Asan Bay Research Articles

Comparing the environmental impacts of pollution from two types of industrial zones on the coast

IntroductionThe construction of coastal industrial zones has significantly impacted the marine environment, with the extent of these effects varying based on the type of industrial activity. This study compares the environmental impact of two prevalent types of industrial zones along South Korea’s coast: ironworks and shipyards.MethodsWe assessed heavy metal pollution near these industrial zones using the Pollution Load Index (PLI) and Nemerow Pollution Index (Pn). To evaluate the impact of heavy metals and organic matter on macrobenthic communities, we employed redundancy analysis (RDA) and Spearman correlation analysis. Additionally, we used the AZTI’s Marine Biotic Index (AMBI), Multivariate AMBI (M-AMBI), and Benthic Pollution Index (BPI) to gauge the ecological quality of the affected marine environments.Results and discussionOur findings indicated that the biodiversity and abundance of species near shipyards were significantly lower than those near ironworks. Results of PLI and Pn revealed that the ecological risk posed by heavy metals from shipyard activities was significantly higher than from ironworks. The AZTI’s Marine Biotic Index (AMBI), Multivariate AMBI (M-AMBI), and Benthic Pollution Index (BPI) demonstrated that the ecological quality of Asan Bay (ironworks) is better than that of Dangdong Bay (shipyard). RDA analysis identified Lumbrineris longifolia, Ancistrosyllis hanaokai, and Theora fragilis as biological indicators for assessing heavy metal and organic matter pollution. Spearman correlation analysis indicated that BPI and species richness index are effective indicators for evaluating such pollution. Overall, the negative impact of shipyards on the marine environment was significantly more significant than that of ironworks. Our study provides valuable insights for the South Korean government in managing coastal industrial zones and formulating relevant policies.

Changes in the suspended floc properties by bed erosion in a macrotidal muddy flat: Case of Asan Bay, Korea

Intertidal flats have closely connected sediment transport systems with tidal channels. The properties of suspended sediments derived by horizontal advection and local erosion were examined under various current and wave. A field campaign was conducted over two weeks (October 17–31, 2021) in the Asan intertidal flat. Suspended sediments were in the form of flocs, which are clumps of particles, with an average floc size (davg) of 70–275 μm. The maximum current velocity and water level at each tidal cycle continuously decreased from 0.19 to 0.04 m s−1 and from 5 to 2 m, respectively. In accordance with the hydrodynamic conditions, continuous decrease in davg from spring to neap tides was superimposed by flood-ebb variations in davg. Geological heterogeneity between channels and flats can be significantly influenced by tide and wind conditions. Under tide-dominant conditions, the spring tidal current was strong enough to transport macroflocs with davg of 200–500 μm into the intertidal flats. The grown macroflocs up to 1.6 times of davg at early flood tide were deposited in the flats during the slack tide and transported back to the channels by ebb tidal current. Under wind-dominant conditions, the suspended flocs originated primarily from the bed by erosion. The deposited macroflocs or microflocs were entrained into water column and transported to adjacent tidal channel as microflocs or flocculi. The structure of the advected flocs had more varied density in the range of 42–147 kg m−3, compared to the eroded flocs. Under severe erosion, the structure of suspended flocs was similar to that of advected flocs despite their smaller size. This suggests that bed erosion supplied more porous flocs into the water column than those transported by advection. Consequently, the intertidal flats are at an increased risk of erosion due to the diverse structure of flocs.

Ecological risk assessment of heavy metals in surface sediments and their impact on macrobenthos in Asan Bay, South Korea

Bay ecosystems with unique economic and ecological value are more vulnerable to heavy metal pollution than other marine ecosystems. In South Korea, rapid economic development has exacerbated heavy metal pollution in bay environments. This study analyzed concentrations of seven heavy metals and the structure of macrobenthic community in Asan Bay. Five heavy metal indices (PLI, Pn, RI, TRI, and MERMQ) were used to assess ecological risk. Additionally, spearman correlation, biota–environment matching (BIO-ENV), and redundancy analysis (RDA) were utilized to determine the influence of heavy metals on macrobenthic communities. Although average concentrations of seven heavy metals were below sediment quality guidelines (SQGs), the average concentration of Cd was close to the threshold effects level (TEL). The nemerow pollution index (Pn) and the potential ecological risk index (RI) indicated that Cd was the primary heavy metal contributing to ecological risk. Spearman correlation, BIO-ENV, and RDA indicated that heavy metals were the main environmental factors influencing macrobenthic communities in Asan Bay. However, five heavy metal indices (PLI, Pn, RI, TRI, and MERMQ) did not show a response to the macrobenthic communities. Overall, low concentrations of heavy metals have a certain negative impact on macrobenthic communities in Asan Bay. This study can serve as an important reference for marine environmental protection and policy-making in Asan Bay.

Contribution of local erosion enhanced by winds to sediment transport in intertidal flat

Field work combining in-situ mooring and erosion experiments was conducted in the intertidal flat of Asan Bay to reveal the relationship between sediment erodibility and external forcing and the contribution of local erosion to sediment transport. A total of 25 tidal cycles occurred during the mooring period with 6-h submergence and 5.7-h air exposure. The erosion rate (E) for sediment bed during air exposure was 0.007 g m−2 s−1, which was 36% of E (0.019 g m−2 s−1) during submergence. Although the sediment bed was influenced by consolidation during air exposure, the erodibility of the submerged bed was closely associated with the unconsolidated deposits of sediments newly supplied from tidal channel and bed shear stress (τcw) induced by current-wave interactions. In particular, τcw could be enhanced by strong winds, which depended on the ratio (Hs/h) of significant wave height and water level, directly disturbing the sediment bed. Under weak winds (Hs/h < 0.06), the newly deposited sediments with high erodibility increased the bed elevation. A small amount of the sediment bed was eroded (E: 0.006 g m−2 s−1), as a floc erosion, with a slight decrease in suspended sediment concentration (SSCT). This increased the contribution (57.2%) of eroded sediments to SSCT. Under strong winds (Hs/h > 0.06) with enhanced τcw, meanwhile, the erodible sediment in the bed was depleted accompanied by a decrease in bed elevation. A large amount of sediment bed was eroded (E: 0.025 g m−2 s−1), as a surface erosion, resulting in the rapid increase in SSCT and the enhanced seaward sediment flux. The sediments eroded from the bed were supplied to water column accounting for 86.8% of SSCT. This suggests that seaward sediment transport under strong winds could be caused by surface erosion shifting from floc erosion in the intertidal flat.

Origin and Establishment Period of Mahan Mounded Tombs

마한 분구묘의 연구에서 개념과 용어, 분포와 출토유물, 시공간상의 전개과정 등 상당한 부분이 아직도 베일에 가려져 있고, 그 실체에 대해 논쟁이 지속되고 있다. 이 중에서 가장 핵심적인 논쟁은 분구묘의 기원과 성립시점이라 할 수 있다. 이 글에서는 최근 자료와 기존 자료의 검토를 통해 마한 분구묘의 기원과 성립시점을 살펴보았다. 분석결과, 먼저 성립기 마한 분구묘의 공통적인 특징으로 구릉 정상 입지·독립 분포·방형계 평면 형태와 단(인)장·수석리와 송국리문화 유물 부장이라는 점을 알 수 있었다. 다음으로 마한 분구묘는 서해안 일대의 수석리문화에서 자체적으로 발생했을 가능성이 가장 높으며, 이후 서해안을 따라 남과 북으로 전파되었던 것으로 추정된다(성립 1기). 또한 수석리와 송국리의 융합문화나 내륙지역의 송국리문화에서도 성립 1기의 분구묘 전통을 수용하여 지역 내 독특한 분묘 전통을 건설하였던 것으로 추정된다. 성립 1기의 마한 분구묘 전통은 만경강 일대에서 시작되었을 가능성이 높으며, 그 연대는 기원전 3~2세기경으로 이해된다. 기원 전후에 시작되는 성립 2기에 이르면 만경강 일대의 분구묘 전통이 점차 쇠퇴하고 영산강 일대가 새로운 중심지로 부상하게 된다. 또한 성립 1기에 분구묘 전통이 거의 보이지 않던 한강 하류권과 아산만권 일대에 분구묘가 활발하게 축조되는데, 이는 역삼동문화 집단이 서해안 일대의 분구묘 전통을 수용한 결과로 추정된다. 따라서 마한 분구묘는 ‘수석리문화에서 발생하여 이후 지역에 따라 다원적으로 전개되었다’고 요약할 수 있다.The concept and terminology, distribution and excavated artifacts, and spatial-temporal development process of Mahan mounded tombs is still uncertain to a large extent, and the substance of the tomb continues to be debated. Among these topics, the most significant discussion concerns their origin and establishment. This article examines the origin and establishment period of the Mahan mounded tombs using recently discovered materials, in addition to the pre-existing data. The results of the analysis revealed that the Mahan mounded tombs of the establishment period feature common characteristics, such as being situated on hilltops, being independently placed, of having a square-planar form, of containing single-individual interments, and of yielding Suseok-ri and Songguk-ri culture grave goods. The tombs are highly likely to have emerged independently in the Suseok-ri culture area along the western coast, and from there spread along the coastline (Establishment Period Phase 1). It is also assumed that the culture that emerged from the fusion of the Suseok-ri and Songguk-ri cultures, or the Songguk-ri culture of the inland region may have adopted the tomb tradition of this Establishment Period Phase 1 to form a unique regional tomb tradition. This Mahan mounded tomb tradition in the Establishment Period Phase 1 most likely emerged in the Mangyeong River region, and can be dated to the 3rd to 2nd centuries BCE. The mounded tomb tradition in the Mangyeong River region gradually declined, and the Yeongsan River region emerged as a new center by the Establishment Period Phase 2, dating to around the turn of the millennium. Additionally, an increase in tomb construction could be observed in the lower reaches of the Haan River region and in the Asan Bay region, areas where tomb construction was hardly seen during Establishment Period Phase 1. This is thought to be the result of the Yeoksam-dong culture’s acceptance of the mounded tomb tradition from the West Sea coastal region. In summary, it can be argued that the Mahan mounded tombs originated from the Suseok-ri culture and developed pluralistically, in each region.

아산만 수로와 항내에서 해저경계층을 포함한 수층별 부유사의 이동 특성

골재채취 또는 준설 등 인위적인 행위로 인하여 발생되는 부유사량을 평가하기 위한 기초연구로서 아산만의 수로와 항내를 대상으로 인위적인 행위가 없는 자연상태에서 해저경계층을 포함한 전 수층의 부유사 이동특성을 조사하였다. 아산만의 입구부(PC1), 유속이 강한 수로(PC2), 유속이 약한 항내(PC3)의 세 정점에서 2019년 여름의 15일간 0.4 mab(meter above bed)부터 표층까지의 유속과 부유사 농도를 연속 관측하였다. 전층에서 창조류가 우세한 PC1과 PC2에서 부유사 순이동량은 창조 방향으로 각각 27.9와 20.0 ton/m/15day이며, 정규화된 수심(해면 1, 저면 0)의 0.15 이하 수층에서 급격히 증가하는 양상을 보인다. PC3의 부유사 순이동량은 정규화된 수심의 0.4를 기준으로 상층부는 낙조 방향, 하층부는 창조 방향으로 향하며, 이는 항내에 유지되는 밀도 성층으로 이층순환이 형성되기 때문이다. 전 수층에서 부유사 순이동량은 창조 방향으로 0.7 ton/m/15day로서 수로의 약 3%에 불과하다. 본 연구를 통하여 골재채취 또는 준설시 해저면 교란으로 발생하는 해저경계층 부근의 부유사 이동 특성 분석이 가능함을 확인하였다. 또한 골재채취 유·무에 따른 현장조사·분석을 수행하여 골재채취시 발생하는 부유사의 영향 범위를 정량적으로 평가할 수 있을 것으로 판단된다.

아산만 중부해역에 서식하는 대형저서동물의 군집구조 및 저서 건강도 평가

This study was carried out to investigate the spatial distributions of the macrobenthic communities and ecological quality in the central Asan Bay from March to November 2014. In total, 78 species was found the mean abundance was 439 inds./㎡, Biomass was 17.28 gWWt/㎡. Based on the Le Bris (1988) index, there were 10 dominant species accounting for approximately 63% of total individuals. The major dominant species were Heteromastus filiformis, Theora fragilis, Sternaspis scutata, Paralacydonia paradoxa and Chaetozone setosa. Cluster and nMDS ordination analysis based on Bray-Curtis similarity identified 3 major station groups. BPI and AMBI analysis, it was found that the overall good status. These results showed that changes in sedimentary characteristics were the main factors behind spatial and temporal changes in the macrobenthic communities of the central area in Asan Bay.

Application of Ecosystem Modeling of Phytoplankton Size Structure Using STELLA to Analyze Asan Bay Coatal Estuary

Application of Ecosystem Modeling of Phytoplankton Size Structure Using STELLA to Analyze Asan Bay Coatal Estuary

아산만 연안에서 소형 저인망에 어획되는 어류의 종조성 및 계절 변동

Seasonal fluctuations in the abundance and species composition of fishes in coastal waters off Asan bay were investigated from April, 2012 to January, 2013. A total of 3,057 fishes were sampled and classified into 71 species, 35 families, and 11 orders. Of the 11 orders, Perciformes, Scorpaeniformes, and Pleuronectiformes accounted for approximately 61.97% of the fishes in this area. Of 71 species identified, Engraulis japonicus, Leiognathus nuchalis, Trichiurus japonicus, Pholis fangi, and Konosirus punctatus accounted for 36.57% of collected fishes. The highest number of individuals was found in July, while the lowest in January. The richness index was highest in July (RI=7.103) and the lowest in January(RI=4.708). The eveness index was the highest in July(E=0.912) and the lowest in October(E=0.766). The diversity index was the highest in July(H’=1.429) and the lowest in October(H’=2.862).

Psychrosphaera aquimarina sp. nov., a marine bacterium isolated from seawater collected from Asan Bay, Republic of Korea.

Cells of strain SW33T, isolated from the seawater of Asan Bay, Republic of Korea, were characterized as Gram-stain-negative, aerobic, rod-shaped, motile and non-spore-forming. Phylogenetic analysis revealed that strain SW33T belonged to the genus Psychrosphaera and clustered distantly with the other genera in the family Pseudoalteromonadaceae in the phylogenetic tree. The 16S rRNA sequences of strain SW33T revealed high similarities to Psychrosphaera saromensis SA4-48T (98.7 %), Psychrosphaera haliotis KDW4T (97.4 %) and Psychrosphaera aestuarii PSC101T (97.3 %). The major fatty acids were C16 : 0 (27.9 %), summed feature 3 (32.2 %) and summed feature 8 (17.2 %). The predominant quinone was Q-8, and the polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified amino lipid. The DNA G+C content was 38.3 mol%. The DNA-DNA relatedness values with the three species of Psychrosphaera saromensis KCTC 23240T, Psychrosphaera haliotis KCTC 22500T and Psychrosphaera aestuarii KCTC 32274T were 22, 23 and 18 %, respectively. Based on the phenotypic characteristics and taxonomic analyses, we propose that strain SW33T represents a novel species within the genus Psychrosphaera, for which the name Psychrosphaera aquimarina sp. nov. with the type strain SW33T (=KCTC 52743T=CICC 24249T) is proposed.

Progressive change of tidal wave characteristics from the eastern Yellow Sea to the Asan Bay, a strongly convergent bay in the west coast of Korea

Although there have been studies on the tide in convergent bay (or estuary), the tide change in terms of phase speed, amplitude, and phase difference between elevation and tidal current from a coastal ocean to a convergent bay has not been clearly shown so far. This study systematically examines the change of tidal wave characteristics from the eastern Yellow Sea to the Asan Bay, a strongly convergent bay on the west coast of Korea, using observations and an analytical model. As the tidal wave propagates from the eastern Yellow Sea into the Asan Bay, the phase speed, amplitude, and phase difference between elevation and tidal current increase along the channel. Such a phenomenon represents a unique example of tide change from a coastal ocean to a convergent bay, indicating dominance of convergence over friction in the Asan Bay. Both analytically computed tidal amplitude and travelling time compare well with observations. In the Asan Bay, the influence of the reflected wave is only felt in the upper one fifth of the bay and is almost unperceivable in the rest of the bay. The analytical analyses presented in this paper are particularly useful for understanding the relative importance of channel convergence, bottom friction, and reflected wave on the tidal characteristics change along the channel and the proposed method could be applicable to other estuaries.

Parahaliea aestuarii sp. nov., isolated from the Asan Bay estuary

A Gram-stain-negative, strictly aerobic and moderate halotolerant bacterial strain, designated S2-26T, was isolated from sediment of the Asan Bay estuary in South Korea. Cells were motile rods with two polar flagella showing oxidase and catalase activities. Growth of S2-26T was observed at 15-45 °C (optimum, 25 °C) and pH 5.5-10.0 (optimum, pH 7.0-8.5) and in the presence of 0-8.0 % (w/v) NaCl (optimum, 2.0 %). S2-26T contained C17 : 1ω8c, summed feature 8 (comprising C18 : 1ω7c and/or C18 : 1ω6c), summed feature 3 (comprising C16:1ω7c/C16:1ω6c) and C17 : 0 as the major fatty acids and ubiquinone-8 as the sole isoprenoid quinone. The polar lipids of S2-26T consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, an unknown phospholipid, an unknown aminolipid, an unknown glycolipid and an unknown lipid. The G+C content of the genomic DNA was 62.2 mol%. The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that S2-26T formed a tight phylogenetic lineage with Parahaliea mediterranea 7SM29T with a 100 % bootstrap value. S2-26T was most closely related to the type strain of Parahaliea mediterranea, with a 97.8 % 16S rRNA gene sequence similarity, and its DNA-DNA relatedness level was 45.2±2.2 %. On the basis of phenotypic, chemotaxonomic and molecular properties, it is clear that S2-26T represents a novel species of the genus Parahaliea, for which the name Parahaliea aestuarii sp. nov. is proposed. The type strain is S2-26T (=KACC 18801T=JCM 31547T).

Effects of Enhanced pCO2and Temperature on Reproduction and Survival of the Copepod Calanus sinicus

We tested the combined effects of increased partial pressure of CO₂ (pCO₂) and temperature on the reproduction and survival of the copepod Calanus sinicus from Asan Bay, the Yellow Sea under laboratory conditions to understand the impact of acidification on copepods. Egg production rate, survival rate, and fecal pellet production of C. sinicus were not affected by 1305 ppm pCO₂ or with combined treatments of temperature and pCO₂, including 8℃ and 289 ppm pCO₂ (ambient), 8℃ and 753 ppm pCO₂ (high pCO₂), 12℃ and 289 ppm pCO₂ (high temperature), and 12℃ and 753 ppm pCO₂ (greenhouse), for 5 or 10 d of exposure. However, egg hatching success of C. sinicus decreased significantly in the greenhouse treatment compared with the ambient or the high pCO₂ treatments. These results suggest that a combined treatment (pCO₂ and temperature) affected egg viability more than a single treatment (pCO₂).

Seasonal Variations in Seawater Quality Due to Freshwater Discharge in Asan Bay

Seasonal Variations in Seawater Quality Due to Freshwater Discharge in Asan Bay

Nutrient Budget and Dam Effluence in Asan Bay

Nutrient Budget and Dam Effluence in Asan Bay

Agarivorans aestuarii sp. nov., an agar-degrading bacterium isolated from a tidal flat.

A Gram-reaction-negative, aerobic, non-spore forming, rod-shaped bacterium motile with a single polar flagellum, designated strain hydD622T, was isolated from the sediment of a tidal flat at Asan Bay, Korea. Strain hydD622T exhibited an agarolytic activity. Comparison of 16S rRNA gene sequences revealed that strain hydD622T was closely related to Agarivorans litoreus KCTC 42116T, Agarivorans albus KCTC 22256T and Agarivorans gilvus KCTC 32555T with similarities of 98.4, 98.0 and 96.5 %, respectively. Strain hydD622T was clustered distantly from the other genera in the family Alteromonadaceae but formed a unique clade within the genus Agarivorans based on the 16S rRNA gene sequence. The DNA-DNA relatedness with Agarivorans litoreus KCTC 42116T and Agarivorans. albus KCTC 22256T was 39.0 and 37.8 %, respectively. The major fatty acids (>10 %) were C16 : 0,C16 : 1ω6c/C16 : 1ω7c and C18 : 1ω6c/C18 : 1ω7c. The respiratory quinone was ubiquinone-8, and the polar lipid profile consisted of phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and an unidentified lipid. The DNA G+C content was 44 mol%. On the basis of physiological, chemotaxonomic and phylogenetic analyses, strain hydD622T represents a novel species within the genus Agarivorans, for which the name Agarivorans aestuarii sp. nov. is proposed. The type strain of Agarivorans aestuarii sp. nov. is hydD622T (=KCTC 32543T=CGMCC 1.12692T).

수산음향기법을 이용한 아산만 멸치(Engraulis japonicus)와 기타어군의 분포 및 현존량 추정

The distribution and abundance of coastal fish species in Asan Bay, Korea, were estimated from hydroacoustic survey and net catches. Acoustic data were collected with 38 and 200 kHz from July to October of 2012, and converted to the nautical area scattering coefficient (NASC, <TEX>$m^2/mile^2$</TEX>) for <TEX>$0.25n{\cdot}mile$</TEX> along ten transects. Japanese anchovy Engraulis japonicus was the dominant specie in the net catches. The virtual echogram technique was used to distinguish E. japonicus from other species based on the differences in the mean volume backscattering strength (<TEX>${\Delta}MVBS$</TEX>) at 38 and 200 kHz. Engraulis japonicus and other fishes are mainly distributed in the center channel and outer part of Asan Bay. E. japonicus tends to move from inner to outer Asan Bay in summer and fall. From NASC data, the target strength and length-weight function of E. japonicus and other fishes were used to estimate the E. japonicus stock at 24.1-93.3 tons, and other fish at 40.6-88.4 tons from July to October 2012. The estimated anchovy biomass compared well with the cumulative catch weight from stow net catches. The hydroacoustic method offers an approach to understanding spatial/temporal structure and estimating the biomass of fish aggregations in coastal areas.

Rapid fluctuations in flow and water-column properties in Asan Bay, Guam: implications for selective resilience of coral reefs in warming seas

Hydrodynamics and water-column properties were investigated off west-central Guam from July 2007 through January 2008. Rapid fluctuations, on time scales of 10s of min, in currents, temperature, salinity, and acoustic backscatter were observed to occur on sub-diurnal frequencies along more than 2 km of the fore reef but not at the reef crest. During periods characterized by higher sea-surface temperatures (SSTs), weaker wind forcing, smaller ocean surface waves, and greater thermal stratification, rapid decreases in temperature and concurrent rapid increases in salinity and acoustic backscatter coincided with onshore-directed near-bed currents and offshore-directed near-surface currents. During the study, these cool-water events, on average, lasted 2.3 h and decreased the water temperature 0.57 °C, increased the salinity 0.25 PSU, and were two orders of magnitude more prevalent during the summer season than the winter. During the summer season when the average satellite-derived SST anomaly was +0.63 °C, these cooling events, on average, lowered the temperature 1.14 °C along the fore reef but only 0.11 °C along the reef crest. The rapid shifts appear to be the result of internal tidal bores pumping cooler, more saline, higher-backscatter oceanic water from depths >50 m over cross-shore distances of 100 s of m into the warmer, less saline waters at depths of 20 m and shallower. Such internal bores appear to have the potential to buffer shallow coral reefs from predicted increases in SSTs by bringing cool, offshore water to shallow coral environments. These cooling internal bores may also provide additional benefits to offset stress such as supplying food to thermally stressed corals, reducing stress due to ultraviolet radiation and/or low salinity, and delivering coral larvae from deeper reefs not impacted by surface thermal stress. Thus, the presence of internal bores might be an important factor locally in the resilience of select coral reefs facing increased thermal stress.

투수성 호안의 해수유통을 고려한 유동 수치모델링

The Inner Port Phase 2 area of the Pyeongtaek-Dangjin Port is enclosed by a total of three permeable sea-walls, and the disposal site to the east of the Inner Port Phase 2 is also enclosed by two permeable sea-walls. The maximum tidal range measured in the Inner Port Phase 2 and in the disposal site in May 2010 is 4.70 and 2.32 m, respectively. It reaches up to 54 and 27%, respectively of 8.74 m measured simultaneously in the exterior. Regression formulas between the difference of hydraulic head and the rate of interior water volume change, are induced. A three-dimensional numerical hydrodynamic model for the Asan Bay is constructed incorporating a module to compute water discharge through the permeable sea-walls at each computation time step by employing the formulas. Hydrodynamics for the period from 13th to 27th May, 2010 is simulated by driving forces of real-time reconstructed tide with major five constituents(M2, S2, K1, O1 and N2) and freshwater discharges from Asan, Sapkyo, Namyang and Seokmoon Sea dikes. The skill scores of modeled mean high waters, mean sea levels and mean low waters are excellent to be 96 to 100% in the interior of permeable sea-walls. Compared with the results of simulation to obstruct the flow through the permeable sea-walls, the maximum current speed increases by 0.05 to 0.10 m/s along the main channel and by 0.1 to 0.2 m/s locally in the exterior of the Outer Sea-wall of Inner Port. The maximum bottom shear stress is also intensified by 0.1 to 0.4 N/m2 in the main channel and by more than 0.4 N/m2 locally around the arched Outer Sea-wall. The module developed to compute the flow through impermeable seawalls can be practically applied to simulate and predict the advection and dispersion of materials, the erosion or deposion of sediments, and the local scouring around coastal structures where large-scale permeable sea-walls are maintained.

논습지에 도래하는 수조류의 서식지 이용과 개체군 특성

BACKGROUND: As natural wetlands are decreased by increment of human demand, the importance of rice fields as an alternative habitat for waterbirds is well documented. However, the relationship between waterbirds use and management practice of rice fields has not been fully understood. The present study attempted to understand the changes in temporal abundance of waterbirds and their preference for habitat types in rice fields all year round. METHODS AND RESULTS: Waterbirds census were conducted in rice fields around Asan bay in Korea during April 2009-March 2010 and April 2011-March 2012. In the bird counts, the locations of the observed birds on a 1/2,500 map were recorded along with the local habitat type (paddy, ditch, levee, road). Thirty five species of waterbirds recorded in the rice fields during the survey period and three major groups (shorebirds, herons, and waterfowls) were characterized according to season and micro-habitat use. Shorebirds visited a flooded paddy for feeding during their spring migration season (April-May), and herons used the rice field as feeding sites during their breeding periods (April-October). Most waterfowls were observed in a dry paddy to feed a fallen rice seed and stubs during the winter season (September-March). Waterbird groups selectively used micro-habitats in rice field. Shorebirds and waterfowls mainly preferred at rice paddies, while herons were attracted to most habitat types. CONCLUSION(S): Rice fields supported various waterbirds all year round and waterbird communities using the rice fields were dramatically changed according to seasonal change of rice field condition.