AUTHOR=Li Ji , Gao Yonghui , Bao Yalin , Gao Xiu , Glibert Patricia M. TITLE=Summer phytoplankton photosynthetic characteristics in the Changjiang River Estuary and the adjacent East China Sea JOURNAL=Frontiers in Marine Science VOLUME=Volume 10 - 2023 YEAR=2023 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1111557 DOI=10.3389/fmars.2023.1111557 ISSN=2296-7745 ABSTRACT=The Changjiang (Yangtze) River is one of the largest rivers in the world, and its estuary and offshore plume create a diversity of ecological habitats for the phytoplankton community. The phytoplankton community has to balance between light limitation in the sediment-laden inshore waters and nutrient availability in the offshore waters. Active fluorescence measurements can provide rapid, non-intrusive estimates of photosynthetic characteristics at high spatial and temporal resolution. In the summer of 2020, a field survey of hydrodynamic characters, availability of nutrients, the maximum quantum efficiency of photosystem II (Fv/Fm), and rapid light curves across the Changjiang River Estuary and its adjacent sea was conducted, assessing relationships between photosynthetic physiology and biomass accumulation. The photosynthetic activities significantly differed among fresh river water, the Estuary Turbidity Maximum (ETM), river plume, and the East China Sea Water. The photosynthetic physiology of phytoplankton was the most activate near the front of Changjiang Diluted Water, where the Fv/Fm was over 0.5. Phytoplankton growth was alleviated from light limitation downstream of the ETM, and benefited from phosphorus supply via tidal mixing and upwelling. The relatively suitable light and nutrients led to high photosynthetic activities, supporting increased productivity and biomass in this water. The phytoplankton in the Changjiang estuary river mouth and the ETM were under intense stress, suggested by the Fv/Fm values under 0.3. Also, the strong vertical mixing process diluted the river nutrients before the phytoplankton consumed them. Nutrients further limited the phytoplankton offshore in the East China Sea.