Spatiotemporal Evolution Of Water Pollution And Its Main Influencing Factors In Suzhou Section Of The Grand Canal

Suzhou as the only city along the Grand Canal with the concept of"ancient city",has been born with the Grand Canal in the precipitation of time,and has nurtured the unique urban culture and humanistic spirit of Suzhou.The Grand Canal was successfully included in the"World Heritage List"in 2014,and it is now an important part of the One Belt One Road project.In May 2019,the General Office of the Central Committee of the Communist Party of China and the General Office of the State Council issued the"Plan for the Protection,Inheritance and Utilization of the Grand Canal Culture",requiring all localities to fully develop the historical and cultural heritage of the Grand Canal,rebuild the ecological environment of the Grand Canal,and create a cultural belt of the Grand Canal in a new era.As the Suzhou section with many cultural heritage sites along the canal,where many rivers and lakes meet in Suzhou,the quality of the water environment has declined year after year,and the water quality has failed to meet the regional water quality standards.In order to create an environment of the Suzhou Grand Canal with green waters and green mountains and work towards the environmental planning goals of the"14th Five-Year Plan",it is important to renovate and improve the water environment quality of the Suzhou section of the Grand Canal.This paper combines several water quality monitoring data from14 monitoring sections of the Suzhou section of the Grand Canal from 2010 to 2019,uses comprehensive identification index method and spatial cluster analysis to analyze the temporal and spatial characteristics of water pollution,uses Pearson index,principal component analysis,and multiple linear regression The analysis analyzes the main pollution components and related influencing factors of water pollution.Based on the BP neural network algorithm,combined with a number of past water quality data of the river,the future water quality of the Suzhou section of the Grand Canal is predicted.A prediction and early warning system for the water environment quality of the Suzhou section of the Grand Canal based on VB and neural network models has been established.The main conclusions are as follows:（1）The water environment quality of the Suzhou section of the Grand Canal has improved significantly from 2010 to 2019.Among them,the Sufang Bridge section of the Inner City River has improved from a poor Grade V water quality in 2010 to a Grade II water in 2019.As of 2019.Among the 14 monitoring sections in the upper,middle and lower reaches,except for the Midu Bridge section,which is in Grade IV water standard,the other sections all meet the Grade III water standard.Among the conventional water quality indicators,the indicators with the highest frequency of exceeding the standard are TN,NH₃-N,and TP,indicating that the main type of pollution in the basin during this time period is nitrogen and phosphorus pollution.（2）Among the conventional water quality indicators,only COD_Mn,COD,BOD,NH₃-N,TN,TP,and petroleum products have exceeded the standards during 2010-2019,and other indicators such as heavy metals meet the regional water quality requirements.The Suzhou section of the Grand Canal entered the fourth phase of the detection of emerging pollutants PPCPs,and a total of 24 PPCPs were detected,of which caffeine,acetaminophen,mosquito amine,and ibuprofen were the highest in average detection concentration,of which caffeine Ecological risk is higher for fish in the basin.Due to seasonal climate changes and the growth characteristics of algae in the water body,the main pollution indicators show different values in the dry,flat,and wet periods and the four seasons.（3）In terms of spatial characteristics,the overall water environmental quality is ranked as follows:downstream section>midstream section>upstream section.From2010 to 2019,the upstream water quality has improved,while the water quality indicators in the middle reaches have dropped significantly.Spatial cluster analysis shows that the monitoring of Suzhou section can be divided into six clusters based on the characteristics of spatial pollution;the detection rate and detection concentration of PPCPs are also the highest among the three urban districts with the highest population density,residential area,commercial area,and cultural and educational area.Yes,there are fewer industrial zones and historical and cultural protection zones with relatively small active populations.Among them,the concentration of human drug-like PPCPs is directly proportional to the surrounding population density.（4）Among the urban development factors of Suzhou,the proportion of tertiary industry GDP,the urban sewage treatment rate,the proportion of precipitation,the proportion of residential land,the proportion of urban green space,the proportion of water area,and the proportion of forest land are directly proportional to the quality of the water environment..Inversely proportional to the primary industry’s GDP,secondary industry’s GDP,surrounding sewage emissions,ammonia nitrogen emissions per unit of GDP,chemical oxygen demand emissions per unit of GDP,industrial land percentage,and arable land percentage.（5）Based on the 2010-2019 massive water quality index data and the training calculation of BP neural network,the water environment quality of the Suzhou section in 2020 was calculated and found that the higher the frequency of the water quality data at the input end,the more accurate the prediction and the smaller the error.The calculation of water quality indicators based on the LSTM neural network model shows that the future trend of water quality indicators can be well predicted based on a large amount of data in the past.（6）Based on VB and MATLAB,a water environment quality forecast and early warning platform for the Suzhou section of the Grand Canal was built.Combined with neural network algorithms,the water quality prediction module and the water eutrophication early warning module can provide information on the future water environment quality of the Suzhou section of the Grand Canal.The monitoring and management of pollution incidents provide certain assistance.