Chemical composition and possible sources of suspended particulate matter in the peripheral environments of Batticaloa lagoon, Sri Lanka

Since coastal lagoons are mixing zones of fresh and saline water, suspended particulate matter (SPM) in different environments within a lagoon exhibits unique properties. Biogeochemical processes of different environments within a coastal lagoon are critically reviewed. In this study, the peripheral environment of Batticaloa lagoon which is a large, semi-enclosed, micro-tidal lagoon in the tectonically inactive tropical climatic zone of Sri Lanka was evaluated for its chemical composition of SPM in the post winter monsoonal season 2016. Further, it was compared with physical conditions of water and general surface sediment geochemistry. Overall physical parameters of the lagoon peripheral indicate low oxygenated brackish water with neutral pH. The concentration of SPM shows a weak correlation with the physical parameters of water. The peripheral environment of the lagoon has higher concentrations of Zn, Cu, Ni, MnO and P2O5 in SPM compared to the surface sediments. Previous studies have shown that these elements are rich in marine micro-organisms. Further, with respect to the statistical correlations, no evidence was found to prove the sorbing nature of iron and manganese coatings as described in other studies. Hence the results suggest that the tropical climates and allied organisms at the peripheral environment of the lagoon have improved the chemical composition of SPM with respect to that of lagoon surface. Environmental concerning elements indicate minor to moderate enrichments compared to upper continental crust with iron as the reference element in the Enrichment Factor calculation. Despite the size and micro-tidal effect of Batticaloa lagoon environment, the concentration of SPM does not vary throughout the entire study area except at the river discharging points.