Input-export fluxes of heavy metals in the Cochin estuary, southwest coast of India.

Abstract

Cochin estuary (CE) is one of the largest tropical estuaries along the southwest coast of India, sustaining rich bio-resources. Several studies enlighten the environmental changes in the CE caused by anthropogenic activities. In the present study, an attempt has been made to quantify the heavy metal (dissolved and particulate) fluxes brought by the six rivers into the CE with their exchange into the coastal ocean through the major inlet at Cochin during a steady flow period (October-November 2015). The water flux across the inlet was quantified using an acoustic doppler current profiler. The measured daily input of dissolved metals from the rivers was 2.43 × 103kg Fe, 334kg Zn, 259kg Ni, and 83kg Cr, while that of particulate metals were 85.30 × 103kg Fe, 8. 6 × 103kg Mn, 236.9kg Cr, and 111.9kg Zn. The net export of metals through the Cochin inlet (per tidal cycle) was 3.3 × 103kg Fe, 515kg Cr, 150kg Zn, and 5kg Ni in dissolved form and 3.32 × 105kg Fe, 1747kg Mn, 1636kg Cr, 1397kg Zn, and 586kg Ni in particulate form. The high concentrations of metals during ebb tides are clear indications of their contribution from the industrial conglomerates (industrial units of metallurgy, catalyst, fertilizer, and pesticides) located in the Periyar River. The significance of this study is that the export fluxes may increase further during the summer monsoon (June to September), which may impact the abundant fishery emanating in the coastal environment during the period due to intense upwelling.