한반도 연안 해역에서 해저 지하수 유출의 환경 생태학적 중요성

Environmental and Ecological Consequences of Submarine Groundwater Discharge in the Coastal Areas of the Korea Peninsula

  • 김규범 (서울대학교 지구환경과학부) ;
  • 황동운 (서울대학교 지구환경과학부) ;
  • 류재웅 (서울대학교 지구환경과학부) ;
  • 이용우 (서울대학교 지구환경과학부)
  • KIM GUEBUEM (School of Earth and Environmental Sciences/RIO, Seoul National University) ;
  • HWANG DONG-WOON (School of Earth and Environmental Sciences/RIO, Seoul National University) ;
  • RYU JAE-WOONG (School of Earth and Environmental Sciences/RIO, Seoul National University) ;
  • LEE YONG-WOO (School of Earth and Environmental Sciences/RIO, Seoul National University)
  • 발행 : 2005.11.01

초록

전통적으로 육지로부터 해양으로의 물질 수송은 눈에 보이는 강을 통해서 이루어 진다고 생각했었다. 하지만, 해저 열수 및 대기를 통한 물질 유입도 상당한 부분을 차지한다는 것이 지난 수십 년 동안 밝혀졌다. 최근에는 해저를 통한 지하수 유출이 물질 수송에 있어 강물 못지 않는 중요한 역할을 한다는 것이 밝혀지고 있다. 특히, 한반도 주변에서의 연구 결과, 해저 지하수 유출이 다른 지역에 비해 더 중요한 해양학적 역할을 한다는 것이 밝혀졌으며, 그 몇 가지 예는 다음과 같다. 남해의 여러 내만 해역에서는 연안의 오염된 지하수가 유출되면서, 과잉의 영양염류가 공급되어 적조 등의 생태계 변화에 큰 영향을 미친다. 암석의 공극률이 큰 제주도에서는 해저 지하수의 흐름이 전세계적으로 아주 높은 범주에 속해, 지하수의 오염이 적어도 연안 생태계 및 부영양화에 결정적 역할을 한다. 황해에서는 전 해양으로 유출되는 지하수 및 지하수에 의한 영양염류 유출량이 황해로 흐르는 양자강 등의 큰 강 못지않게 중요한 역할을 한다. 동해는 해양 퇴적물의 투수성이 높고 단층대가 발달해 있어, 여름철 지하수 유출량이 일반 대륙연안에 비해 아주 크다. 한편, 하구둑이 건설되어 있는 낙동강 하구역에서 댐 안쪽 담수와 바깥쪽 해수 사이의 수위차에 의해, 강물의 방류량이 적고 댐의 수위가 높은 경우 해저 지하수의 유출이 훨씬 더 높게 나타났다. 여태까지 밝혀진 자료를 토대로 볼 때, 해저 지하수 유출은 한반도 주변에서 육상 오염물질을 해양으로 수송하는 가장 중요한 통로 중의 하나이며, 갯벌 생태계, 적조, 산호 생태계, 및 연안 오염에 결정적으로 영향을 미칠 것으로 판단된다. 따라서, 해저 지하수 유출을 고려한 연안 오염 부하량 측정, 샨사댐의 영향 예측, 적조 및 부영양화 원인 규명 등의 연안 환경 정책 수립이 시급하다.

Recognition has emerged that nutrient inputs from the submarine discharge of fresh, brackish, and marine groundwaters into the coastal ocean are comparable to the inputs via river discharge. The coastal areas of the Korea peninsula and adjacent seas exhibit particular importance in the role of submarine groundwater discharge (SGD), in terms of the magnitude of SGD and associated continental material fluxes. For example, in the southern sea of Korea, SGD transports excess nutrients into the coastal regions and thus appears to influence ecosystem changes such as the outbreak of red tides. Around volcanic island, Jeju, which is composed of high permeability rocks, the amount of SGD is higher by orders of magnitude relative to the eastern coast of North America where extensive SGD studies have been conducted. In particular, nutrient discharge through SGD exerts a significant control on coastal ecosystem changes and results in benthic eutrophication in semi-enclosed Bang-du bay, Jeju. In the entire area of the Yellow Sea, tile submarine discharge of brackish groundwater and associated nutrients are found to rival the river discharges into the Yellow Sea, including those through Yangtze River, Han River, etc. In the eastern coast of the Korea peninsula, SGD is significantly higher during summer than winter due to high hydraulic gradients and due to wide distribution of high permeability sandy zones, faults, and fractures. On the other hand, in the estuarine water, downstream construction of the dam in the Nakdong River, SGD was highest when the river discharge was lowest (but water level of the dam was highest). This suggests that even though there is no visible freshwater discharge into this estuary, the discharge of chemical species is significant through SGD. On the basis of the results obtained from the coastal areas of the Korea peninsula, SGD is considered to be an important pathway of continental contaminants influencing tidal-flat ecosystems, red tides, and coral ecology. Thus, future costal management should pay great attention to the impact of SGD on coastal pollution and eutrophication.

키워드

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