Study to detect impacts of pollution on the distribution of Zooplankton in the Northern tropical ponds in Sri Lanka

Abstract

Although the Limnological survey are well documented in Sri Lanka. However, not much work has been done in Northern Province after the early nineteen eighties. Zooplankton community distribution can be taken as an indicator of the well-being of the water bodies. The Ariyakulam pond and Vavuniya tank were chosen to investigate the distribution of major Zooplankton; Rotifera, Cladocera and Copepoda along with the pollution impacts during January-June, 2012. Oil and Grease pollutant is common in Vavuniya tank, not in Ariyakulam, where Biological Oxygen Demand (BOD5) was determined in various regions of the pond to distinguish the polluted and non-polluted regions in both water bodies. Random Plankton sampling was done in the littoral zones, as it was densely packed with vegetation, Sieve-set (50μm) was used to filter the water sample, preserved with 4% formalin and taken to the laboratory for qualitative and quantitative analysis using low-power light microscope. Sedgewick-Rafter cell was used to estimate the zooplankton abundance as individuals/m3. Comparing the distribution of zooplankton community in both non-polluted regions, Rotifers were higher, followed by Cladocerans and Copepods. Relative abundance of Rotifers were significantly higher (p<0.05) in non-polluted region (BOD5=1.095-1.800mgL-1) than polluted region (BOD5=3.500-4.012mgL-1) within Vavuniya tank, justifies the less tolerability to pollution or vulnerability to predation by Copepods. When comparing the Rotifer distribution within Vavuniya tank, there was a significantly higher (p<0.05) abundant was observed in non-polluted (BOD5=1.100-1.800mgL-1) region than the polluted region (BOD5=3.500-4.200 mgL-1). Copepods were significantly (p<0.05) higher in the polluted region of Vavuniya tank than the polluted region of Ariyakulam pond (BOD5=2.000-2.500 mgL-1) indicating the high tolerability to pollution. Cladocerans also showed the second largest abundance in the non-polluted regions compare to the polluted regions in the water bodies, indicating the impact of pollution.