초록 ▼

연구목표
섬진강 하구관리를 위한 환경변화 연구 및 지속 관리 방안 도출

연구내용
○ 섬진강 하구역 지화학 및 기반생태계 특성의 시⋅공간적 변화
- 조석/유량 변화에 따른 염분 최대 확산 범위 규명
- 조석/염분 구배에 따른 지화학 특성 파악 및 영양염 총유출입 플럭스 산출
- 섬진강 하구 퇴적물에서의 유기물 분해 연구
- 기반 생태계(동⋅식물 플랑크톤 및 저서생물) 현황 및 자원 생물(재첩) 조사
○ 섬진강 배출물질(부유퇴적물/영양염류)의 정량 및 과거변화
- 부유퇴적물/영양염

연구목표
섬진강 하구관리를 위한 환경변화 연구 및 지속 관리 방안 도출

연구내용
○ 섬진강 하구역 지화학 및 기반생태계 특성의 시⋅공간적 변화
- 조석/유량 변화에 따른 염분 최대 확산 범위 규명
- 조석/염분 구배에 따른 지화학 특성 파악 및 영양염 총유출입 플럭스 산출
- 섬진강 하구 퇴적물에서의 유기물 분해 연구
- 기반 생태계(동⋅식물 플랑크톤 및 저서생물) 현황 및 자원 생물(재첩) 조사
○ 섬진강 배출물질(부유퇴적물/영양염류)의 정량 및 과거변화
- 부유퇴적물/영양염 농도 모니터링을 통한 배출량 정량화 및 과거 변화 분석
- 섬진강 퇴적체 연구를 통한 하구와 만(bay) 퇴적-지화학-광물학적 퇴적물 특성 및 고환경 복원
○ 섬진강 하구역의 지속가능한 이용을 위한 정책 연구
- 섬진강 하구 지속가능 이용 및 보전을 위한 대응방안 마련

예상 연구성과
○ Target 성과물: 섬진강 하구역 퇴적지화학 및 생태계 특성 정밀 자료 도출, 관련 과학적-기술적 논문, 우리나라 하구 환경 관리를 위한 하구둑 수문 건술 기초 기술(특허) 개발
○ 연구 성과 활용, 남해 연안의 지속 가능한 연안 환경 및 생태계 보존과 관리 정책 수립 기반 자료 도출
- 물 관리 정책을 통한 지자체간 갈등 문제 해결
- 환경⋅생태계⋅생물자원 특성연구를 통한 하구역 생산력 증대
- 섬진강 하구역 염해 피해 저감 정책 기초 자료 제공
○ 우리나라 하구역 환경⋅생태계 관리⋅보전 연구를 위한 기획

종료후 활용계획
○ 중앙 및 지방정부 하구역 관련 해양정책 실현을 위한 해양과학 지식정보로 제공-활용

(출처 : 요약서 5p)

Abstract ▼

Ⅱ. Results and Suggestions
For understanding the spatial-temporal variations of salinity distribution and their causes, and further for estimating the saltwater intrusion in the Seomjin River Estuary (SRE), horizontal-vertical distributions (a total of 75 times) of salinity were intensively inves

Ⅱ. Results and Suggestions
For understanding the spatial-temporal variations of salinity distribution and their causes, and further for estimating the saltwater intrusion in the Seomjin River Estuary (SRE), horizontal-vertical distributions (a total of 75 times) of salinity were intensively investigated in response to river discharges and tides at 18 sites of the estuary during three years (2015~2017).

For better understanding the way salinity distribution in an estuary reacts to external factors, furthermore, the long-term time series salinity data, which was continuously measured at an interval of 10 minutes in the station 14 (~15km area from the river mouth) during 893 days between 2015 and 2017, was acquired. We also investigated the influence of river discharge and tidal level on the salinity distribution for constructing the predictive model (predictive equation) of salinity intrusion (defined by the 1 psu-salinity contour near the bottom). The observation was taken up to 25km upstream from the river (estuary) mouth.

According to the results, the spatial-temporal variability of salinity in the SRE depends on the relative strengths of main forcing mechanisms including river discharge and tide as well as the peculiar bottom morphology of the estuary. The SRE is under the highly stratified condition throughout neap tides, but changes into the partially- or well-mixed condition during spring tides. Overall, the saline water mass with the relatively low salinity (< 5psu) was the most extensive during spring-high tides, stretching into up to 15km upstream in average, but the high-saline water mass (> 20psu) was extensively distributed during periods of neap-high tides, reaching to 12km in average.

On the basis of the long-term time series dataset of salinity and tidal water level, interestingly, the “saltwater residence” phenomenon widely occurred throughout the estuary during neap tides: the seawater did not retreated seaward with ebb flow, and thus the large saltwater pool with high salinity (approximately 15~25 psu) was formed in the bottom layer of the estuary, stretching into 16km upstream. This peculiar phenomenon occurred throughout periods of the neap tide coupled with low river discharge (< 30~40cms) and may be related with the bowl-shaped bottom topographic feature of the SRE. In SRE, accordingly, this “saltwater residence” phenomenon can be suggested as one of the main drivers of a large increase in salinity and saltwater intrusion.

To estimate the response of saltwater intrusion to changes in river discharge and tidal level, quantitative prediction models were developed from the regression analysis between the salinity and external factors: salinity (S) vs. river discharge (Q), and maximum distance (L) of 1 psu-salinity intrusion vs. river discharge and tidal levels (H). The models are as in the following: S = 1314.2Q^-1.568, L = 39.482Q^-0.248, and L = 3.10H + 12.0. In this study, furthermore, the integrated model considering both the river discharge and tidal elevation for estimating maximum saltwater intrusion distance was also constructed: L = -8.86logQ + 2.20H + 23.10. On the basis of the predictive equations, salinity of the SRE at the point (Seomjin Bridge) of 15km upstream has largely increased from 0.84psu in 2010 to 5.80psu in 2017, and also, average distance of saltwater (1psu) intrusion has remarkably extended from 14km upstream in 2010 to 18km in 2017. In the SRE, such a environmental change was also supported by an abrupt variation of sedimentary diatom assemblages after 1998~1999.

Meanwhile, maximum saltwater (1psu) intrusion distance observed between 2015 and 2017 was up to 24km upstream from the river mouth, which has moved to more than 2km inland, compared with that (21~22km in 0.3psu) of 2004~2005. Subsequently, our research showed that the sea environment (e.g., coastal bays) has been continuously expanded towards the upper part of the estuary, probably since 2000 as a result of large increases of salinity caused by the river discharge decrease. Furthermore, the quantity of fresh river water entering the estuary (environmental flow) to maintain the estuarine salinity gradient (less than 5psu at 15km upstream) was evaluated as ~4,000,000ton/day (45cms) at least in Songjung observation station.

According to a comparative analysis study using numerical models, the maximum salt intrusion length based on 1 psu was 21.8km at 390,000tons per day, the river discharge during the dry season, which is 5.1km longer than the 16.7km at 315 million tons per day during the wet season. After the development of Juam Dam, the river discharge decreased by 740,000tons and the maximum salt intrusion length was increased during the normal season, but the difference was very little during the dry season. The effect of the Daap intake facility was smaller than that of dam development in the wet season, but it increased in the dry season. It is analyzed that the effects of river sand extraction on salt water intrusion are mainly due to increased water depth which allows salt water to reach a more upstream zone of the river. As a result of the analysis of the effects of reclamation, it was concluded that the salt concentration was lowed by the reduction of the high water level, but the effect was disappeared and few changes were found in the salt intrusion length. The effect of the development of Gwangyang Bay was relatively smaller than the other factors, as the effects of the reduction in water surface area and the increasing of water depth offset each other.

The estuarine reaction of nutrients in the mixing zone of Seomjin Esturary were surveyed for 3 year (2015 to 2017). From the relationship between the salinity gradient and nutrient, we estimated the fluxes of riverine, estuarine addition and/or removal fluxes in the mixing zone, and fluxes from estuary to coastal water in the South Sea of Korea. The salinity and temperature in the mixing zone were varied with seasonally. The spatiotemporal variation of nutrients concentration with salinity gradients suggested that the biogeochemical cycles of nutrients can be controlled by seasonal variability. Ovreall, the nutrients recycled by estuarine reaction in the mixing zone were transpered into coastal water. Consequently, the biogeochemical cycles in the mixing zone of Seomjin River-Estruary system could be import factor for controlling the coastal water.

In order to understand the ecological function of permeable sand sediment in Seomjin River-Estuary system, we estimated the degradation rate of organic carbon in the sediment using the flow on-off method with O2 planar optode. In addition, the net ecosystem metabolism with season were estimated be the non-invasive eddy correlation method for 12 times from 2015 to 2017. The oxygen consumption rate of the sediment in Galsa Bay were ranged from –16.8 to - 128mmol m^-2 d^-1 (averaging –78.7mmol m^-2 d^-1). The net ecosystem metabolism on the permeable sand sediment were estimated as 9.8mmol m^-2 d^-1 of the gross primary production (GPP), –13.9mmol m^-2 d^-1 of the respiration (R), and –4.16mmol m^-2 d^-1 of the net ecosystem metabolism (NEM). Meanwhile, the GPP, R, and NEM were estimated as 14mmol m^-2 d^-1, –11.9mmol m^-2 d^-1, and 2.1mmol m^-2 d^-1, respectively, which were corresponded to 50% of sediment oxygen comsuption rate in sand sediment. One of most important natural function of in the permeable sediment, the filteration rates by permeable sand sediment of Galsa Bay were estimated bewteen 16 and 480 L m^-2 d^-1 (averaging 6×10⁶ton d^-1). This rate suggest that the capacity of natural filteration volume would be 6 time higher than the sewage treatment plants in Yeosu city.

Evaluating the changes of biotic and abiotic factors and including ecological characteristics along salinity gradient in Seomjin River estuary was also conducted. For nutrients, nitrate + nitrite and silicate concentrations were strongly inputed from fresh water, whereas ammonium and phosphate concentrations were provided from the bottom layer of Gwangyang Bay by tidal water mixing. The concentration of suspended particulate matter (SPM) was high in seawater and low in freshwater. Distribution of phytoplankton assemblage was greatly depended on seasons, which is divided into freshwater and seawater species. In particular, diatoms were dominant in most seasons, and Cryptophyceae was dominant only in autumn. Distributional pattern of mesozooplankton community was characterized by three different environmental zones i.e., seawater, estuary and freshwater. The abundances of mesozooplankton community gradually decreased from estuarine waters towards upstream at the Seomjin River Estuary. The protozoan Noctiluca scintillans was widely and dominantly distributed. The next dominant taxon in the middle-downstream regions are comprised of a copepod Acartia omorii during winter, and Oikopleura spp. and immature copepods pertaining to genus Paracalanus during autumn.

The dominant taxon in the upstream region are consisted of Sapphirina spp. during winter, Sinocalanus tenellus, Tortanus forcipatus and barnacle larvae during spring, and Paracalanus parvus s.l., Acartia sinjiensis and A. ohtsukai during summer. For fish and mollusks, total of 48 species of mollusks and 31 species of fishes were detected from the eDNA. Major species of mollusks were Crassotrea ariakensis, Corbicula japonica, Assiminea hiradoensis, and Ruditapes philippinarum, and of fish were Mugil cephalus, Helichoeres tenuispinis, Engraulis japonicus, and Cyprinus carpio. Distribution of mollusks and fishes in the Seomjin river estuary were affected by salinity.

To investigate the spatial distributions of the macrobenthic communities in the Seomjin River estuary, faunal samples were collected at 7 sites by seasonal sampling using a small grab (0.025m²) from the winter of 2015 to the autumn of 2017. A total of 163 macrobenthic fauna occurred, and the mean density was 1,865 ind. m^-2, and the mean biomass was 204 g⋅wet m^-2 during this study period. The highest number of species and density appeared among polychaetes, whereas the most biomass was contributed by mollusks due to the presence of an estuarine clam, Corbicula japonica in all seasons. A maldanid polychaete species, Praxillella praetermissa was the most dominant species in the marine region of over 30psu during all seasons. C. japonica and Hediste diadroma were dominant species in the middle region of the Seomjin River where the salinity was less than 10 psu. Salinity was found to be the most important environmental factor affecting the formation of macrobenthic communities, and salinity and TOC seemed as the main contributors to the spatial distribution of estuarine macrobenthic faunas in the study area.

The population density of C. japonica was low at st. 11, while the relatively high density was found at st. 13 and st. 15. in the low salinity area. The feeding activity of C. japonica stoped above 20psu but was high at 5 to 15psu. The growth rate of C. japonica was measured up to 1mm per month. Juvenile clams of 3-4mm shell length was observed in spring, and they grew to 12~14mm for one year. Another estuary clam, Potamocorbula nimbosa appeared dominantly at st. 11 where the densities of C. japonica was low since July, 2017. P. nimbosa is classified as a potentially strong competitor to C. japonica because it has the same feeding type and food source with C. japonica. The optimum salinity range of brackish oyster Crassostrea ariakensis was found in 25-30 psu, which is well adapted based on their active feeding.

The sedimentation environments of the Seomjin river-mouth and Gwangyang Bay has evolved from estuary to delta front and delta plain through prodelta stage. After the subaerial exposure at ~10 kyr BP, water depths increased gradually until 7.5 kyr BP and the high stand was maintained for ~ 4 kyrs. Since 1.7 kyr BP, rapid deposition of coarse sands with a sedimentation rate of 9.0 m/kyr formed a thick sand body of >20 m thickness. In the past 20 years, the amount of suspended sediment discharge from the Seomjin river has significantly decreased from ~400,000 ton/yr to ~50,000 ton/yr, based on the model simulation.

The surface sediments of Gwangyang Bay show high concentrations of heavy metals (Cr, Co, Ni, Cu, Zn, and Pb). The concentration decreases gradually toward the outer sea, and then it incrases again in the outer sea. Such spatial characteristics are consistent with the results of the organic carbon analysis, indicating that the sediments on the outer sea flowed from the areas of other than the Seomjin river. Based on the analysis of rare earth elements and the rock-magnetic properties of the sediment, the western sediments from the boundry of Yeosu reveal similar properties of the Central South Yellow Sea sediments and the Huksan Mudbelt, while the eastern sediments are probably originated from the Nakdong river.

(출처 : SUMMARY 12p)

목차 Contents

• 표지 ... 1
• 제 출 문 ... 3
• 과제 요약서 ... 5
• 요 약 문 ... 7
• SUMMARY ... 12
• 목차 ... 17
• 표목차 ... 18
• 그림목차 ... 21
• 제1장 서 론 ... 35
• 제2장 국⋅내외 기술개발 현황 ... 37
• 제1절 국내 기술개발 현황 ... 37
• 제2절 국외 기술개발 현황 ... 38
• 제3장 연구개발 수행 내용 및 결과 ... 40
• 제1절 섬진강 하구역 염분의 장⋅단기 시⋅공간적 변동 특성과 예측 ... 40
• 제2절 섬진강의 염수침입거동 수치해석 ... 129
• 제3절 섬진강 염하구 화학환경 특성 ... 217
• 제4절 기반 생태환경 특성과 자원생물 ... 261
• 제5절 지질 분야 ... 367
• 제6절 정책 및 요약 ... 399
• 제4장 종합 결론 ... 406
• 끝페이지 ... 408