Tide dependent seasonal changes in water quality and assimilative capacity of anthropogenically influenced Mormugao harbour water

Abstract

Water quality data from Mormugao harbour area at the mouth of Zuari estuary in Goa have been obtained over two tidal cycles monthly for the year 2003 to 2004. R-mode factor analyses of the data indicated strong positive loadings of coliforms, nitrogenous substances, PHc and some heavy metals during post-monsoon, suggesting their dominance and significant increase relative to other seasons. Water quality index (WQI) studies showed overall index of pollution (OIP) values of 1.41 to 3.52, categorizing the harbour water as slightly polluted during pre-monsoon. During post-monsoon, the OIP values of 1.75 to 5.4 categorized the harbour water as polluted water, while it was acceptable quality water during the monsoon, with OIP values of 1.13 to 1.79. The higher chlorophyll a (1.4-19 mgm sup(–3) mu g/l) and primary productivity (4.8-14.8 mg/l) of the monsoon was followed by that of the post-monsoon season, with the least during pre-monsoon. Modeling studies using Ecolab module of MIKE 21 suggested slightly higher assimilative capacity for harbour water during the pre-monsoon relative to post-monsoon, which showed a reduction in assimilative capacity.