Spatial variations in zooplankton diversity in waters contaminated with composite effluents

Zooplankton species are cosmopolitan in their clean freshwater habitat and are also found in industrial and municipal wastewaters. The present study records for the first time the aspects of zooplankton diversity in relation to physico-chemical environment of five selected sites of the East Calcutta wetlands, a Ramsar site of Kolkata city, India, heavily contaminated by industrial and municipal wastewaters. The study revealed the occurrence of 22 species of zooplankton, among these 3 species of Cladocera, 2 species of Copepoda, 15 species of Rotifera, and 2 species of Ostracoda were recorded. The copepod Mesocyclops leuckarti was found in all the five sites, rotifers Asplanchna brightwelli, Brachionus angularis, B. calyciflorus and Cladocera Ceriodaphnia cornuta were found in four sites; Moina micrura and Diaphanosoma sarsi were found at three sites. Site wise variation in dominance, diversity, evenness and richness were calculated. Site 1, a fish-pond that stabilized composite wastewater, showed the maximum species richness having 17 species, while Site 2, SWF wastewater carrying canal, showed only 4 species. The calculated Jack 1 values of Sites 1 to 5 were 21.78, 3.77, 18.63, 12.5 and 16.95 respectively. Shannon-Wiener species diversity index (HI) values were almost similar for all the three relatively less polluted sites viz, Site 1 (1.959), Site 4 (2.010), Site 5 (2.047). However, at highly polluted sites viz., 2 and 3, H-1 value of 1.336 and 0.984 respectively, were calculated. Simpson's Dominance index (D-simp) value was highest at Site 3(0.618) indicating maximum dominance, whereas at Site 5 dominance was lowest (0.1680) and diversity was highest. We discuss the role of zooplankton in the amelioration of wastewater.