Total phosphorus speciation and transport flux dynamics driven by tidal variations in the Shuidong Bay coastal water during summer, China.

Phosphorus (P) is a vital nutrient for the growth of marine organisms. Tidal cycle had major influence on various biogeochemical parameters of the bay and changed nutrients input with the ebb and flow of the tide. Seawater was collected by synchronous continuous observation during summer in 2021, to investigate tide drives total phosphorus (TP) variation on the concentration, speciation and exchange flux between Shuidong Bay (SDB) and South China Sea (SCS). Results indicated that there was significant tidal variation in exchange flux of TP between SDB and SCS. DIP and DOP were the main speciation of TDP in different tidal periods, accounting for 53.9 % and 46.1 %TP flowed from SCS to SDB, and monthly exchange flux was about 21.26 t. This study provides new insights in P tidal cycling across the semi-enclosed bay-coastal water continuum, which was implications for understanding P biogeochemical process and primary production dynamics in coastal water.