Spatial and Temporal Variations of Chlorophyll a and Primary Productivity in the Hangzhou Bay

Abstract

The Hangzhou Bay (HZB) is an important part of the Zhoushan fishing ground, the most productive region in the Eastern China Seas. Although HZB remains eutrophication all year round, its chlorophyll a (Chl) and primary productivity (PP) are usually significantly lower than those in the adjacent waters. In the present study, we presented the Chl and PP distributions in the HZB and analyzed their correlations with environmental factors in four seasons. The field observation showed that Chl and PP had significant seasonal variations, and was highest in the summer (1.66 ± 0.61 mg·m−3 and 12.11 ± 12.25 mg C·m−3·h−1, respectively). Total suspended matters (TSM) concentration was the key environmental factor that constrains PP in the study area. High concentration of TSM reduced light exposure (LE, the annual mean value was 0.92 ± 0.81 Einstein·m−2·day−1) in the mixed layer of the HZB, which was much lower than the saturated light intensity of phytoplankton growth, and thus caused a strong light limitation in the HZB. However, the seasonal variations in the photosynthesis rates (PB) and Chl did not coincide. This fact suggested that the growth rate was not the only factor controlling seasonal variations of phytoplankton biomass. In winter, the very high TSM and strong mixing might reduce the zooplankton grazing rate, and lead to a relatively high concentration of Chl during the very low LE and PB period. These results implied that, in the HZB, the extremely turbid water could affect both phytoplankton growth and loss, which was probably the major mechanism responsible for the complex phytoplankton spatial and temporal variations.

Positive Feedback Between the Tidal Flat Variations and Sediment Dynamics: An Example Study in the Macro‐Tidal Turbid Hangzhou Bay

“…The strong tidal mixing and very high turbidity (surface SSC > 5 kg/m 3 , X. He et al., 2013) impacts the ecosystem (Y. Wang et al., 2022). The entire estuary has narrowed and meandered owing to tidal flat reclamation.…”

“…He et al, 2013) impacts the ecosystem (Y. Wang et al, 2022). The entire estuary has narrowed and meandered owing to tidal flat reclamation.…”

Spatial and seasonal variations of chlorophyll a in Zhanjiang Bay, China, and controlling factors

“…In summer, where there is abundant rainfall and high land runoff, coastal waters contain high concentrations of Chl a (Ho et al, 2010;Wang et al, 2022). Summer is the rainy season in Zhanjiang Bay, when discharge from the Suixi River is high.…”

Suspended Sediment Concentration and Fluxes in the High-Turbidity Zone in the Macro-Tidal Hangzhou Bay

“…Another sixteen stations collected depth-and-monthly averaged salinity in December 2006 (Figure 1d). Measured salinity data are from Wang et al [37]. The validation of the model was performed by comparing the simulated and observed tidal elevation (Figure S1I), tidal currents (Figure S1II), and SSC (Figure S1III) at the field stations.…”

“…Error analysis between modeled and observed salinity. The observed salinity data were from Wang et al[37].…”