assessment of function of bivalve (anodonta cygnea) in filtration of nitrogen and phosphorus compounds

in this study the filtration rate of nitrogen and phosphorus components by swan mussel anodonta cygnea in a closed system was investigated. the system was built of a 100 liters main tank and 4 recipients of 2.5 liters each (one of these as control) and one tank for returning of water. three treatments of different concentrations of nitrogen (80, 100 and 200 mg/l) and of phosphorus (20, 40 and 60mg/l) separately were examined. in all treatments, sampling was repeated 3 times. results showed that in tree treatments during over the time, the filtration rates were reduced. also an increase in nitrogen concentration caused filtration rates to be increased. filtration rates in the first treatment increased from 6.53 to 7.15 and then to 8.07 ml.min-1 .gr -1 afdw from the first to the third treatment respectively. the filtration rates in phosphorus treatment has also increased when the concentration increased. this has been changed from 5.61 to 6.5 and 7.58 ml. min-1 gr -1 afdw from first to third treatment. comparing results of filtration in two media containing nitrogen and phosphorus separately suggest that the performance of anodonta cygnea in the absorption of nitrogen component may be higher than phosphorus ones.