Environmental Engineering Reference
In-Depth Information
6.4.1 Impact on Health
The impact on public health due to activities associated with food production has been
studied by many international organizations. Although agricultural yields have increased,
irrigation, land conversion, and disturbances of the ecosystems have increased the rates of
even older diseases such as malaria. Irrigation has increased the number of diseases, up
to 30 diseases, including mosquito-borne diseases in Central and South America (WHO,
1996), malaria, and Japanese encephalitis due to rice paddy irrigation. Irrigation systems in
hot climates are directly linked to schistosomiasis incidences.
Deforestation and increasing cultivation decreases the soil's ability to retain contami-
nants and nutrients. Chemicals such as mercury, which are normally stabilized by iron
oxyhydroxide adsorption, can bioaccumulate in ish. Erosion destabilizes mercury, thus
increasing the release of mercury into the water supply. Freshwater ish can contain an
average of 48 μg/L of mercury, a potential health hazard (Richard et al., 2000).
The decrease in water quality due to pollution from a variety of urban and industrial
sources also can contaminate crops and lead to the poor health of farm workers and con-
sumers of the contaminated crops. Agriculture cannot be viewed in isolation to the other
sectors. It has been called both a cause and victim of water pollution (Ogaji, 2005).
6.4.2 Impact on Biodiversity
One of the major impacts of land transformation for food production and other uses has
been the extensive loss of biodiversity. Food production activities in the agricultural sector
has led to the extinction of more species than any other sector. The rates of extinction have
increased from 100 to 10,000 times the level prior to the industrial revolution. Decreases
in the amounts of pollinating insects have negatively impacted yields of particular crops
(Nabhan and Buchmann, 1997). The diversity of soil organisms has also decreased due to
the decreased opportunity for organic decomposition and increased nutrient content. As a
result, specialized predators and weeds will also develop due to the low diversity of spe-
cies in agricultural lands. Changes in land use has affected the various cycles within the
global system including the carbon, water, biogeochemical and biotic, to name a few. For
example, lack of SOM and soil organisms will impact the carbon cycle.
Biological diversity is the highest in forested areas. For example, although inter-tropical
forests make up only about 6% of the surface area, they nevertheless make up half of all
plant and animal species. Thus, conversion of these forested areas to agriculture can be
highly detrimental to biodiversity. Modifying rivers and lakes for irrigation purposes can
lead to extinction of the fauna, lora, and terrestrial organisms due to variations in water
composition, temperature, and low. Water pollution from runoff of pesticides, fertilizers,
and salinization can inluence biodiversity. Salinity levels in the Aral Sea have tripled
due to cotton irrigation (WRI, 1992). This has led to extinction of 24 species of ish (Postel,
1992). In addition, erosion can be detrimental to ish and other aquatic organisms due to
siltation of breeding grounds. Mulholland and Lenat (1992) estimated that there has been a
decrease of up to 50% of the species in streams affected by agriculture. Increasing the use
of surface water for agriculture can also damage ecosystems in lakes and watersheds. The
biodiversity losses or changes may not be evident initially but in the long term can have
signiicant impacts on the sustainability of agricultural practices.
New breeding methods have caused a signiicant loss of agricultural biodiversity. Some
of these impacts are shown in Figure 6.7. The schematic diagram shows that although there
is a large number of species available, only a small portion is utilized for food production.
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