A Study On The Decomposition Of Three Kinds Of Emerged Plants And The Release Of Pollutants

In recent years,the use of aquatic plants to repair eutrophic water technology has become increasingly mature,emergent aquatic plants as an important representative of large aquatic plants,with plant repair and lake landscape and other functional characteristics.And when the emergent aquatic plants into the decay stage,the decomposition of nitrogen and phosphorus and other nutrients will re-enter the water body,nutrients in the water-sediments-plants between the migration and transformation,will cause secondary pollution of the river.Therefore,this paper studies the pollutants such as nitrogen and phosphorus in the overlying water and sediments during the decay and decomposition of different species of plants by constructing the indoor test system with the common emergent aquatic plants(Typha orientalis,Canna indica and Thalia dealbata)as the experimental materials.Under the condition of different environmental factors,the decomposition rate of emergent aquatic plants and the release laws of N,P and other pollutants were analyzed.From the point of view of molecular ecology,the anaerobic ammonium oxidizing bacteria(Anammox)community structure,abundance and diversity of microbial indicators in sediments were analyzed.The main conclusions are as follows:(1)Different plants decomposition has different effects on the water quality of overlying water.At the beginning of the decomposition,DO in the overlying water drops rapidly and the water is anaerobic.The changes of TP and COD in the process of plant decay were similar and first rise then decreased,and during the same period,the TP change of water quality among different plants was Canna indica > Thalia dealbata > Typha orientalis.The change of N content in the process of decomposition was similar,TN and NH4+-N were the first rise and then decreased.The difference is that TN is in the late trend of fluctuation,and the NH4+-N size in the overlying water in the same time is Thalia dealbata> Canna indica> Typha orientalis.In the process of plant decay,TP in sediments showed a significant upward trend,and there was a significant negative correlation with TP in overlying water.The effect of plant decomposition on the TN in sediments was more complex,Canna indica and Thalia dealbata was a significant negative correlation between TN in overlying water and TN in sediments.The Thalia dealbata sediments NH4+-N increased in the early stage and reached the maximum at 125 days.(2)The level of temperature on the decomposition of emergent aquatic plants is essential.The decay rate of the same plant at different temperatures: T4> T3> T2> T1.The nitrogen content of the plant increased at 6 days before the experiment,and the higher the temperature,the higher the trend of TN was,and the TN in the late stage of the experiment showed a rising-decreased trend.At 300 days of decontamination,the plant nitrogen content was related to the temperature,that is,the higher the temperature,the higher the plant TN content.The trend of phosphorus content in the three plants was: decreased-increased slowly.In the first 6 days,TP decreased rapidly,and with the increase of temperature,TP decreased the trend.At the later stage of the experiment,the trend of TP increased slowly.With the increase of temperature,the nitrogen and phosphorus of different plants was not obvious.During the whole experiment,the change of TP concentration in water body increased and decreased.Canna indica and Thalia dealbata under the conditions of T3 and T4,TP was the first increase-the trend after the decline.During the same period of different plant decomposition process,the size of water TP is: Canna indica > Thalia dealbata > Typha orientalis.The change rule of TN in the process of plant decay was similar to that of TP,and the TN content of water among different plants was: Canna indica > Thalia dealbata > Typha orientalis.(3)In the plant decay experiment with or without sediment conditions,the decomposition process of plants can be divided into three stages: in the period of 0-6 days for rapid decomposition;6-145 days for the slow decomposition period;145-300 Day and accelerated decomposition.Typha orientalis and Canna indica in 145 days to 300 days,under the conditions of sediment decomposition rate of plants is higher than no sediment.The decomposition rate of the three kinds of plants was: Canna indica > Thalia dealbata > Typha orientalis,in the presence or absence of sediment under the conditions of decomposition rate constant Typha orientalis(0.002/d),Canna indica(0.004/d),and then Thalia dealbata(with sediment: 0.002/d;no sediment: 0.003/d).In this experiment,TN changes in plants: increased-decreased-slowly increased.The change of plant nitrogen was similar to that of the plantlets.In the first 6 days,TN was rapidly increased and TN was higher than that without sediment,and TN increased alternately in the later stage.Plant phosphorus changes rapidly in the early stage,then stabilized and alternately increased at 165 days.Typha orientalis in 165-300 days,no sediment under the conditions of TP is always higher than the sediment.And then Thalia dealbata phosphorus content in the early rapid reduction,and the conditions under the sediment TP are higher than no sediment.(4)Decomposition of different plants will affect the distribution and abundance of Anammox bacteria in sediments,and it is related to the relationship between ammonia and nitrogen and nitrate and other physical and chemical factors.The abundance of Anammox bacteria in the sediments after plant decomposition was as follows: MRJ> XP> ZLH> CK.The pH,TP and ammonia nitrogen were positively correlated with the abundance,and Shannon and Chao1 were negatively correlated with ammonia and nitrogen in sediments.The colonies of Anammox bacteria in the sediments of the plants are mainly composed of Anammoxoglobus and Brocadia clusters,in which the Brocadia cluster is dominant.