The Cause Of Eutrophication And Phosphorus Source In Mianyuan River

As the main source of Tuojiang river,the Mianyuan river has provided water for the residents along the river for long time.The quality of its water,hence,directly affects the safety of drinking water for thousands of people.Due to the abundant phosphate resources in the upper reaches of Mianyuan river,the long-term phosphate mining and the massive emission of phosphorus element in domestic sewage and farmland soil in the basin,the total phosphorus concentration in Mianyuan river exceeds the standard seriously..Phosphorus is a limiting factor for biological growth in both terrestrial and marine ecosystems.High concentration of phosphorus in water environment can lead to eutrophication,which causes blue-green algae bloom in lakes,water quality deterioration and even accelerates the extinction of lakes and rivers.This article mainly focused on Mianyuan river water quality and the source of phosphorus in watert.pH,Eh,DO,TN and TP content of river water were determined.The isotope compositions of phosphate oxygen in river water and domestic sewage were analyzed.Addionally this study explored the utilization of phosphorus in water by microorganisms in the Mianyuan river and distinguishes the possible sources of phosphorus in different sections of mianyuan river.Research results show that:The pH value of Mianyuan river water rangeed from 7.90 to 8.70,and the overall water quality was alkaline.The dissolved oxygen content in the river water ranged from 5.55mg/L to 9.01mg/L.The range of total nitrogen concentration in water was0.58-8.32mg/L,with an average value of 2.22mg/L.The total phosphorus concentration ranged from 0.04 to 0.26mg/L,with an average value of 0.11mg/L.The N/P ratio of Mianyuan river was 6.73-40.00,with an average value of 18.90.It is concluded that Mianyuan river may be phosphorus-restricted river.According to the standard of surface water environment quality(GB3838-2002)",the average total nitrogen content of surface water exceeded environment quality Ⅴclass;The average total phosphorus content followed surface water environment Ⅲclass.By comparing the changes of total phosphorus in Mianyuan river basin in recent years,the total phosphorus content showed a continuous decline from 2010 to 2018,and the water quality was improved to a large extent.The range of oxygen isotope values in Mianyuan river is-11.2‰~-10.3‰,showing a trend of gradual increase from the upstream to the downstream.The theoretical equilibrium value of phosphate oxygen isotope in Mianyuan river water was 10.3‰~11.8‰,and the measured value of phosphate oxygen isotope in Mianyuan river water was 12.0‰~20.0‰.When the measured isotope compostion of phosphate oxygen in Mianyuan river was compared with the theoretical equilibrium value,it was concluded that in the upper reaches of Mianyuan river,the utilization degree of phosphate in water body was relatively low by microorganisms,however,in the middle and lower reaches,the utilization degree of phosphate in water body was relatively high by microorganisms.The possible phosphorus sources in the upper,middle and lower reaches of Mianyuan river were analyzed,and it was speculated that the main possible phosphorus inputs in the upper reaches of Mianyuan river were the removal of phosphorus minning and phosphorus emission related to the phosphorus industry.The possible phosphorus source input in the middle Mianyuan river was the removal of phosphorus from the soil of a large area of farmland.The possible phosphorus sources in the lower reaches of Mianyuan river are mainly domestic sewage.