Study On Nitrogen Removal Of Stream Aquatic Plants

Agricultural streams are important channels which transfer nonpoint source pollutants from arable land to big water body. During the transportation, nitrogen could be removed through plant assimilation, sediment absorption, and so on. In this study, fours kind of aqutic plants including Myriophyllumverticillatum, Lythrumsalicaria, Acoruscalamus, and Water Hyacinth were chosen for the analysis of nitrogen transportation and transformation under different control conditions.Greenhouse-Based Laboratory-Scale wetland mesocosms were used for the simulation of control conditions including different nitrogen concentration continued flooding, and intermittent flooding. The study provided important imformation for the simulation of nitrogen cycle in agricultural streams and evalution of nitrogen removal efficiency analysis. The main results are as follows:（1） Nitrogen removal efficiency of agricultural streams is high. TN removal rate of Calamusteatments was higher than 74% within 17 days under all the different nitrogen concentration. TN removal rate for Hyacinth experiment were 100mg/L nitrogen teatment（99%）>200mg/L nitrogen teatment（82%）>400mg/L nitrogen teatment（73.5%）. Under continued flooding condition, TN concentration of the overlying water of different plant treatments were only 3% of the original concentration on the fourth day of the experiments. Under intermittent flooding condition, N in the overlaying water was almost removed in 10 days and 7 days after adding nitrogen two times, respectively.（2） Sediment absorption of N is the most important process of nitrogen retention from overlaying water. Sediment absorption extended the time of N stay in the stream system, which will allowed more time for the nitrogen removal by plant absorption, N₂O, N2 emissions and NH3 volatilization.（3） N absorbed by Calamus and Hyacinth under different N concentrations were 10% ～30%. Percentage of N absorption by plants decreased with the increasing of N concentration of overlaying water. TN removal rate has significant positive correlations with plant above ground biomass and nitrogen content （correlation coefficient were 0.989 and 0.985, P< 0.05）. Absoption ability of Myriophyllumverticillatum is the highest of all the four experiment plants.（4） N₂O emissions increased with the increasing of N input. N₂O emission flux of plant treatment and blank treatment were between-3.56-9.31 μg N m-2h-1 and-1.26～2.2 μg N m-2 h-1, respectively. Intermittent flooding treatment could effectively increase the release of N₂O.,The biggest N₂O emission flux of plant treatment and blank treatment increased to 93.19 μg N m-2h-1 and 33.21 μg N m-2h-1. N₂O emission flux has significant correlation with the content of nitrate nitrogen in the water （P< 0.01）. However, compared to N input, N₂O emission flux is not very high.,then removal ability through N₂O release of all experimental plants are:Myriophyllum verticillatum> Water Hyacinth>Acorus calamus>Lythrum salicaria.（5） Aqutic plants can reduce and stabilize the pH of the water, keeping pH in slightly alkaline state（7.5-8.3）. Eh of water was improved by plants. Under continued flooding conditions, Eh and the nitrate nitrogen in the water has significantly negative correlation （P < 0.05）. Plants also have effects on DO concentration of the water. In order to efficiently removal of N in the streams and keep the water suitable for the living beings, it is better to harvest the platns regularly.