• Journal of Korean Society of Environmental Engineers
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• v.28 no.4
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• pp.438-446
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• 2006

A lab-scale batch test was conducted to develop capping materials to reduce the sediment phosphorus in the stagnant water zone of Gyeongancheon in Paldang Lake. The mean grain size(Mz) of sediment in the investigated area was 7.7 ${\phi}$, which is very fine, and the contents of organic carbon($C_{org}$) was 2.4%, which is very high. For the phosphorous release experiment to select the optimal capping material, sand layer, powder-gypsum($CaSO_4{\cdot}2H_2O$), granule-gypsum, complex layer(gypsum+sand) and the control were compared and evaluated in the 150 L reactor for 45 days. In case of the capping with the sand, it was found that the phosphorous from the sediment could be reduced by around 50%. However, it was found that this caused the reduction of the dissolved oxygen in the water column(by less than 3 mg/L) due to the resuspension of sediment and the organic matter decomposition that comes from the generation of $CH_4$ gas in the 1 cm of the sand layer. Therefore, it is likely that the sand layer has to be thickener in case of the sand capping. Powder-gypsum and granule-Gypsum reduced phosphorous release by more than 80%. However, the concentration of ${SO_4}^{2-}$ in the water column increased, making it difficult to apply it to the drinking water protection zone. We developed Fe-Gypsum and $SiO_2$-gypsum materials to reduce the solubility of ${SO_4}^{2-}$. Powder-Gypsum creates the interception film that does not have any aperture on the sediment layer when it is combined with the water. However phosphorous release caused by the generation of $CH_4$ gas may happen at a time when the gypsum layer has the crack. Capping through the complex layer(granule-Gypsum+sand(1 cm)) found to be suitable for the drinking water protection zone because it was effective to prevent phosphorus release. Moreover, this leads to the lower solubility from the concentration of ${SO_4}^{2-}$ into the water column than the powder-Gypsum and granule-Gypsum. The addition of gypsum($CaSO_4{\cdot}2H_2O$) into the sediment can reduce the progress of methanogensis because fast early diagenesis and sufficient supply of ${SO_4}^{2-}$ to the sediment, stimulate the SRB(sulfate reducing bacteria) highly.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.687-697
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• 2019

By monitoring sediment grain size and level variation of tidal flat surface for 6 years (2005-2011), and also by mooring TISDOS (tidal-flat sediment dynamics observation system) on the low intertidal flat in 2008, we investigated the sedimentary environment of tidal flat in the dammed Yeongsan River Estuary. The tidal flat of the Yeongsan River Estuary lost 82 % of its area because of coastal development projects, and a narrow tidal flat below mean sea level now remains. Most of the tidal flat sediments are composed of silt up to 70-94 %, and show the characteristics of clay deficiency and silt dominance. This is closely related with the coastal development, which led to the destruction of high tidal flats where most mud settled, and the modification of tidal current patterns. Moreover, the estuarine tidal-flat sediments reveal seasonal variation. They are coarse with abundant silt during windy autumn to spring, fine with abundant clay during the less-windy and high-discharge summer. This phenomenon indicates that the behavior of sediment particles on the low intertidal flats of the Yeongsan River Estuary is influenced by wind waves for silt and fresh water discharge and the tidal process for clay. Monitoring results of the altitude of tidal flat surface showed that the study area had eroded at an average rate of -2.6 cm/y during the period of 2005-2011, and also that an unusual deposition with a rate of 4 cm/y occurred in 2010. The erosion can be explained by an increased tidal amplitude and a strengthened ebb-dominant tidal asymmetry after the construction of an estuary dike and the Yeongam Kumho Seawall. The deposition in 2010 seems to have been closely related to the mass production of suspended materials from dredging of the estuary.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.2
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• pp.117-126
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• 1999

Hampyong Bay is a semienclosed and macrotidal bay which opens to the eastern Yellow Sea through a narrow inlet in the southwestern coast of Korea. In order to understand the tidal-flat sedimentation in the semienclosed setting, morphology, sediments, accumulation rate and sea cliff erosion were investigated in the tidal flat of Hampyong Bay. The tidal flat of Hampyong Bay lacks intertidal drainage systems, and generally shows the concave-upward profile whose relief is designated by marked morphological features such as high-tide beaches, intertidal sand shoals and tidal creeks. Surfacial sediments of the tidal flat mainly consist of mud, sandy mud, gravelly mud, gravelly sand and muddy gravel, thus showing the textural characteristics of multimodal grain-size distribution, poorly sorting and positive skewness. The sediments generally coarsen landward due to the increase in coarse fraction content. Sedimentary structures are deeply bioturbated, but parallel lamination and lenticular bedding are locally found in the mudflat near mean low water line. Annual accumulation rates across the tidal flat (along Line SM) average -5.2 cm/yr with a range of -45.8~+4.2 cm/yr, indicating that the tidal flat is erosional. In general, erosion rates of upper and lower tidal flat are higher than those of middle tidal flat. Seasonally, the erosion rates are much higher during spring and winter when dominant wind direction corresponds to the long axis of Hampyong Bay. Sea cliffs are eroded at a rate of 1.4 m/yr. The biggest sea cliff erosion generally occurs 1~2 months later after tidal flats were extensively eroded. Such erosions of tidal Oats and sea cliffs in the semienclosed bay setting are interpreted to be due to wind waves coupled with local sea-level rise.

• Journal of The Korean Society of Grassland and Forage Science
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• v.33 no.2
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• pp.87-93
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• 2013

'Okhan' (Avena sativa L.), an oat cultivar for winter use, was developed by the breeding team at the Department of Rice and Winter Cereal Crop, NICS, RDA in 2011. It was derived from an original cross between 'Early80', exhibiting early heading, and 'Maine PI-590' (CI 7518), exhibiting large-size grain, in 1995. Subsequent generations as well as cross-bred cultivars were handled in bulk, and pedigree selection programs took place at Suwon and Yeoncheon, respectively. A promising line, 'SO95027-B-45-16-10-6-2-Y7-10', was selected in 2004, and was designated 'Gwiri74' after being selected from a yield trial for three years from 2005 to 2008. The breeding line 'Gwiri74' was subsequently evaluated for earliness of heading and forage yield in four different locations, Yesan, Iksan, Kimjae, and Jeju, from 2009 to 2011, and was finally named as 'Okhan'. Over 3 years, the heading date of 'Okhan' was about 6 days earlier than that of the check cultivar 'Samhan', and their average forage dry matter yield harvested at the milk-ripe stage was 15.0 ton $ha^{-1}$, compared with 14.1 ton $ha^{-1}$ of check cultivar. Cultivar 'Okhan' was lower than the check cultivar 'Samhan' in terms of the protein content (9.2% and 9.9%, respectively) and total digestible nutrients (58.5%, and 59.3%, respectively), while the TDN yield per ha was more than the check (8.70 and 8.36 kg, respectively). Fall sowing cropping of 'Okhan' is recommended only in areas where average daily minimum mean temperatures in January are higher than $-7^{\circ}C$, and it should not be cultivated in mountain areas, where frost damage is likely to occur.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.11
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• pp.1180-1185
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• 2006

Lab-scale batch experiments using several 25-L transparent acrylic reactors were conducted to develop optimum capping materials that can reduce phosphorus released from polluted sediments. The sediment used in the experiment was very fine clay(8.8 $\Phi$ in mean grain size), and organic carbon($C_{org}$) content was as high as 2%. Four kinds of batches with different capping materials Brucite($Mg(OH)_2$), Sea sand($SiO_2$), Granular-gypsum($CaSO_4{\cdot}2H_2O$), Double layer(brucite+sand), and one control batch were operated for 30 days. Phosphorus fluxes released from bottom sediments in the control batch were estimated to be 14.6 $mg{\cdot}m^{-2}{\cdot}d^{-1}$, while 9.5 $mg{\cdot}m^{-2}{\cdot}d^{-1}$, 5.2 $mg{\cdot}m^{-2}{\cdot}d^{-1}$, 4.2 $mg{\cdot}m^{-2}{\cdot}d^{-1}$, and 3.1 $mg{\cdot}m^{-2}{\cdot}d^{-1}$ in the batch capped with Sea sand, Granular-gypsum, Double layer, and Brucite, respectively. The results obtained from lab-scale batch experiments show that there were 70% reduction of phosphorus for some materials such as Brucite, Double layer(brucite+sand), and whereas sea sand only about 35%. The pH range of surface sediment to which Brucite was applied showed about $8.0{\sim}9.5$ in the weak alkaline state. This effect can prevent liberation of $H_2O$. The addition of gypsum into the sediment can reduce the progress of methanogenesis because of fast early diagenesis and sufficient supply of $SO_4^{2-}$ to the sediments, stimulate the SRB highly. Therefore, the application of Brucite and Gypsum can reduce phosphorus release from the sediment as a result of formation of $Mg_5(OH)(PO_4)_3$, pyrite($FeS_x$), and apatite-mineral.