Abstract:
This research was carried out to identify the main courses for eutrophication by measuring Nitrate and Phosphate level at different location in Vavuniya tank and to identify the main algae species of and find out environmental friendly methods to control eutrophication. Water samples were collected from eleven locations in Vavuniya tank by using water sampler at the depth just below the water surface. Locations were marked by coordinates using GPS and samples were collected once in two months from July to November 2011. The NO3- was significantly (p=0.053) higher in November than July due to runoff water from different land (agricultural land, waste disposed land) after heavy rain. But all the values were below WHO permissible limit of 10 ppm. Phosphate values in all samples except S4 were above the WHO drinking water standard permissible limit of 2 ppm of in July 2011 and also all the samples except S1 were above 2 ppm in November 2011. Samples S3, S5, S6, S7 and S8 showed higher PO43- value than other locations. These are main non-point sources of pollutant to Vavuniya tank and cause eutrophication. Therefore action has to be taken to minimize pollutant coming to Vavuniya tank from these location Eichhornia crassipes and Polygonum barbatum were the common eutrophication species in Vavuniya Tank and spread of these species can be minimized by participation of all (Fishing community, Department of irrigation, Environmental Officers, UC and other stakeholders). Polygonum barbatum has an antimicrobial activity and further study has to be carried out to confirm the antimicrobial effect of above weeds in Sri Lanka to be used as bio-pesticide.
