J. Ocean Univ. China (Oceanic and Coastal Sea Research)
DOI 10.1007/s11802-017-3210-2
ISSN 1672-5182, 2017 16 (5): 727-737
http://www.ouc.edu.cn/xbywb/
E-mail:xbywb@ouc.edu.cn

Influence of a Water Regulation Event on the Age of
Yellow River Water in the Bohai
LI Zhen1), WANG Haiyan1), 2), GUO Xinyu1), 3), LIU Zhe1), a), *, GAO Huiwang1),
and ZHANG Guiling4)
1) Key Laboratory of Marine Environment and Ecology (Ocean University of China), Ministry of Education,
Qingdao 266100, P. R. China
2) National Marine Environmental Forecasting Center, SOA, Beijing 100081, P. R. China
3) Center for Marine Environmental Studies, Ehime University, 2-5 Bunkyo-Cho, Matsuyama 790-8577, Japan
4) Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China,
Qingdao 266100, P. R. China(Received May 19, 2016; revised June 20, 2016; accepted January 20, 2017)© Ocean University of China, Science Press and Springer-Verlag Berlin Heidelberg 2017
Abstract Abrupt changes in freshwater inputs from large rivers usually imply regime shifts in coastal water environments. The
influence of a water regulation event on the age of the Yellow River water in the Bohai was modeled using constituent-oriented age
and residence time theory to better understand the change in the environmental function of the hydrodynamic field owing to humanactivities. The water ages in Laizhou Bay, the central basin, and the Bohai strait are sensitive to water regulation. The surface ages inthose areas can decrease by about 300 days, particularly in July, and the age stratification is also strengthened. A water regulation
event can result in declines in the water age in early July ahead of declines in the water age under climatological conditions (without
the regulation event) by about 1 and 5 months in the central basin and Laizhou Bay, respectively. The change in the coastal circulation due to the water regulation event is the primary reason for the change in the Yellow River water age. The high Yellow River flowrate can enhance the density flow and, therefore, reduce the age of the Yellow River water. The subsequent impact of a single water
regulation event can last about 1.0 to 4.0 years in different subregions.
Key words

water regulation event; water age; constituent-oriented age and residence time theory; Yellow River; Bohai

1 Introduction
A quantitative evaluation of river water transport processes in coastal waters will benefit the understanding ofmarine environmental issues (e.g., eutrophication). The
water age is a useful auxiliary variable to describe watertransport timescale (Bolin and Rodhe, 1973; Takeoka,
1984; Delhez et al., 2014), which is defined as the time
elapsed from the departure of a water parcel from a source
to its arrival at a location of interest (Bolin and Rodhe,
1973; Takeoka, 1984; Delhez et al., 2014). Constituentoriented age and residence time theory (CART, see www.
Climate.be/cart) (Deleersnijder et al., 2001) has been widely used to calculate the water ages in coastal sea areas (e.g.,
Shen and Haas, 2004; Shen and Lin, 2006; Meier, 2007;
Shen and Wang, 2007; Liu et al., 2008; Gong et al., 2009;
Hong et al., 2010; Wang et al., 2010; Hong and Shen,* Corresponding author. Tel: 0086-10-62327157
E-mail: liuzhe_ecnu@163.coma) Now works in the Department of Earth Sciences, National
Natural Science Foundation of China, Beijing, P. R. China

2012; Liu et al., 2012; de Brye et al., 2013; Wang et al.,2013; Ren et al., 2014; Wang et al., 2015; Yuan et al.,2016).
Located in the northwestern Pacific Ocean, the Bohai is
a shallow semi-enclosed sea and is connected to the Yellow Sea through the Bohai Strait (Fig.1). It covers a surface area of 7.7×104 km2 (117˚35΄–122˚25΄E, 37˚07΄–
41˚00΄N) and has an average depth of about 18 m. The
Bohai can be geographically divided into five major subregions: Laizhou Bay, the central basin, Bohai Bay, Liaodong Bay, and Bohai Strait. The Yellow River, which isone of the largest rivers in East Asia, discharges a substantial amount of fresh water with sediments and nutrients
into the Bohai. Liu et al. (2012) investigated the spatial
and temporal distributions of the age of Yellow River
water in the Bohai under climatological conditions. Since
2002, the Yellow River Conservancy Commission has
carried out water regulation events, typically in June andJuly, to create a balance between water and sediment (e.g.,
Li, 2002; Wu et al., 2015). It is important to know how
water regulation events affect the transport timescale of
Yellow River water in the Bohai. In this study, the age of
Yellow River water in the Bohai was simulated over a

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water regulation event.
This study is organized as follows. The hydrodynamic
model and the age model are described in Section 2. Section 3 presents the spatial and temporal changes in the ageof Yellow River water due to the water regulation event.
In Section 4, the influencing dynamic factors are identified, and the impact of a single water regulation event isalso discussed. The results of this study are summarized
in Section 5.

results of the harmonic constants of four major tidal constituents (M2, S2, K1, and O1) at 29 stations and the distributions of water temperature and salinity in the Bohai
were in good agreement with the observations (see Figs.
4–7 in Wang et al., 2008).
The water age module used in this study is based on
CART (Deleersnijder et al., 2001) and from Liu et al.
(2012). According to CART, the mean age of a waterparcel can be calculated using the concentration C and theage concentration β transport equations:C  (uC  K  C )  0 ,
t

(1)


  (u  K   )  C ,t(2)

where u is the velocity vector and K is the diffusivity
tensor. The mean age a of the water parcel then can becalculated as follows:a /C .

Fig.1 Model domain and bathymetry (units: m). The
black dot designates the position of the Yellow Rivermouth. The solid line denotes Transect AB. The dashedlines demarcate the subregions of the Bohai. The line
labeled OB indicates the location of the model open
boundary.

2 Model Description
The Princeton Ocean Model (POM) used in this study
is from Wang et al. (2008). The horizontal grid resolution
is 1/18˚ in both the zonal and meridian directions andthere are 21 sigma levels in the vertical direction. Detailed descriptions of the hydrodynamic model are provided in Mellor (2004) and Wang et al. (2008). The Yellow River discharge data during the water regulation
event were recorded at Lijin Station in 2010. It should be
noted that the water regulation event mainly changed theseasonal variation in river discharges. However, there wasdifference between climatological annual discharges andthe year 2010 discharges. To eliminate the difference, the2010 discharge data were multiplied by R1/R2, where R1
and R2 are the climatological and 2010 annual dischargesof the Yellow River, respectively. The Yellow River discharges with and without the water regulation event are
shown in Fig.2. It should be noted that the hydrodynamic
field was calibrated in Wang et al. (2008). The simulation(3)

The concentration of Yellow River water in a given
grid C is the ratio of the volume of Yellow River water tothe total water volume within the grid domain. The valuesof C therefore range from 0 to 1. The open boundary of
the outer sea was set along the line labeled OB in thesouthern part of the Yellow Sea (Fig.1), allowing waterexchange between the Bohai and the Yellow Sea throughthe Bohai Strait. Liu et al. (2012) verified the age module
by comparing numerical results with three typical analytical solutions. The same three solutions were used tocheck the present numerical module, which is used tosolve 1) the advection process only, 2) the diffusion process only, and 3) the combined processes of advection anddiffusion.
Table 1 shows the numerical experiments in this study.
The models without and with the water regulation event

Fig.2 Yellow River discharges (units: m3 s−1) for the control case (dashed line) and Case 2 (solid line).

Table 1 Numerical experiments
Case
1
2
3
4

Hydrodynamic model

Age model

Note/usage

Climatological hydrodynamic field Climatological river discharge The control case; without considering the water regulation event
With the water regulation event
With the water regulation event To study the influence of the water regulation event on water age
With the water regulation event
Climatological river discharge To reveal the different roles of the hydrodynamic field and river
Climatological hydrodynamic field With the water regulation event discharges

LI et al. / J. Ocean Univ. China (Oceanic and Coastal Sea Research) 2017 16: 727-737

are denoted as the control case (i.e., the climatologicalstate, or Case 1) and Case 2, respectively. The modeling
results for the control case are from Liu et al. (2012). In
addition, two other cases (Case 3 and Case 4) were designed to determine governing dynamic factors, which aredescribed in Section 4.1.

3 Response of the Yellow River Water
Age to the Water Regulation Event
3.1 The Horizontal Distribution
We mainly focused on the horizontal distribution of thesurface water age as well as the concentration of the Yellow River water in the Bohai because freshwater is lighter
than seawater. In the north temperate zone, February, May,
August, and November are usually regarded as the typicalmonths of winter, spring, summer, and autumn, respectively. Because the water regulation event lasted from
June to July (Fig.2), the ages and the concentrations of729

the Yellow River water in June and July are shown together with those in February, May, August, and November (Fig.3). The surface age of the Yellow River water was
low in the vicinity of the Yellow River mouth and increased with distance from the Yellow River mouth under
Case 2, while the surface concentration of the Yellow
River water was high at the river mouth and decreased
with distance from the river mouth (Fig.3). There weremore significant seasonal variations in the horizontal distribution of the age and the concentration of the Yellow
River water in Laizhou Bay, south of the central basin,
and in the Bohai Strait than in other areas of the Bohai(i.e., the northern central basin, Bohai Bay, and Liaodong
Bay). A notable spread of the Yellow River water was
found towards the northeast offshore from the Yellow
River mouth in July and a southward spread in Laizhou
Bay in November, which was consistent with the results
for the control case (Wang et al., 2008; Liu et al., 2012).
The difference between Case 2 and the control case forthe surface water ages and concentrations are shown in

Fig.3 (a)–(f) Horizontal distributions of the surface concentration (left panels, unit: %) and age (right panels, units: d) of
the Yellow River water for Case 2 in (a, b) February, (c, d) May, (e, f) June. The color legend shows the range of (i)concentration and (ii) age, respectively. The contour interval for concentration is 2% and that for age is 100 days.

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Fig.3 (g)–(l) Horizontal distributions of the surface concentration (left panels, unit: %) and age (right panels, units: d) of
the Yellow River water for Case 2 in (g, h) July, (i, j) August, and (k, l) November. The color legend shows the range of(i) concentration and (ii) age, respectively. The contour interval for concentration is 2% and that for age is 100 days.

Fig.4, which illustrates that the influence of the water
regulation event on the surface age and concentration of
the Yellow River water has a distinct seasonal pattern (Fig.
4). In February, the most notable decrease in the Yellow
River water age (about 50 days) and increase in the Yellow River water concentration occurred near the Yellow
River mouth. The water age also decreased and the concentration increased along the west coast of Laizhou Bay.
Nevertheless, the ages and the concentrations in the middle and eastern part of Laizhou Bay, the central basin,
Bohai Bay, and south of the Bohai Strait increased anddecreased, respectively. The most notable increase in thewater age (about 100 days) occurred in the eastern part ofLaizhou Bay (Figs.4a and 4b). In May, the areas where
the age decreased spread to the middle of Laizhou Bay,the central basin, and southern part of Bohai Bay, while
the concentration increased in these areas. The most notable increase in age (about 50 days) occurred near theBohai Strait (Figs.4c and 4d). The Yellow River discharge

abruptly increased from about 400 m3 s−1 on 16 June to>2700 m3 s−1 on 25 June due to the water regulation event(Fig.2). The artificial flood lasted approximately half amonth (Fig.2) and contributed about 20% of the total annual Yellow River water that was discharged to the Bohai
Sea. In June, the Yellow River water decreased in age andincreased in concentration in the areas of the Bohai, except in the eastern part of Laizhou Bay, the northern partof Bohai Bay, and in Bohai Strait. It is noteworthy thatthe age decreased by about 150 days near the river mouth(Figs.4e and 4f). In the following month (i.e., July), theage of the Yellow River water decreased throughout almost all of the Bohai; however, the concentration of the
Yellow River water increased. The substantial decrease in
age and increase in concentration occurred in Laizhou
Bay, followed by the central basin and even the Bohai
Strait, with a maximum decrease of about 300 days in water age (Figs.4g and 4h). Unlike the previous months, theCase 2 results in August indicated that the Yellow RiverLI et al. / J. Ocean Univ. China (Oceanic and Coastal Sea Research) 2017 16: 727-737

water in the vicinity of the river mouth became less concentrated and older than that of the control case. The increase in water age and the decrease in concentration
gradually weakened with increasing distance from theriver mouth. In contrast, the water in the eastern part ofBohai remained more concentrated and younger than thecontrol case; however, the age difference decreased toabout 150 days near the Bohai Strait (Figs.4i and 4j). In
November, the older water area extended from the vicinity of the river mouth to the entire Laizhou Bay, thesouthern part of the central basin, and the southern part ofBohai Bay, because of less Yellow River water in theseareas. The younger water area remained smaller, with amaximum decrease of only about 50 days in water age in
the northern part of the Bohai Strait (Figs.4k and 4l).

3.2 The Vertical Distribution
Located on the main axis of the diluted water, Transect
AB (see the location in Fig.1) was selected to study the731

impact of the water regulation event on the vertical distribution of the Yellow River water age (e.g., Wang et al.,2008). The water age was always lower near the Yellow
River mouth than that near the Bohai Strait regardless of
the water regulation event (Fig.5). The age of the Yellow
River water was nearly homogeneous vertically in theautumn and winter (figure not shown) but was stratified
in the spring and summer (Fig.5). The stratification in
May occurred from the mouth of the Yellow River to the
middle of the central basin and was about 5 m beneath thesurface. It spread northeastward in June. By July and August, the front of the younger water dominated all ofTransect AB and the mixed layer deepened.
However, the water regulation event changed the vertical distribution of the stratification in the spring andsummer. In May, the stratification of the water age near
the river mouth strengthened (Fig.5b) compared with thecontrol case (Fig.5a). Because of the water regulation
event in June, the increasing stratification area spread toFig.4 (a)–(f) Differences in surface concentration (left panels, unit: %) and age (right panels, units: d) of the Yellow
River water between Case 2 and the control case in (a, b) February, (c, d) May, (e, f) June. The color legend shows therange of (i) concentration and (ii) age, respectively. The contour interval for concentration is 1%, and for age is 50 days.

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Fig.4 (g)–(l) Differences in surface concentration (left panels, unit: %) and age (right panels, units: d) of the Yellow
River water between Case 2 and the control case in (g, h) July, (i, j) August, and (k, l) November. The color legendshows the range of (i) concentration and (ii) age, respectively. The contour interval for concentration is 1%, and for age
is 50 days.

Laizhou Bay and the southern part of the central basin.
For example, in the western part of Laizhou Bay, the water age difference between the bottom and surface layers(WADBS) increased from about 260 days (Fig.5c) in thecontrol case to about 410 days in Case 2 (Fig.5d). In July,
the stratification along the entire Transect AB was stronger
than that of the control case. In the western part of Laizhou Bay, the WADBS increased from about 420 days in
the control case to about 620 days in Case 2 and fromabout 520 days to about 760 days in the central basin(Figs.5e and f). In August, the age became less stratified
because of the less Yellow River discharge from the regulation event. For example, the WADBS in the western part ofLaizhou Bay recovered from about 480 days in the control case (Fig.5g) to about 260 days in Case 2 (Fig.5h).

3.3 The Average Surface Water Ages in Subregions
Freshwater from the Yellow River is mainly transported

in the upper layer. Thus, the average ages at the surface
were our primary concerns for the five Bohai subregions(i.e., Laizhou Bay, the central basin, Bohai Bay, Liaodong
Bay, and the Bohai Strait). Unlike the other subregions,
Laizhou Bay and the central basin were sensitive to thewater regulation event (Fig.6).
In comparison with the control case, the water regulation event reshaped the annual cycle of the Yellow River
discharge by adding an artificial flood peak (>2700 m3 s−1)
from late June to early July to the natural discharge peak(about 930 m3 s−1) in mid-August (Fig.2). Consequently,
the lowest age (<450 days) was identified approximately
on 9 July in Laizhou Bay, which responded to the artificial flood peak almost instantaneously, with a time lag of
about 2 days (solid lines in Figs.2 and 6a). This first lowage period occurred ahead of that in the control case by
about 5 months (Fig.6a). Similar to the control case, theother low-age period in Case 2 appeared in early December, with a time lag of approximately about 110 days toLI et al. / J. Ocean Univ. China (Oceanic and Coastal Sea Research) 2017 16: 727-737

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Fig.5 Vertical distributions of the Yellow River water age (units: d) along Transect AB for the control case (left panels)
and Case 2 (right panels) in (a, b) May, (c, d) June, (e, f) July, and (g, h) August. The contour interval is 200 days.

the natural discharge peak in mid-August. There was a
distinct decrease in lag time with increased discharge.
This indicates that the abrupt increase in freshwater input
from the Yellow River accelerates its transport timescale
substantially.
When Yellow River water discharges into the Bohai,
the orientation of the main axis of the diluted water isnortheastward. The central basin receives the highest
amount of the Yellow River freshwater first. Hence, theage of the Yellow River water in the central basin responds to the change in the Yellow River discharge synchronously. Compared with the control case, the low-age
period occurred in early July, an advance of about 1 month,and the marked decrease in the age of the Yellow River
discharge was about 170 days (Fig.6b).

4 Discussion

Fig.6 Average surface ages of the Yellow River water(units: d) in (a) Laizhou Bay and (b) the central basin.
The dashed and solid lines represent the control case andCase 2, respectively.

4.1 Dynamic Factors
The water regulation event abruptly and substantiallyaltered the temporal variation of the Yellow River discharge (Fig.2) and also changed the hydrodynamic fieldin the Bohai. Therefore, Cases 3 and 4 were conducted(Table 1) to determine which dynamic factor (i.e., hydrodynamic field or riverine input) governed the differ-

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ence in the water age between Case 2 and the control case
(Figs.4 and 5). Case 3 used the regulated flow, whereas
the Yellow River open boundary in the age module remained unchanged (i.e., the same as that in the controlcase). Case 4 took into account the river discharge in theage module as in Case 2, whereas the hydrodynamic
model was the same as that in the control case. Comparedwith the control case, Case 3 (Fig.7), resulted in an age
difference that was notably close to that in Case 2 (Fig.4),
but Case 4 did not show the similarity in the age difference (Fig.8). Hence, the change in hydrodynamic field

was an important factor for interpreting the influence of
the water regulation event on the Yellow River water age
relative to the river open boundary condition in the age
module. The circulation differences between Case 2 andthe control case at the surface and in Transect AB are
shown in Figs.9 and 10, respectively, which explain theinfluence of the hydrodynamic field on water age.
In February, the increase in riverine freshwater input(Fig.2) resulted in slightly stronger surface density current in the offshore direction off the river mouth (see thered arrow in Fig.9a), and, therefore, the slightly younger

Fig.7 Differences in the surface ages of the Yellow River water (units: d) between Case 3 and the control case in (a)February, (b) May, (c) June, (d) July, (e) August, and (f) November. The contour interval is 50 days.

Fig.8 Differences in the surface ages of the Yellow River water (units: d) between Case 4 and the control case in (a) February, (b) May, (c) June, (d) July, (e) August, and (f) November. The contour interval is 50 days.

LI et al. / J. Ocean Univ. China (Oceanic and Coastal Sea Research) 2017 16: 727-737

Fig. 9 Differences in the surface circulation between Case 2 and the control case in (a) February, (b) May, (c) June, (d)July, (e) August, and (f) November. The color arrows indicate the direction of water transport.

Fig.10 Vertical differences in circulation component projected onto Transect AB (units: m s−1) between Case 2 and thecontrol case in (a) May, (b) June, (c) July, and (d) August. The positive values denote the flow direction from A to B,
whereas the negative values denote from B to A.

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water in the vicinity of the river mouth (Figs.4b and 7a).
The southward current (see the blue arrow in Fig.9a)along the west coast of Laizhou Bay also induced the
low-age water (Figs.4b and 7a). In May, another low-age
water area was identified in the central basin and thesouthern part of Bohai Bay, except for the areas in thevicinity of the river mouth and the western part ofLaizhou Bay (Figs.4d and 7b). This low-age water area
was due to the plume of the Yellow River water discharging towards the central basin and Bohai Bay (see thepurple and green arrows in Fig.9b). The current shear invertical was enhanced in the vicinity of the river mouth(Fig.10a), resulting in a stronger age stratification (Figs.5a
and 5b). In June, the water regulation event produced astronger surface current flowing towards the central basin(see the green arrow in Fig.9c, and Fig.10b), resulting in adecrease in the surface water age and an increase in theage stratification in Laizhou Bay and the central basin(Figs.4f and 7c; Figs.5c and 5d). In July, the stronger surface current covered the central basin and even reachedthe Bohai Strait (see the green arrow in Fig.9d, and Fig.
10c). In addition, starting from the river mouth, a current
flows along the shoreline in Laizhou Bay, and then to theeastern part of the Bay (see the blue arrow in Fig.9d).
Those changes in the hydrodynamic field induced thesubstantial decrease in the water ages in Laizhou Bay, thecentral basin, and the Bohai Strait (Figs.4h and 7d) andenhanced the age stratifications in those areas (Figs.5e
and 5f). In August, the riverine discharge in Case 2 waslower than the control case (Fig.2). As a result, the surface
circulation turned shoreward in the vicinity of the rivermouth (see the red arrow in Fig.9e, and Fig.10d), which
was opposite to that in the previous months (e.g., Figs.
9a–d and 10a–c). Accordingly, the surface water age increased (Figs.4j and 7e) and the age stratification decreased (Figs.5g and 5h) near the river mouth. The surface current in the eastern part of the central basin continued to flow toward the Bohai Strait (see the green arrow in Fig.9e, and Fig.10d), which reduced the water age(Figs.4j and 7e). In November, there was a strong surface
current that moved from the eastern coast of Laizhou Bay
to the river mouth (see the red arrow in Fig.9f), which
prevented the Yellow River water from leaving Laizhou
Bay and consequently increased the water age (Figs.4l
and 7f).
In general, as the riverine freshwater input increased, thedensity current increased and the water age decreased.
This phenomenon was noted in the spring, summer, andautumn. In the winter, the density current also occurred in
the vicinity of the river mouth, while water columns were
well mixed by strong wind in the other areas (Wang et al.,2008).

4.2 Residence Time of the Yellow River Water
Under the Influence of the Water
Regulation Event
The residence time was calculated to further evaluate
the influence of the water regulation event on the trans-

port processes of Yellow River water in the Bohai using
the approach proposed by Takeoka (1984): 

 C (t )0 C (t0 )

dt ,

(4)

where θ is the average residence time, t0 denotes the initial time, t is the time afterward (t−t0 > 0), and C(t) is theconcentration of Yellow River water. The average residence time of the Yellow River water throughout the surface of the entire Bohai was 883 days under the influenceof the water regulation event. It varied spatially as follows:
270 days in Laizhou Bay, 612 days in the central basin,
1110 days in Bohai Bay, and 1515 days in Liaodong Bay(Fig.11). Compared with the residence time without the
influence of the water regulation event, the average residence time of the Yellow River water in the central basin
decreased by about 17%, while the residence time in theother subregions was less sensitive to the influence by theevent. The average residence time represents the transport
timescales of the Yellow River water throughout the Bohai and its subregions and is an indication of the how longa water regulation event can influence the environment in
the Bohai.

Fig.11 Average residence times (unit: d) of the Yellow
River water in the surface of the Bohai and its subregions. The black and blue bars show the average residence time of the Yellow River water with and without
the water regulation event, respectively.

5 Summary
The influence of the Yellow River water regulation
event on the Yellow River water age in the Bohai wasstudied using CART. The water regulation event primarily
affected the Yellow River water age in Laizhou Bay, andthen in the central basin and Bohai strait. These threesubregions were characterized by a lower age of the Yellow River water at the surface, with a maximum age decrease of about 300 days, and notable age stratification,
especially in July. The artificial flood peak caused by thewater regulation event produced the youngest water in
Laizhou Bay and the central basin in early July. In comparison with the climatological condition without theLI et al. / J. Ocean Univ. China (Oceanic and Coastal Sea Research) 2017 16: 727-737

regulation event, the first time period with the lowest age
occurred about 1 and 5 months earlier for the central basin and Laizhou Bay, respectively, as the water regulation
event was triggered. The change in the hydrodynamic
field due to the water regulation event primarily affected
the Yellow River water age. The higher Yellow River flowrate enhanced the density current and therefore reduced
the age of the Yellow River water. Under the water regulation event, the duration change because of the Yellow
River water ranged from about 1.0 to 4.0 years in the
Bohai Sea and its subregions.

Acknowledgements
This study was funded by the National Natural Science
Foundation of China (Nos. 41176007 and 40706007). The
authors are grateful to Mr. Biao Shen of the High Performance Computer Center of the Ocean University of
China for his technical assistance.

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(Edited by Xie Jun)