Characteristics of Phytoplankton Community Structure and Eutrophication in Hasu Sea

In this paper, we first obtained the data of each water quality monitoring point in May and July of Hassel Sea in 2021, and analyzed the spatial distribution of each element of total phosphorus (TP), total nitrogen (TN), transparency (SD), high manganese index (CODmn) and chlorophyll a (Chl. a) in the data, and then used the integrated trophic state index method and algal species quotient method to evaluate the trophic state of the lake. The results of the integrated trophic state index method and the algal species quotient method were then used to assess the lake’s trophic status. The results of the integrated trophic state index method showed that the measured value in July was 1.15 times the value in May, in which the points H1, H2, and H3 were moderately eutrophic, H4, H5, and H6 were mildly eutrophic, while the six monitoring points in July were all moderately eutrophic, indicating that the eutrophication in summer was higher than that in spring, and there was a trend of gradual deterioration during the interannual variation, which needed attention and It is necessary to pay attention to and strengthen the management. Comparing the nutrient status index values of each parameter, chlorophyll (Chl. a), transparency (SD), and total phosphorus (TP) play a significant role in the eutrophication degree of Hassel Sea, accounting for 23.94%, 23.05%, and 20.18%, respectively. The evaluation results of the algal species quotient method showed that all monitoring points were heavily eutrophic when the green algae quotient was applied, and the rest of the points were heavily eutrophic when the composite algae quotient was applied, except point H4 which was heavily eutrophic (located in Xianglu area). Comparing the results of the two evaluation methods, it can be found that the results evaluated by applying the algal species quotient method are more serious, indicating that the algae are more sensitive to the response of the eutrophication degree of the lake, and there is a great chance of water bloom disaster in the late stage of Hassel Sea.