Spatio-temporal variability of trace metals and major ions in a small tropical river, southwest coast of India

Sita, a small tropical river originating in the Western Ghats, southwestern India, was chosen for this study to understand the spatial and temporal variability of dissolved trace elements and major ions. Sampling was done in monsoon, post-monsoon and pre-monsoon seasons across the river catchment. Dissolved elements like Zn, Ni, Cu and Co showed high concentrations during monsoon which could be because of the intense chemical weathering of silicate rocks in the catchment, surface runoff and wet atmospheric deposition. In the remaining seasons, the river is fed by the groundwater and anthropogenic effluents which is contributing to higher concentrations of dissolved Pb, Fe and Cd. The results are analysed using factor analysis (SPSS 12), which helped to delineate the sources of metal assemblages. Factor 1 is dominated by major ions (Na, K, Cl, Mg, Ca), which could be naturally sourced from atmospheric deposition and weathering of rocks. Factor 2 is dominated by trace metals (Cd, Pb, Co) and sulphates (SO₄) which may have anthropogenic sources such as the discharge of domestic and industrial effluents and agricultural effluents.