Carbon-to-chlorophyll ratio and carbon content of phytoplankton community at the surface in coastal waters adjacent to the Zhujiang River Estuary during summer

Chlorophyll a (Chl a), particulate organic carbon (POC) and biogenic silica (BSi) were determined in coastal waters adjacent to the Zhujiang (Pearl) River Estuary (ZRE) during summer, in order to examine the C:Chl a ratio of phytoplankton and phytoplankton carbon in the plume-impacted coastal waters during summer, as well as to assess the relative contribution of diatoms to the phytoplankton biomass, by the regression between Chl a, POC and BSi. Our results showed that the C:Chl a ratio (g/g) of phytoplankton was high (up to 142), likely due to high light intensity and nutrient limitation. The river plume input stimulated phytoplankton growth, especially diatoms, resulting in higher relative contribution of phytoplankton carbon (55%) and diatoms (34%) to POC in the plume-impacted region than those (33% and 13%) in high salinity area, respectively. Phytoplankton carbon (up to 538 mu g/L) in the plume-impacted region was much higher than that (<166 mu g/L) in high salinity area. Our findings were helpful to improve the biogeochemical model in coastal waters adjacent to the ZRE.