| In recent years,with the rapid economic development,a large number of pollutants have entered the Zhangze Reservoir with the southern source of Zhuozhang river,resulting in high levels of nutrients in the reservoir,the eutrophication of the reservoir has gradually increased,and the tail of the reservoir has been developed for severe eutrophication.To clarify the impact of environmental factors on phytoplankton and the limiting factors of phytoplankton growth is of great significance to the management of the water environment.In this study,Zhangze Reservoir was used as the research object.Through the detection of physical and chemical factors,nutrients and phytoplankton,the spatial and temporal distribution characteristics of physical and chemical factors and nutrients,phytoplankton community structure were determined,and the correlation between environmental factors and phytoplankton was explored.Using nutrient enrichment experiments to clarify the limiting elements of phytoplankton growth in the reservoir.The research work and results of the paper are summarized as follows:(1)During the testing time,the pH was higher in autumn and winter and lower in spring and summer.Both SD and DO showed higher in spring and winter and lower in summer and autumn.The concentrations of CODMn and Chl-a were higher in summer and lower in spring.The concentration of TN was higher in spring and lower in summer.TP pollution was opposite to TN.In terms of spatial distribution,pH,SD and do all show a small tail value,while CODMn,Chl-a,TN and TP all show a gradually larger value along the sampling point direction,and the tail part of the reservoir is more polluted.According to the calculation results of the comprehensive nutritional status index method,the degree of eutrophication along the sampling point shows an increasing trend,and the time is that the comprehensive nutritional status index is the highest in July and the lowest in December.(2)A total of 133 species of 54 genus and 7 phytoplankton species were detected in Zhangze Reservoir,with Chlorophyta being the largest,followed by Cyanophyta and Euglenophyta.The phytoplankton species detected in summer are few and low in diversity.The cell density of phytoplankton in each sampling point of the reservoir is between 8.424～47.14×106 Cells/L,and the biomass varies from 9.48～57.36mg/L.Both of them show that July is significantly higher than October and November.At the same time in July,the cell density at the tail sampling point was significantly higher than other sampling points,and there was not much difference between the sampling points in autumn.The P-IBI score of each sampling point is between 6.795～1.428,the three months showed a trend of decreasing score along the sampling point.The phytoplankton integrity was the best in October,and the integrity was the worst in July.Moreover,the integrity of phytoplankton in front of the dam is good,and the integrity near the tail of the reservoir is poor.(3)According to the classification method of phytoplankton functional groups,the phytoplankton detected in the reservoir are divided into 24 functional groups,and the dominant functional groups are those with relative abundance more than 10%in at least one sampling point,and a total of 8 dominant functional groups among the 24 functional groups.According to the correlation between phytoplankton and environmental factors,it can be seen that the correlation between TN and dominant groups is not significant,while TP has a strong positive correlation with some dominant groups,and the density of algae cells is related to T,Chl-a,CODMn,TP The correlation between the significant positive correlation and TN is relatively weak,and TP is the first limiting factor in nutrients.(4)Through the experiment of enrichment of nutrients,it was found that the enrichment culture of chlorophyll a and nutrient concentration at the S3 sampling point and the S6 sampling point were basically the same.Adding P alone and adding N and P groups at the same time,the control group was related to the chlorophyll a of the experimental group.The analysis results show that the difference is significant and P is the limiting element of the reservoir.During the cultivation process,the highest value of chlorophyll a appeared at TN:TP=17,and the larger value of chlorophyll a concentration appeared in the ratio of 12-20.The correlation between TP and Chl-a in the water environment of the reservoir is stronger than that of TN.The relationship between the TN:TP ratio of the water environment of the reservoir and Chl-a shows that the optimal nitrogen to phosphorus ratio for the growth of phytoplankton in Zhangze Reservoir is 7.5～17.5,Basically consistent with the law of the best ratio of phytoplankton growth.This conclusion indicates that in the process of eutrophication control,special attention should be paid to the input of the reservoir P,and the monitoring of phytoplankton limiting factors should be done.To a certain extent,avoid increasing eutrophication. |
