Aquatic Pollution and Coastal Zone Managememnt (2+1)

Unit 2 : Sewage and domestic wastes, treatment and reuse

2.4.1. Physio-Chemical Characteristics
The chemistry of water is greatly affected by organic pollution because of the accumulation of degradation products and decline in oxygen. The hypoxic conditions prevent the oxidation of ammonia and hydrogen sulphide formed after the degradation of organic matter, thus allowing their build up to dangerous levels. The original quantity of nitrate (NO₃) present in the system also falls because of its conversion to ammonia or nitrogen gas by a process of denitrification, under low oxygen conditions. In the flowing waters, however, the initial decline in nitrate can be made good by nitrification of ammonia as the oxygen starts increasing in water.
Organic pollution also increases the phosphorus content because it is released in the medium after decomposition. The build up of CO₂ affects pH and equilibrium in waters.

The reduction in pH and DO₂ modifies the redox potential that governs the movement of nutrients across the water and sediment interface.
Large quantity of suspended sediments also gets settled at the bottom and promotes anaerobic conditions in the sediments.