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

pH was chosen as a regular parameter to be monitored because it is indicative of the
degree of the saline water intrusion, biogeochemical processes and contamination. Fresh
water is generally acidic where as seawater is alkaline. Thus the pH variation around the
year, covering all seasons, was expected to be revealing. Alkalinity, conductivity,
chloride, hardness and sulphate are directly related to salinity intrusion. When salinity
starts picking up, all the above parameters show a rising tendency, unless some other
chemical sub-routes are involved. Hence the rise and fall could be in phase with the
migration of salinity. This possibility was explored by monitoring the above parameters.
Nitrate and phosphate are the essential plant nutrients and their ratio is indicative of
sewage contamination. Increased pH and the intrusion ofmarine cations could lead to the
flocculation of phosphate. Nitrate is a very unstable component in an oxygen-depleted
aquatic ecosystem and hence, the concentration ofnitrate and DO are complimentary. In
the absence of DO, nitrate is reduced by the oxygen-demanding wastes. Again DIP and
DIN are the essential parameters for the budgetary modeling of the water body.
Solubility of iron is directly related to pH and DO. Iron is immediately precipitated to the
sediments by hydrogen sulfide in anoxic conditions. On interaction with alkaline marine
water, Fe was expected to be removed from the water column. DO, COD and BOD are
the most important parameters required to define the quality of a water body. Percent
saturation of DO is a direct measure ofthe purity ofwater.
(The standard Operating Procedure has been documented)
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