| Eutrophication of water body is one of the hot topics in the world today.It has a great negative impact on people’s living environment,and even has become a restriction factor of social and economic development in many countries.Therefore,how to repair eutrophic water body,reduce the content of nitrogen and phosphorus nutritive salt in it,and restore the comprehensive function have become the focus of global environmental research.At present,the technology of eutrophication treatment with aquatic plants as the core has become the focus of current research.Especially,as an important measure to restore aquatic ecosystem and to absorb and purify water body nutrients,it attracts more and more attentions..In this article,taking the typical shallow grassy river in the Haihe River Basin—the lower reaches of the Dashi River（Beijing section）as the research area,five dominant emergent plants in the lower reaches of the Dashi River are simulated and studied in the laboratory.The removal effect and absorption kinetics characteristics of nitrogen and phosphorus in different levels of eutrophic water bodies.At same time,the distribution characteristics of the nutrient elements nitrogen and phosphorus in various organs of different emergent plants during different periods of the experiment were analyzed,and the following conclusions were drawn:（1）The five emergent plants,Acorus calamus L.,Typha orientalis,Lythrum salicaria L.,Sagittaria trifolia L.,Alisma plantago-aquatica Linn,had obvious removal effect on N and P in the eutrophic water body downstream of Daishi river,and the purification effect of the five plants was better than TP.The removal effects of five emergent plants on TN in water were:A.plantago-aquatica>A.calamus>S.trifolia>L.salicaria>T.orientalis.The removal effects of TP were as follows:A.plantago-aquatica>A.calamus>L.salicaria>T.orientalis>S.trifolia.The concentration of TN and TP decreased with time,and the purification rate of T.orientalis,A.calamus,L.salicaria,S.trifolia,and A.plantago-aquatica to eutrophic water increased with the prolongation of their residence time in water.The nitrogen absorption effect of the five emergent plants was different,and the nitrate removal effect was obviously increased when the ammonium nitrogen in water was less than 0.05 mg·L-1.（2）There are differences in the kinetic characteristics of five plants in absorbing nutrients in experimental water.Under the three phosphorus levels,A.calamus and A.plantago-aquatica are suitable for the removal of ammonia nitrogen at low to moderate and high phosphorus levels,respectively,while T.orientalis has the strongest absorption of nitrate nitrogen at all phosphorus levels.Under the three nitrogen levels,A.plantago-aquatica and L.salicaria are suitable for the removal of phosphorus at low to moderate and high nitrogen levels,respectively.It can be seen from the Michaelis-Menten constant values that A.calamus and A.plantago-aquatica have the strongest barren tolerance to ammonia nitrogen and nitrate nitrogen.Meanwhile,T.orientalis and L.salicaria have the same phenomenon to phosphorus.Therefore,they can be used to maintain water quality with a low nitrogen to phosphorus ratio.（3）The distribution characteristics of vegetative element in five emergent plants in the lower reaches of Daishhe River are as follows:the nutrient element content of leaves and stems in upper part is higher than that of roots in lower part of the ground,the fruit is enriched with P,and the leaves with N relatively.It can be seen that by harvesting the aboveground part of the standing water plants,most nutritive salt could be brought out,and the pollution of lakes and rivers caused by the decaying and depositing of plants after autumn and winter death could also be prevented.Consequently,this study can be applied for further clarifying the mechanism of nitrogen and phosphorus removal from water bodies,and for selecting of emergent plants in ecological restoration projects for eutrophic water bodies with different nutritional characteristics. |
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