Anthropogenic impact influences the episodic events in the coastal waters of Chennai metropolitan city

The paper deals with several episodic events of fishkill, harmful algal blooms (HABs), and seafoam formation arising in the coastal waters of Chennai during the last decade. Harmful algal blooms (HABs) were encountered at different time scales. The major blooming species are Diatom- Asterionellopsis glacialis, green alga- Chlorella salina, cyanobacteria- Trichodesmium thiebautii, and Trichodesmium erythreaum, coccolithophores- Phaeocystis sp. are attributed to high concentrations of nutrients i.e., nitrogen (N), phosphate (P), and silicate (Si). Fishkill incidences of Mugil cephalus, Chanos chanos, and Tilapia mosssambica had happened twice in the Adyar estuary after a heavy spell of sudden rain ensued low salinity and altering the water quality to great extent. The pollution load index (PLI) of sediment suggested that Pb and Cd were high (1.04 - 1.13) and the Geo-accumulation index (Igeo) indicates high contamination by Cd (2.23-2.60), and moderate contamination by Pb (2.5 - 3.25). Heavy metal contaminations are one of the reasons for the fish kill. Seafoam formed several times could be linked to leakage of sewage-laden water with high phosphate (58.1 µM) and ammonia (440.5 µM). Physical processes such as breaking waves and longshore current disperse the foam to a larger region along the shore within the breaker zone. These episodic events demonstrate that recreational and fishing activities along the coast are exceedingly vulnerable and demand immediate attention for better management of coastal water quality. It is suggested that efficient measures through appropriate interventions and strategies for restoration programs need to be adopted for nutrient control by curbing the sewage leakage to the coastal environment and increasing awareness among stakeholders.