Seasonal algal bloom and water quality around the coastal Kerala during southwest monsoon using <i style="">in situ</i> and satellite data

Abstract

Algal bloom has been observed using IRS-P4 (Oceansat-1) OCM data and <i style="">in situ</i> observations during September 2002 and 2003 around the Kerala coastal and shelf water off Calicut. Algal bloom features have been observed in the total radiance, remote sensing reflectance, chlorophyll and diffuse attenuation coefficient images. <i style="">In situ</i> observations indicated the dominance of dinoflagellate <i style="">Noctiluca</i> <i style="">scintillensis</i> in the 1^st, 2^nd and 3^rd weeks of September 2002. Red colour of water was seen even upto 30-35 kilometer from coastline and this has been got reflected in OCM derived chlorophyll images with the dense algal bloom features with very high chlorophyll concentration (20-50 mg/m³). During September (8, 20, 22, 24 and 30) 2003, high dense algal bloom patches (chl>20 mg/m³) were seen around the Calicut coast in the OCM images and spreads across the Kerala coast in the shelf water up to 20-30 km from coastline. Water colour has been found even green due to toxic micro algae <i style="">Hornelia marina</i>. Water quality parameters like SST, dissolved oxygen, salinity, pH, productivity and nutrients have been correlated with the bloom phenomenon.