Factors controlling physico-chemical characteristics in the coastal waters off Mangalore--a multivariate approach

Water quality parameters (temperature, pH, salinity, DO, BOD, suspended solids, nutrients, PHc, phenols, trace metals--Pb, Cd and Hg, chlorophyll-a (chl-a) and phaeopigments) and the sediment quality parameters (total phosphorous, total nitrogen, organic carbon and trace metals) were analysed from samples collected at 15 stations along 3 transects off Karnataka coast (Mangalore harbour in the south to Suratkal in the north), west coast of India during 2007. The analyses showed high ammonia off Suratkal, high nitrite (NO(2)-N) and nitrate (NO(3)-N) in the nearshore waters off Kulai and high nitrite (NO(2)-N) and ammonia (NH(3)-N) in the harbour area. Similarly, high petroleum hydrocarbon (PHc) values were observed near the harbour, while phenols remained high in the nearshore waters of Kulai and Suratkal. Significantly, high concentrations of cadmium and mercury with respect to the earlier studies were observed off Kulai and harbour regions, respectively. R-mode varimax factor analyses were applied separately to surface and bottom water data sets due to existing stratification in the water column caused by riverine inflow and to sediment data. This helped to understand the interrelationships between the variables and to identify probable source components for explaining the environmental status of the area. Six factors (each for surface and bottom waters) were found responsible for variance (86.9% in surface and 82.4% in bottom) in the coastal waters between Mangalore and Suratkal. In sediments, 4 factors explained 86.8% of the observed total variance. The variances indicated addition of nutrients and suspended solids to the coastal waters due to weathering and riverine transport and are categorized as natural sources. The observed contamination of coastal waters indicated anthropogenic inputs of Cd and phenol from industrial effluent sources at Kulai and Suratkal, ammonia from wastewater discharges off Kulai and harbour, PHc and Hg from boat traffic and harbour activities of New Mangalore harbour. However, the strong seasonal currents and the seasonal winds keep the coastal waters well mixed and aerated, which help to disperse the contaminants, without significantly affecting chlorophyll-a concentrations. The interrelationship between the stations as shown by cluster analyses and depicted in dendograms, categorize the contamination levels sector-wise.