Occurrence of phytoplankton bloom and its effect on coastal water quality

Abstract

An intense bloom of phytoplankton dominated by Asterionella glacialis was observed during the second week of May 1993 in the coastal waters of Kalpakkam. During this period a marked reduction in dissolved oxygen (1.2 mg/l) in the surface water was noticed. A decrease in nitrate and silicate and increase in phosphate levels were also observed. Asterionella glacialis contributed 66% (5.45 x 10(10) cells/m(3)) of total diatoms. Chlorophyll-a value was as high as 22.7 mu g/l. Substantial decrease in total viable count (TVC) was observed (1000 cfu/ml) and this coincided with the Ic west DO value observed during the investigation. Suspended matter (SM) value during the bloom period was as high as 131.5 mg/l. Changes in physico-chemical characteristics of the coastal waters associated with the occurrence of bloom are discussed.