Effects of different water levels on phytoplankton in the Harbin section of the Songhua River

The functional diversity index of a phytoplankton body has gradually become a new mean of measuring and research. To explore the response of phytoplankton taxonomy and the functional diversity index to interannual environmental changes, a survey on the structure of the phytoplankton community and water physicochemical characteristics of the water was carried out at 28 sampling points in the Harbin section of the Songhua River for three consecutive years in every May from 2021 to 2023. The taxonomy diversity index and the functional diversity index were calculated. Firstly, The relationship between the structure of the characteristics of the community and environmental factors was explored; secondly, we reveal the responses of taxonomic and functional diversity indices to different habitats between years; finally, we explore the main environmental factors that control the taxonomic and functional diversity indices of phytoplankton. Results show that, initially, environmental factors in water changes caused by different water levels between years affected the composition of phytoplankton communities. Subsequently, by comparing the taxonomic diversity index and the functional diversity index on a time scale, we found that the taxonomic diversity index was more responsive to environmental changes. Ultimately, the main environmental factors on the phytoplankton taxonomic diversity index were dissolved oxygen, Taxonomic diversity index, and specific conductivity, and the main environmental factors that affected the functional diversity index were dissolved oxygen, turbidity, and water temperature. This study reveals the important role of the taxonomic diversity index in river water quality evaluation, obtained new information on the relative precision of the taxonomic diversity index and the functional diversity index in the evaluation of ecological health of the water, and provided a reliable tool for monitoring river water quality based on aquatic organisms.