• Economic and Environmental Geology
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• v.48 no.5
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• pp.379-390
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• 2015

Multibeam backscatter strength is dependent not only on seafloor sediment facies but also on changed incidence angle due to the actual bottom slope. Therefore, the correction for actual bottom slope should be considered before the analysis of backscatter strength. This paper demonstrates the backscatter correction technique for the actual incidence angle and ensonified area. The target area is a part of the eastern Yellow Sea with water depths of 46~55 m. The area is located between the sand ridges and covered by large dunes with various bottom slopes. The dunes usually have the gentle slopes of about $1{\sim}3^{\circ}$, but show some steep slopes of $5{\sim}15^{\circ}$ on the crest. The backscatter strength values on the crest range from -34 to -23 dB, assuming that the bottom is flat. However, this study shows that the backscatter strength range was somewhat reduced (-32~-25 dB) after correction for actual bottom slope. In addition, the backscatter imagery was significantly improved; high and low backscatter strength values on the crest due to the actual bottom slope were normalized. The results demonstrate that the correction technique in this study is an effective tool for processing backscatter strength.

• Journal of Environmental Science International
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• v.13 no.12
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• pp.1089-1102
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• 2004

Seasonal variation of biogeochemical characteristics was determined in Lake Shihwa from October 2002 to August 2003. When the lake was artificially constructed for the freshwater reservoir in 1988, the development of the strong haline density stratification resulted in two-layered system in water column and hypoxic/anoxic environment prevailed in the bottom layer due to oxidation of accumulated organic matters in the lake. Recently, seawater flux to the lake through the sluice has been increased to improve water quality in the lake since 2000, but seasonal stratification and hypoxic bottom layer of the lake still developed in the summer due to the nature of artificially enclosed lake system. As the lake is still receiving tremendous amount of organic matters and other pollutants from neighboring streams during the rainy summer season, limited seawater flux sluicing into the lake may not be enough for the physical and biogeochemical mass balance especially in the summer. The excess of accumulated organic matters in the bottom layer apparently exhausted dissolved oxygen and affected biogeochemical distributions and processes of organic and inorganic compounds in the stratified two-layered environment in the summer. During the summer, ammonia and dissolved organic carbon remarkably increased in the bottom layer due to the hypoxic/anoxic condition in the bottom layer. Phosphate also increased as the result of benthic flux from the bottom sediment. Meanwhile, dissolved organic carbon showed the highest value at the upstream area and decreased along the salinity gradient in the lake. In addition to the sources from the upstream, autochthonous origin of particulate organic carbon from algal bloom in the lake might be more important for sustaining aggravated water quality and development of deteriorated bottom environment in the summer. The removal of trace metals could be attributed to scavenging by strong insoluble metal-sulfide compounds in the hypoxic/anoxic bottom layer in the summer.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.6
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• pp.101-109
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• 2012

Silt curtains are constructed for minimizing pollution of sediment dispersion in water bodies. In spite of wide uses of the silt curtains, there are few studies for analyzing the effectiveness of them with respect to their dimension and hydraulic characteristics. Currently, the market of silt curtains does not provide the various dimension of them due to the limit of information regarding its effectiveness on reducing sediment pollution. In this study, a series of experiments were conducted to investigate hydraulic characteristics around the silt curtains under the different flow conditions. For this study, a silt curtain was fabricated and an open channel with 30cm of width and 40cm of depth was used. The results indicated that the silt curtain was not effective in preventing dispersion at flow velocities over 0.5m/s in real conditions. Based on the experimental results, it is required that approaching velocity should be minimized and the weight of bottom be increased in order to reduce deformation. The results of this study will provide information required to design appropriate dimension of silt curtains in various water environment such as velocity and water depths.

• The Korean Journal of Ecology
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• v.28 no.3
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• pp.121-127
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• 2005

To reveal vegetation history and environmental changes in Mt. Jiri, sediment cores were collected from Wangdeungjae moor of Mt. Jiri. Overall dry matter accumulation rates and sedimentation rates by $^{14}C-dating$ were 0.027 $kg{\cdot}m^{-2}{\cdot}yr^{-1}$ and 0.184 mm/yr since 1250 ($760{\pm}40$ yrs BP, 14 cm in depth). There are three pollen zones; the first zone is below 14 cm depth where Quercus dominated, the second zone is from 14 cm to 6 cm depth where Gramineae increased and Quercus and Salix dominated and the third zone is from 6 cm depth to the top where Pinus and Quercus dominated. Total pollen concentration gradually increased from bottom to the top of sediment core, which implies wet, anaerobic and cool condition during covered period by the core. Calcium and magnesium contents had increased since 14 cm depth, with peaks at 13 and 20 cm depths. This indicates that groundwater had recently become relatively more important than surface water as water source of Wangdeungjae moor Exotic plant or Chenopodiacea pollen was less than 1%. There was little variation in total N and P contents along the length of the core. These results support that Wangdeungjae moor has been little affected by anthropogenic activities. Also, nutrients and heavy metal contents indicate the baseline condition of Wangdeungjae moor.

• Journal of Environmental Science International
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• v.18 no.11
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• pp.1299-1307
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• 2009

In order to measure in-situ suspended particle size, volume concentration of suspended particulate matter and current speed, mooring observation was performed at the Gwangyang Bay by using of an optical instrument, 'LISST-100' and an acoustic instrument, 'ADV'(St. S1). And the sediment flux was obtained based on the concentration of suspended particulate matter and current speeds measured at three lines of Gwangyang Bay during ebb and flood tide of August 2006. To investigate the spatial variation of suspended particulate matter, profiling observations were measured difference echo intensity and beam attenuation coefficient by using of ADCP and Transmissometer (Line A, B, C). The suspended sediment flux rate at the mouth of Gwangyang Bay was observed to be higher during asymmetrical than symmetrical of current speeds. The flux of suspended particulate matter concentration and current speeds were transported to southeastern direction of surface layer and northwestern direction of bottom layer at the western area at line A of Gwangyang Bay. Small suspended particles have been found to increase attenuation and transmission more efficiently than similar large particles using acoustic intensity (ADV/ADCP) or optical transmit coefficient (LISST-100/Transmissometer). The application and problems as using optical or acoustic instruments will be detected for use in time varying calibrations to account for non-negligible changes in complex environments in situ particle dynamics are poorly understood.

• Ocean Science Journal
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• v.43 no.3
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• pp.153-160
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• 2008

The distribution of the taxonomical composition and the density of meiobenthos depending on some factors of environment has been studied in bottom sediments of the northern estuary part of Ha Long Bay (Cua Luc estuary). The basic factor of influence on meiobenthic community structure was the granulometric composition of sediment. The greatest taxonomic diversity is noted in the silted sands, lowest - in the silty sediments. The density of meiobenthic community was higher in the silty sediments. Slightly expressed correlation between the density of nematodes and the percentage of silty particles in the sediments is detected (Spearman rank correlation coefficient was $0.49{\pm}0.21$, p=0.035). The nematodes were dominant at all stations. In total, representatives of 66 species of nematodes belonging to 17 families and 52 genera were identified.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.31-43
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• 1989

Tidal asymmetry and the associated sediment dynamics in the Keum River Estuary has been investigated from a numerical tidal model. Modeling efforts were focussed on the simulation of large drying sandflat exposed at the mouth of the Estuary and dynamic combination of two-dimensional estuary model and one-dimensional river model. Despite strong frictional attenuation within the estuary, the M4 tides reach significant amplitude, resulting in strong tidal distortion. Model results show that the asymmetry over the area exhibit more intense flood flows transport than do less intense ebb flows of longer duration. This causes filling of the estuary as evidenced by large sandflats spread over the inner area. The spatial distribution of peak bottom stress computed from the tidal model suggest that present tidal sedimentation regime may be altered significantly, especially in the approach channel to outer Kunsan port and downstream part of the dike, due to the construction of cross-channel barrier.

• Journal of Environmental Science International
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• v.21 no.10
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• pp.1187-1193
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• 2012

The aim of this research is to enhance the bottom environment of Geoje fish farm that has been severely contaminated. Treatment of microbial agent and/or calcium oxide significantly changed that environment: in ignition loss, either treatment (25% or 21%) showed better than mixed treatment (13.2%). In COD, the oxygen releasing agent or mixed treatment reduced the index by more than 20%. In T-P and T-N, the effects of $CaO_2$ on them were overwhelming (50% or more) meanwhile that of the microbial agent on them was less than 20%. Also, $CaO_2$ influenced on the microbial flora: Desulfobvibrio thermophilus, a sulfate reducing bacterium decreased in number, considering the increase of pH and rise of redox potential. In contrast, Pseudomonas sp., Pseudoalteromonas sp., Pseudomonas aeruginosa were remarkably dominant over other species with mixed treatment as a PCA analysis confirmed it.

• Geomechanics and Engineering
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• v.33 no.2
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• pp.121-131
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• 2023

Clay sedimentation has been widely analyzed for its application in a variety of geotechnical constructions such as mine tailing, artificial islands, dredging, and reclamation. Chemical flocculants such as aluminum sulfate (Al₂(SO₄)₃), ferric chloride (FeCl₃), and ferric sulfate (Fe(SO₄)₃), have been adopted to accelerate the settling behaviors of clays. As an alternative clay flocculant with natural origin, this study investigated the settling of xanthan gum-treated kaolinite suspension in deionized water. The sedimentation of kaolinite in solutions of xanthan gum biopolymer (0%, 0.1%, 0.5%, 1.0%, and 2.0% in a clay mass) was measured until the sediment height was stabilized. Kaolinite was aggregated by xanthan gum via a direct electrical interaction between the negatively charged xanthan gum molecules and positively charged edge surface and via hydrogen bonding with kaolinite particles. The results revealed that the xanthan gum initially bound kaolinite aggregates, thereby forming larger floc sizes. Owing to their greater floc size, the aggregated kaolinite flocs induced by xanthan gum settled faster than the untreated kaolinite. Additionally, X-ray computed tomography images collected at various depths from the bottom demonstrated that the xanthan gum-induced aggregation resulted in denser sediment deposition. The findings of this study could inspire further efforts to accelerate the settling of kaolinite clays by adding xanthan gum.

• The Korean Journal of Malacology
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• v.18 no.1
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• pp.53-59
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• 2002

The distribution and density of the pen shell, Atrina (Servatrina) pectinata japonica, were investigated to estimate population ecological parameters and biomass. Samples were collected during cruises from April to June 1999 in the coastal waters of Chungchung-namdo, Korea. The oceanographic conditions such as depth, temperature, transparency and suspended solids were measured from sampling stations. Seawater depth ranged from 3.9 m to 75.9 m and the mean was 28.5 m (SE = 0.97). The mean density of the pen shell was higher in the depth of 18.0-30.8 m. The water temperature of the bottom ranged from 7.0-21.5$^{\circ}C$ and the mean was 14.$0^{\circ}C$. The transparency ranged from 1.2-13.5 m and the mean was 4.8 m. The suspended solids ranged from 6.0-93.5 mg/l and the mean was 48.0 mg/l. The sand proportion of the sediment was > 50%. The mean densities of the pen shell by sediment type were 7.3 individuals/40 m$^2$ (SE = 2.16) in the sand, 5.6 individuals/40 m$^2$ (SE = 1.48) in the muddy sand, 3.0 individuals/40 m$^2$(SE = 1.89) in the sandy mud, and none in the mud. The sandy bottom, accounting for 29.8% of the overall habitat area, had a maximum density of 7.3 individuals/40 m$^2$.