There are several issues that
affect water-quality relating to urbanization. This includes population growth,
erosion and sedimentation, urban runoff, nitrogen, phosphorous, sewage
overflows, waterborne pathogens and pesticides.
Population growth is particularly
affecting big cities. There is a large influx of people and with that there
must be new housing developments, roads, shopping areas, and commercial and
industrial facilities. The pressure on the water-supply systems is substantial
and is growing to be too much for the systems to handle. This is not a new
issue; 1980’s Atlanta, Georgia saw this problem and the city’s systems could
not handle the stress from the population growth in the city. Atlanta is still
on of the fast growing urban areas in the United States.
Much of the erosion and
sedimentation is the aftermath of storms. Along with plenty of water into the
rivers, storms lead to eroded soil and debris in the water supply. Sediment
deposited on the banks and flood plains of a river is, more often than not,
mineral-rich and makes for excellent farming conditions. What is the downside
with erosion and sedimentation? Sediment can shorten the lifespan of dams and
reservoirs because sediment is unable to maintain suspension in the water and
builds up in the reservoir. This means that eventually the reservoir is no
longer usable for its original function. Erosion may also occur during runoff.
Runoff occurs during storms and may be classified according to speed of
appearance. Much of rainfall is absorbed into forested watersheds and is stored
as groundwater slowly discharging into springs. This natural process lessens
the amount of runoff during a storm. Urbanization of watersheds has affected
the surface area where infiltration of ground water would normally take place.
This means that more storm runoff must be collected by drainage systems that
will carry the water runoff directly to streams. These drainage systems collect
water from curbs, storm sewers, and ditches. Too much water too quickly will cause
severe flooding and with the heavy flow of water comes sediment and pollutants
picked up along the way.
Nitrogen and phosphorus are
introduced to water supply via agricultural runoff. This runoff leads to nearby
streams and lakes and leads to excessive plant growth and hypoxic conditions,
meaning there is a lack of oxygen in the water. Excessive amounts of nitrogen
and phosphorus in drinking water can lead to oxygen transport issues in the
body. There is a high risk of nitrogen contamination in shallow groundwater in
some aquifers in the United States.
There are three types of sewer
systems: storm sewers, sanitary sewers, and combined sewers. Storm sewers carry
runoff from streets and parking lots to streams while sanitary sewers carry raw
sewage from homes and businesses to wastewater-treatment plants; combined
sewers carry a mix of both. When there is an excessive amount of storm water
and the system cannot carry the load, runoff will expose human and industrial
wastes, oil, toxic metals, pesticides and litter into streams.
Sewage overflow
has led to waterborne pathogens in the water supply systems. This can include
bacteria, viruses, and protozoans that are particularly harmful to children,
the elderly, and the immune-compromised. While the water supply is regularly
monitored, overflow is a possibility. Many waterborne pathogens affect the
digestive system such as Giardia, Cryptosporidium, and E. coli.
Sources:
