Water Environment Safety Assessment Of Daxia River Basin

Water environment safety is very important for regional social and economic development.Daxia River,located in the middle of Gansu Province,is an important tributary of the right bank of the Yellow River,which plays a key role in the social and economic development and ecological environment nourishment in the middle of Gansu Province.Therefore,the assessment of water pollution and water environment safety in Daxia river basin can provide a reference for ensuring the stable development of regional economy and the virtuous cycle of ecological environment.However,there is a lack of research on the combination of river water quality and the overall water environment safety of the basin.In view of this,this paper first uses single factor evaluation method and grey evaluation method to evaluate the water quality of Daxia River Basin from 2006 to 2021;On this basis,PCA-PSO-BP neural network comprehensive model is further introduced to simulate water quality;Secondly,based on the above water quality evaluation indicators,physical geographical indicators and socio-economic indicators,DPISR model is used to evaluate the water environment safety of Daxia river basin through analytic hierarchy process,entropy method and comprehensive index method;Finally,combined with the actual situation of the basin,the relevant suggestions and measures for the safe development of water environment in the basin are put forward.The main conclusions are as follows:(1)From 2006 to 2021,the indexes of dissolved oxygen,ammonia nitrogen,total phosphorus and potassium permanganate in Xiahe,Shuangcheng and Zheqiao water quality monitoring sections changed by 3.96%-9.06%,44.5%-79.5%,70.1%-0.00%and-42.9%-17.6% respectively.Ammonia nitrogen is the main pollutant in Daxia River Basin.The overall water quality of Daxia river basin is class I ～ III,and the water quality of all sections is up to standard.Among them,the overall water quality of the upstream Xiahe and Shuangcheng sections in the middle reaches is grade I～II;the overall water quality of the downstream Zheqiao section is grade I～III.The upstream water quality is better than the downstream water quality,and the change range of water quality is small in the upstream and large in the downstream;Through further analysis of the water quality data from September to December 2021 of the Zheqiao section with the worst water quality,it is found that the water quality of this section becomes better month by month,and the water quality in each month is class I.(2)Ammonia nitrogen is the most important pollutant index affecting the water quality of the Daxia River Basin,and its simulation can directly reflect the water quality of the watershed to a certain extent.Select the Zheqiao monitoring section with the most serious ammonia nitrogen pollution,and use the PCA-PSO-BP neural network comprehensive model to take the principal component variables of 9 water quality monitoring indicators such as p H,dissolved oxygen,and potassium permanganate index as the input variables of ammonia nitrogen simulation,respectively.Establish training set and test set to optimize model parameters and test the performance of the model.The results show that the optimized model has better simulation effect.The fitting MSE of the training set is 0.018,and the correlation coefficient R is 0.95;the simulation results of the test set are basically consistent with the true value trend,the error is between 0 and 0.182,the MSE is 0.01,and the correlation coefficient R is 0.904.The neural network comprehensive model constructed in this paper can well simulate the ammonia nitrogen concentration in the watershed,and can be used for water quality prediction in the Daxia River Basin,and then for the monitoring and evaluation of pollutants in the watershed.(3)Based on the assessment results of water quality in Daxia River Basin,the water environment safety of Daxia river basin is evaluated by using DPISR model,combined with analytic hierarchy process,entropy method and comprehensive index method.The results show that the comprehensive index of water environment safety in Daxia River Basin in 2006,2010,2015 and 2020 is 0.3102,0.5816,0.4103 and 0.7299 respectively,and the water environment safety level has changed from less secure to safer,and the water environment status is generally getting better.(4)According to the water quality status and water environment safety evaluation results of the basin,combined with the current situation of the basin,it is proposed to establish the environmental protection concept of green development,energy conservation and emission reduction,increase investment in ecological environment protection,and build a development pattern of ecological priority.