Korean Journal of Environmental Biology (환경생물)

Korean Society of Environmental Biology (한국환경생물학회)
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Water quality characteristics and spatial distribution of phytoplankton during dry and rainy seasons in Bunam Lake and Cheonsu Bay, Korea

부남호·천수만의 갈수기와 강우기 수질 오염 특성과 식물플랑크톤의 공간 분포 특성

  • Lee, Minji (Ecological Risk Research Divisions, Korea Institute of Ocean Science & Technology) ;
  • Seo, Jin Young (Ecological Risk Research Divisions, Korea Institute of Ocean Science & Technology) ;
  • Baek, Seung Ho (Ecological Risk Research Divisions, Korea Institute of Ocean Science & Technology)
  • 이민지 (한국해양과학기술원 위해성분석연구센터) ;
  • 서진영 (한국해양과학기술원 위해성분석연구센터) ;
  • 백승호 (한국해양과학기술원 위해성분석연구센터)
  • Received : 2021.01.28
  • Accepted : 2021.05.20
  • Published : 2021.06.30
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Abstract

Since the construction of a dike in 1983, the water quality in the Bunam Lake has continued to deteriorate due to algal bloom caused by agricultural nutrient loading. Therefore, we evaluated the change in water quality and phytoplankton ecological characteristics in Bunam Lake and Cheonsu Bay, Korea. Water temperature, salinity, dissolved oxygen, chemical oxygen demand (COD), chlorophyll, and phytoplankton community were surveyed in April during the dry season and in July during the rainy reason. As a result, during the dry period, phytoplankton proliferated greatly and stagnated in the Bunam Lake while a very high population of cyanobacteria Oscillatoria spp. (8.61×107 cells L-1) was recorded. Most of the nutrients, except, nitrate and nitrite, were consumed due to the large growth of phytoplankton. However, during the rainy period, concentrations of ammonia, phosphate, silicate, nitrate, and nitrite, were very high towards the upper station due to the inflow of fresh water. Cyanobacteria Oscillatoria and Microcystis spp. were dominant in the Bunam Lake during the rainy period. Even in the Cheonsu Bay, cyanobacteria dominated due to the effect of discharge and diatoms, such as, Chaetoceros spp. and Eucampia zodiacus, which also proliferated significantly due to increased levels of nutrients. Since the eutrophication index was above 1 in Bunam Lake, it was classified as eutrophic water and the Cheonsu Bay was classified as eutrophic water only during the rainy season. In addition, a stagnant seawater-derived hypoxia water mass was observed at a depth of8m in the Bunam Lake adjacent to the tide embankment and the COD concentration reached 206 mg L-1 in the bottom layer at B3. Based on this result, it is considered that the water quality will continue to deteriorate if organic matters settle due to continuous inflow of nutrients and growth of organisms while the bottom water mass is stagnant.

부남호는 하굿둑 건설 이후 수질이 급격히 악화되어 농업용수로 사용이 불가할 만큼 본래의 기능을 상실하였다. 따라서 해수 교환이나 유통의 필요성이 있으나, 극히 오염된 부남호의 물을 대량 방류할 시 문제가 야기될 수 있기 때문에 시기에 따른 환경 조사가 중요하다. 따라서 본 연구에서는 갈수기(4월)와 강우기(7월)에 천수만과 부남호의 수질 및 식물플랑크톤 분포 특성을 조사하였다. 갈수기에는 부유 생물이 정체되어 부남호 내에서 남조류 Oscillatoria spp. 세포수가 8.92×107 cells L-1로 대증식하였고, Nitrate+Nitrite을 제외한 영양염 대부분이 소비되었다. 강우기에는 담수 유입의 영향으로 부남호에서 용존 영양염이 크게 증가하였고 부남호에서 식물플랑크톤이 대증식하였다. 강우기 방류의 영향으로 천수만 내측 역시 높은 농도의 생물량을 보였다. 강우기 부남호에서 우점했던 남조류 Oscillatoria spp.와 Microcystis spp.가 천수만 내측에서도 다수 출현하였으며, 해수에서는 Cheatoceros spp., Eucampia zodiacus와 같은 규조류가 빠르게 증식하였다. 부영양화 지수는 부남호 내측에서 1을 초과하여 부영양 해역으로 평가되었다. 천수만은 강우기에 담수 방류의 영향을 받을 경우 부영양화 해역으로 평가되었다. 특히 부남호 내 방조제에 인접한 B3 정점의 8 m 이상 수심에서 정체된 해수 기원의 강한 빈산소 수괴가 관찰되었고, Nitrate+Nitrite를 제외한 영양염 농도가 극단적으로 높았다. 특히 COD 농도가 206 mg L-1로 심하게 오염된 상태임을 확인하였다. 따라서 부남호는 지속적으로 육상기원의 영양염이 누적되며, 식물플랑크톤의 대발생과 침강으로 수질이 더욱 악화될 가능성이 높은 수역으로 판단되었고, 이를 근본적으로 해결하기 위해서는 해수유통을 통한 생태계 복원이 필수적이다.

Keywords

Acknowledgement

본 논문은 한국해양과학기술원 '생지화학 순환 및 해양환경변동 연구(E99912)', 충청남도 '부남호 역간척에 따른 해양환경 영향분석 및 대응방안 마련 연구(PG52000)'의 지원을 받아 수행되었다.

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