Diatom Indices and Water Quality Index of the Cauvery River, India: Implications on the Suitability of Bio-Indicators for Environmental Impact Assessment

Physico-chemical properties of water are routinely utilized for understanding environmental quality. Diatoms are used as bio-indicators to assess the water quality of surface waters. Independent assessments of environmental quality of the surface waters from the Cauvery River were made and the resultant quality-indicators were assessed in the light of national river water quality standards. Occurrences of sixty (60) species belonging to 21 genera are recorded from the Cauvery River. Water samples were analyzed for various physico-chemical parameters, viz., pH, Electrical Conductivity (μS/cm), Dissolved solid (mg/l), Biochemical Oxygen Demand (BOD) (mg/l), Calcium (Ca) (mg/l), Magnesium (Mg) (mg/l), Sodium (Na) (mg/l), Potassium (K) (mg/l), Chloride (Cl) (mg/l), Bicarbonate (HCO₃) (mg/l) and Sulphate (SO₄) (mg/l). These physico-chemical parameters formed the basis of computing the Water Quality Index. The results of the present study on diatom assemblages in the Cauvery River revealed moderate pollution at Siluvampalayam and Koneripatti and high levels of pollution at Peramachipalayam, Kottampatty, Sanyasipatti and Bhavani. The Water Quality Index revealed pristine nature of the Cauvery River water in upstream regions that became unsuitable for human consumption downstream of Bhavani Town. The values of DO and BOD levels indicated absence of major organic pollution. Comparative validation of the physico-chemistry and bio-indicators suggested sensitive nature of the Diatom indices to environmental variables and thus the diatom indices can be a reliable tool for environmental impact assessment.