The determination of N: P ratio in Cyanobacterial bloom of Anabaena flos- aquae in the Caspian Sea, Iran in situ

The aim of this study is determining the N: P ratio which causes the maximum bloom of toxic cyanobacteria: Anabaena flos- aquae of the Caspian Sea and finding the N: P ratio that eliminates its bloom. To perfect this study, the effect of different phosphorus concentrations on the growth level was also inspected. The experiments were carried out in situ (the temperature and light intensity were kept at 25± 2 degrees centigrade and 3500± 350 lux respectively). Different N: P ratios and varying phosphorus concentrations were applied as treatments with respect to logarithmic calculations. Three replicates were considered for each treatment and one control (Zinder media). The laboratory experiments lasted 96 hours. Visual counting at the start and end of the experiments were carried out to assess the growth percentage. In this project, Anabaena bloomed in Zinder media (control) with 9.9 μg/lit ofnitrogen, 2.96 mg/lit of phosphorous and the 0.0033N:1P ratio. N: P ratios of 15: 1 to 22: 1 resulted in the maximum bloom of Anabaena flos- aquae. The maximum level of growth percentage was reached to 5219.84± 1486.69 in 18.15N: 1P ratio with 53.72 mg/lit of nitrogen and 2.96 mg/lit of phosphorus. The bloom ended at 218.86N: 1P. Studies on the effect of phosphorus concentration showed phosphorus concentration in Zinder media (2.96 mg/l) is the optimum value for Anabaena bloom. The whole results indicate, although in the presence of enough phosphorusconcentration, Anabaena bloomed even with low nitrogen concentrations (9.9 μg/l in Zinder media)by fixing atmospheric nitrogen when enough phosphorus and nitrogen concentrations supplied withlow N: P ratio the maximum bloom intensity was observed.