초록 ▼

• 산샤댐 프로젝트(Three Gorges Dam project)가 종료된 2009건보다 1년 늦은 2011년 11월초에 산샤댐 최종 수위 목표인 175 m 에 도달했으며, 향후 본격적인 수위유지를 지속할 것이다. 2003년 산샤댐 1차 물막이 공사이후의 여름철 장강 담수 및 부유사 매출량 감소율이 이전보다 각각 약 13% 와 56% 로 현저하게 감소하였는데, 이는 산샤댐 건설로 인해 동중국해(East China Sea)로의 장강(Changjiang River) 유출량이 크게 영향 받음을 입증하고 있다.
• 2006년부터 20

• 산샤댐 프로젝트(Three Gorges Dam project)가 종료된 2009건보다 1년 늦은 2011년 11월초에 산샤댐 최종 수위 목표인 175 m 에 도달했으며, 향후 본격적인 수위유지를 지속할 것이다. 2003년 산샤댐 1차 물막이 공사이후의 여름철 장강 담수 및 부유사 매출량 감소율이 이전보다 각각 약 13% 와 56% 로 현저하게 감소하였는데, 이는 산샤댐 건설로 인해 동중국해(East China Sea)로의 장강(Changjiang River) 유출량이 크게 영향 받음을 입증하고 있다.
• 2006년부터 2011년까지 7윌 하순과 8윌 초순 사이에 저염수 핵은 주로 제주도와 장강 하구의 중간해역에서 관측되었다. 조사해역에서 저염수 분포가 산샤댐 건설로 인하여 변화하였다는 뚜렷한 증거는 나타나지 않은 반면 저염수의 거동은 바람장에 의하여 조절되고 있음을 보여주었다. 저염수는 동쪽으로 이동하면서 수평적으로는 주변해수와 활발한 혼합과 수직적으로는 약층 수심대의 내부파 등에 의한 수직 혼합으로 고염화되는 것으로 나타났다.
• 산샤댐 완공 이후 장강희석수의 영향을 받는 지역에서 질산염 농도는 증가하는 경향을 보였고, 규산염과 부유물질은 점차 감소하는 경향을 보이고 있다. 이러한 영양염 농도 및 비의 변화와 부유물질의 감소가 표층해역에서 나타나 향후 이에 대한 식물플랑크톤의 생체량 빚 군집구조의 변화가 나타날 것으로 예측된다.
• SeaWiFS 자료를 이용하여 장기적인 변화를 분석한 결과, 2003년 이후부터 10 g/㎥ 농도 이상의 부유물질이 현저히 줄어든 형태를 보였는데 이것은 장강 하구를 통해 동중국해로 유엽되는 부유물의 양이 감소하였기 때문으로 판단되고, MODIS과 GOCI 등 다양한 위성자료를 이용하여 녹조 및 적조에 대하여 분포 특성 및 모양, 이동 패턴 등을 분석하였고, 해색위성을 이용하여 추정된 알고리즘 개발을 통하여 1997년부터 2007년까지 장기적인 장강의 영향을 모니터링한 결과 유기탄소는 장강으로부터 유입되는 담수의 영향으로 공간적인 변화가 이루어지고 있음을 알 수 있다.
• 2006년~2011년 하계 조사결과 장강 저염수의 세력에 따라 동중국해 북부해역의 식물플랑크톤 생채량과 군집구조 빚 열차생산력이 변화하였다. 엽록소 a 농도는 장강 저염수의 영향이 강한 서쪽수역에서 높고 쿠로시오 분지류의 영향을 받는 동쪽 수역에서 낮았다. 박테리아 개채수 빚 생산력은 염분과 유의한 음의 상관관계를 보여, 장강 희석수의 유엽이 하계 동중국해 북부 해역의 박테리아의 성장을 증가시킬 수 있음을 시사하였다. 그동안 연구결과로부터 장강하구의 영양염 농도증가와 탁도감소에 의한 식물플랑크톤의 빈번한 bloon에 의해 N/P 비율이 증가하며, 이러한 저염수의 이동에 의해 동중국해의 식물플랑크톤 성장과 열차생산력이 낮아질 가능성이 있다.
• 본 연구과제를 수행하면서 장강 저염수 순환모델이 개선되었으며 저염수의 이동을 정확히 계산할 수 있게 되었다 그 결과 2010-2011년에는 장강 저염수의 이동을 예측하여 저염수 피해에 대비할 수 있도록 하였고, 장강 저염수를 따라 이동하는 해파리 , 가시파래 , 해양쓰레기의 이동상황을 파악할 수 있었으며, 산샤댐 건설로 인한 염분의 영향을 계산할 수 있었다 산샤댐 건설로 장강 유출량이 줄어든 것은 장강 유역의 큰 염분증가로 나타나지만 우리나라 주변해역에서는 강수량변화나 계절변화 등에 의한 변화보다 아직은 크지 않은 것으로 보인다.

Abstract ▼

1. Variations of Changjiang freshwater and suspended sediments discharges.
The water level alter completion of the Three Gorges Project would be to reach 175 m high in late October or early November, 2009, but the final water level reach was done in early November, 2010. Monthly water discharges

1. Variations of Changjiang freshwater and suspended sediments discharges.
The water level alter completion of the Three Gorges Project would be to reach 175 m high in late October or early November, 2009, but the final water level reach was done in early November, 2010. Monthly water discharges have generally decreased since the TGD impoundment in 2003. Water discharges in summer time(May-October) in 2003~2010 decreased by about 13% compared with the same months of historic average. Moreover, Monthly sediment discharges have changed much more dramatically than water discharges.
Maximum reduction of sediment discharges during in summer season(May-October) in 2003~2009 was about 56% of their discharges in 1995~2000.
2. Variations of Changjiang Diluted Water
The hydrographic surveys in the area south of Jeju-do are carried out in the period between later July and early August in 2006-2011. The low salinity core was generally observed in the area of mid point between Jeju-do and Changjiang mouth. No clear evidence for the effect of the construction of Three Gorge Dam on variations in CDW distribution is observed. CDW distribution in the servey area is governed more by the wind field. Salinity of CDW is gradually increased by lateral mixing with surrounded high salinity water and vertical mixing in the halocline due to internal processes such as internal gravity waves.
3. Distribution of nutrients and suspended sediment.
Water masses in the northern East China Sea were classified into four types based on the T-S distribution : the CDW an, the TCW, YSMW, and YSCW. In the eastern part of the study area, surface waters were characterized by the TCW, and the western surface were characterized by the CDW during all six curies. Surface concentration of nutrients were affected to the CDW in the western parts of study area, and to the TCW in the eastern parts where the surface water of TCW had been known to the oligotrophic. After the construction of the TGD, nitrate concentration may be increased in the study area. In the vertical distribution of nutrients at the C line, nutrient concentration between the station C02 to c04 showed increasing trend in the bottom layer due to the fronts of water massed. The property of surface nutrient distribution may be affected to the surface distribution of chlorophyll-a concentration in the study area, which showed high concentration in the western parts and low concentration in the eastern parts. We observed the distribution of suspended sediment in the northern East China Sea. Lower suspended sediment but higher particulate organic carbon concentrations were observed in CDW. Concentrations of suspended sediment were gradually reduced year by year in the northern ECS surface water in 2006~2011. This phenomenon was caused by the TGD construction, which is verified from in-냐셔 measurement and old data.
4. Monitoring of the ocean environmental changes using satellite data
To investigate the ocean environmental changes using satellite data in the South Sea of Korea(SSK) (included East China Sea(ECS)), in-situ, SeaWiFS, MODIS and GOCI data are used to determine the spatial and temporal variations of the suspended matter, red tide/green algal blooms, and particulate organic carbon(POC). First, in order to monitor the spatial and temporal variability of suspended sediment in the ECS, 11-year SeaWiFS data(1998-2008) are used.
After 2003 higher suspended sediment distribution(10g/㎥) was apparently devreased in the ECS(especially estuarine area of the Yangtze River), because of decreasing suspended sediment with river discharge. Second, the spatial pattern and distribution of large green algae patches and red tide using MODIS and GOCI satellite data were analyzed. During the spring and summer season of 2008 and 2009, the extensive green macroalgae blooms covered in China coastal area as well as the SSK(ECS). During 2011 GOCI detected the massive green algal bloom located from west to east in Yellow Sea and ECS offshore. The results suggested that the green algae originated from the China coast. Third, the estimate of paritculate organic carbon(POC) from SeaWiFS monthly data(1997-2007) used to determine the spatial and temporal variation of Changjiang Diluted Water(CDW). First mode of the analysis was spatially and temporally correlated with the area influenced by the Changjiang River discharge. Second mode of the analysis was temporally less sensitive with the Changjiang River discharge but spatially correlated with north-south patterns. Relatively higher POC variations during 2000 and 2003 were shown in the southern East China Sea. These patterns during 2004 and 2007 moved to the northern East China Sea. This phenomenon was better related to spatial variations of wind-direction than the amount of Changjiang River discharge, which is verified from in-situ measurement.
5. Lower trophic level ecosystem
Results of summer sruises in 2006~2011 showed that summer phytoplankton biomass and community structure as well as primary production were variable in relation to strength of low salinity Changjiang diluted water(CDW) in the northern East China Sea. Chlorophyll a concentrations were higher in the western part of the East China Sea where the effect of low salinity CDW is stronger, and they were comparatively lower in the eastern part of the East China Sea where the effect of the Kuroshio warm current is stronger. however, chlorophyll a concentrations and primary production were decreased when the very low salinity(<27 psu) CDW was developed in 2010. Concentrations of fucoxaanthin and peridinin, indicative pigments of diatoms and dinoflagellates showed increasing trend toward the western part of the East China Sea where the effects of low salinity CDW were stronger. However, decreasing trends were observed for those indicative pigment in the low salinity(<27 psu)waters. The average primary productions were variable ranging 456.4±168.2~1008.1±681.5 mgCm^-2d^-1 during the study period of 2006~2011. The higher productions were observed in the western part of the East China Sea suggesting the link between increasing phytoplankton biomass due to low salinity CDW with dincreasing primary production. However, there were no clear increasing primary production trend were observed when the lowest salinity waters were developed in 2010 and 2011. Bacterial abundances and productions showed large variations in summer, ranging from0.3~4.8x10⁹ cells ℓ^-1 and 0.2~36.6 mg C m^-3d^-1, respectively. Both bacterial abundances and productions showed negative relationships with salinity, suggesting that input of CDW could stimulate bacterial growth in the northern part of the East China Sea. Further, ratios of euphotic depth-integrated bacterial production to primary production tended to increase at low salinity waters, showing that input o f CDW might increase the energy flow through microbial foodweb in the East China Sea. However, bacterial growth decreased significantly in samples with low-salinity water less than 27 psu, suggesting that massive input of CDW might distrub ecosystem of the East China Sea. These results suggested that summer plankton ecosystem in the East China Sea is sensitive to changes in strength and extension of the low salinity CDW. Particularly, frequent phytoplankton bloom events probably due to increasing nutrient concentrations of Changjiang estuary and decreasing turbidity may result in increasing N/P ratio, and transport of such low salinity water may lower the phytoplankton growth and primary production in the East China Sea.
6. Ocean circulation modeling
The Changjiang Diluted Water(CDW) seriously influences the marine ecosystem of the south sea of Korea by its low salinity in summer. Its seriousness had been known after massacre around Jeju Island in 1996, however, at that time we did not know when and where CDW comes from, and so how to cope with the situation except finding CDW by chance in the west sea of Jeju Island. During the time, the ocean circulation model for CDW have been developed through this project and now we are able to forecast the movement of CDW from the early stage. Also, we can systematically monitor the movement of CDW by complementary cooperation with forecasting and observation. In 2010 and 2011, we could control the CDW situation by monitoring the movement of CDW and providing the informations through internet in Jeju province. The two year's success shows that we can successfully forecast the distribution and movement of CDW. CDW brings troublesome materials such as low salinity water, jellyfish, green tide, marine litter in the adjacent seas of Korea as well as nutrients. In this project, we calculated their movements with the ocean circulation model to provide the way to cope with them. At present, the model includes only physical process, however, if the model deals with biological or chemical processes in the future, we can forecast the change of marine ecosystem and provide the way to reduce possible damage by climate change. According to the model calculation, the decrease of the Changjiang river discharge by the construction of Three gorges Dam results in large salinity increase around the river mouth, but small in the adjacent seas of Korea compared with other variations such as seasonal variation. Although its influence has not been large enough to be distinguished from other variations, it is expected larger in a long time period. Therefore, the observation needs to be continued to understand clearly its influence of the construction of Three Gorges Dam.