1. Title
Study on the Response Mechanism of Primary Production in the East China Sea to theChange of Nutrient Inputs from the Yangtze River
2. Members’ names and affiliations

SHI Jie Ocean University of China
Gao Huiwang Ocean University of China
3. AimThis project aims to explore the effects of changes in nutrient fluxes and ratiosof rivers on nutrient structure and primary production in East China Sea. What’smore, it promotes cooperation and student exchange between the College ofEnvironmental Science and Engineering of Ocean University of China and theCenter for Marine Environmental Studies (CEMS) of Ehime University.
4. Procedure
First, we used a 3-dimensional physical-biogeochemical coupling model to simulate
the nutrient structure and primary production of East China Sea forced by climate
conditions. Then, we analyzed the seasonal characteristics of DIN, DIP, and SIL on thesurface and bottom layers. Finally, we validated the model by comparing the simulated
results and observed results. We showed the seasonal characteristics of DIN, DIP, and
SIL in Section 5 for the space limitation.
5. Results
Figure 1, Figure 2, and Figure 3 show the seasonal changes in the distribution of DIN,
DIP, and SIL concentrations on the surface and bottom layers, where February
represents winter, May represents spring, August represents summer, and October
represents Autumn; water depth of 2 m represents the surface layer, and the vertical
20th layer of the model (the last layer of water column) represents the bottom layer.
Figure 1 shows the seasonal changes in the distribution of DIN on surface and bottomlayers. In winter, the surface high DIN concentration areas are mainly distributed in theYangtze River estuary, Hangzhou Bay, and northern Jiangsu shoal area. Secondly, thehigh DIN concentration areas along the coast of Fujian and Zhejiang are distributed instripes, reaching the Taiwan Strait all the time. The trend of the southward expansionof the edge is consistent. The area outside the middle shelf of the East China Sea (under100 m deep) has a lower concentration, and the lowest concentration occurs in the slopebreak area of the continental shelf. In the shallow water of northern Jiangsu Shoal, theYangtze River estuary, and Hangzhou Bay, strong winter monsoon and tidal processes
bring strong mixing, making the distribution of DIN concentrations at the bottom andsurface layers similar; while in areas outside the continental shelf in the East China Sea(under 50 m deep), the bottom DIN concentration is much higher than that on the surface
layer, especially in areas outside the land slope, the highest DIN concentration is greaterthan 25 mmol/m3.

1 / 5

In spring, the DIN concentration in the surface layer was lower than in winter, and areas
with high DIN concentrations still appeared in the Yangtze River estuary, Hangzhou Bay,and the northern Jiangsu shoal area; the DIN concentrations in the central East China
Sea and the Korean Peninsula coast decreased significantly, and the concentration
values were less than 2 mmol/m3; area of high DIN concentration is strip-shaped in thecoastal areas of Fujian and Zhejiang, and it retracts northward in winter. The
distribution of DIN concentration in the bottom layer is basically the same as that inwinter, but the concentration value is different from that in winter. The DINconcentration in the northern part of the East China Sea shelf decreases and the central
part increases. The DIN concentration in the region from the northern part of Taiwan
Island to 28°N increases from ~ 2 mmol/m3 to ~ 5 mmol/m3. The reduction of surface DIN
concentration is affected by both biological and physical processes. Phytoplankton
growth activities enhance the absorption of large amounts of nutrients and lead to areduction in DIN concentration. On the other hand, the increase in solar radiation inspring and the seasonal stratification of seawater gradually form, and the stability of thewater body makes it difficult to supplement the high DIN concentration in the bottom
layer to the upper layer, resulting in a reduction in the DIN surface layer concentration.
At the same time, DIN, which is produced by the decomposition of granular organismsthat settle to the bottom, is retained, which increases the bottom DIN concentration. In
addition, the intrusion of the Kuroshio subsurface water into the East China Sea shelfintensified in the spring, and water transport brings more nutrients, which also makesThe DIN concentration in the middle shelf and outer shelf of the East China Sea
increased.
In summer, the Yangtze River dilutes water with a large amount of nutrients into thesea, and expands eastward and northeastward. At the bottom, the DIN concentration in
the northern part of the East China Sea shelf (southwest of Jeju Island) increased, which
was caused by the increase in salt transported by Kuroshio subsurface water to the shelf;
the DIN concentration in the Yangtze River estuary and the northern Jiangsu shoal area
also increased slightly due to the water depth is shallow, and the DIN concentration in
the surface layer can reach the bottom layer through vertical mixing.
In the autumn, as the Yangtze River dilute water extends south along the shore, the DIN
concentration in the surface layer of the Fujian-Zhejiang coast increases, and the DIN
concentration in the northern layer of the East China Sea shelf decreases, but the DIN
concentration in the East China Sea inland shelf still maintains a high value; at thebottom layer, the DIN concentration increased from the south of Jeju Island to the shelfslope break area compared to summer, but decreased in the offshore area outside theYangtze River Estuary.

2 / 5

Figure 1. Seasonal distribution of DIN concentration on the surface layer (2 m) andbottom layer (mmol/m3). (a) ~ (d) represent the surface layer in February, May, August,and October, respectively, and (e) ~ (f) represent the bottom layer in February, May,August, and October, respectively.
The seasonal changes in the distribution of DIP concentration levels (Figure 2) are
different with DIN. Looking at the whole year, the surface DIP concentration is generally
lower than the bottom layer, especially DIP concentration on the bottom layer in theouter shelf area can reach 2 mmol/m3, while the surface DIP concentration is only ~ 0.2
mmol/m3, and the former is ten times the latter. In winter, due to the low watertemperature and weak light, the growth of phytoplankton is limited, and theconsumption of nutrients is low, which makes the surface DIP concentration reach thehighest level throughout the year. Due to the strong vertical mixing in winter, the surface
and bottom layers of DIP concentrations in the inland shelf area are similar. In springand summer, the temperature rises and the light increases. Phytoplankton grows
vigorously and absorbs a large amount of DIP. Due to the apparent lack of DIP from theYangtze River compared to DIN, DIP has become a limiting nutrient for phytoplankton
growth in areas affected by the Yangtze River's diluted water. The concentration of DIP
along the Yangtze River's dilute water expansion path to the Tsushima Strait is very low,while DIN is relatively abundant and still maintains a high value. This is also asignificant difference between the surface distribution of DIP and DIN concentrations;the bottom layer, the northern part of the East China Sea shelf (Southwest of Jeju Island)
DIP concentration increased, and the increased area extended northwest to 34ºN. Inautumn, due to the reduction of phytoplankton consumption, the surface DIP
concentration in the northern East China Sea slightly increased; at the bottom, the highvalue DIP area was stripe-shaped, along the shelf slope break north to southwest of Jeju
Island and then to the northwest, with high DIP concentration bands The distribution

3 / 5

indicates the intrusion path of Kuroshio subsurface water in the East China Sea shelfarea.

Figure 2. Seasonal distribution of DIP concentration on the surface layer (2 m) andbottom layer (mmol/m3). (a) ~ (d) represent the surface layer in February, May, August,and October, respectively, and (e) ~ (f) represent the bottom layer in February, May,August, and October, respectively.
The distribution characteristics of SIL concentration on the surface layer and bottomlayer (Figure 3) are almost the same as DIN. This is because the main sources of bothare the Yangtze River and Kuroshio subsurface water inputs, and they are not restricted
nutrients for phytoplankton growth in the shelf area. The concentration distribution ismainly controlled by changes in nutrient sources and physical processes in the sea.

4 / 5

Figure 3. Seasonal distribution of SIL concentration on the surface layer (2 m) andbottom layer (mmol/m3). (a) ~ (d) represent the surface layer in February, May, August,and October, respectively, and (e) ~ (f) represent the bottom layer in February, May,August, and October, respectively.
6. Publication/Conference presentation
Conference presentation (poster presentation)
Title: Study on the Response Mechanism of Primary Production in the East China Sea
to the Change of Nutrient Inputs from the Yangtze RiverLecturer: LENG Qian
Time: 14~15 November 2019.
Location: Ehime University.
7. Perspectives in Future
To explore the mechanism about Yangtze River nutrient flux influencing thenutrient structure and primary production of East China Sea.
To enhance the cooperation researches and exchanges of faculties and students
between the Ocean University of China and CEMS of Ehime University.

5 / 5