长江大坝建设对东海生态系统的影响：营养盐比例变化与初级生产力下降

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本文主要探讨了长江（中国最大的河流）对东海（East China Sea，ECS）生态系统的影响，特别是由于三峡大坝（The Three Gorges Dam，TGD）建设导致的变化。长江的庞大径流量和营养物质输入对该海域的生产力和营养素比例具有显著影响。每年长江注入东海的水量达到约924.8万亿立方米，输送的无机氮（N）、磷（P）和硅（Si）分别为6.1万亿摩尔、7.7亿摩尔和9.4万亿摩尔。在洪水季节，长江淡水与海水混合形成富含营养的长江稀释水（Changjiang Diluted Water，CDW），这一区域是高生产力（Primary Productivity，PP）区，对于渔业和大气二氧化碳吸收至关重要。然而，自1994年三峡大坝开始建设以来，这种自然环境正在发生变化。大坝的建设控制了洪水、改善了航道并提供了水电资源，但同时也影响了沉积物负载、径流季节性和营养物质输入到沿海地区的模式。据先前的研究，洪水季节（6月至8月）时，由于高营养负荷和适宜的生长条件，东海的传统营养富集区（TNR）通常有高的初级生产力。然而，关于大坝建设对TNR地区生态系统具体影响的出版数据相对有限。在2003年大坝首次填充阶段后，我们的研究发现，受大坝影响的河口区域，如达通站，硅与氮的比例从1998年的1.5下降到2004年的0.4，沉积物负载显著减少约55%。更为关键的是，从1998年到2003年，高洪水季节的初级生产力大幅度下降了86%。这些结果表明，三峡大坝的建设已经对东海的生态平衡产生了显著的影响，包括营养物质比例的改变和生产力的降低，这可能会影响到海洋生物群落的结构和功能。此外，文章还暗示了大坝建设对海洋生态系统的一般性影响，即随着全球各大河流上大坝的增多，营养物质和沉积物的输入到沿海地区正在减少，从而间接地影响了整个海洋生态系统的动态。因此，三峡大坝的建设不仅仅是局部的水利工程，它还引发了对大型水利工程对全球海洋生态影响的广泛关注和深入研究。通过了解和分析这些影响，科学家们可以更好地预测和管理人类活动对海洋生态系统可能产生的长远效应，以实现可持续发展的目标。

Reduction of primary production and changing of nutrient ratio in the

East China Sea: Effect of the Three Gorges Dam?

Gwo-Ching Gong,

Jeng Chang,

1,2

Kuo-Ping Chiang,

1,3

Tung-Ming Hsiung,

Chin-Chang Hung,

Shui-Wang Duan,

and L. A. Codispoti

Received 19 January 2006; revised 1 March 2006; accepted 6 March 2006; published 15 April 2006.

[1] It has been documented that the global proliferation of

dam construction on the major river has reduced nutrient

and sediment loading to coastal environments. As a

consequence, dams can impact marine ecological systems

by changing nutrient concentrations and ratios in the coastal

zone. From 1998–2004, we conducted a high resolution

oceanographic investigation of the East China Sea (ECS)

before and after the first filling phase (June 2003) of the

Three-Gorges Dam (TGD). We found that the Si:N ratio in

the River affected region changed from 1.5 in 1998 to 0.4 in

2004 with sediment loading significantly reducing (about

55%) at the Datong station after June 2003. Most importantly,

we found that the PP had declined by 86% between 1998 and

2003, both measured during the high flood season. The

results suggest that the ECS ecosystem may respond

sensitively to changes in the nutrient supply arising from

the TGD project.

Citation: Gong, G.-C., J. Chang, K.-P.

Chiang, T.-M. Hsiung, C.-C. Hung, S.-W. Duan, and L. A.

Codispoti (2006), Reduction of primary production and changing

of nutrient ratio in the East China Sea: Effect of the Three Gorges

Dam?, Geophys. Res. Lett., 33, L07610, doi:10.1029/

2006GL025800.

1. Introduction

[2] The Changjiang (Yangtze) River, the fifth largest river

in the world in terms of water discharge, empties into the

northwest corner of the East China Sea (ECS), one of the

largest fisheries in the world. Annual water discharge

reaches 924.8  10

1

, and the nutrient flux of

inorganic nitrogen (N), phosphate (P) and silicate (Si) is

6.1  10

, 7.7  10

, and 9.4  10

mole y

1

, respec-

tively [Tian et al., 1993; Liu et al., 2003; Duan et al., 2000].

Fresh water discharge before 2003 peaked between June

and August, during which time the mixing of fresh water

and seawater forms the Changjiang Diluted Water (CDW)

zone in the ECS [Beardsley et al., 1985; Gong et al. , 1996;

Chen et al., 2003]. The CDW generally has a salinity of less

than 31 psu, and as being influenced by the southwest

monsoon, it is widely distributed through out a trapezoidal

region within the 60-m isobath between the latitudes of 27

and 32 N (Figure 1). This traditionally nutrient-rich (TNR)

region has been characterized by high primary productivity

(PP), which develops beyond the turbid zone associated

with the river mouth [Gong et al., 2003]. For this reason, the

ECS has become an extremely rich fishing ground and an

important sink for atmospheric CO

[Tsunogai et al., 1999;

Peng et al., 1999; Chen and Wang, 1999].

[

3] Notwithstanding the wealth and the importance of the

ECS, the construction of the Three-Gorges Dam (TGD) was

begun in 1994 about 2000 km upstream from the mouth of

the Changjiang River, with the first filling stage of the

reservoir completed in June 2003. Slated to begin full-scale

operations in 2009, this dam will be the largest dam in the

world. The TGD will have important positive effects, such

as controlling flooding, aiding navigation, and hydroelec-

tricity, but it will also change sediment loading, seasonality

of flow rate and nutrient flux to coastal area (W. C. Jones

and M. Freeman, Schiller Institute Grea t Infrastructure

Projects, Three G orges Dam, 2005, available at http://

www.schillerinstitute.org/economy/phys_econ/phys_

econ_3_gorges.html, hereinafter referred to as Jones and

Freeman, 2005). According to previous high-frequency

investigations, high PP usually appears in the TNR region

of the ECS between June and August (i.e., flood season)

due to high nutrient loading and appropriate growth con-

ditions [Gong et al., 2003]. However, there is little pub-

lished data to show how the ecosystem of the TNR region in

the ECS is affected by the construction of the TGD. In this

paper, we will report the preliminary response of the ECS’s

ecosystem to the construction of TGD, especially in terms

of shifts in river discharge, nutrient flux, sediments loading,

PP, and phytoplankton species shift. This paper will also

help in our understanding of how marine ecosystems are

influenced by giant dam construction.

2. Sampling and Methods

[4] The data presented in this study were collected from

six cruises between June 1998 and July 2004 on board the

R/V Ocean Researcher I. The date of each of the six was

arranged in summer, because the summer cruises are the

time of maximum river discharge and hence the biggest

signal in the reduction in the river discharge after damming.

The stations where samples were taken on each cruise

(except for July 2001) are shown in Figure 1. Nutrient

(silicate and nitrate), chlorophyll (Chl a) concentrations and

light-saturated PP were measured according to Gong et al.

[1996, 2003]. The abundance of algal groups was deter-

mined using CHEMTAX, a matrix factorization routine for

GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L07610, doi:10.1029/2006GL025800, 2006

Institute of Marine Environmental Chemistry and Ecology, National

Taiwan Ocean University, Keelung, Taiwan.

Also at Institute of Marine Biology, National Taiwan Ocean University,

Keelung, Taiwan.

Also at Department of Environmental Biology and Fishery Science,

National Taiwan Ocean University, Keelung, Taiwan.

Institute of Bioscience and Biotechnology, National Taiwan Ocean

University, Keelung, Taiwan.

Department of Marine Science, Texas A&M University, Galveston,

Texas, USA.

Horn Point Laboratory, University of Maryland Center for Environ-

mental Science, Cambridge, Maryland, USA.

0094-8276/06/2006GL025800$05.00

L07610 1of4

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