Physicochemical studies on coastal pollution off Bombay

Abstract

Variations of salinity, dissolved oxygen (DO) and biochemical oxygen demand (BOD) in the creeks, bays and coastal region around Bombay, Maharashtra, India were studied. Currents varied depending on the tide and their direction in creeks and streams was dominated by the physical features of the channel. Currents did not vary appreciably from the surface to bottom. Salinity varied widely from < 5% during August to >34 % after March. Generally, the monsoon period was characterised by well marked vertical salinity gradient except in the coastal region, which disappeared at most of the stations during the postmonsoon period. Coastal water was vertically homogeneous throughout the year while some lateral salinity gradient was observed during August. DO profiles were similar at most stations. In general, higher DO observed in August sharply decreased during September and then gradually increased to maximum in February, followed by a gradual decrease till May. This trend appears to be due to the combined effect of BOD, temperature and photosynthetic activity. Abnormally low DO and high BOD were observed at Upper Thana, Mahim Bay and Versova Creek due to the influence of waste water discharged at these locations. Mahim Bay was worst affected with DO levels sometimes falling to <1 mg/litre.