Assessment of element distribution and heavy metal contamination in Chilika Lake sediments (India)

Abstract

AbstractChilika Lake is situated on the Indian east coast. It is one of the largest lagoons in the world, with a unique assemblage of marine, brackish water and freshwater species. Due to the opening of new connections to the sea in the years 2000 and 2008, an environmental change is expected in the lagoon. The study gives an assessment of sediment contamination by heavy metals on the verge of this change (sampling campaign in 2000). Sediment samples from two surface levels (0–5 and 30–35 cm), and from depth profiles, were analysed for mineralogical composition, main and trace element concentrations, and element bonding forms. Background concentrations from a depth profile were also examined. The profile spans a time of ≈13 500 years. Age determinations by radiocarbon dating and the 137Cs‐ and 210Pb‐method were carried out. The composition of the surface sediments is generally uniform. The heavy metals exhibit slightly decreasing concentrations from NE to SW, thus indicating the supply of contaminants from the Mahanadi River. The anthropogenic portion of the heavy metal supply is mainly bound to Fe‐oxide‐hydroxides. Phosphorus is enriched in the sediments of the southern lake sector. Changes in element concentrations in the last 13 500 years have occurred mainly in two steps. The long‐term variations exceed the anthropogenic changes caused by the Mahanadi River inputs. The very sensitive response of coastal area fabrics on climate changes also causes fast geogenic changes in element concentrations in sediments (similar grain sizes). This prevents the use of element concentrations from deep sediment horizons to define contaminations in those areas.