• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.10 no.1
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• pp.19-30
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• 2005

To investigate the seasonal distribution and grazing impacts of benthic protozoa in mud flat, their abundance, biomass and grazing rates of benthic protozoa were evaluated at interval of two or three month in Gangwha Island from April, 2002 to April, 2004. Heterotrophic flagellates and ciliates accounted for an average 98% of benthic protozoa biomass. Abundance and carbon biomass of heterotrophic flagellates ranged from $0.2{\times}10^5$ to $5.9{\times}10^5\;cells\;cm{-3}$ and from 0.02 to $9.2\;{\mu}gC\;cm^{-3}$, respectively. Biomass of heterotrophic flagellates was high in spring and fall, and showed no differences among stations. Abundance and biomass of heterotrophic flagellates decreased with the depth and were high within the surface 2.5 m sediment layer. The majority of heterotrophic flagellates were less than $10\;{\mu}m$ in length, and few euglenoid flagellates were larger than $20\;{\mu}m$. Abundance and carbon biomass of ciliates ranged from $0.1{\times}10^3$ to $17.8{\times}10^3\;cells\;cm^{-3}$ and from 0.02 to $9.1\;{\mu}gC\;cm^{-3}$, respectively, and those of ciliates were high in spring and fall. Biomass of ciliates was high within the surface 2.5 mm sediment layer and was higher at st. J2 and st. J3 than st. J1. Among the revealed benthic ciliates, the hypotrichs were the most important group in terms of abundance and biomass. During the sampling periods, an average 66% of benthic protozoa biomass was covered by ciliates. The seasonal distribution of benthic protozoa showed an almost similar fluctuation pattern to that of chlorophyll-a. The results suggest that the biomass of benthic protozoa were mainly controlled by prey abundance, for example, diatoms. Based on ingestion rates, benthic protozoa removed from 13.4 to 40.7% of bacterial production and from 20.1 to 36.4% of primary production. Ingestion rates of benthic protozoa on bacteria and microphytobenthos were high in April. Benthic protozoa in this study area may play a pivotal role in the carbon flow of the benthic microbial food web during spring.

• Korean Journal of Environment and Ecology
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• v.29 no.5
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• pp.743-752
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• 2015

We studied the spatio-temporal microalgal (phytoplankton and benthic diatoms) and environmental changes of the Hajeonri intertidal zone from February to November 2014. Seawater and phytoplankton analysis were conducted all through the months. The species, composition and abundance of phytoplankton and environmental factors were measured. As a result, diatom was dominant among a total of 113 species identified. On a seasonal basis (Feb. May, Aug., Nov.), we carried out studies on benthic diatoms on the surface of the sediments and their habitats at nine stations on the transect line at Hajeonri at low tide. The grain of the surface sediments was mainly composed of sandy silt and sandy mud. Organic pollution level was low. Benthic microalgal biomass (chlorophyll ${\alpha}$) was high in the spring and summer. A total of 163 benthic diatom species were identified. Navicula sp.1 and Paralia sulcata were dominant over the study period. Five diatom species were observed both in water column and on surface sediment at the same time.

• Korean Journal of Ecology and Environment
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• v.57 no.2
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• pp.61-74
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• 2024

Daemadeung, located in the estuary of the Nakdong River, is formed by sand dunes and possesses well-developed intertidal flats. This study aimed to investigate the habitat of benthic microalgae, photosynthetic pigments, and photosynthetic efficiency in the intertidal flats of Daemadeung from January to December 2011. The inorganic nitrogen content in the sediment pore water was primarily composed of ammonium, while nitrate + nitrite was dominant in the upper layer water. The concentration of chlorophyll a and fucoxanthin in the sediment surface was significantly higher than the mean of all the sediment layer. The average Fv/Fm of benthic microalgae during the entire survey period was 0.52±0.03, with the highest value (0.61±0.08) observed in February. The rETR_max showed a seasonal trend, being high from spring to early autumn (April to October) and low from winter to early spring (January to March, November, December), with the highest value (153.05±2.30 µmol electrons m^-2 s^-1) in July and the lowest (38.49±5.17 µmol electrons m^-2 s^-1) in January. The average Fv/Fm of diurnal microalgae was 0.48±0.03, with the highest value (0.61±0.08) observed at noon. The rETR_max showed a highest peak at noon (54.24±11.35 µmol electrons m^-2 s^-1) and reached its lowest point at 16:00 (26.17±4.75 µmol electrons m^-2 s^-1). These findings suggest that the productivity of benthic microalgae varies significantly depending on the survey time and sediment depth. Therefore, to quantify the productivity of benthic microalgae using Diving-PAM, surveys should be conducted based on tidal conditions, and simultaneous pigment analysis of sediment layers should also be performed.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.4
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• pp.32-41
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• 2001

We measured the fluxes of COD, TN and 55 in addition to composition and quality of sediment in Komso Bay, West Coast of Korea. The fluxes of TN, SS and COD were measured during flood tide and ebb tide in April and August, 2000. Denitrification rates in the sediments was also measured by direct produced $N_2$ gas technique on April and August from 1999 to 2000 in the same sea area. The composition of the sediments were 0.33~5.67 % of sand, 20.2~25.6 of gravel and 68.7~77.0 % of silt. Ignition loss of the sediments were 6.58~7.50 %. The concentration of hydrogen sulfide in the sediments were 0.028~0.326 mg/gㆍdry and oxidation reduction potential of the sediments were -28~-15 mV Diurnal fluxes of COD, total nitrogen, and suspended solids with tidal current and denitrification rate in the tidal flat have been determined in Komso Bay The diurnal net flux of COD was same in April. While 14.4 ton COD/hr of net influx into the tidal flat was recorded in August. The diurnal net influx of total nitrogen was 0.16 ton N/hr in April and 1.13 ton N/hr in August. The diurnal net influx of suspended solids was 0.05 ton SS/hr in April, and also net influx of suspended solids was 0.29 ton SS/hr in August. The overall purification ability of the tidal flat were estimated 0.00~5.69 g COD/$m^2/day$, 0.06~0.45 g N/m²/day and 0.02~0.12 g SS/$m^2/day$ for COD, TN and SS, respectively. Denitrification rate was 0.009~1.720 m mole ${N_2}/m^2/day$ (average 0.702 m mole ${N_2}/m^2/day$) in April and 0.033~0.133 m mole ${N_2}/m^2/day$ (average 0.077 m mole ${N_2}/m^2/day$) in August, 1999. 0.000~l.909 m mole ${N_2}/m^2/day$ (average 0.756 m mole ${N_2}/m^2/day$) in April, 0.000~1.691 m mole ${N_2}/m^2/day$ (average 0.392 m mole ${N_2}/m^2/day$) in August, 2000. Even with a wide range of denitrification rate depending on the sampling location and studied periods, the average denitrification rate was estimated 0.482 m mole ${N_2}/m^2/day$ in the tidal flat of Komso Bay.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.17 no.2
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• pp.87-94
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• 2012

To compare monthly variations of phytoplankton biomass and community composition between in seawater and sediment of the Gomso Bay (tidal flat: approximately 75%), the photosynthetic pigments were analyzed by HPLC every month in 1999 and every two months in 2000. Ambient physical and chemical parameters (temperature, salinity, nutrients, dissolved oxygen, and chemical oxygen demand) were also examined to find the environmental factors controlling structure of phytoplankton community. The temporal and spatial variations of chlorophyll a concentration in seawater were correlated well with the magnitude of freshwater discharge from land. The biomass of microphytobenthos at the surface sediments was lower than that in other regions of the world and 2-3 times lower than phytoplankton biomass integrated in the seawater column. Based on the results of HPLC pigment analysis, fucoxanthin, a marker pigment of diatoms, was the most prominent pigment and highly correlated with chlorophyll a in seawater and sediment of the Gomso Bay. These results suggest that diatoms are the predominant phytoplankton in seawater and sediment of the Gomso Bay. However, the monthly variation of chlorophyll a concentration in seawater at the subtidal zone was not a good correlation with that in sediment of the Gomso Bay. Although pelagic plankton was identified in seawater by microscopic examination, benthic algal species were not found in the seawater. These results suggest that contribution from the suspended microphytobenthos in the tidal flat to the subtidal zone of the Gomso Bay may be low as a food source to the primary consumer in the upper water column of the subtidal zone. Further study needs to elucidate the vertical and horizontal transport magnitude of the suspended microphytobenthos in the tidal flat to the subtidal zone.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.1
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• pp.48-55
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• 2009

Seasonal variations of microalgal biomass and community composition in both the sediment and the seawater were investigated by HPLC pigment analysis in an estuarine muddy sandflat of Gwangyang Bay from January to November 2002. Based on the photosynthetic pigments, fucoxanthin, diadinoxanthin, and diatoxanthin were the most dominant pigments all the year round, indicating that diatoms were the predominant algal groups of both the sediment and the seawater in Gwangyang Bay. The other algal pigments except the diatom-marker pigments showed relatively low concentrations. Microphytobenthic chlorophyll ${\alpha}$ concentrations in the upper layer (0.5 cm) of sediments ranged from 3.44 (March at the middle site of the tidal flat) to 169 (July at the upper site) mg $m^{-2}$, with the annual mean concentrations of $68.4{\pm}45.5,\;21.3{\pm}14.3,\;22.9{\pm}15.6mg\;m^{-2}$ at the upper, middle, and lower tidal sites, respectively. Depth-integrated chlorophyll ${\alpha}$ concentrations in the overlying water column ranged from 1.66 (November) to 11.7 (July) mg $m^{-2}$, with an annual mean of $6.96{\pm}3.04mg\;m^{-2}$. Microphytobenthic biomasses were about 3${\sim}$10 times higher than depth-integrated phytoplankton biomass in the overlying water column. The physical characteristics of this shallow estuarine tidal flat, similarity in taxonomic composition of the phytoplankton and microphytobenthos, and similar seasonal patterns in their biomasses suggest that resuspended microphytobenthos are an important component of phytoplankton biomass in Gwangyang Bay. Therefore, considering the importance of microphytobenthos as possible food source for the estuarine benthic and pelagic consumers, a consistent monitoring work on the behavior of microphytobenthos is needed in the tidal flat ecosystems.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.2
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• pp.49-67
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• 2006

A mesocosm, an artificial tidal flat ecosystem, was constructed outdoors to simulate in situ physical and biochemical environmental conditions of natural tidal flat as much as possible. During the experiment from February to August 2004, the study was focused on the biogeochemical variations of superficial water and porewater after introduction of freshwater into the mesocosm. The mesocosm has three experimental conditions; SW-M-T: maintaining the saline water of approximately 20 psu; FW-M-T: complete exchange of freshwater ul the mesocosm with continuous mixing of water column: FW-NM-T: complete exchange of saline water to freshwater in the mesocosm without mixing of water column. Mass extinction of benthic macrofauna appeared due to drastic decrease of porewater salinity from 20 psu to less than 10 psu between the 63th and 91st day of freshwater introduction in FW-M-T and FW-NM-T. Throughout the periods, 7/8 of bivalves and 2/3 of polychaete populations have been extinguished in the sediment. In FW-NM-T, as temperature rises, both evident decrease of DO in water column and active release of DIP from sediment were observed. ${NO_3}^-$ was removed from water column into sediment throughout the periods. Therefore extremely low ${NO_3}^-$ was found during late spring and summer. Whereas ${NH_4}^+$ exhibited only $1/2{\sim}1/8$ of ${NO_3}^-$ concentration. Unexpectedly even after mass extinction of benthic macrofauna, we were not able to find high ${NH_4}^+$. This mesocosm study suggests that when fresh water introduce to natural tidal flat, its sediment activity functions as a potential source of DIP, but a sink of ${NO_3}^-$.

• Journal of the Korean earth science society
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• v.28 no.1
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• pp.64-74
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• 2007

The marine seismic prospecting using a research vessel in the shallow sea near the coastal area has certain limits according to the water depth and survey environment. Also, for the electrical resistivity survey at seashore area, one may need a specially designed high-voltage source to penetrate the very conductive surface layer. Therefore, we have conducted a feasibility study on the application of magnetotelluric method (MT), a passive geophysical method, on investigating of shallow marine environment geology. Our study involves both theoretical modeling and field survey at the tidal flat area which represent the very shallow marine environment. We have applied the audio-frequency magnetotelluric (AMT) method to the intertidal deposits of Gunhung Bay, west coast of Korea, and analysed the field data both qualitatively and quantitatively to investigate the morphology and sedimentary stratigraphy of the tidal flat. The inversion of AMT data well reveals the upper sedimentary layer of Holocene intertidal sediments having a range of 13-20 m thickness and the erosional patterns at the unconformable contact boundary. However, the AMT inversion results tend to overestimate the depth of basement (30-50 m) when compared with the seismic section (27-33 m). Since MT responses are not significantly sensitive to the resistivity of middle layer or the depth of basement, the AMT inversion result for basement may have to be adjusted using the comparison with other geophysical information like seismic section or logging data if possible. But, the AMT method can be an effective alternative choice for investigating the seashore area to get important basic informations such as the depositional environment of the tidal flat, sea-water intrusion and the basement structure near the sea shore.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.1
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• pp.1-17
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• 2019

In this study, the surveys were carried out from October (2016) to October (2017) along the tidal flat of Geunso Bay, Taean Peninsula of the western edge of Korea. The sampling trips were carried out for a total of 16 times, once or twice a month. In order to investigate the monthly variation of the microphytobenthos (MPB) biomass, community composition and photo-physiology were analyzed by HPLC (High performance liquid chromatography). The total chlorophyll a (TChl a) concentrations used as an indicator of biomass of MPB in the upper 1 cm sediment layer ranged from 40.4 to $218.9mg\;m^{-2}$ throughout the sampling period. TChl a concentrations showed the maximum level on $24^{th}$ of February and remained high throughout March after which it started to declined. The biomass of MPB showed high values in winter and low values in summer. The monthly variations of Phaeophorbide a concentrations suggested that the low grazing intensity of the predator in the winter may have partly attributed to the MPB winter blooming. As a result of monthly variations of the MPB community composition using the major marker pigments, the concentrations of fucoxanthin, the marker pigment of benthic diatoms, were the highest throughout the year. The concentrations of most of the marker pigments except for chlorophyll b (chlorophytes) and peridinin (dinoflagellates) increased in winter. However, the concentrations of fucoxanthin increased the highest, and the relative ratios of the major marker pigments to TChl a except fucoxanthin decreased during the same period. The vertical distribution of Chl a and oxygen concentrations in the sediments using a fluorometer and an oxygen micro-optode Chl a concentrations decreased with oxygen concentrations with increasing depth of the sediment layers. Moreover, this tendency became more apparent in winter. The Chl a was uniformly vertical down to 12 mm from May to July, but the oxygen concentration distribution in May decreased sharply below 1 mm. The increase in phaeophorbide a concentration observed at this time is likely to be caused by increased oxygen consumption of zoobenthic grazing activities. This could be presumed that MPB cells are transported downward by bioturbation of zoobenthos. The relative ratios (DT/(DD+DT)) obtained with diadinoxanthin (DD) and diatoxanthin (DT), which are often used as indicators of photo-adaptation of MPB, decreased from October to March and increased in May. This indicated that there were monthly differences in activity of Xanthophyll cycle as well.

• Korean Journal of Ecology and Environment
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• v.56 no.3
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• pp.207-217
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• 2023

This study was conducted to investigate the current status of seagrass species in the Nakdong River estuary from May to June 2023. To survey the seagrass habitat area, the Nakdong River estuary was divided into seven zones. Aerial photography using drones was conducted to find seagrass areas, GPS tracking was carried out on foot in the intertidal zone and by boat and SCUBA diving in the subtidal zone. To analyze the seagrass status, we measured the morphological characteristics, shoot density, and biomass of representative seagrass species in each zone. Four seagrass species were found in this area: Zostera japonica, Z. marina, Ruppia maritima, and Phyllospadix japonicus. The distribution areas of each species was 338.2 ha, 92.9 ha, 0.9 ha, and 1.4 ha, respectively, with a total area of 432.5 ha. Z. japonica was widely distributed in most of the tidal flats and mudflats of the Nakdong River estuary, while Z. marina was restricted to Nulcha-do, Jinu-do, and Dadae-dong. R. maritima occurred within the habitat of Z. japonica in Eulsukdo and Myeongji mudflats, and P. japonicus inhabited rocky areas in Dadae-dong. The shoot density of each species was 4,575.8±338.3 shoots m^-2, 244.8±12.0 shoots m^-2, 11,302.1±290.0 shoots m^-2, and 2862.5±153.5 shoots m^-2, respectively. The biomass of each species was 239.7±18.5 gDW m^-2, 362.3±20.5 gDW m^-2, 33.3±1.2 gDW m^-2, and 1,290.0±37.0 gDW m^-2, respectively. The results of this study revealed that Z. japonica was dominant in the Nakdong River estuary. In particular, Z. japonica habitats of Eulsukdo, Daema-deung, and Myeongji mudflats were identified as the largest in Korea. The Nakdong River estuary is an important site of ecological, environmental, and economic value, and will require continuous investigation and management of the native seagrasses.