Salinity Intrusion and Seasonal Water Quality Variations in the Tidal ...

nutrients, particularlyphosphate. Much of the rain fall in the villages is absorbed in the
porous soils and is stored up as ground water. When urbanization comes much of the
vegetation and top soil is replaced by impervious surfaces. And the rain water used to be
absorbed into the ground will be collected in storm sewers that send the runoff into local
streams. These streams are not conditionedby nature to contain urban runoff and flooding
and contamination occurs. Urban areas generate both point and non point sources of
contaminants. Point sources that impact surface water include industrial and municipal
waste discharges and also leaky underground storage facilities as well as miscellaneous
accidental organic and inorganic contaminants. Ground water contamination by organic
volatile compounds is common place in urban settings due to heavy use of fuels and
solvents.
The city, like any other system, feeds on matter and energy and leaves behind both
matter and energy qualitatively degenerated. In a balanced system the flux of energy is
unidirectional but matter undergoes circulation. In a city matter and energy are on one
way traffic. Theenergyrefuse ofthe city degraded as unavailable energy manifests itself
in the form of urban heat domes and thermal pollution in the water bodies it relies on.
Most of the ecosystems of the world are propelled by the sun and things happen in the
earth-atmosphere system during the flux of solar energy from a high energy level to a
low energy level and cities also join forces in this process. For every 10° C rise in
temperature oxidation rate is doubled and DO is decreased (Tebbut, 1998). Hence the
oxygen requirement of the aquatic fauna increases with temperature and availability of
oxygen sharply falls in urban environment.
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