Distribution of Chlorophyll a and Carbon Fixation at HABs Coast of Yangtze River Estuary in Summer

Abstract:

The environmental factors in the water column were investigated along the 2 transects at the Harmful Algae Blooms （HABs） coast of the Yangtze River Estuary and Hangzhou Bay during summer in 2018 and 2019. Based on two datasets of Chl a obtained via in situ sensor-monitoring and simultaneously water sample analysis， it showed that the distribution of Chl a in summer was featured with the maximum concentration not only existing at a surface depth of 2m， but down to a depth range of 10~15 m. The in situ observed Chl a concentrations showed the positively linear regression （r > 0.8，p < 0.05） with those determined from water samples through the water columns， suggesting that the observed Chl a data with high depth-resolution may be reliable to represent the vertical distribution of phytoplankton biomass. Therefore， based on that， the primary productivity of the whole blooming water column was estimated by the vertically generalized production model （VGPM） using the optimized method of the integrated Chl a concentrations with the photic depths. The optimized VGPM pattern may reflect the vertical distribution feature of Chl a and carbon fixation rate of the whole blooming waterbody， to improve our knowledge on the role of HABs coast water under the impacts of severe anthropogenic activities in the carbon neutrality and fixation in the marine carbon cycle.

Key words:Yangtze River Estuary;Chl a;in situ observation;primary productivity;carbon cycle