The Bioassessment Of Water Quality Based On The Macroinvertebrates And Diatom

Assessment of water quality is very significant for guiding protection and engagement of river health.At present,bioassessment has comprehensively applied to Europe and the United States and other countries,but it is under researching in our country.In order to further improve Aquatic biological evaluation methods,it is very meaningful to study the consistency of traditional phy-chemical methods and aquatic biological methods for developing an effective biological evaluation model.There are a wide range of macroinvertebrates and diatom in the river,which play an immeasurable role in the material circulation and energy flow of the river ecosystem.Moreover,they can be very sensitives to the environmental changes of aquatic ecosystems and respond accordingly to the composition and distribution of communities,so they are very suitable to be an indicator of water quality.This paper selects macroinvertebrates and diatom to develop macroinvertebrates and diatom evaluation model,respectively.And we compared the biological model and phy-chemical methods for their consistence in water quality.This study conducts an investigation of macroinvertebrates and diatom in the main reaches of Lijiang River Basin on January and August 2017.We totally collected 82 samples of macroinvertebrates and 36 samples at 41 sampling sites in two seasons.We developed respectively phy-chemical metrics assessment system,Benthic macroinvertebrates Multimetric Index(BMMI)and Diatom Multi-metric Index(D-MMI)with phy-chemical metrics,macroinvertebrates metrics and diatom metrics:(1)We used Principal Component Analysis(PCA)to identify main environmental factors.The results of PCA showed that the conductivity(Cond),dissolved oxygen(DO)and total phosphorus(TP)were the main environmental factors affecting the water environment in the Lijiang River Basin.Then we based on the three main factors to develop traditional phy-chemical assessment system.(2)We selected 9 reference sites according to main environmental factors and Percent Model Affinity,and the rest were all damaged.The differences of biological metrics between reference points and damaged points were analyzed by a range test,a sensitivity test and a redundancy test.The result indicated that the number of EPT(Ephemeroptera,Plectoptera and Trichoptera)taxon,Shannon-Wiener index,(Crustacea and mollusca)%,sensitive taxa%and Biotic Index(BI)are core metrics of macroinvertebrates.We used ratio method to make responding direction consistent,and get B-MMI with their theory range from 0-100.The 25%percentile of reference sites was designated as the threshold of healthy(“Excellent”),and the rest of values range is divided into three equal parts,so we can defined the water quality assessment criterion of macroinvertebrates as bad(<36.54),moderate(36.54～53.98),good(53.98～71.41),excellent(≥71.54).And then we adopted historical macroinvertebrates data to validate reliability of model,which show that there is a significant differences between references and damaged sites.So we can declare that the developed model is very effective to distinguish degree of interference.(3)We conducted the diatom analysis with the same references sites and impaired sites.The results indicated that the total taxa,Achnanthidium minutissimum% and Trophic Diatom Index(TDI)are core metrics of diatom.We used ratio method to make responding direction consistent,and get D-MMI with their theory range from 0-100.The 25% percentile of reference sites was designated as the threshold of healthy(“Excellent”),and the rest of values range is divided into three equal parts,We can defined the water quality assessment criterion of diatom as bad(<27.27),moderate(27.27～53.21),good(53.21～79.14),excellent(≥79.14).(4)Compared between bioassessment and phy-chemical assessment,we can find that the results of macroinvertebrates and phy-chemical assessment completely consistent accounted for 36.59% of total samples,and the difference was 31.71% in a level,and the difference was 13.41% in two levels,and the difference was 18.29% in three levels.We can find that the results of diatom and phy-chemical assessment completely consistent accounted for 26.32% of total samples,and the difference was 42.11% in a level,and the difference was 26.32% in two levels,and the difference was 5.26% in three levels.On the basis of the same set of reference sites,the reliability of the two water quality bioassessment model and traditional phy-chemical assessment system were 68.49% and 68.42%,respectively.The consistency degree of evaluation results is basically the same,but the results of the evaluation in three levels were prominently lower than those of macroinvertebrates assessment.So diatom assessment model has better stability and applicability in Lijiang River Basin.