Effect of thermal power effluents on the community structure and primary production of phytoplankton

Abstract

Effluents discharged by the coal-fired thermal power house at Obra (22° 52′ N lat. and 83°5′ E long.) reach into the nearby flowing Rihand river and alter the ecological features of the river ecosystem. Temperature and pH of the receiving river water increased while the transparency, dissolved oxygen, chloride, NO 3-N, and PO 4-P decreased. In the effluent zone of the river, no phytoplankton existed during a one-year study period (January to December 1987). Chlorophycean members like Spirogyra and Scenedesmus which were present in the unaffected upstream (control site) were replaced by Bacillariophycean members like Pinnularia and Nitzschia with reduced phytoplankton density in the downstream-affected water. At the control site (average of 12 months), Chlorophyta density contributed 335 unit L −1 to the total phytoplankton density (774 unit L −1) followed by Cyanophyta (260 unit L −1) and Bacillariophyta (188 unit L −1). At the affected site maximum of 112, the unit L −1 contribution was by Bacillariophyta followed by 90 unit L −1 of Chlorophyta and 60 unit L −1 of Cyanophyta to the total phytoplankton density (221 unit L −1). Phytoplankton diversity indices and primary production were reduced in the affected zone. Chloride and PO 4-P together accounted for 54% (p<0.01) of thevariability to the Bacillariophyta density, while no clear influence on Chlorophyta and Cyanophyta density was observed. Total phytoplankton density was changed by 28% (p<0.05) by chloride itself. Gross and net primary productivities were significantly (p<0.01) influenced by alteration of the NO 3-N concentrations of the water.