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

6. Iron and calcium do not appreciably precipitate phosphate in the later stages of
salinity intrusion.
7. A mechanism of C03-HC03 balance is existing to resist pH and alkalinity
variations and the chloride levels do not cross a critical value that triggers
salinity-induced changes.
8. Approximately in January and in March, two peaks are found for chloride
hardness, calcium hardness, sulfate, COD and BaD.
9. It could possibly be construed that chloride and associated parameters actually
fall after a winter maximum to peak again in late March or early April because
fresh water consumption rises in the hot and sultry summer months. In major
canals like Chittoor and Chithrapuzha, such a double peak is not observed,
whereas in the lesser canals draining the city, this pattern is evident. This fact
reinforces the above conclusion.
10. In most canals, phosphate reaches a minimum level in early January when
chloride maximizes for the first time and thence phosphate steadily rises with
chloride and both hit their vernal peak somewhere in late March or early April.
This would suggest that phosphate is diluted when sea water barges in for the
first time and thereafter dissolved phosphate is not anymore bothered by
salinity invasion. Marine cations precipitate phosphate in appreciable
amounts when the rainy season peters out, when the dry season advances
sewage influx apparently out weighs the marine cation intrusion and the rare
afternoon rains wash out accumulated terrestrial phosphate. But Poorni puzha
III