Impacts of Changjiang River Discharge and Kuroshio Intrusion on the Diatom and Dinoflagellate Blooms in the East China Sea

Abstract

The coastal area adjacent to the Changjiang River estuary is a high‐risk region for harmful algal blooms. Both Changjiang River discharge and Kuroshio intrusion influence the hydrological conditions and nutrient composition in this area which could affect the onset of diatom and dinoflagellate blooms. However, current understandings on their roles in regulating different microalgal blooms are limited. In this study, changes in stratification, water masses, and the ratio of phosphorus to nitrogen were examined during the diatom and dinoflagellate blooms in 2005 using ship cruise data. The observations showed that both the diatom and dinoflagellate blooms occurred in the continental coastal water. By enhancing the pycnocline and phosphorus stress, the Changjiang diluted water plays an important role in affecting the diatom bloom. The dinoflagellate bloom is partly supported by the supply of phosphate transported by Kuroshio intrusion and upwelling. The results of this study will help elucidate the mechanisms of large‐scale harmful algal blooms in the coastal area adjacent to the Changjiang River estuary.

Riverine and Oceanic Nutrients Govern Different Algal Bloom Domain Near the Changjiang Estuary in Summer

“…Dinoflagellates (such as Prorocentrum donghaiense, Alexandrium catenella, and Karenia mikimotoi) and diatoms (such as Skeletonema species) are the main phytoplankton species causing harmful algal blooms near the Changjiang Estuary (Gao & Song, 2005;Guo et al, 2014;Ye & Huang, 2003). Based on observations made during 2005, Zhou et al (2019) report that dinoflagellate growth near the Changjiang Estuary was mainly influenced by coastal upwelling of PO 4 -rich KSSW. The difference in model simulated dinoflagellate biomass between Figures 17b and 17d confirms that high dinoflagellate biomass in the southern region and around Zhoushan Islands is mainly controlled by PO 4 supplied by the Kuroshio Current.…”

“…For example, analyses of field observations made in 2005 (Z. X. Zhou et al, , 2019 suggest that while diatom blooms near the Changjiang Estuary are mainly influenced by Changjiang River discharge, subsequent dinoflagellate blooms are mainly influenced by coastal upwelling of PO 4 -rich KSSW. Despite many reports over recent years on nutrient supply to the ECS continental shelf, the response of algae in the Changjiang Estuary and adjacent coastal sea to oceanic nutrient inputs during summer is poorly understood.…”

Wind-driven stratification patterns and dissolved oxygen depletion in the area off the Changjiang (Yangtze) Estuary

“…Likewise N/P ratio and primary production in the CDW is considerably modified by upwelling (Tseng et al, 2014). Phosphate transport by upwelling reduces phosphorus deficiency in the CDW water and therefore promote phytoplankton growth and nitrate uptake (Chen et al, 2004;Zhou et al, 2019). 390…”

“…Nutrient rich freshwater mixes with ocean water to form the Changjiang Diluted Water (CDW). Enhanced 65 primary production in the CDW causes intense detritus accumulation and DO consumption in the near-bottom layers (Chen et al, 2017;Wang et al, 2017Wang et al, , 2016Zhou et al, 2019). The CDW is separated from the deeper water with a shallow halocline, which often coincides with the seasonal thermocline (Zhu et al, 2016).…”

“…CC BY 4.0 License. nutrients to the surface layer (Wang and Wang, 2007), which cause increase of primary production and decrease 85 of DO concentrations in the near-bottom layer (Chen et al, 2004;Zhou et al, 2019).…”