REMOTELY-SENSED INVESTIGATION OF THE IMPACT OF YANGTZE RIVER’S
DISCHARGE TO THE EAST CHINA SEA
Chuqun CHEN1*, Shilin TANG1,2 ,Ping SHI13, and Haigang ZHAN1
1.
2.
3.
LED, South China Sea Institute of Oceanography, Chinese Academy of Sciences, Guangzhou
510300, Guangdong, China.
Laboratory of Digital Earth Sciences, Center for Earth Observation and Digital Earth, Chinese
Academy of Sciences, Beijing, 100190, China.
Yantai Institute of Coastal Zone Researches for Sustainable Development, Chinese Academy of
Sciences, Yantai 264003, Shandong, China.
* Email address: [email protected]
ABSTRACT
The influence of big rivers’ discharge on the ocean is an
important theme for land-ocean interaction studies. The
Yangtz River (Chang Jiang) is the longest river in China
and Asia, and the third-longest in the world. It has a mean
annual runoff of 905 billion m3, and averagely carries
about 0.433 billion tons of sediments and 0.15 billion tons
of dissolved matters to the East China Sea (ECS) each year.
The terrestrial materials provide rich substrates for
biological activities in the ocean.
In this study, the monthly average discharge data of the
Yangtze River were collected from 1997 to 2002, and the
monthly average water-leaving radiance (Lw) and the
chlorophyll_a concentration (Chl_a) in the ECS were
processed and calculated from SeaWiFS data acquired from
December 1997 to December 2002. Then the correlations of
the monthly average discharge to the monthly average Lw at
555nm and Chl_a were analysed respectively. And a series
correlative coefficient image maps were achieved.
Index Terms—ocean color, SeaWiFS, Land-ocean
interaction, correlative coefficient image map, East China
Sea. Yangtz River.
1. INTRODUCTION
The land-ocean interactions are the main occurent geoprocesses on the Earth’s surface, which have continuously
impacts on marine ecosystem and environment. The
material flux transferred by river runoff from the continent
to the ocean is the important theme of land-ocean
interactions studies (Shen et al. 2001). The runoff brings not
only great quantity of freshwater, but also lots of suspended
sediments and dissolved matters to the ocean, and provides
with rich nutrients for marine phytoplanktons, which form
the basis of aquatic food webs. The terrestrial materials
provide rich substrates for biological activities and alluvial
978-1-4244-3395-7/09/$25.00 ©2009 IEEE
processes. They make the coastal and continental shelf sea
areas becoming the most productive areas of the ocean(chen
& Wang 1999). It is believed that most terrestrial materials
are detained and consumed in the continental shelf areas. In
order to understand the global material fluxes, it is
important to study the material fluxes at the local scale and
then synthesize it over the regional and global scales. The
rivers and continental shelf seas are excellent sites for
studyng the material fluxes and the land-ocean interactions.
Mnay investigation on land-ocean interactions have
been conducted in the Yangtze River estuary and the East
China Sea(ECS) since 1980s. The investigation includes the
transportation of sediments from the Yangtz River to ECS
(Yang et al 1983; John et al 1985, Su and Wang 1989), The
numerical calculation of the sesdiments transportation (Peng
and Hu 1997;Yuan et al, 1999), the materials fluxes from
the Yangtz River to ECS (Hu et al 2000) and their influence
on the continental shelf ecosystem (Gao & Wang 2008).
The rivers’ discharge is typically rich in suspended
sediments and dissolved matters. The optical properties of
the continent-original freshwater is remarkably different
from those of the oceanic water. Generally, the continentoriginal water with suspended sediments has much stronger
remote sensing reflectance (water-leaving radiance) than the
oceanic water. The river plume can be detected by satellite
sensors (e.g. Nikolay et al 2005).
In this paper the Satellite ocean color data acquired by
SeaWiFS were utilized to investigate the influence of the
discharge from the Yangtz Rivers on the ECS.
2. RESEARCH AREA
The Yangtz River (Changjiang) estuary and the Esat China
Sea (ECS) are the research area. The Yangtze River (Chang
Jiang) is the longest river in China and Asia, and the thirdlongest in the world, after the Nile in Africa and the
Amazon in South America. The river is about 6,380 km
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IGARSS 2009
long and with 1,800,000 km² of catchment area. According
to the hydrological records from 1950 to 2000, the river has
a mean annual runoff of 905 billion m3, with variation from
676 billion m3 to 1360 billion m3, and averagely carries
about 0.433 billion tons of sediment with variation from
0.239 billion tons to 0.678 billion tons, and about 0.15
billion tons of dissolved matters to ECS each year. The
terrestrial materials provide rich substrates for biological
activities and alluvial processes in the estuary and ECS.
The Yangtze River delta is one of the most developed
regions and becomes an important center for industry,
transportation and economy in China. The biggest port,
Shanghai Port, is located at the estuary of Yangtze River. In
order to effectively utilize the water resources of Yangtze
River, the Three Gorges Dam, the biggest hydrological
project in the world, was built at the middle reaches of the
river near Yichang city, Hubei Province in late 2002, The
dam was designed to have feasibility for normal storage
level of 175 m. On 1 st June 2003, the reservoir began its
storage, the water height reached at 135 m on 10 June and at
139 m on 5 November, 2003. It is widely concerned that the
impact of the Three Gorges Dam to the environment of the
river and ECS. One of the main influences of the dam on
ECS is that the dam would change of the river’s discharge
which is the main terrestrial input to ECS. It is important to
know how the discharge of Yangtze River affects on the
ECS.
coefficient was calculated pixel by pixel, and a series
correlation coefficient image maps were achieved.
4. RESULTS
The correlative analysis shows that the correlative
coefficient between discharge and water-leaving radiance at
555nm is negative in the main area around the river’s
estuary, and only in a narrow zone along the coast the
correlative coefficient is positive. It is interesting that the
distribution pattern of the area with high negative
correlative coefficient (from -0.6 to -0.9) just like a huge
alluvial fan with a radius of more than 400 km from the
river’s mouth to the fan’s front edge, which expands
eastward to the south of Cheju Island at 126.35°E and
southward to the Taiwan strait (Fig. 1).
3. METHODS
The river’s discharge is typically rich of suspended
sediments, which could be taken as an indicator of
terrestrial matters and the discharged freshwater. On the
other hand, the suspended sediments is the main contributor
of the water-leaving radiance of coastal waters. The higher
the suspended sediments concentration in waters, the higher
water-leaving radiance.
In this study, the monthly average discharge data of the
Yangtze River were collected from 1997 to 2002, and the
monthly average water-leaving radiance data in the area of
the ECS were processed and calculated from SeaWiFS data
acquired from December 1997 to December 2002. The
ocean color SeaWiFS data with full spatial resolution (1.1
km) were processed by SeaDAS (SeaWiFS Data Analysis
System V5.4). The chlorophyll-a concentration were
retrieved with the SeaDAS default algorithms. Then the
correlations of the monthly average discharge to the
monthly average water-leaving radiance centered at 555nm
and chlorophyll-a concentration were analysed respectively.
On considering the delayed influence of the revier discharge,
the correlations of the monthly average discharge to onemonth, two-month and three-month later water-leaving
radiance and the satellite-retrieved chlorophyll_a
concentration were analysed respectively. The correlative
Fig.1. The distribution of correlative coefficient between the monthly
average discharge and monthly average water-leaving radiance at 555nm.
However the correlative coefficient between discharge
and SeaWiFS-retrieved chlorophyll-a concentration is
positive around the esturay, although the value is smaller
(varing from 0.1 to 0.6) and the distribution area of the
correlative confficient with chl_a is smaller than that with
the water-leaving adiance. The distribution pattern of the
positive correlative confficient is not a typical shape to an
alluvial fan (Fig.2).
Fig.2. The distribution of correlative coefficient of the monthly average
discharge and the monthly average SeaWiFS-retrieved Chl_a
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The correlations of discharge to one-month and twomonth delayed Lw and Chl_a have similar charaters to that
of their own un-delayed data. However, the correlations of
discharge to three-month delayed Lw and Chl_a are
different. The distribution pattern is also different. The
correlative coefficient between discharge and the threemonth delayed water-leaving radiance Lw is positive in
most area of ECS(Fig.3), althuogh the value of the
correlative coefficient is quite low. And around the esturay
an alluvial fan-shaped distribution can be identified.
Fig.3 The distribution of correlative coefficient of the monthly average
discharge and three-month delayed SeaWiFS Lw at 555nm.
The correlative coefficient between discharge and the
three-month delayed Chl_a is positive in most area of ECS
(Fig.4), and the value of the correlative coefficient is also
quite low. And in the middle area of ECS, along the
discharge direction, negative correlative coefficient can be
found.
negative correlative coefficient between the monthly
average discharge and monthly average water-leaving
radiance shows that the suspended sediments do not expand
to far away.
The distribution pattern of the negative correlative
coefficient of the discharge to the water-leaving radiance is
in the shape of an typical alluvial fan, which showed the
directly-affected area in the ECS from the Yangtz River’s
discharge, although the forming mechanism of the negative
correlation is unclear.
The correlative coefficient between the discharge and
the chlorophyll_a concentration is positive in the area
around the estuary. The river discharge brings a lot of
nutrients for the phytoplanktons. The more the discharge,
the more nutrients and the more phytoplanktons and higher
chlorophyll_a concentration. And the distribution pattern is
not in a typical alluvial fan for its edge is blurry and not
regular.
The satellite ocean color data with huge coverage and
high spatial resolution is useful for land-ocean interaction
investigation. This study revealed that the Yangtz River can
directly affects the ECS as far away to more than 400km
from the discharge point.
In order to check the influence of the Three Gorges
Dam on the ECS, it is necessary to analyse the data after its
storage (in 2003). In the near future, we will consider to use
the satellite ocean color data acquired by MODIS or by
MERSI aboard FY-3 (Chinese Meteorological satellite) for
the investigation.
6. ACKNOWLEDGEMENT
This research was jointly supported by the key project from
The Chinese Academy of Sciences (KZCX1-YW-12-01)
and the national 973 project from the Ministry of Science
and Technology of China (2001CB409708). Many Thanks
to the SeaWiFS project within NASA GSFC for providing
the SeaWiFS data and the SeaDAS software.
7. MAIN REFERENCE
Fig. 4 The distribution of correlative coefficient of discharge and threemonth delayed SeaWiFS-retrieved Chl_a.
5. DISCUSSION
The water-leaving radiance at 555 nm is mainly contributed
from the suspended sediments, which is mostly from the
river discharge. At the beginning, it was expected that the
correlative coefficient between the discharge and the waterleaving radiance should be positive in the area around the
estuary. However, the area with positive correlative
coefficient is much smaller than that the our expected. The
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