Water Environmental Quality Assessment Of The Middle And Lower Reaches Of The Pearl River Based On Phytoplankton

Phytoplankton refers to micro-organisms living in a water body.Usually phytoplankton refers to phytoplankton.Because phytoplankton is sensitive to its habitat and responsive to water quality,it can respond rapidly to changes in the water environment.Therefore,it can be used as a good indicator of life.In this paper,31 kinds of water quality evaluation methods based on phytoplankton at home and abroad are analyzed and introduced,and they are divided into seven categories,and the development trend and application status of each class are introduced.And18 international methods are analyzed by bibliometrics in order to provide scientific reference for the future selection and application of water quality assessment methods,so as to provide scientific reference for different water areas in the future.The most suitable water quality rating method is selected to provide a theoretical basis.Based on the results of 18 diatom indices calculated by OMNIDIA software,we analyzed the correlation between the 13 common diatom indices and environmental factors,such as temperature,transparency,dissolved oxygen,total nitrogen,total phosphorus,ammonia nitrogen,and selected several methods with strong correlation,which have a strong correlation between diatom index and environmental factors,such as temperature,transparency,dissolved oxygen,total nitrogen,total phosphorus and ammonia nitrogen.And the CEE commonly used in EU water environment assessment was analyzed by SOM.The results showed that,IBD,ROTT-TI,IDG were used in 13 diatom indices.IDAP,HURL,TDIL,PDI,PDI,SHE showed a strong correlation with physical and chemical factors.The spatial distribution patterns of PDI,HURL and SHE,TDIL were similar to those in the other three groups.The results of SOM showed that there were three groups with similar spatial distribution pattern.Among them,Cluster 1 represents the stations along the Xijiang River(Fengkai,Deqing,Zhaoqing,Qingqi,left Beach,Outer Sea,New Wai),and Cluster 2 represents the central site of the Pearl River Delta Network(Siu Lam,Xiaotang,Bei Kau,Lam Core,Hong Li,Chen Cun,Shi Qiao),Cluster 3 represents the site adjacent to Guangzhou(Lianhua Mountain,Zhujiang Bridge).Finally,through analysis and discussion,we conclude that among the 18 diatom indices,the,PDI(South American prairie diatom index),HURL(Herman index),TDIL(lake-enriched diatom index)are suitable for water quality assessment in Pearl River Delta(PRD).At the same time,based on the data of environmental factors and phytoplankton in the dry season(March,December)and high water period(June,September)in 2015,the water quality of the Pearl River Delta(PRD)network was systematically evaluated.Firstly,the self-organizing mapping model(SOM)was used to screen four similar methods from six phytoplankton water quality evaluation methods,evenness index,richness index and biomass index.Then,the water quality evaluation grades of four environmental factors and four phytoplankton indices were compared and analyzed.The results show that although the spatial distribution patterns of environmental factors and phytoplankton indices correspond to the water environment quality,there are differences in the assessment results of water quality grade.The results show that the evaluation results of total nitrogen and total phosphorus belong to class Ⅴ or inferior class Ⅴ,and there is almost no difference in space and season,because the content of total nitrogen and total phosphorus seriously exceeds the standard has become the general status of water quality in natural water body of our country.The dissolved oxygen is greatly affected by the change of water temperature,and the evaluation results of water quality in dry season are better than those in high water season.Ammonia nitrogen is greatly affected by human activities.The spatial and temporal differences of water quality evaluation results are mainly reflected in the peripheral stations of cities which are greatly affected by human activities.The results of water quality evaluation of phytoplankton index were concentrated in II and III water,which was close to that of dissolved oxygen and ammonia nitrogen.