Research Of The Purification Efficiency Of Nitrogen-phosphorus In Eutrophic Water And The Physiological Mechanism Of Elodea Canadensis

It is easy to occur eutrophication in the aquaculture water. Using the befitting submerged species can remove a large number of nitrogen and phosphorus in the eutrophic aquaculture water. But the high concentration of nitrogen and phosphorus in water may affect the growth of submerged plant. So it is important to select the befitting species in the treatment of eutrophic aquaculture water. In this paper, Elodea canadensis was used to study the purification efficiency of nitrogen-phosphorus in eutrophic water during its growth cycle and whether the high concentration of nitrogen-phosphorus in the eutrophic water would stress on its growth in a long term. The experimental results are summarized as follow:(1) During the vigorous growth of Elodea canadensis, it can maintain the balance of ion concentration in eutrophic water and keep water in slightly alkaline state (pH:7～9).(2) Elodea canadensis has a satisfactory decontaminate function on total nitrogen in different concentrations of eutrophic water. The higher initial concentration of total nitrogen is, the better effect of purification it will be. After ten weeks, the rate of the removal of total nitrogen in each group (C1～C5) reached72.00%～91.82%.But the removal capability on total phosphorus was lower than total nitrogen. The maximum rate of the removal on total phosphorus was56.15%.(3) Sediment plays an important role in the purification of total nitrogen and phosphorus in the eutrophic water. During the text, the maximum enrichment rate of sediment on total nitrogen in each group (C1～C5) was reached1.32%,7.31%,17.57%,20.38%and24.22%, respectively in different stage. But the maximum enrichment rate of sediment on total phosphorus in each group (C1～C5) was13.53%～21.07%.(4) During the text, nitrogen and phosphorus in the water played a proactive role on the growth of Elodea canadensis, and in a certain range of concentrations of nitrogen and phosphorus (TN:1.0～6.0mg/L, TP:0.2～1.2mg/L), the higher concentration is, the more obvious effect on promoting the growth of Elodea canadensis.(5) In the concentration range of nitrogen and phosphorus during the text, there was a correlation between the plant height of Elodea canadensis and the treatment time. It was suit the Growth model. The model equation:y=e(b0+b1·x)(b0:3.052～3.094; b1:0.120～0.123). The correlation between branch number and the treatment time was suit the Linear model. And the model equation:y=a·x+b (a:1.270～1.725; b:0.608～1.63). The correlation between internode number and the treatment time was also suit the Linear model. And the model equation:y=a·x+b (a:13.335～15.163; b:31.786～38.990).(6) The determination results of antioxidant enzyme activity of Elodea canadensis showed that in all treatment groups and control group, the activities of superoxide dismutase(SOD), preoxidase(POD), catalase(CAT) and the content of malondialdehyde(MDA) were increased in the first2to3weeks, and then decreased in the later time. That meant the high concentration of nitrogen and phosphorus stressed on the growth of Elodea Canadensis in the first several weeks. But Elodea canadensis can adapt to the high concentration of nitrogen and phosphorus (TN:8.0mg/L; TP:1.6mg/L). So Elodea canadensis can be a generalizable plant in the aquaculture water. And it is significance for the healthy breeding.