Biochemical Indicators of Algal Bloom in Sewage-Contaminated Lakes

Abstract

Pollution of Bengaluru lakes with partially treated sewage and stormwater runoffs has led to frequent algal blooms and fish kills in the lakes. This study examined the biochemical parameters of four polluted Bengaluru lakes to arrive at a proposal to control excess algal growth in the lakes. Results of the study indicate that during nonbloom conditions, the lakes classify as oligotrophic and mesotrophic lakes. During bloom conditions, the lakes mainly classify as eutrophic and hypereutrophic lakes. Reduction in bicarbonates, increase in pH, and insensitivity of chemical oxygen demand (COD) during algal growth experiments in the laboratory suggest the dominance of autotrophic algae in the lakes. Regulating COD levels of Bengaluru lakes at or below 15 mg/L is recommended to reduce microbial activity and associated bicarbonate production. Reduction in nutrients and bicarbonate levels will in turn control excess algal growth. Alkaline lake water from photosynthetic metabolism of algae causes precipitation of calcite, dolomite, and magnesite minerals and concomitant reduction in Ca, Mg, and bicarbonate ion concentrations in the lake water.