if
liquid manure is produced because of the large amounts of pollutants. Diffuse nutrient
losses from agriculture can reach receiving waters and are responsible for deterioration
of surface and groundwater quality.