Short‐Term Phytoplankton Dynamics During Typhoon Season in and Near the Pearl River Estuary, South China Sea

Abstract

The effect on phytoplankton dynamics of nutrient inputs from rivers within the highly eutrophic Pearl River Estuary (PRE) in China is well understood. However, the role that typhoons play in enhancing or reducing phytoplankton blooms is less well known. The primary factors controlling phytoplankton dynamics in the PRE in June-July 2009 were determined by coupling satellite remote sensing data with field observations during two successive typhoons: Nangka and Soudelor. The results revealed that the magnitude of chlorophyll a concentration (Chl) near the PRE was controlled by several key factors.(1) Vertical mixing of seawater induced by Typhoons Nangka and Soudelor led to a sudden decrease in Chl and phytoplankton abundance near the PRE, especially in picophytoplankton. (2) Following the typhoon events, increased nutrient availability associated with significant freshwater runoff promoted phytoplankton (especially Synechococcus) growth, recovery, and blooms in and near the PRE. (3) Increased freshwater input or easterly winds enhanced the extension of highly abundant phytoplankton with brackish water from the estuary into the adjacent nearshore water. (4) Phycocyanin-rich Synechococcus was endemic and a dominant picophytoplankton group in the estuarial brackish water. We propose a mechanism that describes the interactions of vertical mixing, terrestrial precipitation, freshwater discharge, nutrient inputs, and winds on short-term phytoplankton dynamics in and near the PRE during typhoon season.

Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River Estuary

“…1c, d) and offshore spreading of the river plume. A stronger bloom was identified in the surface plume, widely spreading from the mouth of the Lingdingyang sub-estuary to near the Huangmaohai sub-estuary, potentially fueled by nutrients mixed upward from the deep in addition to riverine inputs , Qiu et al 2019. The maximum Chl a concentration was > 40 μg L -1 off the Modaomen sub-estuary, accompanied by an extraordinarily high DO concentration of > 350 μmol kg -1 (Fig.…”

Typhoon Merbok induced upwelling impact on material transport in the coastal northern South China Sea

“…In contrast, in the bottom water, high nutrient concentrations were observed during the pre-typhoon period. The reasons for this may be nitrification caused by a strong thermocline and halocline during the summer [9,23]. The study carried out by Chen et al in the offshore NSCS showed that the ammonia concentration was significantly lower than the nitrate one in the bottom water, where dual nitrate isotopic characterization confirmed that nitrification occurred [23].…”

“…In summer, particularly, heavy rainfall resulted in greater discharges from local rivers into nearshore areas. These discharges might have carried more domestic sewage into the coastal seawater, leading to the higher nutrient concentrations observed in that season [4,9,29,30]. Furthermore, fertilizers were applied widely in the agriculture of Guangdong Province in spring and summer [5,23], and could have been carried to the coastal area by the river discharges of the latter season.…”

“…Accordingly, these δ 13 C-POC patterns could be resulted from the breeding and reproduction of microorganisms. We speculated that the river diluted water originated in adjacent coastal cities brought abundant water discharge and suspended particulates to the nearshore area during the rainy seasons [4,5,9,30]. Furthermore, suspend particulates are suitable for the breeding and reproduction of microorganisms, leading to intensive microbial activity and severe organic matter decomposition [33,34], resulting in relatively enriched δ 13 C-POC.…”

“…Recently, the input of nutrients to the coastal SCS area has greatly increased because of anthropogenic activities, causing several environmental issues, such as the formation of hypoxic areas and the acceleration of eutrophication [1][2][3][4][5][6][7]. However, in addition to the anthropogenic inputs from the coastal area, extreme weather events, such as typhoons and hurricanes, have been reported to influence the biological activity and geochemical cycling of nutrients in marine ecosystems [8][9][10][11][12][13][14][15].…”