Study On The Remediation Of Eutrophic Water By Aquatic Ornamental Plants And Combination Of Plants

Eutrophication has become an important ecological problem in lakes,rivers and landscape waters.Because of its low cost of investment,maintenance and operation,high landscape value,convenient management and good ecological benefits,phytoremediation technology has been widely used in the practice of ecological restoration of eutrophic water.In the current practice of ecological restoration,there is a problem of focusing on ecology rather than landscape,which seriously affects the landscape effect of constructed wetland.Therefore,it is necessary to select aquatic ornamental plants with good landscape effect and water purification ability.In the restoration of eutrophic water,it is necessary to combine different aquatic plants to form a plant community in order to purify the water permanently and stably.There are few studies on the typical community model of"emergent plant+floating plant+submerged plant".Most of the existing studies also focus on the plant growth and water purification effect.There are few studies on other ecological processes in aquatic plant communities,which is not conducive to the scientific and reasonable formulation of restoration plan.Based on the above points,two groups of experiments were carried out.In the first experiment,six kinds of aquatic ornamental plants were selected.which are Pontederia cordata,Cortaderia selloana Hydrocotyle verticillata,Canna indica,Acorus calamus,Iris tectorum.Three high concentration eutrophication treatments were set up to explore the plant growth,purification effect and physiological response.The experiment can provide reference for the selection of plant species and water quality conditions of planting.In the second experiment,three aquatic plants with different life forms were selected,which are Pontederia cordata,Pistia stratiotes,Hydrilla verticillata.The experimental research should be comprehensive and systematic.The growth,purification effect,interspecific competition,nitrogen and phosphorus accumulation and physiological response of different combinations were studied.The purpose of the experiment is to provide reference for the establishment of application strategies such as plant community construction,plant harvesting.There are five conclusions in the experiment:（1）The water purification ability of different plants is different.The results showed that Pontederia cordata and Canna indica had better purification effect on low concentration and medium concentration eutrophic water.The maximum removal rates of TN in low concentration and medium concentration eutrophic water were higher than 32.40%and 29.73%respectively.The maximum removal rates of TP in low concentration and medium concentration eutrophic water were higher than 35.83%and 32.92%respectively.The maximum removal rates of TN and TP in high concentration eutrophic water were more than38.85%and 46.11%,respectively.Pontederia cordata and Hydrocotyle verticillata had better purification effect on TN in high concentration eutrophic water,and Pontederia cordata and Canna indica had better purification effect on TP in high concentration eutrophic water.（2）Different aquatic ornamental plants have different adaptability and tolerance to water.Pontederia cordata and Canna indica can adapt to eutrophic water with different concentrations.The adaptability of Acorus calamus and Cortaderia selloana to low concentration eutrophic water is better,but the adaptability to high concentration eutrophic water is slightly worse.Hydrocotyle verticillata can alleviate the eutrophication stress through its own growth.It grows better at low concentration eutrophic water,but worse at medium and high concentration eutrophic water.Iris tectorum was inhibited in different concentrations of eutrophic water,and its adaptability was poor.（3）The purification effect of plant combination treatment on eutrophic water was significantly better than that of single plant treatment.The results showed that the best purification effect was the combination of‘Pontederia cordata+Pistia stratiotes+Hydrilla verticillata’,which can transform water from turbid to clear and improve dissolved oxygen.The removal rates of TN,NH₃-N,NO₃-N and TP were 40.89%,33.50%,46.81%,43.55%respectively,indicating that comprehensive removal rate was the highest.（4）Plant combination treatment can effectively improve the assimilation capacity of nitrogen and phosphorus,forming the effect of‘1+1>2’.Eutrophication treatment can affect the content of nitrogen and phosphorus in different tissues of plants.In addition to the decrease of phosphorus content in leaves,the contents of nitrogen and phosphorus in leaves,stems,rhizomes and fibrous roots increased.The phosphorus content of leaves,rhizomes and roots increased and the nitrogen content decreased in most treatment groups.The phosphorus content of Hydrilla decreased,but there is no obvious rule of nitrogen content.（5）The combination of the three plants can effectively alleviate the stress of Pontederia cordata.Pistia stratiotes and Hydrilla verticillata can alleviate or resist stress injury through antioxidant enzyme system.The different tissues’s tolerance of Pontederia cordata to stress showed the rule of root>stem>leaf The different tissues’s tolerance of Pistia stratiotes to stress showed the rule of root>leaf.