| Liangxi River is the main channel between Meiliang Bay of Taihu Lake and the Beijing-Hangzhou Canal.It is the oldest natural river in Wuxi and is known as the mother river of Wuxi people.In recent years,the water quality of Liangxi River has deteriorated,transparency has decreased,and water environmental problems have become more serious.In order to understand the cause of the deterioration of water quality,the monitoring of water quality indicators such as cyanobacteria particulates,nitrogen,phosphorus,and dissolved oxygen in rivers was conducted in spring,summer,and autumn.The hydrochemical characteristics of different forms of nitrogen in the river,determine the main sources of nitrogen in the Liangxi River and the contribution ratio of the main pollution sources,and reveal the influence of cyanobacteria blooms in lakes on the water quality of connected rivers,so as to prevent the blooms,restore ecological functions and ecological Provide evidence for protection.In this study,a total of 21 sampling points were set up based on the drainage area of the Liangxi River and the surrounding environmental characteristics.Samples were collected from March 2019 to October 2019,and the physical and chemical indicators of water quality at each sampling point were monitored while phytoplankton were identified.By analyzing the species composition of phytoplankton,the distribution characteristics of phytoplankton functional groups in different seasons were discussed.Through nitrogen and oxygen stable isotope technology,the source of nitrate and nitrogen pollution in the surface water of the study area was initially identified,the factors affecting surface water water chemistry were revealed,and the source of nitrate nitrogen pollution in the area was further identified.Finally,with the help of isotopes based on Bayesian analysis The source analysis model SIAR analyzes the contribution rate of each nitrate-nitrogen pollution source in the study area and draws the following conclusions:The water quality factors of Liangxi River have significant differences in time,but the spatial differences are not obvious.Both the Carlson trophic state index and the comprehensive trophic state index show that the water body has reached the level of eutrophication.During the survey,a total of 40 phytoplankton and 65 species containing variants were found,of which Chlorophyta was the largest,with 31 species,accounting for 47.69%of the total;followed by diatom,22 species,accounting for 33.85%,and 10 species of cyanobacteria,Accounting for 15.38%of the total;2 species of Cryptophyta,3.08%of the total.There are spatial and temporal differences in the nitrogen concentrations of various forms of water in the study area.The average concentration of total nitrogen and nitrate nitrogen in the upstream water period is significantly higher than the average concentration in the high water period,and the average concentration of ammonia nitrogen in the high water period is slightly higher than that in the low water period;The average concentration during the flood season.The changes of?15N-NO3-and?18O-NO3-in the dry season were6.27-18.16and 2.02-13.90,respectively,and the wet seasons were 1.43-12.30and 2.13-15.12.The value of?18O-NO3-in the water period is higher than that in the dry season,and the value of?15N-NO3-in the dry season is obviously higher than that in the flood season.The nitrate in the water body of Liangxi River mainly comes from manure and domestic sewage,soil organic nitrogen and chemical fertilizer.According to the output of the SIAR model,the highest contribution rate of the four types of pollution sources to the nitrate in the Liangxi River is manure and sewage sources?approximately 52.5%?,and the contribution rates of chemical fertilizer sources and soil sources are close to 19%and 21%The contribution rate of atmospheric deposition sources is only 7.5%.Therefore,according to the geographic location and spatial layout of the Liangxi River,it is necessary to focus on the control of human and animal manure and domestic sewage imported from non-point source pollution,which can effectively reduce the nitrate pollution load into the river,improve the water environment quality of the Liangxi River,ensure the water environment quality of Wuxi City and Meiliang Lake area and the safety of flood control and drainage. |
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