the effects of nitrate and phosphate on growth of algae, ulva rigida

Nutrients especially nitrate and phosphate are the main limiting factors of algal growth in aquatic ecosystems. the present study was conducted to examine the effects of different concentrations of nitrate and phosphate simultaneously on growth of macro algae, ulva rigida. for this purpose, algae were fed various concentrations of nitrate and phosphate during 28 days in 300 l tanks in the form of 4 experimental treatments with three replicates. the experimental treatments were: t1: 10 mg l^-1 no3+5 mg l^-1 po4, t2: 20 mg l^-1 no3+10 mg l^-1 po4po4, t3: 30 mg l^-1 no3+15 mg l^-1 po4, t4: 40 mg l^-1 no3+20 mg l^-1 po4 and one control treatment was considered. according to the results, all experimental treatments showed increased growth compared to the control treatment (p<0.05). there were no significant differences in growth of algae between t3 and t4 (p>0.05). the highest values of gain weight (88.02±0.74 g, nearly 17 times more than the initial weight) and daily growth percent (60.57±1.29 %) were observed in algae of t3 and then t4 (daily growth percent: 42.95±1.56 %). in conclusion, our results suggest that a concentration of 30 mg l^-1 no3+15 mg l^-1 po4 is more suitable for the growth of macro algae, u. rigida.