Implementation Of The Extensible Evaluation System For Heavy Metals In Watershed Soil Based On WebGIS

Daxia River stretches through many counties and cities in Gansu Province as a significant first tributary of the Yellow River System.However,with the development of industry,a large amount of industrial wastes assembled on the riverbanks have deteriorated the ecological environment in the river basin.Heavy metals account for most of the pollutants emitted by industry,so it is urgent to undertake the management and prevention of heavy metals in river basins.In this paper,based on the content of heavy metals in Daxia River Basin,the author develops a WebGIS-based extension evaluation system for heavy metals in the basin.First of all,the Daxia River Basin is divided into districts and sampled.Strahler and Shreve,two classification methods for basins,are used to divide the Daxia River Basin into seven sub-basins,according to which 45 sampling points are selected.Then,the author analyzes the contents of As,Cd,Cr,Cu and Pb in each sub-basin respectively,and draws a conclusion that Cr,Cu and Pb exceed the standard in some sub-basins,As exceed the standard in the whole,and Cd will soon exceed the standard in the whole.The order of the contents of five heavy metals from more to less is: Cr,As,Cu,Pb,Cd.The coefficient of variation from large to small is Cr,As,Cu,Cd,Pb.Among them,four heavy metals Cr,As,Cu and Cd show severe variation with instability,while Pb show weak variation with stability.Based on data analysis,the author establishes an evaluation model of soil heavy metals in Daxia River Basin,which is implemented on MATLAB platform with improved extension matter-element theory and comprehensive toxicity factors.The evaluation results show that the whole Daxia River Basin is slightly and stably polluted.Besides,of the seven sub-basins,the Hezuo basin and Shuangcheng basin are not polluted,while Tongren basin,Ganjia basin and Zheqiao basin are lightly polluted,and Sangke basin and Xiahe basin are moderately polluted.Comparing the evaluation results of the improved model and the unimproved model,it is found that the improved extension evaluation model can more accurately reflect the impact of the comprehensive toxicity coefficient of heavy metals on the evaluation results than the unimproved model,so the improved extension comprehensive evaluation model is more suitable for the evaluation of heavy metals pollution in the soil of Daxia River Basin than the unimproved model.Finally,according to the proposed extension evaluation model for heavy metals in basin,the author develops a comprehensive extension assessment system of soil heavy metals in Daxia River basin based on WebGIS.For engines,Baidu map engine,which is well developed and convenient in China,is selected after it is compared with three mainstream WebGIS map engines at home and abroad.For the development mode,the separation mode between front end and back end is determined,in which the front end is JavaScript+Vue+elementUI,with the development tool Visual Studio Code,while the back end is Asp.net Core WebAPI,with the development tool Visual Studio 2017.Besides,the storage database is Mysql,the cache database is Redis,and the database management tool is Navicat.The mixed programming technology of C# and MATLAB is utilized in the evaluation module for heavy metals in bases.The system functions include user rights allocation,map scaling,sampling data query and visualization of evaluation results for basin soil heavy metals.In a word,this paper provides a basis for pollution control and decision-making for the pollution control staff in Daxia River Basin.