Biogenic element concentration and TOC/N ratio analysis in Veli-Akkulam Lake, Kerala: seasonal changes and urbanization impacts.

Rapid urbanization and increased tourism in urban catchments cause a greater input of nutrients and organic matter into lacustrine systems, leading to ecological degradation. The sixth Sustainable Development Goal, which focuses on reducing pollution and improving water quality in lakes and reservoirs, may only be achieved by identifying the sources of pollutants and depositions in the waterbody. Veli-Akkulam is a well-known tourist destination and environmentally significant location in Thiruvananthapuram. It is a small urban lake that borders the Arabian Sea, having an average length of 3.2 km and a depth of 2.4 m. The purpose of this study is to determine the sources of organic pollution in Veli-Akkulam Lake by analysing the spatio-temporal variations in the concentration of biogenic elements and TOC/N of the lake surface sediment samples taken from eight selected stations. The study's findings indicate that silt and clay predominate the eastern portion of the lake, where concentrations of total carbon, total organic carbon, total nitrogen, and total phosphorus were 6.26%, 5.1%, 0.9%, and 14.5%, respectively. During the pre-monsoon, monsoon, and post-monsoon seasons, the TOC/N varied between 0.95 and 5.04, 0.18 and 4, and 1.01 and 30, respectively, indicating the presence of both autochthonous and allochthonous sources of organic matter. There was a substantial positive correlation between the biogenic elements and the TOC/N ratio. According to the findings, the lake has been affected by eutrophication caused by organic contaminants. Dredging, sediment elution, sewage treatment, and other management techniques must be implemented so as to sustainably manage the lake.