Pollution induced tidal variability in water quality of Mahim Estuary

Abstract

Variability of water quality due to release of wastewater in Mahim Estuary (Maharashtra, India) and associated nearshore waters is discussed. The mixing of low salinity contaminated estuary water with high salinity bay water was considerably hindered inducing lateral as well as intermittent vertical stratification which severely polluted the northern bay as compared to the southern region. The high wastewater fraction varying between 0.3 (spring) and 0.98 (neap) of estuarine volume in absence of river runoff, resulted in severe deterioration in water quality due to weak tidal flushing. The overall character of the particulate suspended matter changed considerably with increase of inorganic component from 50 per cent in the estuary to 65 and 80 per cent in the bay and in the offshore respectively. The low estuarine pH increased with increase in salinity and attained seawater values in the coastal water. The stress of anthropogenic organic load though marginal outside the bay, the dissolved oxygen (DO) replenished with the incursion of high tide was quickly consumed leaving very low to undetectable levels in the northern bay unlike in the southern bay