| Periphytic diatoms occur in various water bodies(stone,plant and gravel,etc.),and play an important role in aquatic ecosystem.It is widely used in water quality monitoring because of its widely distribution,short reproductive cycle and sensitivity to environmental changes.In this study,we selected 34 lakes in the lower reaches of the Yangtze River,and diatoms samples were collected from 116 sampling sites in August 2017 to August 2018,and environmental factors of the water body were determined at the same time.In order to study the influence of seasonal variation,we selected 20 sampling sites for collected diatoms samples in each season in Poyang Lake.In order to study the influence of substrate,artificial was substrate placed in Qiandao Lake and Taiping Lake for sample collection.The species composition and distribution characteristics of Periphytic diatoms in lakes in the lower reaches of the Yangtze River were analyzed,and their correlation with environmental factors were discussed.A diatom index for eutrophication assessment of lakes in the lower reaches of the Yangtze River was established.To provide a basis for the application of diatom index-based biological monitoring method in lake eutrophication assessment.The main results are as follows:1.In this study,354 species(including varieties and forms)of 67 genera of periphytic diatoms were identified.The main species of diatoms are Biraphidinales,with 184 species,accounting for 52 % of the total species,followed by 9 genera and 61 species of Aulonoraphidinales,accounting for 17 % of the total species,14 genera and 36 species of Centricae,accounting for 10 % of the total species,8 genera and 32 species of Araphidiales,accounting for 9 % the total species,7 genera and 31 species of Monoraphidinales,accounting for 9 % of the total species,and 1 genera and 10 species of Eunotiales,accounting for 3% of the total species.Three new species of Achnanthidium were found in this study.The number of species in each sample varied from 7 to 45.2.11 dominant species of diatoms in lakes of the lower reaches of the Yangtze River were defined as dominant species with dominance Y ? 0.02,and three dominant species with dominance than 0.05,they are Achnanthidium minutissimum(Y=0.109),Nitzschia palea(Y=0.068)and Gomphonema enula(Y=0.051).Achnanthidium minutissimum is the first dominant species with the highest relative abundance was 74.5 % which relative abundances showed a decreasing trend with the increase of eutrophication,and reached the highest level in oligotrophic water.Nitzschia palea is the second dominant species with the highest relative abundance was 71 % which relative abundances showed an increasing trend with the increase of eutrophication,and reached the highest level in medium eutrophication water.The relative abundance of Gomphonema lagenula is the highest in the mesotrophic water with 49.5 %.3.All samples were divided into six groups based on Cluster analysis,there are differences in the composition of the Periphytic diatoms in each group.According to the evaluation criteria of the TLI index,it can be concluded that the eutrophication degree from group 1 to group 6 decreases gradually.Classified regression tree analysis showed that electrical conductivity,total phosphorus and chemical oxygen demand were the main predictors.4.By using weighted average regression method with reduced tolerance weight methods,we developed the transfer function model of total phosphorus,model of total nitrogen,and model chemical oxygen demand.In the total phosphorus model correlation between the predicted and observed and diatom inferred total phosphorus(R2=0.661,RMSE=0.064 mg/L),In the chemical oxygen demand model correlation between the predicted and observed and diatom inferred chemical oxygen demand(R2=0.699,RMSE=5.818 mg/L),and in the total nitrogen model correlation between the predicted and observed and diatom inferred total nitrogen(R2=0.423,RMSE=1.007 mg/L).Through the test of the control group,it is found that these transfer function models can accurately predicted the concentration of total phosphorus,total nitrogen and chemical oxygen demand in the lake water of the lower reaches of the Yangtze River.The optimum and tolerance values of total phosphorus,chemical oxygen demand and total nitrogen of 78 major diatoms were determined by weighted average method,which provided basic data for the establishment of diatom index.5.Based on the results of the optimal and tolerant values of diatoms between total phosphorus,chemical oxygen demand and total nitrogen,established of comprehensive indicator(v)and sensitive indicator(s)were based on total phosphorus,chemical oxygen demand and total nitrogen for periphytic diatoms in lakes in the lower reaches of the Yangtze River.Then,a Comprehensive Diatom Index(CDI)was established to evaluate the eutrophication degree of Lake water based on Zelinka & Marvan(1961)equation.The CDI values are between 1 and 100,when the CDI value is 100,the lake eutrophication is the worst,conversely,when the CDI value is 0,the lake eutrophication is the lowest.6.The assessment grade of eutrophication state of lake in the lower reaches of the Yangtze River is given by CDI index,and got a good assessment result.By comparing the evaluation results of water quality indicators,it showed that the CDI index was applicability in assessing eutrophication state of water body.7.By comparing the species composition of diatom,the result of CDI index and physicochemical index in different seasons in Poyang Lake,and the applicability of CDI index was validated by two-way indicator species analysis method,it was found that the CDI index was applicability in assessing eutrophication in each season,and seasonal variation does not affect the use of CDI index.The effect of CDI in spring and summer was slightly better than that in autumn and winter.The effects of different substrates such as stone,plants,dead wood and artificial substrates(acrylic plate)on CDI index were compared.The results showed that the selected substrates did not affect the evaluation results of CDI index.Additionally,this study found that the CDI index didn't changed when the number of diatom valves counted reached 400. |
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