1. Title
Estimate of environmental capacity of dissolved inorganic nitrogen in the Xiangshan Bay.
2. Members’ names and affiliations
Junyong Zheng

Ocean University of China

Mao Xinyan

Ocean University of China

3. Aim
1. With the full consideration of tide, river discharge, wind, sea surface heat flux and etc.,
a three-dimensional nonlinear baroclinic ocean model based on the Regional Ocean Model
System (ROMS) and the North Pacific Ecosystem Model for Understanding Regional
Oceanography (NEMURO) will be established to carry out numerical studies of thebiogeochemical process in the Xiangshan Bay.
2. On the basis of the model results, the environmental capacity (EC) of dissolved inorganic
nitrogen (DIN) will be calculated and allocated by the nonlinear method of the discharge
optimization.
3. Enhance bilateral cooperation between our team (Coastal Dynamics Group, Ocean
University of China) and the Center for Marine Environmental Studies of Ehime University onacademics.
4. Procedure
The pollution of DIN in the Xiangshan Bay is becoming so serious that a series ofaccompanying problems, such as eutrophication, are needed to be solved urgently. In ourstudy, a three-dimensional ocean model was established based on ROMS and NEMURO tosimulate the distribution of DIN in the Xiangshan Bay. In the condition of class Ⅳ water quality
standard, the discharge optimization method was applied to calculate the EC of DIN.
5. Results
A three-dimensional water quality model was established based on ROMS and NEMURO
to simulate the distribution of DIN in the Xiangshan Bay (Fig.1). Ten land-based dischargesources were involved in this coupled model. The eight principal tidal constituents M2, S2, N2,K2, K1, O1, P1, and Q1 are used as tidal forcing in the model, and the tidal data are derived
from the Global Inverse Tide Model data set. Besides, the comprehensive influence of wind,heat flux, evaporation, precipitation and so on were also considered. Outputs from thiscoupled model, including tide level, temperature and DIN concentrations match measured
data well, so it is proved to be accurate and reliable.

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Fig.1 The distribution of water depth, discharge sources (S1-S10),
water quality control points (P1-P10) and tidal stations (B2, D2) in the Xiangshan Bay
Tab.1 DIN environmental capacity and discharge flux under four cases
Case aEstuary

Case bCase cCase dPresent
Allow

ReduceAllow

ReduceAllow

ReduceAllow

ReduceS6

112.62

44.02

68.60

48.46

64.17

49.32

63.30

38.92

73.71

S7

160.73

11.25

149.4813.70

147.0315.99

144.7418.61

142.11

S8

39.70

39.70

-

7.66

32.04

3.43

36.28

3.99

35.71

S4

14.67

14.67

-

14.67

-

1.50

13.17

1.74

12.92

S5

16.09

16.09

-

16.09

-

10.73

5.36

1.69

14.39

S2

57.96

57.96

-

57.96

-

57.96

-

44.93

13.02

S3

59.03

59.03

-

59.03

-

59.03

-

6.70

52.33

S9

2.15

2.15

-

2.15

-

2.15

-

1.69

0.46

S10

24.40

24.40

-

24.40

-

24.40

-

3.99

20.42

S1

4.90

4.90

-

4.90

-

4.90

-

4.90

-

Total

492.25274.17218.08249.02

243.24229.41

262.85127.16325.07In the condition of class Ⅳ water quality standard, the discharge optimization method wasapplied to calculate the EC of DIN in the Xiangshan Bay. The minimum DIN discharge
concentration of the ten land-based discharge sources (Rmin), as a constraint, is also usedto optimize the calculation of EC. The Rmin can be divided into four cases (Case a:0≤Rmin≤0.10 mg/L, Case b： 0.10＜Rmin≤0.12 mg/L, Case c： 0.12＜Rmim ≤0.14 mg/L,
Case d: 0.14＜Rmin≤0.17 mg/L) after 18 numerical experiments. The results show that theEC of DIN in the Xiangshan Bay is 127.16~274.17 t/a (Tab.1). The capacity will decrease

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when Rmin gets larger, which means more discharge flux of DIN needed to be cut down.
According to the reduction priority, ten discharge sources can be divided into four levels (Ⅰ、Ⅱ、Ⅲ、Ⅳ), which mainly depends on the water half-exchange time and annual DIN discharge
flux (Fig.2).

Fig.2 The reduction priority, water half-exchange time and annual DIN discharge flux of thedischarge sources

6. Publication/Conference presentation
1) Publication
Zheng, J., X. Mao, X. Sheng, J. Sun, and W. Jiang, Estimate of environmental capacity ofdissolved inorganic nitrogen in the Xiangshan Bay. Marine Sciences (In Chinese, accepted).
2) Conference presentation
Conference: The International Symposium on Coastal Ecosystem Change in Asia:
Hypoxia, Eutrophication, and Nutrient Conditions

Presentation: Poster presentation
Title: Estimate of environmental capacity of dissolved inorganic nitrogen in theXiangshan Bay. Marine Sciences

Date: Nov. 14-15th, 2019
Location: Ehime Univesity
7. Perspectives in Future
The JCOPE (Japan Coastal Ocean Predictability Experiment) model and MIROC(Model for Interdisciplinary Research on Climate) data were coupled by Professor Xinyu
Guo and his research group, which provides a key to reveal the variation of volumetransport and its mechanism on the Tsushima Warm Current from the palaeoceanographicview. Therefore, Junyong Zheng will go on general collaboration with Professor Xinyu Guo
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to discuss the millennial-scale fluctuations of volume transport and its mechanism based on
the coupled model and data. All of the collaborations will be helpful to Enhance bilateral
cooperation between the Coastal Dynamics Group, Ocean University of China and theCenter for Marine Environmental Studies, Ehime University.

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