The Phytoplankton Community Characteristics And Water Quality Evaluation In Ba River Urban Section

Ba river,the ancient name zi water,is a tributary of the wei river tributary of the Yellow River,is located in shan'xi province.As one of the eight major water systems of"eight rivers around chang'an",the Ba river has a long history of irrigation,which plays a vital role in the development of agriculture and agriculture in xi'an.In recent years,due to the development of industrialization and urbanization in xi'an,a large number of without strict treatment of industrial wastewater and sewage into the Ba river,causes the water ecological system is destroyed.In this study,the spatial and temporal difference analysis of water environment factors and plankton community structure of different sampling points in urban section of Ba river from September 2016 to July 2017 was conducted,and the relationship between plankton and environmental factors was further explored by using Person correlation analysis and model corresponding analysis?CCA?.The purpose of this study was to understand the water quality of Ba river and the purification capacity of landscape channel to water body,and to provide theoretical basis for the protection of urban river ecosystem.The results of the study are as follows:Ba river urban section for each sample point temperature change range of 5.1⁵.1?,the difference was significant in season;The pH range of water is 7.56⁹.75,all of which are more than 7,which is weakly alkaline;The dissolved oxygen range is from 4.12 to 13.82mg/L,which is high in the whole year,except for the individual sample points;The change range of permanganate index and total phosphorus is 3.09¹3.52 mg/L,0.01⁰.70 mg/L respectively,its content is relatively high at the downstream sampling point;The content of total nitrogen was higher in all the year,with an average value of 10.98mg/L;Except that the content of mercury in the heavy metal is relatively high,the balance is low.According to the single factor evaluation method,comprehensive water quality identification index method and comprehensive nutritional status index method to evaluate the water quality in the study area,the results show that the pollution factors of the water in the urban section of Ba river are mainly TN,TP,COD_Mnn and Hg,and the downstream water quality is significantly worse than the upstream,especially the water quality at the outlet of the sewage treatment plant.In the urban section of Ba river,7 phyla,63 genera of phytoplankton were identified,in which the Chlorophyta has the most abundant species,followed by Bacillariophyta and cyanophyta.The variation range of cell abundance was 0.73×10⁴⁹8.50×10⁴ind/L,and the overall expression of spatial and temporal distribution was significantly high in summer and fall,and the downstream sampling point was higher than the upstream sampling point.The dominant species were found 7 phyla 35genera,which were dominated by chlorophyta and cyanophyta in summer and Bacillariophyta in winter;The main dominant species were chlorella,oscillatoria,Cyclotella and Cryptomonas,which mainly indicate the middle and heavy polluted water,show that the water in the urban section of Ba river has been polluted to a certain extent.The variation range of the Shannon diversity index,Pielou evenness index and Margalef abundance index of phytoplankton respectively was 2.14⁴.10,0.45⁰.92and 1.04¹.86,according to the comprehensive evaluation of species diversity,the water body is polluted in light to middle pollution,and the downstream pollution is serious.Canonical correspondence analysis and correlation analysis showed that the phytoplankton community distribution of Ba river urban section mainly related to WT,TN,pH,DO and Hg,phytoplankton abundance mainly related to Chla,COD_Mn,WT,SD,Cd and Pb.In the urban section of Ba river,45 zooplankton species from 4 class were identified,in which the Rotifera has the most abundant species,followed by Protozoa,Cladocera and Copepoda.The variation range of zooplankton abundance was 20¹084ind/L,and the spatial and temporal distribution characteristics were basically consiscent with phytoplankton.The dominant species were found in 4 class of 30 species,the main dominant species were Asplanchna,Monia macrocopa,Brachionus calyciflorus,Brachionus urceus,Mesocyclops leuckarti and Vorticella,and they were mainly the indicators of the middle polluted water.The variation range of the Shannon diversityindex,Pielou evenness index and Margalef abundance index of zooplankton respectively was 1.08³.25,0.42¹.06 and 0.70¹.73,according to the comprehensive evaluation of species diversity,the water body is polluted in middle pollution.Canonical correspondence analysis and correlation analysis showed that the zooplankton community distribution of Ba river urban section mainly related to WT,TN,TP,Chla and Hg,zooplankton abundance mainly related to Chla,TN,TP,COD_Mn,WT,PH,DO,SD,Hg and Pb.The comprehensive analysis shows that the effluent of sewage treatment plant is a major source of pollution aggravation in the downstream of Ba river urban section,and the inflow of the chan river also brings some pollutants;The landscape channel has a certain effect on the polluted water,which will provide the theoretical basis for the restoration and treatment of urban water.The canonical correspondence analysis and correlation analysis show that heavy metal has a certain influence on the growth distribution of plankton in addition to the conventional influencing factors.Among them,Hg has a great influence on the phytoplankton community structure.