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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, C03005, doi:10.1029/2008JC004891, 2009
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Effects of the Changjiang (Yangtze) River discharge on planktonic
community respiration in the East China Sea
Chung-Chi Chen,1 Fuh-Kwo Shiah,2,3 Kuo-Ping Chiang,3,4 Gwo-Ching Gong,3
and W. Michael Kemp5
Received 27 April 2008; revised 3 November 2008; accepted 11 November 2008; published 6 March 2009.
[1] Planktonic communities tend to flourish on the western margins of the East China Sea
(ECS) fueled by substrates delivered largely from the Changjiang River, the fifth largest
river in the world. To study the effects of the Changjiang River discharge on planktonic
community respiration (CR), physical-chemical variables and key processes were
measured in three consecutive summers in the ECS. Results showed that concentrations of
nitrate and Chl a, protozoan biomass, bacterial production, as well as CR in the surface
water were all negatively correlated with sea surface salinity, reflecting the strong
influence of river discharge on the ECS shelf ecosystem. Moreover, mean values of
nitrate, Chl a concentrations, and CR rates were proportionally related to the area of
Changjiang diluted water (CDW; salinity 31.0 practical salinity units (psu)), an index of
river discharge rate. Presumably, higher river flow delivers higher nutrient concentrations
which stimulate phytoplankton growth, which in turn fuels CR. CR exhibited significant
monthly and interannual variability, and rates appear to be dominated by bacteria and
phytoplankton. Although the plankton community was relatively productive
(mean = 0.8 mg C m2 d1) in the CDW, the mean ratio of production to respiration was
low (0.42). This suggests that the heterotrophic processes regulating CR were supported
by riverine organic carbon input in addition to in situ autotrophic production.
Citation: Chen, C.-C., F.-K. Shiah, K.-P. Chiang, G.-C. Gong, and W. M. Kemp (2009), Effects of the Changjiang (Yangtze) River
discharge on planktonic community respiration in the East China Sea, J. Geophys. Res., 114, C03005, doi:10.1029/2008JC004891.
1. Introduction
[2] The discharge of large rivers has a striking impact on
coastal ecosystems, especially related to organic carbon production and consumption [e.g., Dagg et al., 2004; Hedges et
al., 1997, and references therein]. For example, freshwater
run-off of the Amazon River forms a huge plume that
influences the biogeochemistry of numerous elements for
hundreds of kilometers along the continental shelf [e.g.,
Müller-Karger et al., 1988]. Associated with such fluvial
plumes is the delivery of substantial inorganic nutrients into
coastal regions, where they tend to enhance primary productivity [e.g., Dagg et al., 2004; Nixon et al., 1996]. These large
rivers also typically discharge a significant quantity of particulate and dissolved organic matter which can support high
rates of microbial metabolism in adjacent coastal ecosystems
1
Department of Life Science, National Taiwan Normal University,
Taipei, Taiwan.
2
Research Center for Environmental Changes, Academia Sinica, Taipei,
Taiwan.
3
Institute of Marine Environmental Chemistry and Ecology, National
Taiwan Ocean University, Keelung, Taiwan.
4
Department of Environmental Biology and Fisheries Science, National
Taiwan Ocean University, Keelung, Taiwan.
5
Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, Maryland, USA.
Copyright 2009 by the American Geophysical Union.
0148-0227/09/2008JC004891$09.00
[e.g., Hedges et al., 1994; Malone and Ducklow, 1990]. In
general, the magnitude of the impact of river plumes on coastal
regions is proportional to the amount of river discharge [e.g.,
Dagg et al., 2004; Tian et al., 1993]. Thus, our understanding
of global carbon cycling in the coastal oceans depends on our
knowledge of how large river discharges influence ecological
processes in the adjacent sea. One such large river system, on
which there is limited information, is the Changjiang River,
which discharges into the East China Sea (ECS) [e.g., Gong et
al., 2006; Shiah et al., 2006].
[3] The Changjiang (a.k.a. Yangtze) River is the fifth
largest river in the world in terms of volume discharge.
Annually, huge amounts of water (924.8 109 m3 a1),
inorganic nitrogen (6.1 1010 mole a1), and particulate
organic carbon (4.4 106 t a1) are conveyed into the
northwest corner of the ECS, one of the widest continental
shelves in the world [Dagg et al., 2004; S. M. Liu et al.,
2003; Tian et al., 1993]. During maximum summer discharge, freshwater mixing with seawater forms the Changjiang Diluted Water (CDW) zone, generally with salinity
31 practical salinity units (psu), and it generally extends
eastward or northeastward to the middle shelves [Beardsley
et al., 1985; Chu et al., 2005].
[4] The Changjiang River plume (CDW) contains some
of the most productive planktonic communities in the
ECS, characterized by high abundances of phytoplankton,
bacterioplankton, and protozooplankton [Chiang et al.,
2003; Gao and Song, 2005; Wang, 2006]. During summer,
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Figure 1. Map of all the sampling stations marked with solid dots in the East China Sea (ECS) with
station number above the mark. Bottom depth contours are shown as dashed lines here and in other
graphs. It should be noted that the number of sampling stations varied in different periods as shown in
Figure 3. In addition, please also note that the annual freshwater flux of the Ch’ien-t’ang River is only
2.2% compared to that of the Changjiang River, using a long-term average.
high rates of plankton primary production and community
respiration dominate biological activity in the CDW regulating the regional carbon balance [Chen et al., 2006; Gong
and Liu, 2003]. In contrast, the ‘‘Continental Shelf Pump’’
hypothesis proposes that the cool dense shelf water tends to
accelerates the absorption and transport of atmospheric CO2
to deep waters, and biological metabolism is relatively
unimportant in the region’s ‘‘Continental Shelf Pump’’ even
during summer [Tsunogai et al., 1999]. In our previous
study, we suggested that much of the dissolved inorganic
carbon regenerated through high rate of planktonic respiration in summer could be stored in the subsurface layer,
thereby buffering fCO2 levels in the region’s surface water
[Chen et al., 2006]. To help resolve these conflicting views,
it is important to quantify thoroughly the carbon cycling
processes associated with plankton in the ECS and to
determine the major factor(s) influencing these processes
on seasonal and interannual scales.
[5] To investigate how river discharge influences the ECS
shelf ecosystem, a number of variables were examined
during five cruises over three consecutive summers. Variations in salinity and nutrient concentrations were compared
with indices of plankton community production and respiration over time and space. A central motivation for this
study was to understand the relative importance of nutrientdriven autotrophic production versus riverine input of
organic matter in support of heterotrophic processes in the
ECS shelf ecosystem. The spatial scales of our analysis
focused on the euphotic zone of the CDW.
2. Materials and Methods
2.1. Study Area and Sampling
[6] This study is part of the Long-term Observation and
Research of the East China Sea (LORECS) program.
Samples were collected from five cruises on board R/V
Ocean Researcher I in three consecutive summers (June and
August, 2003, June and July, 2004, and June, 2005) in the
ECS, with the number of stations ranging from 21, 35, 25,
33, and 27 in the respective chronology (Figure 1). The
location of sampling stations was designed to cover the
inner shelf, especially the Changjiang River plume region,
in the most efficient manner. Samples at each station were
collected from 6 to 10 depths at intervals of 2, 3, 5, 7, 10,
15, 20, 25, and 50 m, depending on water column depth,
using Teflon coated Go-Flo bottles mounted on a General
Oceanic rosette assembly. Samples taken at water depths of
2 m in June 2003 and at 3 m in other cruises were assumed
to represent the ‘‘surface waters.’’ Subsamples were taken
immediately for further analyses (i.e., nutrients, chlorophyll
a, bacterial abundance, and protozoan abundance) and
onboard incubations for primary production, bacterial production, and planktonic community respiration (CR). It
should be noted that primary production was measured with
samples taken at stations occupied during daytime. Samples
for CR rates were incubated and measured in samples taken
from the top 6 sampling depths at each station. For detailed
methods for hydrographic data and all the presented variables please refer to Chen et al. [2006]. In the following, only
brief descriptions for methods were given.
2.2. Physical and Chemical Hydrographics
[7] Temperature and salinity were recorded throughout
the water column with a SeaBird CTD. Photosynthetically
active radiation (PAR) was measured throughout the water
column with an irradiance sensor (4p; QSP-200L). The
depth of the euphotic zone (ZE) was taken as the depth of
1% surface light penetration. The mixed layer depth (ZM)
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Figure 2. Monthly water discharge rate (m3 s1) for long-term averaged values (in black frame) and for
2003, 2004, and 2005 at Datong Station, the seaward-most station of the Changjiang River (Figure 1).
Sampling periods of this study are indicated by arrows. The horizontal dashed line is used as a guideline
where monthly water discharge rate is 40,000 m3 s1.
was based on a 0.125 unit potential density criterion
[Levitus, 1982].
[8] A custom-made flow-injection analyzer was used for
nitrate analysis [Gong et al., 2003]. Integrated values for
nitrate and other variables in the water column above the ZE
were estimated by trapezoidal method, whereby depthweighted means are computed from vertical profiles and
then multiplied by ZE [e.g., Smith and Kemp, 1995].
Average nitrate concentration over ZE was estimated from
the vertically integrated value divided by ZE, and this
calculation was also adopted with other variables.
2.3. Biological Variables
[9] Water samples for chlorophyll a (Chl a) analysis were
immediately filtered through GF/F filter paper (Whatman,
47 mm) and stored at liquid nitrogen. The Chl a retained on
the GF/F filters was determined fluorometrically (Turner
Design 10-AU-005) [Parsons et al., 1984]. If applicable,
Chl a was converted to carbon units using C:Chl value of
52.9, estimated from shelf waters of the ECS [Chang et al.,
2003]. A biomass specific rate of respiration of 0.25 d1
was used to estimate phytoplankton respiration [Geider,
1992].
[10] Bacterial abundance was determined by acridine
orange epifluorescence microscopy, and it was converted
to carbon units using a conversion factor of 20 1015 g C
cell1 [Hobbie et al., 1977; Lee and Fuhrman, 1987].
Bacterial production (PB; mg C m3 d1) was estimated
by 3H-thymidine incorporation for 2 h incubation [Chen et
al., 2005], and converted with a thymidine conversion
factor of 1.18 1018 cell mole1 [Cho and Azam, 1988;
Fuhrman and Azam, 1982]. We are aware that published
thymidine and carbon conversion factors both vary by more
than 100-fold [Ducklow and Carlson, 1992]. To avoid
overestimation, lower published values of conversion factors were used here. To estimate bacterial respiration (RB), a
20% bacterial growth efficiency (i.e., PB/RB + PB) was
assumed [del Giorgio et al., 1997].
[11] Samples for protozoa (i.e., autotrophic and heterotrophic nanoflagellates as well as ciliate) were fixed with
neutralized formalin, and identified and counted using an
inverted epifluorescence microscope at 200 or 400 magnification [Chiang et al., 2003]. The cellular carbon
of nanoflagellates was converted using a factor of 4.7 1012 g C cell1 [Charpy and Blanchot, 1998], and values
were calculated for ciliates assuming standard geometric
shapes and a conversion factor of 190 1015 g C mm3
[Putt and Stoecker, 1989]. Protozoan respiration was estimated assuming a respiratory turnover rate of 45.6% of cell
C d1 [Stoecker and Michaels, 1991]. It also should be
noted that nanoflagellates were not measured in June 2005.
[12] Primary production (PP) was measured by the 14C
assimilation method, and incubated samples were collected
from 3 depths within ZE at stations occupied during daytime
[Gong and Liu, 2003; Parsons et al., 1984]. Samples were
prescreened through 200 mm woven mesh (Spectrum), and
1
inoculated with H14CO
3 (final conc. Ten mCi ml ) in 250 ml
clean polycarbonate bottles (Nalgene). Samples were incubated on board for 2 h in chambers filled with running
surface seawater and illuminated by halogen bulbs with a
light intensity corresponding to the in situ irradiance levels
[Gong et al., 1999]. To estimate the euphotic zone-integrated
PP at stations where incubation was not performed, an
empirical function as following was applied,
3 of 15
0:957
B
PP ¼ 2:512 * CS *Popt
*Kd1
;
Figure 3. Contour plots of salinity (SSS) in the surface water (2 – 3 m) of the ECS in (a) June and (b) August 2003,
(c) June and (d) July 2004, and (e) June 2005. Sampling stations during periods are marked by a cross; this also applies to
Figures 4, 6, and 7. Contour interval of salinity is 0.5 practical salinity units (psu), and the range of salinity is also shown at
the top of each panel. Area of the Changjiang Diluted Waters (CDW) is shown where SSS 31 psu.
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June 2005
(June 9 – 17)
July 2004
(July 10 – 19)
June 2004
(June 11 – 18)
Aug 2003
(Aug 13 – 23)
a
During specific sampling periods, where mean (±SE) values in parentheses and in brackets are for all sampling stations and for stations in the area of the Changjiang Diluted Water, respectively. Surface waters: 2 –
3 m. Variables include water temperature (Temp; °C), salinity (SSS; practical salinity units (psu)), nitrate (NO3; mM), chlorophyll a (Chl a; mg Chl m3), biomass (BB) and production (BP) of bacterioplankton,
biomass of nanoflagellate (NF; autotrophic and heterotrophic nanoflagellates) and total ciliates (TC), primary production (PP), and planktonic community respiration (CR), with units for biomasses and rates of mg C
m3 and mg C m3 d1, respectively. The area of the Changjiang Diluted Water (CDW; km2), where SSS 31 psu, is also included for reference; nd: no data measured.
b
Excludes data for unusual observation of oligotrophic ciliates at station 28 in June 2004 for analysis.
15063
435
3856
CDW
43062
24.8 – 381.8
(128.4 ± 31.5)
[167.7 ± 16.3]
3.7 – 284.0
(52.2 ± 9.5)
[152.2 ± 38.1]
16.8 – 311.5
(91.4 ± 13.8)
[136.9 ± 9.6]
2.7 – 433.6
(89.5 ± 17.5)
[273.9 ± 26.6]
0.0 – 428.5
(103.8 ± 24.5)
[256.6 ± 18.0]
CR
PP
9.5 – 61.2
(27.2 ± 9.0)
[41.2 ± 8.1]
2.6 – 70.9
(20.0 ± 5.1)
[63.7 ± 5.1]
7.3 – 102.7
(31.6 ± 7.9)
[70.7 ± 22.6]
3.3 – 973.8
(118.5 ± 73.3)
208.7
6.8 – 146.3
(32.0 ± 9.6)
[70.4 ± 22.1]
TC
0.1 – 15.5
(2.9 ± 0.8)
[4.4 ± 0.4]
0.1 – 17.6
(2.0 ± 0.7)
[5.2 ± 2.3]
0.0 – 151.4
(14.1 ± 8.7)b
[8.6 ± 1.0]
0.5 – 13.1
(4.8 ± 1.1)
[6.8 ± 1.0]
0.2 – 63.0
(4.0 ± 2.3)
[13.2 ± 4.1]
NF
2.5 – 52.6
(13.5 ± 3.2)
[10.7 ± 1.7]
0.0 – 11.8
(2.4 ± 0.5)
[2.5 ± 0.6]
0.0 – 7.6
(1.0 ± 0.3)
[2.4 ± 0.6]
0.0 – 94.0
(3.3 ± 2.8)
[1.1 ± 0.2]
nd
BP
1.7 – 54.3
(6.8 ± 2.7)
[10.7 ± 1.7]
1.7 – 16.7
(4.5 ± 0.6)
[7.2 ± 0.8]
1.3 – 18.7
(5.5 ± 1.0)
[11.7 ± 1.0]
2.1 – 40.3
(9.5 ± 1.2)
[21.6 ± 2.3]
1.3 – 27.6
(7.3 ± 1.2)
[15.8 ± 1.4]
11.8 – 53.1
(22.4 ± 2.9)
[26.3 ± 1.4]
1.3 – 20.8
(9.4 ± 1.0)
[4.0 ± 0.9]
6.7 – 40.4
(15.6 ± 1.8)
[12.5 ± 0.6]
6.6 – 23.1
(14.7 ± 0.7)
[17.4 ± 1.1]
3.3 – 1188.9
(95.9 ± 43.8)
[315.4 ± 72.6]
BB
Chl a
0.2 – 14.4
(3.6 ± 1.1)
[6.0 ± 0.5]
0.1 – 1.6
(0.4 ± 0.1)
[0.8 ± 0.2]
0.2 – 5.0
(0.9 ± 0.2)
[1.6 ± 0.2]
0.1 – 23.9
(1.6 ± 0.7)
[3.5 ± 0.3]
0.2 – 6.1
(0.9 ± 0.3)
[2.9 ± 0.3]
0.8 – 20.1
(5.2 ± 1.4)
[9.0 ± 0.7]
0.0 – 10.5
(1.0 ± 0.4)
[5.8 ± 1.7]
0.0 – 9.4
(0.8 ± 0.4)
[2.9 ± 0.8]
0.1 – 27.3
(3.0 ± 1.1)
[15.5 ± 2.0]
0.0 – 17.3
(0.9 ± 0.7)
[3.7 ± 1.1]
18.9 – 26.7
(23.1 ± 0.4)
[22.2 ± 0.2]
26.9 – 30.2
(29.0 ± 0.2)
[28.3 ± 0.3]
21.9 – 26.2
(24.2 ± 0.3)
[22.8 ± 0.1]
23.8 – 28.5
(27.1 ± 0.2)
[25.2 ± 0.2]
21.9 – 27.6
(24.8 ± 0.3)
[23.5 ± 0.2]
June 2003
(June 18 – 26)
27.0 – 33.8
(30.8 ± 0.5)
[29.2 ± 0.2]
29.6 – 34.4
(33.4 ± 0.2)
[30.7 ± 0.3]
30.1 – 34.5
(33.2 ± 0.3)
[31.0 ± 0.1]
23.4 – 34.7
(32.9 ± 0.4)
[28.4 ± 0.6]
25.3 – 34.5
(32.8 ± 0.4)
[29.4 ± 0.4]
NO3
SSS
Temp
Cruise
Table 1. Summary of Ranges and Mean Values for Key Physical, Chemical, and Biological Variables in Surface Waters of the ECSa
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CHEN ET AL.: COMMUNITY RESPIRATION IN THE ECS
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where CS, PBopt and Kd were the sea surface chlorophyll a
concentration, optimal biomass-specific photosynthetic rate
and the mean attenuation coefficient within ZE, respectively
[Gong and Liu, 2003]. A photosynthesis quotient (PQ) of 1
was assumed to convert from carbon to oxygen units
[Williams, 1998].
[13] The planktonic community respiration (CR) was
measured as decrease in dissolved oxygen (O2) during dark
incubation [Gaarder and Grann, 1927]. Incubation was
conducted at most of the stations in the ECS with duplicate
samples taken from several (4 – 6) depths within ZE at each
station. The treatment involved incubating bottles for 24 h in
a dark chamber [C.-C. Chen et al., 2003]. The difference in
O2 concentration between initial and dark treatment was
used to compute the CR. To convert respiration from
oxygen to carbon units, a respiration quotient (RQ) of
1 was assumed [Hopkinson, 1985; Parsons et al., 1984].
To compare and assess the relative contribution of major
functional groups to measured CR, an estimated rate of CR
was computed by summing individual estimated rates for
phytoplankton, bacteria, and protozoa (above).
3. Results and Discussion
3.1. Changjiang Diluted Water and Hydrographic
Patterns in the ECS
[14] The continental shelf of the ECS is composed of
several distinct water masses, including (1) coastal riverine
run-off, (2) intrusion and upwelling of the Kuroshio surface
and subsurface waters, (3) the Yellow Seawaters, and (4) the
Taiwan Strait waters [e.g., K.-K. Liu et al., 2003]. Regardless of its various sources, the largest spatial variations of
sea surface salinity and temperature in the ECS have been
observed in summer, mainly influenced by high river
discharge from the mainland China coast, especially from
the Changjiang River [Chen et al., 1994; Tseng et al., 2000].
The highest river discharge occurs in summer (44,600 m3
s1 during the period from June to September) as indicated
by the long-term monthly averaged rate at the seaward-most
station of the Changjiang River (Figure 2). River discharge
rates were also high during our study periods, ranging from
35,700 to 46,500 m3 s1 (in June of 2004 and 2005,
respectively; see Figure 2). Freshwater discharge from the
Changjiang River into the ECS usually mixes with seawater
to form the Changjiang Diluted Water (CDW) zone, which
generally has sea surface salinity less than 31 distributed
within the 60-m isobath region between the latitudes of
27 and 32°N along the coast [e.g., Beardsley et al., 1985;
Gong et al., 1996]. Similar physical hydrography was
observed in this study, with low-salinity water along the
coast and sea surface salinity (SSS) increasing from the
inner shelf to the slope, parallel with the shoreline; values of
SSS ranged from 23.36 to 34.70 (Figure 3 and Table 1). In
addition, there was a relatively shallow, low-salinity plumelike structure found in the northern ECS in most of our
study periods (Figure 3). This feature has been commonly
found in the Changjiang River plume in summer, and it
extends to the middle shelf, on average, toward the east or
the northeast [Beardsley et al., 1985; Chu et al., 2005].
[15] Surprisingly, however, there was no significant correlation between the Changjiang River discharge rate and
the area of the CDW (p = 0.81). Gong et al. [2006] has
5 of 15
Figure 4. Contour plots of nitrate (NO3) in the surface water (2 – 3 m) of the ECS in (a) June and (b) August 2003,
(c) June and (d) July 2004, and (e) June 2005. Contour interval of nitrate is 1 mM, and the range of nitrate concentration is
also shown at the top of each panel.
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7 of 15
12 – 75
(37.7 ± 4.5)
[22.6 ± 1.1]
20 – 107
(58.4 ± 3.6)
[44.4 ± 7.6]
20 – 85
(48.6 ± 4.1)
[29.6 ± 1.4]
14 – 110
(59.1 ± 4.8)
[23.6 ± 1.5]
17 – 86
(52.5 ± 4.1)
[24.8 ± 7.7]
June 2003
(June 18 – 26)
7 – 62
(28.2 ± 4.2)
[14.0 ± 0.7]
7 – 41
(20.9 ± 1.3)
[19.0 ± 1.5)
5 – 42
(20.4 ± 2.3)
[10.4 ± 0.5]
6 – 59
(19.9 ± 1.8)
[13.6 ± 1.2]
7 – 43
(16.8 ± 1.7)
[10.0 ± 3.2]
ZM
1.2 – 20.6
(5.5 ± 1.2)
[7.6 ± 0.7]
0.3 – 9.6
(3.3 ± 0.5)
[7.7 ± 0.6]
0.1 – 9.1
(2.5 ± 0.4)
[5.4 ± 0.5]
0.1 – 22.4
(3.7 ± 0.8)
[11.4 ± 1.4]
0.0 – 8.8
(2.3 ± 0.4)
[3.4 ± 3.2]
NO3
Chl a
0.3 – 30.8
(3.8 ± 1.6)
[3.3 ± 0.4]
0.2 – 1.7
(0.5 ± 0.1)
[0.9 ± 0.3]
0.4 – 3.9
(1.0 ± 0.2)
[1.7 ± 0.1]
0.3 – 10.6
(1.1 ± 0.3)
[2.3 ± 0.2]
0.3 – 14.2
(1.5 ± 0.5)
[4.8 ± 4.9]
8.5 – 40.3
(18.5 ± 2.2)
[19.2 ± 1.0]
3.0 – 18.8
(8.8 ± 0.6)
[5.3 ± 0.8]
7.9 – 76.2
(17.6 ± 3.2)
[12.0 ± 0.6]
7.3 – 16.2
(11.9 ± 0.4)
[14.3 ± 0.4]
8.0 – 956.7
(79.1 ± 35.4)
[261.0 ± 350.1]
BP
1.4 – 39.4
(6.8 ± 2.1)
[10.3 ± 1.3]
1.5 – 9.9
(3.9 ± 0.3)
[5.0 ± 0.8]
1.3 – 10.9
(3.5 ± 0.5)
[6.5 ± 0.7]
1.5 – 17.2
(7.2 ± 0.7)
[13.7 ± 0.6]
1.6 – 21.4
(5.9 ± 0.9)
[11.7 ± 6.0]
PP
3.2 – 232.2
(50.0 ± 14.4)
[57.5 ± 5.5]
1.6 – 40.4
(9.9 ± 1.5)
[20.8 ± 6.3]
3.2 – 98.7
(19.8 ± 4.5)
[40.2 ± 3.7]
2.7 – 486.9
(43.5 ± 16.4)
[125.2 ± 15.7]
1.8 – 176.6
(24.4 ± 7.7)
[80.7 ± 63.1]
IPP
170 – 3751
(1041 ± 230)
[1190 ± 100]
128 – 1221
(460 ± 43)
[635 ± 134]
202 – 1975
(695 ± 89)
[1098 ± 56]
213 – 9303
(1225 ± 310)
[2749 ± 319]
141 – 3224
(704 ± 129)
[1658 ± 941]
CR
27.2 – 412.6
(114 ± 25)
[101 ± 9]
11.9 – 237.4
(47 ± 8)
[69 ± 6]
9.7 – 184.9
(61 ± 8)
[74 ± 6]
7.0 – 183.4
(55 ± 9)
[144 ± 10]
6.7 – 420.4
(77 ± 19)
[190 ± 122]
ICR
1361 – 5515
(2865 ± 332)
[2239 ± 93]
769 – 20783
(2580 ± 621)
[2850 ± 373]
555 – 6732
(2424 ± 276)
[2032 ± 99]
555 – 6230
(2251 ± 202)
[3586 ± 411]
439 – 12439
(2708 ± 502)
[4668 ± 3827]
CHEN ET AL.: COMMUNITY RESPIRATION IN THE ECS
a
For different variables with mean (±SE) in the ECS given for each sampling period, where mean (±SE) values in parentheses and in brackets are for all sampling stations and for stations in the area of the Changjiang
Diluted Water, respectively. Units for euphotic depth (ZE) are meters. Variables include nitrate (NO3; mM), chlorophyll a (Chl a; mg Chl m3), bacterial biomass (BB; mg C m3) and production (BP; mg C m3 d1),
primary production (PP; mg C m3 d1), and planktonic community respiration (CR; mg C m3 d1). In addition, integrated values (per m2) of primary productivity (IPP; mg C m2 d1) and planktonic community
respiration (ICR; mg C m2 d1) over ZE are also shown. For reference, the mixed layer depth (ZM; m) is included.
June 2005
(June 9 – 17)
July 2004
(July 10 – 19)
June 2004
(June 11 – 18)
Aug 2003
(Aug 13 – 23)
ZE
Figure 5. Relationships between nitrate (NO3) versus
salinity in the surface water for all the pooled data. The
estimated linear regression (dashed line) with r2 and p values
is also shown.
Cruise
BB
suggested that accumulation of water near coastal areas
around the mouth and adjacent areas of the Changjiang
River might be one of the explanations for this weak
relationship. In addition, the flow rate was measured from
the seaward-most station (Datong hydrostation), the location of which (>500 km upstream from the river mouth; see
Figure 1) produced a considerable time lag of transport
between flow observations and river plume discharge. In
this paper, we define the area of the CDW as the water
surface where SSS 31, and we use it as an index of the
amount of freshwater water discharge into the ECS. We
estimated the area of the CDW (km2) to be 43,061 in June
2003, 15,063 in July 2004, 7,855 in June 2005, 3,855 in
August 2003, and 434 in June 2005 (Table 1).
[16] During the wet season (May to September) there is a
large discharge of riverine nutrients from the Chinese coast
into the ECS. The average dissolved inorganic N flux is
1010 mole month1 in this flood season, which is sufficient
to produce a mean concentration of 43 mM in the CDW
assuming no plankton uptake [Gong et al., 2003; S. M. Liu
et al., 2003; Zhu et al., 2005]. During our study, nitrate
levels reached 27.3 mM in surface waters, and most of the
elevated nitrate concentrations were observed in the CDW
(Figure 4 and Table 1). Spatially, distribution of isopleths of
surface nitrate concentration corresponds to patterns of SSS,
and the two variables were significantly correlated, according to both pooled data and individual data from each cruise
(all p 0.01; see Figures 3, 4, and 5). Surface nitrate also
showed a significant negative exponential decrease in
relationship to SSS, especially in the salinity range of 29
to 32. Similar nonconservative decreases in the nutrientsalinity relationship observed along the river/ocean mixing
gradient in the ECS were attributed to biological uptake
[Tian et al., 1993]. In addition, significant inverse relationships with SSS were also observed for other nutrients
(phosphate and silicate) using the pooled data (p < 0.001;
data not shown), further suggesting that riverine sources for
nutrients are being diluted within the plume ecosystem of
the ECS shelf.
Table 2. Range of Values Averaged Over the Euphotic Depth of the ECSa
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CHEN ET AL.: COMMUNITY RESPIRATION IN THE ECS
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Table 3. Linear Regressions Between Mean Nitrate (NO3)
Concentration in the Surface Water and the Mean of Averaged
Values of Chlorophyll a and Primary Production Over ZE of the
Entire ECS Against Area of the Changjiang Diluted Watersa
Variables
Slope
Intercept
r2
NO3
0.09
0.07
0.8
0.74
0.60
17.9
0.91b
0.90b
0.72
Chl a
PP
a
Slope, intercept, and r2 values of linear regression are shown. Please
refer to section 3.1 and Table 1 for definition of the CDW.
b
Significant at p = 0.01.
[17] In general, the amount of fluvial nutrient discharge to
the adjacent shelf tends to be proportional to the river flow
at seasonal or interannual scales for the ECS and other
coastal ecosystems [e.g., Dagg et al., 2004; Shen et al.,
2003]. In this study, the mean ± SE values of nitrate (mM) in
surface waters (5.2 ± 1.4 for June 2003, 3.0 ± 1.1 for July
2004, 1.0 ± 0.4 for August 2003, 0.9 ± 0.7 for June 2005,
and 0.8 ± 0.4 for June 2004; Table 1) and averaged values
over the euphotic zone (5.5 for June 2003, 3.7 for July
2004, 3.3 for August 2003, 2.5 for June 2004, and 2.3 for
June 2005; Table 2) were significantly correlated with the
area of the CDW (both p = 0.01), implying that nutrient
loading on to the ECS was scaled to China’s coastal river
run-off during the summer (Table 3). Although other
nutrient sources may also be important in some circumstances, e.g., upwelling and intrusion of the Kuroshio waters
[e.g., Cauwet and Mackenzie, 1993; K.-K. Liu et al., 2003],
riverine inputs of inorganic nutrients and organic matter
may have a profound impact on planktonic community
dynamics in the ECS shelf ecosystems [Gong et al., 2006;
Ning et al., 1988; Tian et al., 1993].
3.2. Autotrophic Planktonic Activities Associated With
the Changjiang River Discharge
[18] To compare planktonic activities, all biological
parameters (both biomass and rate) were integrated over
the euphotic depth. This was not only because our measurement was mostly done within ZE but also because the
ZE was on average deeper than the mixed layer depth in
summer in the ECS (Table 2). During study periods, the ZE
varied from 12– 110 m, with mean values ca. 40– 60 m, and
ZE was deeper in the middle (i.e., July and August) than the
early (i.e., June) summer in the ECS (Table 2).
[19] Biomass distribution of planktonic communities
within the CDW followed a consistent pattern with phytoplankton > bacterioplankton > protozooplankton, accounting for, on average, 65.2, 28.9, and 5.9% respectively of
combined planktonic biomass (mg C m3) over the study
periods. Phytoplankton biomass ranged from 0.1 to 23.9 mg
Chl m3 in the surface water (Table 1), with ECS blooms
reaching Chl a concentrations >20 mg Chl m3 [C. S. Chen
et al., 2003; Gao and Song, 2005]. Phytoplankton biomass
in the surface water was generally higher in the region of
the Changjiang River plume or the CDW (mean value =
3.96 mg Chl m3) than that in the middle to outer shelves
(mean value = 0.89 mg Chl m3) in the ECS (Figure 6
and Table 1). This is consistent with previous studies
documenting phytoplankton blooms in the Changjiang
River plume during May to August [Gao and Song, 2005;
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Wang, 2006, and references therein]. Diatoms have been
observed to be the dominant phytoplankton class in this
region, with a prokaryotes and eukaryotic flagellates also
abundant during summer cruises, in the CDW during this
period [Furuya et al., 2003]. Despite shallower ZE recorded
in the early summer, mean phytoplankton biomass was
higher early in the summer than in the middle of the
summer (Table 2). For example, phytoplankton biomass
(mean ± SE values; mg Chl m3; Table 2) in June varied
from 1.0 ± 0.2 (2004) to 1.5 ± 0.5 (2005) to 3.8 ± 1.6
(2003), while in July and August it varied from 0.5 ± 0.1
(2003) to 1.1 ± 0.3 (2004). Further linearly regression
analysis showed that phytoplankton biomass was positively
correlated with the area of the CDW (p = 0.01; Table 3),
implying that summer phytoplankton growth in the ECS
was strongly related to the Changjiang River discharge.
[20] Primary production in the surface water was also
high on several occasions, particularly in the CDW, with
rates in the range of 2.6 to 973.8 mg C m3 d1 (Table 1).
Integrated primary productivity was also high, with a mean
value of 791 mg C m2 d1, and rates ranging from 128–
9303 mg C m2 d1 (Table 2). These summer rates are
generally higher than those reported previously in the ECS
(mean = 515 mg C m2 d1 in the work of Gong et al.
[2003]). Mean primary production rates over ZE ranged
from 1.6 to 486.9 mg C m3 d1, with a relatively deep
euphotic depth (mean = 53 m; Table 2). These primary
production rates in the CDW are at the lower end of the
range of rates reported for pelagic coastal ecosystems
worldwide [Duarte and Agustı́, 1998, and references therein]. Rates also exhibited temporal variations similar to those
for Chl a, with mean (±SE) values (mg C m3 d1) of 50.0
(±14.4) for June 2003, 43.5 (±16.4) for July 2004, 24.4
(±7.7) for June 2005, 19.8 (±4.5) for June 2004, and 9.9
(±1.5) for August 2003 (Table 2). There was also a
marginally significant linear relationship between mean
values of primary production from each cruise and area of
the CDW (p = 0.07; Table 3). These results all suggested
that the size and orientation of the CDW influences both
biomass and production of phytoplankton, perhaps driven
by fluvial nutrient discharge from the Changjiang River
[e.g., Chen et al., 2007; C. S. Chen et al., 2003]. Similar
impacts have been observed in many estuaries and coastal
regions [e.g., Malone and Ducklow, 1990; Smith and
Demaster, 1996; Wawrik and Paul, 2004].
[21] The hypothesis of the importance of fluvial nutrients
in algal growth is supported by the significant linear
relationship between nitrate versus Chl a concentration
and primary production in the surface water, using data
pooled from all the cruises (both p < 0.001). In addition,
primary production was significantly related to nitrate for
four of the five individual cruises (all but June 2005). At an
individual cruise level, this relationship between nitrate and
Chl a concentration was significant only for August 2003,
suggesting the influence of other factors such as light and
phosphate levels [e.g., Gong et al., 2003; Harrison et al.,
1990]. Biomass of phytoplankton was significantly correlated with phosphate concentration in the surface water,
again indicated by both pooled data and data from each
cruise (all p 0.01; data not shown). Regardless of limiting
factors, the inverse relationship between surface Chl a
concentration and SSS (p < 0.001) emphasizes the over-
8 of 15
Figure 6. Contour plots of chlorophyll a (Chl a) in the surface water (2 –3 m) of the ECS in (a) June and (b) August 2003,
(c) June and (d) July 2004, and (e) June of 2005. Contour interval of Chl a is 0.5 mg Chl m3, and the range of Chl a
concentration is also shown at the top of each panel.
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arching importance of the Changjiang River and associated
CDW in regulating phytoplankton dynamics. In turn, stimulation of phytoplankton growth in the CDW may support
high levels of trophic dynamics in the ECS shelf ecosystem.
3.3. Heterotrophic Planktonic Activities in the ECS
[22] As expected, bacterial biomass and production
were higher in the CDW than in other areas in the ECS,
with mean (±SE) values of 39.0 (±13.9) and 24.1 (±8.1) mg
C m3 respectively for biomass, and 11.9 (±2.1) and
4.4 (±0.3) mg C m3 d1 respectively for production. Similar
patterns for summer bacterioplankton in the inner versus
middle to outer shelves of the ECS were reported from
previous studies [Chen et al., 2006; Shiah et al., 2006].
Enormous amounts of organic matter derived from both
autochthonous marine production and fluvial runoff are
available as potential substrates to stimulate bacterial
growth along the coast of the ECS in summer [Chen et
al., 2006; Shiah et al., 2006]. The importance of autochthonous production is supported by the significant linear
relationships found for Chl a concentration versus both
biomass and production of bacterioplankton with slope of
0.55 and 1.93, respectively, as indicated by surface water
data pooled from all cruises (both p < 0.01). There was,
however, no significant relationship for similar analyses
using vertically integrated bacterial rate and biomass data.
We suspect that protozoan grazing effects may have blurred
the phytoplankton – bacterioplankton relationship at these
scales since mean bacterial biomass was significantly related
to mean abundance of heterotrophic nanoflagellates and
ciliates (r2 = 0.35 and 0.34, respectively, p 0.001; data
not shown).
[23] Protozoa have been recognized as important microbial grazers and heterotrophic consumers in the ECS, as in
many coastal ecosystems [e.g., C.-C. Chen et al., 2003;
Sherr and Sherr, 1984]. Seasonally, the highest ciliate
abundance in the ECS was observed in summer when
bacterial production was stimulated by riverine inputs of
allochthonous organic carbon [Chiang et al., 2003]. In this
study surface water biomass of protozoan (i.e., autotrophic
+ heterotrophic nanoflagellate + planktonic ciliate) ranged
from 0.3 to 151.8 mg C m3 with mean ± SE value of 9.4 ±
2.0 mg C m3 (Table 1). Contribution of total protozoan
biomass in surface waters were generally similar for ciliates
and total nanoflagellates but varied in different years. For
example, nanoflagellate comprised 70% of protozoan
biomass in 2003 but only 23% in 2004. Although total
protozoan biomass has variable taxonomic composition, it
was still linearly regressed against SSS when all data were
pooled (r2 = 0.25; p < 0.001). Biomass values of nanoflagellates and ciliates were both linearly correlated with
SSS for pooled data (both p < 0.001). These results suggest
that variations in protozoan abundance were associated with
changes in bacterial growth induced by fluctuations in
organic substrates derived from the Changjiang River
[Chiang et al., 2003]. In turn, high production rate of
nanoflagellates with mean value of 0.46 mg C l1 h1 has
been observed in the southern ECS during high river flow
period [Tsai et al., 2005]. Significant linear relationships
that were found between the pooled data for bacterial
biomass versus both ciliates and heterotrophic nanoflagel-
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lates further support this interpretation (all p 0.001; data
not shown).
3.4. Effects of the Changjiang River Discharge on
Planktonic Community Respiration
[24] Planktonic community respiration (CR) provides an
integrated measure of heterotrophic activity in planktonic
communities [e.g., Hopkinson et al., 1989; Kemp et al.,
1994; Rowe et al., 1986]. In this study, CR in the surface
water ranged from 2.7 to 433.6 mg C m3 d1, with mean
(±SE) values (mg C m3 d1) of 128.4 (±31.5) for June
2003, 103.8 (±24.5) for June 2005, 91.4 (±13.8) for June
2004, 89.5 (±17.5) for July 2004, and 52.2 (±9.5) for
August 2003 (Table 1). The range in CR values measured
in this study nearly equals the previous compiled range of
rate (2.3 – 485.3 mg C m3 d1, assuming RQ = 1) for the
coastal, shelf and slope regions world wide [Biddanda et al.,
1994; Williams, 1984]. Values of CR averaged over ZE
exhibited a range similar to surface rates (Table 2). CR was
generally higher in the inner shelf and in the CDW
compared to the middle and outer shelves of the ECS
(Figure 7). CR was inversely related to SSS according to
either surface water or depth averaged rates pooled data
(r2 = 0.33 and 0.24, respectively, p < 0.001; see Figure 8),
further suggesting that CR in the ECS was mainly governed
by processes derived from the Changjiang River. River
discharge has been shown previously to regulate ecosystem
processes in many estuarine and coastal regions [e.g.,
Boynton and Kemp, 2000; Dagg et al., 2004; Shiah et al.,
2006; Smith and Hollibaugh, 1993; Wawrik and Paul,
2004].
[25] Biotic controls on CR were examined by regressing
these rates against phytoplankton, bacteria, and protozoa
biomass, as well as bacterial and primary production using
pooled data over ZE. CR was significantly related to all
these variables (all p 0.01). In addition, CR was significantly related to total planktonic biomass (i.e., the summed
biomass of phytoplankton, bacteria, and protozoa; r2 = 0.60;
p < 0.001) with a relationship almost identical to one
reported previously [see Chen et al., 2006, Figure 7]. These
results emphasize covariation in key ecosystem properties at
interannual scales.
[26] To assess the relative contribution of major functional groups to CR, we used physiological and allometric
relationships to estimate respiration rates of phytoplankton,
bacteria, and protozoa (see ‘‘Methods’’ for details). An
calculated rate of CR was computed by summing individual
rates for phytoplankton, bacteria, and protozoa, and this was
significantly related to measured CR with a slope of 0.96
(p < 0.001; see Figure 9a). The positive intercept of this
regression (22.8 mg C m3 d1; see Figure 9a) suggests that
‘‘estimated’’ CR rates were lower by 14%. This underestimation may be largely attributed to our omission of
mesozooplankton. Although phytoplankton had the highest
contribution to total plankton biomass (per mg C m3
basis), bacterioplankton contributions (60%) dominated
CR with phytoplankton (35%) and protozoa (5%) were also
important. Allometric considerations suggest that the smaller
cells of bacterioplankton might dominate CR [Fenchel, 2005].
Although measured CR was marginally related to the area
of the CDW (p = 0.058; see Figure 9b), ‘‘estimated’’ CR,
which included more stations than our measured values,
10 of 15
Figure 7. Contour plots of averaged values of planktonic community respiration (CR) over ZE in the ECS in (a) June and
(b) August 2003, (c) June and (d) July 2004, and (e) June of 2005. Contour interval of CR is 50 mg C m3 d1, and the
range of CR is also shown at the top of each panel.
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Figure 8. Relationships between salinity in the surface
water and averaged CR over the euphotic zone for all the
pooled data. The estimated linear regression (dashed line)
with r2 and p values is also shown.
Figure 10. Log-log relationships between averaged volumetric rates of primary production (PP, converted to O2 units)
versus (a) volumetric rates of CR and (b) the ratio of primary productivity to CR, i.e., the P/R ratio. Please note the
log scale in both axes. The relationships are also shown
as a power function of primary production with solid lines.
For comparison, the estimated power functions between
CR versus PP (CR = 1.1 PP0.72) and P/R ratio versus PP
(P/R = 0.91 PP0.28) are also shown with gray lines for reference [Duarte and Agustı́, 1998]. The horizontal gray dashed
line in Figure 10b is a guideline where the P/R ratio is equal
to 1.
Figure 9. Relationships between (a) measured values of
planktonic community respiration (CR) versus calculated
CR and (b) area of the Changjiang Diluted Waters (CDW)
versus mean (±SE) CR for both measured and estimated
(symbols and line marked in gray) data. See section 2.3 for
detailed methods used to calculate CR. Also shown are
linear regressions (dashed lines) with r2 and p.
was more strongly related to the CDW area (p = 0.01; see
Figure 9b).
[27] As is often the case for aquatic ecosystems [e.g.,
Duarte and Agustı́, 1998], CR in the ECS was significantly
correlated to primary production (PP) both in the pooled
data and in the data from each cruise. CR (g O2 m3 d1;
averaged rate over ZE) was significantly scaled as a power
function of PP (g O2 m3 d1; averaged rate over ZE) for
the ECS where CR = 0.58 PP0.46 (Figure 10a). Note that the
exponential (0.46) is the slope of the log-log regression.
This differs from the relation reported for other coastal
ecosystems in the world (CR = 1.1 PP0.72 in Table 1 of
Duarte and Agustı́ [1998]). This indicates that CR in the
ECS was generally less dependent on in situ primary
production compared to other coastal ecosystems. This
suggests that allochthonous organic materials transported
from the river into the ECS during the high-flow summer
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Duarte and Agustı́ [1998]), vertically integrated rates of P
(or IPP) were high compared to other continental shelf
systems, with mean values ranging from 0.5 to 1.2 g C
m2 d1 (Table 2). What is startling, however, is the
remarkably high mean rate of R (or ICR) calculated for
the integrated euphotic zone (ZE), where values range from
2.3 to 2.9 g C m2 d1 (Table 2). Evidently, both P and R in
the ECS, and particularly the CDW, are strongly stimulated
by nutrient and organic matter input from the Changjiang
River.
4. Conclusions
Figure 11. Relationships between planktonic community
respiration (CR) and particulate organic carbon (POC) in the
surface water in June 2004. The estimated linear regression
(dashed line) with r2 and p values is also shown. Please
refer to C.-C. Chen et al. [2003] for details of POC
measurement.
season provide important external substrates supporting
plankton respiration [Cauwet and Mackenzie, 1993; C.-C.
Chen et al., 2003; Deng et al., 2006]. High concentrations
of particulate organic carbon have been measured in the
surface water of CDW, with values reaching levels
approaching 481 mg C m3 and positively regressed with
CR (p < 0.001; see Figure 11).
3.5. Ratio of Production to Respiration and Its
Implication for Coastal Ecosystems
[28] The ‘‘P/R ratio’’ of primary production (PP) to CR
provides an index of metabolic balance in the ECS shelf
plankton community. The system can be considered autotrophic when P/R ratio > 1 or heterotrophic when P/R ratio
< 1. Calculated P/R ratios for ECS were compared with data
from other coastal ecosystems for perspective. It should be
noted that the estimated P/R ratios for ECS do not reflect the
entire plankton community because values for P (i.e., PP)
and R (i.e., CR) were integrated only over ZE rather than the
whole water column. Calculated P/R ratios for ECS ranged
from 0.01 to 4.06, with mean ± SE value of 0.42 ± 0.05 over
the entire study period (Figure 10b). This mean value was
much lower than the P/R ratio (=1.17) reported from other
coastal ecosystems [e.g., Duarte and Agustı́, 1998]. The
lower mean value in this study might be mainly attributed to
the fact that there were only a few stations with a P/R ratio
larger than 1, and these were mostly measured at stations
with high primary production (mean 166 mg C m3 d1
or 0.44 g O2 m3 d1).
[29] The P/R ratio can also be expressed as a power
function of primary production for ECS data, where P/R =
1.70 PP0.54 (p < 0.001; see Figure 10b). This power function
is similar to that described by Duarte and Agustı́ [1998],
where P/R = 0.91 PP0.28. The difference in slope between
two relationships reflects the generally lower P/R ratios in
the ECS shelf ecosystem (Figure 10b). Despite the fact that
the mean value (=0.42) of P/R ratio in the ECS during
summer was lower than the averaged value calculated from
previous coastal studies (i.e., P/R = 1.17 in the work of
[30] To understand better how a large river discharge (i.e.,
Changjiang River) impacts carbon cycling processes on the
continental shelf, five cruises in three consecutive summers
were conducted in the ECS. Results indicate a large fluvial
transport of nutrients from the Changjiang River into the
ECS during the summer period of maximum flow, and
elevated concentration of nitrate in the Changjiang Diluted
Water (CDW) area, with values reaching 27.3 mM in the
surface water. The spatial distribution of surface nitrate
concentration were negatively correlated with sea surface
salinity (SSS), indicating that river run-off as a nutrient
major source on the ECS shelf. Correspondingly, several
biotic variables, e.g., Chl a concentration, protozoan biomass, bacterial production, as well as planktonic community
respiration (CR), in the surface water were also significantly
increased with decreasing SSS. These all clearly illustrated
that the Changjiang River discharge has a vivid influence on
the ECS shelf ecosystem.
[31] To explore further whether the magnitude of impact
is scaled to the amount of river discharge, the area of the
CDW (where SSS 31 psu) was used as an index of the
relative discharge into the ECS [Gong et al., 2006, 1996].
As expected, the mean value of nitrate concentration from
each cruise was proportionally relative to the area of CDW.
This indicates that the amount of fluvial nutrients discharge
from the Changjiang River has corresponded to the magnitude of river run-off, which varied monthly or interannually
in the ECS. Phytoplankton biomass followed a pattern
parallel to that of nitrate. Furthermore, CR also followed
salinity dilution. CR, which varied monthly and interannually and was dominated by bacteria and phytoplankton,
was statistically related to total planktonic biomass (i.e.,
phytoplankton + bacterioplankton + protozoa). Planktonic
respiration was also strongly related to primary production,
and the ratio of production to respiration (P/R ratio)
integrated over the euphotic zone was low (mean ± SE =
0.42 ± 0.05) in the ECS in summer, compared to that
reported from other coastal ecosystems (i.e., P/R = 1.17 in
the work of Duarte and Agustı́ [1998, and references
therein]). This lower P/R value in the ECS suggests substantial inputs of allochthonous organic matters discharged
from the Changjiang River.
[32] Acknowledgments. This study is part of the multidisciplinary
Long-Term Observation and Research of the East China Sea program
(LORECS; NSC 95-2611-M-019-020-MY3; NSC 95-2611-M-019-021MY3), and it was supported by the National Science Council, Taiwan,
under grants NSC-94-2611-M003-001, NSC-95-2611-M-003-003-MY3,
and NSC-95-2918-I-003-007 to C.-C. Chen. This work was also partly
supported by Center for Marine Bioscience and Biotechnology, NTOU. We
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would like to thank Y.-F. Tseng, Chin-Chou Yeh, and Y.-J. Tszo for helping
with measurements on planktonic community respiration. We are also
indebted to the officers and crew of Ocean Researcher I for their assistance.
The authors are also grateful to associate editor, Piers Chapman, and two
anonymous reviewers for providing valuable and constructive comments to
improve the manuscript. Part of this work was done by C.-C. Chen during
his visit to the Horn Point Laboratory, University of Maryland Center for
Environmental Science, Cambridge, Maryland, United States, and we are
greatly appreciative of their support and friendship.
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K.-P. Chiang, Department of Environmental Biology and Fisheries
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