Research And Application On Watershed Water Environment Early-warning Technology Based On Water Quality Indicators

Watershed water environment early-warning technology is an important technical support for watershed water environment monitoring and management.At present,the watershed environment early-warning system of China is imperfection.Typical watersheds lack targeted early-warning indicators and corresponding thresholds which obstructs the development of water quality monitoring and early-warning work in China.In response to the needs of water quality monitoring and management,watershed water environment early-warning technology based on water quality indicators was studied systematically depending on the work foundation of surface water quality monitoring network.Three key technologies,i.e.,watershed water environment early-warning system construction technology,water quality early-warning indicators screening technology and water quality early-warning indicator threshold setting technology were researched and applied,respectively.The Songhua River Basin was selected as the case study object,and the Songhua River Basin early-warning system was constructed.The result of the study was applied and verified through‘Songhua River Basin Water Quality Early-warning System'.The following main results are obtained.?1?The goal of watershed water environment early-warning system based on water quality indicator is to control the quality and change of water environment.Therefore,the characteristics of water environment pollution in the basin are the basis for screening and thresholding of early-warning indicators.The analysis method of watershed pollution source emission characteristics was constructed by frequency analysis method.The spatial and temporal characteristics analysis method of water quality was constructed by cluster analysis and improved self-organizing mapping method.The improved method can automatically generate a mesh topology based on the original data,which retains the important information of the original data and can reflect the hierarchical level of classification results.The water pollution characteristics of Songhua River Basin was analyzed by the methods.The results show that the emissions of COD_Cr,ammonia nitrogen,total nitrogen,volatile phenol,arsenic,lead and mercury in the Nenjiang sub-watershed are more prominent.The emissions of total phosphorus,petroleum,cadmium,total chromium and hexavalent chromium in the Second Songhua River sub-watershed are more prominent.The emissions of volatile phenol and cyanide in the Sonhua River main stream sub-watershed are more prominent.The water quality of the Songhua River Basin is generally improving year by year.The change of water quality in 15 years can be devided into 3 time periods and 3 water quality conditions.Among them,the water quality in Zhaoyuan and Nenjiangkounei sections is the worst.The water quality in Baiqi, Baisha,Jiangqiao and Liuyuan sections are the best,and the water quality in other sections is in a medium state.According to the final analysis results,combined with the spatial distribution of the section,the study area was divided into three levels of early-warning zones.?2?Combined with the analytic hierarchy process and the important indicator screening method,the screening method of water quality early warning indicators was established.The pre-selected indicators from the same whole can be cross-weighted from different factors.The final result reflects the comprehensive influence of multiple factors on the screening indicators.The hierarchical structure of water quality early-warning indicator screening system was constructed,and the construction method of criterion layer and index layer judgment matrix was studied.Further analysis of the spatial and temporal characteristics of water quality was studied by using the principal component analysis/factor analysis method when constructing the index layer judgment matrix under the water quality characteristic factor.Correlation analysis was used to exclude factors that express duplicates.The results show that the first-level early-warning zone warning indicators are ammonia nitrogen,DO,CODMn,CODCr,BOD5,total phosphorus,mercury and fluoride.The second-level early-warning zone warning indicators are ammonia nitrogen,COD_Cr,DO,petroleum,fluoride,pH,total phosphorus,BOD₅ and COD_Mn.The third-level early-warning zone warning indicators are BOD₅,total phosphorus,COD_Cr,ammonia nitrogen,petroleum,conductivity,water temperature,DO and COD_Mn.The traditional method that only setting the concentration limiting value as threshold has been broken.The model parameter threshold was added as indicator threshold.Standard limit model,statistical limit model,trend change model and probability density model were constructed as mathematical models for formulating thresholds of water quality warning indicators.According to the historical data nature of the early-warning indicators,the appropriate threshold model was selected and the threshold calculation was performed for each early-warning indicator.?3?The Songhua River Basin was seleted as a case study.The water quality monitoring data and pollution source monitoring statistics of the study area were collected and analyzed.The water environment pollution characteristics,early-warning indicator screening and threshold setting results were summarized,and the Songhua River Basin early warning system was constructed.The Songhua River Basin early warning system and water quality early-warning indicator threshold setting technology were integrated into the“Songhua River Basin Water Quality Early-warning System”for implementation based on national control automatic monitoring station real-time monitoring data,and a typical early-warning example was analyzed.The analysis results show that the system successfully warned the real pollution“exceeding the standard value”,the abnormal trend of data was found 6 hours earlier before the ammonia nitrogen exceeded the standard limit.It has gained valuable time for early-warning emergency work.Thus,the practicality and effectiveness of the system and technology were verified.