Study On The Decay Process And Pollution Release Flux Of Main Aquatic Plants In Nansi Lake

Nansi Lake is the largest reservoir lake for the South-to-North Water Transfer Project.It is a typical grass-type shallow lake with abundant aquatic plants.During the growth of aquatic plants,not only nutrients such as nitrogen and phosphorus can be absorbed from the water.Moreover,it can also secrete some organic substances to promote the metabolic activities of microorganisms and improve the water quality of water bodies.Winter plant decay is likely to cause secondary pollution of water bodies,and the decay process and water quality effects vary depending on the plant species and the amount of decomposition of the residues.At present,there are few studies on the decay process of typical plants in Nansi Lake.In this study,the common aquatic plants such as potamogeton crispus,alternanthera philoxeroides,lotus,cattail and reed in Nansi Lake were used to simulate the decay process of aquatic plants in the laboratory,and the process of pollution release intensity under different growth densities of different aquatic plants was studied.The influence of the decay process on the release of major pollutants in the decomposition process of aquatic plants.Based on the spatial and temporal distribution characteristics of aquatic plants in Nansi Lake,the release fluxes of five aquatic plants were estimated,and the management measures for aquatic plants harvesting in Nansi Lake based on water quality improvement were proposed.This study draws the following conclusions:?1?Changes in pollution release intensity during the decay of different aquatic plants:different aquatic plants have different effects on water quality.By measuring the pH value,DO,TN,NH₄⁺-N,TP,TOC content in water,the effect size shows alternanthera philoxeroides>lotus>potamogeton crispus>reed>cattail;Under different plant densities?0.2 g/L,0.5 g/L,1.0 g/L?,the higher the plant density,the greater the impact on water quality.When the plant density is 0.2g/L,five aquatic plants are The influence of water quality is small.Under the plant density of 1.0g/L,the release of five aquatic plants has obvious adverse effects on water quality,and the water quality of alternanthera philoxeroides and lotus leaf is the worst during the decay process;The release processes of the five aquatic plants showed rapid release in the early stage,slowed down in the medium term,and finally stabilized.?2?The effects of different plant species and main components on the release process of aquatic plants were studied.The results showed that the components of different types of aquatic plants were significantly different.The contents of N and P were as follows:alternanthera philoxeroides>lotus>potamogeton crispus>cattail>reed;reed and cattail had higher lignin and cellulose content,while alternanthera philoxeroides andlotus were lower.The higher the initial N and P percentages of aquatic plants,the faster the decomposition rate,and the higher the content of lignin and cellulose,the slower the decomposition rate of decay.The rate of decay of aquatic plants showed a correlation with the content of plant components such as C,N,P,lignin,and cellulose.?3?The variation of O₂ concentration in the overlying water in the process of aquatic plant decay is in accordance with the oxygen deficit curve equation.The faster the decomposition rate of plant decay,the larger the K_d value of the overlying water and the smaller the K_r value.The kinetic model of the overlying water nitrogen release from the decay process of aquatic plants showed that the faster the decomposition rate of plant decay,the higher the degradation rate constant K₁ of organic matter in the overlying water and the decomposition rate constant K₂ of ammonia nitrogen,the higher the concentration of the heterotrophic bacteria and nitrifying bacteria...?4?Based on the spatial and temporal distribution characteristics of the main aquatic plants in the Nansi Lake,the annual releases of major pollutants such as NH₄⁺-N,TN,TP and TOC of different aquatic plants were 3945.38 t?14145.82 t?1575.46 t?56245.73 t,respectively.Management measures such as water plant density allocation and seasonal harvesting in Nansi Lake based on water quality improvement were proposed to provide theoretical basis for water quality improvement in Nansi Lake.