Geography Reference
In-Depth Information
of major floods, which lead to sewage
contamination of drinking water systems, increases
exposure to disease agents. Population growth,
increasingly concentrated husbandry of domestic
animals and declining water supplies have
exacerbated the occurrence of waterborne disease.
In the future, changes in the distribution of
freshwater pathogens and the vectors of water
habitat diseases, such as snails, mosquitoes and flies,
can be expected through increased water
temperatures associated with future global
warming (Webb 1997) and through other water
quality trends such as increased eutrophication.
Pollution of freshwaters by pathogens can be
combated by waste water and water supply
treatment, and water bodies have the potential for
self-purification. However, even in developed
countries, traditional water treatment processes
may not effectively eradicate newly recognised
pathogens such as
Cryptosporidium
(Department of
the Environment and Department of Health 1990;
1995), which has caused health problems recently
in the UK and in the United States. MacKenzie
et
al
. (1994), for example, report that in 1993 more
than 400,000 people were infected with
cryptosporidiosis in Milwaukee, Wisconsin, as a
result of contamination of the drinking water
supply from Lake Michigan. The outbreak killed
more than 100 people and led to hospitalisation
of more than 4000 others.
lakes since the 1930s, and especially over the last
thirty years (Figure 11.3). Although industrial and
sewage effluents can contain high nitrate
concentrations, much of the nitrogen reaching
Figure 11.3
Examples of rising nitrate concentrations in
(A) rivers, (B) groundwaters and (C) lakes.
Nutrients
Nitrogen (N) and phosphorus (P) are regarded as
key nutrients in surface and groundwaters
(Heathwaite
et al
. 1997). Human activities have
increased the concentration and loading of these
elements in freshwaters, leading to pollution
problems at regional and potentially wider scales.
Considerable attention has been focused on
nitrates in recent years (Royal Society 1983; Burt
et al
. 1993) because of concerns that high
concentrations in drinking water may be
responsible for methaemoglobinaemia (blue baby
syndrome) and stomach cancer. Monitoring has
revealed rising nitrate concentrations in European
and North American rivers, groundwaters and
Sources:
Roberts and Marsh 1987; CIPEL1986.
