Water Chemical Integrity Assessment In A Typical Watershed

Watershed chemical integrity is an important part of ecological integrity.At present,the research and application of water chemical integrity assessment is scarce,which restricts the protection and management on water ecosystem in China.Based on the requirement of watershed ecosystem protection,this paper constructed the watershed water chemical integrity evaluation system,and perform case analysis on Songhua River Baisin by means of field investigation,sampling and laboratory analysis,which has mainly achieved the following results:Based on the characteristics of watershed water ecological environment,the watershed chemical integrity evaluation system was established.Chemical indicators screening method,reference sites of chemical measures,ecological threshold derivation method and evaluation model are projected.Following the scientific and operable screening principles,by meanings of 3S technology,Partial Least Square Regression,Generalized Additive Methods and ranking analysis,the indicator screening method is established based on chemical index representative analysis,chemical index sensitivity analysis on human factors,and analysis of the impact of chemical indexes on the structure of biological communities.As for the selection of reference sites,quantitative standards for non-point source pollution and land use,as well as restrictions on point source pollution were added.An ecological threshold derivation method based on field surveys was established.In which classification and regression trees?CART?was selected to explore the ecological thresholds of chemical indicators based on biological indexes,while thresholds indicator taxa analysis?TITAN?was selected to derive ecological thresholds based on the protection of sensitive species,and identify major indicator species.A chemical integrity evaluation model was constructed based on the target-element-index.The indicators were weighted by constructing a structural equation model?SEM?,and a comprehensive index of chemical integrity?CII?with evaluation standard was constructed.The evaluation index system and method were carried out in the study of Songhua river basin.Results show that the diversity of zoobenthos and function richness of mountainous and hilly region are higher than that of plain region,and thickness of organic subsistence and nutrient salts is higher in plain region.The key chemical integrity indicators were selected,for mountainous and hilly region:pH,EC,DO,COD_Mn,BOD₅,LAS,NH₃-N,NO₃-N,TP and oil,while for plain region:pH,EC,DO,COD_Cr,BOD₅,NH₃-N,TN,TP,oil,Cu and Zn.The key anthropogenic factors influencing chemical indictors were identified.Population density showed significant explanatory ability to DO,TP and petroleum.ED and LSI on classification level were more explanative to chemical indicators than land use.Organic matters and nutrients were the main chemicals influencing the distribution and structure of macroinvertebrate community as well as its functional traits.All reference sites in Songhua river basin are located in mountainous and hilly region,the reference conditions of all measures has significant seasonal difference.Cu and Zn had a significant impact on benthic community diversity and functional richness in plain areas.The ecological thresholds of chemical indicators such as DO,COD,COD_Mnn and so on in different topographic region,at the same time identifying indicator species.The thresholds of chemical indicators and indicator species were spatially different.TP was was higher than that in plain region,while the thresholds of other chemical indicators of plain area are greater than that of hilly area.In hilly and mountainous region,the main negative and positive species of the chemical indicators were Mayoptera and Chironomidae,respectively,while in plain region were Gastropoda and Oligochaete,respectively.The assessment studies show that the overall water chemical integrity of Songhua river basin was generally good.During the three water periods,68.7%to76.5%of the sites were in a“complete”state,13.8²4.1%of the sites in the"normal"state,and 7.4²4.1%of the sites in the"less complete"state.There is no site in“not complete”state.The chemical integrity of the middle and lower reaches of the Songhua River was superior to the upstream area,and the chemical integrity of the left bank of the Nenjiang River is better than that of the right bank.The chemical integrity of the Yitong River Basin,Yinma River Basin,Ash River Basin,Woken River Basin and Uyur River Basin was poorer.The water chemistry integrity status of the reference points had seasonal differences and was superior to other monitoring points,which verifies the rationality of the constructed evaluation system.