Study On Community Characteristic Of Macrobenthos And Phytoplankton And Health Evaluation Of Qingshui River

In recent years,river ecosystem has been seriously damaged and river health has been stressed due to the increasingly intense interference of human activities.How to use effective methods and means to characterize the health status of rivers and to protect and restore damaged rivers to play their ecological functions has become an important issue to be solved urgently to promote the sustainable development of economy,society and environment.Macrobenthos and phytoplankton are important functional groups of river ecosystem,which can effectively represent the health status of river ecosystem.In order to scientifically diagnose the health status of Qingshui River and to provide basis for future adaptive management,a systematic ecological investigation was carried out on Qingshui River in August 2020,and statistical analysis of community ecology was combined with indoor analysis.The characteristics of macrobenthos and phytoplankton community structure(including species composition and distribution,dominant species composition,abundance and biomass)and biodiversity were studied.Based on the characteristics of macrobenthos and phytoplankton community,B-IBI and P-IBI evaluation systems were constructed,and then the biological health situation of Qingshui River ecosystem was evaluated.At the same time,the comprehensive index system of river health was used to evaluate the river health situation.The main research results are as follows:1.A total of 42 taxa of macrobenthos were found,belonging to 3 phyla,4 classes,11 orders and 32 families.There were 35 species(83.33%)of aquatic insects,3 species(7.14%)of soft crustaceans,3 species(7.14%)of mollusks,and 1 species(2.39%)of Bdelloid.The dominant species were Sigara substriata、dytiscidae sp.、Hydropsyche sp.and Baetis sp..By comparing the ecological parameters of macrobenthos community,it was found that the distribution of macrobenthos species,abundance and biodiversity in Qingshui River was consistent.The upper and lower reaches were obviously higher than the middle reaches,and the biomass in the upper and lower reaches was higher than the middle and reaches.Based on the analysis of water environmental factors in Qingshui River,the results of correlation analysis and canonical correspondence analysis(CCA)showed that electrical conductivity,ammonia nitrogen and fluoride concentration were the main environmental factors affecting the macrobenthos community structure in Qingshui River.2.A total of 106 species of phytoplankton were collected in this study,including 40 species of Diatoms(37.74%),40 species of Chlorophyta(37.74%),16 species of Cyanobacteria(15.09%),8 species of Euticobacteria(7.55%),and 2 species of other classes(0.94%).The dominant species was Oscillatoria sp.、Cyclotella sp.、 Synedra sp.and Pseudanabaena.Comparing phytoplankton biological parameters,it was found that phytoplankton species and biodiversity in the upper and lower reaches of Qingshui River were significantly higher than those in the middle and lower reaches of the yellow estuary。And the abundance and biomass are the highest in the reservoir area,and gradually decrease along the reservoir area.In addition,it was also found that the species,abundance and biomass of phytoplankton in the reservoir showed the same spatial variation trend,that is,the reservoir was obviously affected by other points.Correlation analysis and redundancy analysis(RDA)showed that transparency,velocity and total phosphorus were the main environmental factors affecting phytoplankton community structure in Qingshui river.3.In order to construct the biological integrity evaluation system suitable for the characteristics of Qingshui river,macrobenthos and phytoplankton were selected as indicator species to conduct the biological assessment of river health.The reference points and damaged points were determined by the clustering of water quality physical and chemical parameters.Four core parameters,including total taxon number,hemiptern taxon number,Shannon-Wiener index and ASPT index,were screened out by the analysis of variability,discriminant ability and correlation in order to construct the Qingshui River B-IBI evaluation system.The P-IBI evaluation system was constructed with five core parameters: total number of taxon,number of Diatomate species,percentage of Diatomate density,Shannon-Wiener index and Pielou index.The results of B-IBI evaluation showed that 60% of the points in Qingshui main stream were in very healthy state,30% were in sub-healthy state and 10% were in unhealthy state.The results of P-IBI evaluation showed that 81.8% of the points in Qingshui were in very healthy state and 18.18% were in sub-healthy state.The results of the two evaluation methods showed that the points of sub-health state were the same as S2 and S9,which were the reservoir area and the inlet of tributaries respectively.Due to the accumulation of pollutants in Qingshui Reservoir area and the erosion of water and soil in its tributaries,the water quality and ecological environment of this section of the river are poor,which are the main factors affecting the biological integrity of Qingshui River.4.On the basis of the biological integrity health evaluation of Qingshui River,based on the comprehensive evaluation concept of river health with the balanced play of river ecological functions and social service functions,this study established a health evaluation index system of Qingshui River that include 10 indexes in four aspects,namely,"basin","water" integrity,biological integrity and social service function integrity.The health of Qingshui River was evaluated.The results showed that the Qingshui River is in the "healthy" level on the whole,but the natural conditions of the shoreline and the satisfaction degree of ecological flow need to be further improved.Based on this,the main management countermeasures for maintaining the health of Qingshui River are put forward.