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Occurrence of toxic cyanobacteria before and after copper sulphate treatment in a water reservoir, Istanbul, Turkey
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2003
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EutrophicationCopper Sulphate TreatmentEngineeringOmerli ReservoirCyanobacteriaToxic CyanobacteriaDrinking WaterEnvironmental ChemistryTotal NitrogenWater TreatmentMicrobial EcologyEnvironmental MicrobiologyDrinking Water TreatmentWater ReservoirWater BiologyWater QualityEcotoxicologyChemical PollutionEnvironmental EngineeringMetal ToxicityMicrobiologyEnvironmental ToxicologyMedicine
Omerli reservoir, one of the reservoirs supplying drinking water to most of Istanbul, suffers from eutrophication. Luxuriant growth of chroococcal cyanobacterium, Microcystis aeruginosa (Kutz.) Kutz., was recorded in water samples obtained after an immense fish mortality in October 1999. 2.1 μg microcystin-LR equiv. l -1 was measured in the raw water and 5.84 μg microcystin-LR equiv.mg -1 was measured in the scum (as dry weight) samples. After disappearance of the bloom, very few cyanobacterial species were recorded during the following winter and spring. In the following year, the Istanbul Municipal Water Authority decided to apply copper sulphate (algicide) to the reservoir in order to prevent cyanobacterial blooms. Treatment started in April 2000. 1600 kg CuSO 4 (53.3 kg d -1 ) were applied to the surface waters. The dose was then increased to 4800 kg (160 kg d -1 ) and to 5050 kg (168.3 kg d -1 ) in May and June respectively. In mid-July, after the addition of 5000 kg (166.67 kg d -1 ), treatment was stopped. M. aeruginosa appeared again and the treatment recommended at the beginning of August. Between 1 and 19 September algicide treatment was stopped and. M. aeruginosa bloomed again. Its biomass reached 78.91 mg.l -1 (fresh weight) at the surface water and 120.72 mg.l -1 at I m depth, on September 20, 2000. After adding 800 kg algicide (26.67 kg d -1 ) to the surface water M. aeruginosa's biomass decreased to 34.75 mg.l -1 at the surface water and 38.88 mg.l -1 at 1 m depth. A considerable difference of water quality was observed before and after the treatment. At the water surface, total phosphorus (TP) was 123.47 μg.l -1 before and 97.36 jg.l -1 after; pH was 10.11 before and 9.5 after; Euphotic zone (Z eu ) was 2.43 m before and 3.31 m after; Z eu /Z mix (Z mix : mixing zone) was 0.27 before and 0.41 after and M. aeruginosa biomass decreased by 3.1 fold after adding algicide. On the contrary, total nitrogen (TN) concentration increased slightly after algicide application.