| Biography | |
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 Prof. E.I.L. Silva Water Resources Science and Technology (WRST), Sri Lanka |
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| Title: Recent Outbreaks of Cyanobacteria Blooms in Irrigation Reservoirs in Sri Lanka – A Case Study of Rajangana Irrigation Tank in the Kala Oya Basin | |
| Abstract: Generally, the irrigation reservoirs in the lowland dry zone of Sri Lanka are eutrophic although some of them becomes mesotrophic under monsoon rains. Nevertheless, the lowland terminal irrigation reservoirs may become hypereutrophic with increasing drawdown towards the July and August at the end of water release to the command area. The low water level, coupled with calm, stable waters enriched with nutrients provides an ideal environmental conditions for the growth of cyanobacteria of which some species are toxigenic. The ideal combination of these factors may lead to the outbreaks of blooms of toxic cyanobacteria impairing suitability of water for drinking after conventional treatment. Nevertheless, it is common practices to attribute this scenario to nutrient enrichment. At the beginning of July 2018 a sudden algal bloom with a surface scum was reported in the Rajangana reservoir, the terminal reservoir in the Kala Oya basin in Sri Lanka. The bloom was reported as Microcystis aeruginosa, a non-nitrogen fixing toxic cyanobacteria. A study was carried out for six months from October 2018 to March 2019 after the outbreak of algal bloom, comparing the past hydrological characteristics of the Rajangana reservoirs with its upstream reservoir, Kala Wewa together with general physicochemical characteristics, phosphorous and nitrogen nutrients, chlorophyll-a content and phytoplankton population. A stable, high water levels persisted in both reservoirs due to heavy monsoon rains and subsequent inflows throughout the sampling period. However, nutrients, physiochemical parameters and chlorophyll-a did not show significant variation (p < 0.05) during the study period. Further, a high population density of cyanobacteria was not observed in either reservoir. When hydraulic water retention time was competed for two reservoirs for a period of one year (February 2018 to March 2019), including time of outbreak of algal bloom, a significant difference was found between two reservoirs. A high water retention time was computed for the Rajangan reservoir compared to the Kala Wewa during the outbreak of Microcystis bloom. Hence, the present study concludes that the water retention time induces a rapid growth of blue-green algae when N and P nutrients are adequate, but the N/P ratio determines whether it is a nitrogen fixing or non-fixing form. Accordingly, terminal reservoirs are more susceptible to cyanobacteria outbreaks compared to flow-through systems in reservoir cascades. Keywords: Terminal Reservoirs, nutrient enrichment, toxic blooms, water retention, Sri Lanka | |
| Biography:
Professor E.I.L. Silva, graduated from the University of Kelaniya, Sri Lanoka, also earned his Master of Philosophy degree from the same university. He earned his doctoral degree from the University of Calgary, Canada on Aquatic Sciences. He is a trained limnologist from the Undercity of Vienna, Austria, who also followed fellowships at the University of Nara, Japan, on Environmental Biology, at the University of Dalhousie, Halifax, Canada for Ocean Management and Ocean Law, at the Washington State University of Pullman USA, on Ecological Modelling and at the IIT of India on Coastal Zone Management. He headed the Department of Environmental Sciences of the Institute of Fundamental Studies (IFS) for twenty years and was a former Director General of the National Institute of Fisheries and Nautical Engineering and the National Aquaculture Development Authority of Sri Lanka. Prof Silva, who has received Presidential Awards for six consecutive years for outstanding publications is the Chairman of the Water Resources Science and Technology (WRST).
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