Distributions of POC and DOC in the Changjiang (Yangtze) River Estuary in response to the extreme flood occurring in the river basin in summer of 2020

In order to trace the influence of this extreme flood which occurred in 2020 on the river-dominated marine ecosystem, two cruises were carried out in the Changjiang (Yangtze) River Estuary and the adjacent area. During the cruises the concentrations of suspended particulate matter (SPM), particulate organic matter (POC), and dissolved organic matter (DOC) were measured in the surface samples collected at all stations. We compared the results of the above two cruises with those obtain in July 2019. Our results showed that, the flood event in July 2020 greatly elevated the concentrations of SPM, POC and DOC in the Changjiang that were ready to be transported out to the adjacent oceans. There existed a time lag for the influence of the flood on the adjacent area. In the pelagic oceans with higher salinities, concentrations of SPM, POC, and DOC generally showed highest values in July 2020, when compared with the other two cruises in July 2019 and July 2020. During the August 2020 cruise, the three parameters indicating the chemical properties of organic matter, i.e., POC (%), POC/DOC (mol/mol) and POC/PN (mol/mol), also showed the strongest terrestrial signals among the three cruises conducted in the study area.