Pollution - Environmental Science - page 159

panies may have access to certain types of genetically modified products, allowing these few companies to
control markets, restricting the freedom of competition.
Economic impacts of genetic engineering (both positive and negative) are dramatic and far-reaching, affecting
farmers, fishermen, ranchers, markets, and nations.
Water Pollution
Water pollution can be very harmful to the environment as well as to people and wildlife. This section ad-
dresses freshwater and marine water.
Cultural Eutrophication
Eutrophication is the addition of excess nutrients to water. If these excess nutrients are due to human activity, it
is called cultural eutrophication. Nutrients are added to an ecosystem through runoff, including excess nitro-
gen and phosphorus from fertilizers, untreated sewage, detergents, animal waste, or fossil fuel combustion.
Nitrogen has a greater impact on marine ecosystems, and phosphorus has a larger impact on freshwater ecosys-
tems.
Groundwater Pollution
Groundwater and surface water can be polluted by anthropogenic sources such as leaking oil tanks, agricultural
runoff, chemical spills, untreated sewage, storm runoff, development, and mining operations.
Pollutants that affect freshwater sources are:
• Toxic chemicals: These can run off or leak into waterways. Toxic chemicals include pesticides; volatile
organic compounds; petroleum products; heavy metals such as arsenic, chromium, mercury, and lead;
and other dangerous substances.
• Nutrient pollution: This results from nutrient runoff from agricultural practices, sewage, lawns, golf
courses, and fields. Excess nutrients can cause eutrophication in both freshwater and marine environ-
ments, resulting in an alteration of the balance of the ecosystem.
• Temperature pollution: This results from the release of water that is either warmer or colder than nor-
mal for the specific environment. This temperature change can affect individual species as well as the
balance of an entire ecosystem. Thermal (heat) pollution occurs when water is used in factories and
manufacturing processes. The water becomes heated as it cycles through the manufacturing processes
and is then discharged into the local water source. Heating of water also can occur when vegetation is re-
moved from the banks of a river, allowing more sunlight to hit the water's surface. Cold water pollution
can occur when a dam releases cold water from the bottom of a reservoir into a river, as in the case of
most hydroelectric power stations. Both extremes affect ecosystem balance.
• Sediment can become excessive in freshwater systems. Although it is a natural part of aquatic ecosys-
tems, sediment in disproportionate amounts can change the aquatic balance. Excess sediment suspended
in the water causes cloudiness that is called turbidity. Turbidity affects some fish that cannot adjust to
changes in sediment levels and leads to a lack of sunlight and, thus, available energy in deeper waters.
Once sediment settles it also can impact the benthic environment and alter the flow of water. Contamin-
ants, such as heavy metals, can accumulate in sediment as well, ultimately settling on the bottom where
they can be ingested by benthic organisms.