Microscopic view of phytoplankton along the Yangtze River

Phytoplankton play an important role in nutrient cycling and energy conversion. However, phytoplankton community is poorly understood in large river ecosystems. Based on the large-scale samplings conducted in spring and autumn of 2017, a systematic study has been made on seasonal and spatial distributions of phytoplankton community along the mainstream of the Yangtze River. As results, 6 phyla were identified and 59 phytoplankton species were detected using microscopy, including Bacillariophyta (29 species), Chlorophyta (13 species) and Cyanophyta (8 species) as the dominant group. Moreover, the density of phytoplankton was ranged 0.05 x 10(6)-1.90 x 10(6) cells/L and the biomass was 0.01-1.01 mg/L, both reaching their maximum in the middle reach from Yichang to Wuhan. Significant seasonal difference of phytoplankton community was observed and spatial dissimilarity in spring was revealed. The cell abundance and biomass of phytoplankton could be fairly estimated by chlorophyll-a, and redundancy analysis indicated that water temperature, dissolved oxygen, biochemical oxygen demand, nitrite, and ammonia nitrogen were the most important explanatory environmental factors for phytoplankton compositions in the Yangtze River.