Seasonal and spatial variations in elemental distributions in surface sediments of Chilika Lake in response to change in salinity and grain size distribution

Chilika lake, the largest brackish water lagoon in Asia, has a unique setting, where the north-eastern part receives freshwater from the terrestrial runoff, and the south-eastern part receives seawater from the Bay of Bengal. The seasonal variability in the quantity of inflowing water and their mixing in the lake controls the mobilization and precipitation of various elements. Seasonal sediment samples were collected from both the river and seawater influenced regions of the lake to understand the spatio-seasonal distributions of various elements along the salinity gradient. The major elements present in the sediments are mostly derived from the parent rock weathering in the source region and subsequently transported into the lake by the rivers. Seasonal variations in trace element concentrations are more prominent in the north-eastern part of the lake (i.e., low salinity region), and their higher concentrations have been observed during the post-rainy period. The affinity of the elements (Al, Fe, Mn, Li, V, Co, Cr, Cu, Th, and Zn) towards fine-grain sediments suggests that the size distribution pattern controls their accumulation, retention, and remobilization. The concentrations of Cr, Cu, and Pb exceeded the effects range low, and effects range median benchmarks indicating the potential biological risk in the low salinity region as compared to the high salinity region. The statistical analysis indicated that the concentrations of elements in the region proximal to the sea mouth are controlled by grain size and physicochemical condition of the lake water. In contrast, the element concentrations in the interior region are associated with anthropogenic activities and weathering processes. Continuous monitoring and assessment of element concentrations of the lake sediments can help to protect the lake ecology from the harmful element contaminations.