• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.522-525
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• 2003

Mine waters, surface waters and groundwaters were sampled around seven Au-Ag mine areas (Dongil, Okdong, Dongjung, Songcheon, Ssangjeon, Dogok and Gubong Au-Ag mines). The main contamination sources of As in these abandoned Au-Ag mines can be suggested as mine tailings and waste rocks including the sulfide gangue minerals (arsenopyrite). The relatively high concentration of As in mine waters was shown in the Dongil (524 ${\mu}g/L$) and the Dogok (56 ${\mu}g/L$) mine areas. Arsenic concentrations in stream waters from the Dongil ($0.9\~118{\mu}g/L$), the Songchon ($0.8\~63{\mu}g/L$), the Ssangjeon ($1.6\~109{\mu}g/L$) and the Gubong ($3.6\~63{\mu}g/L$) mine areas exceeded the permissible level for stream water in Korea. Groundwaters collected from the Dongil ($0.9\~64{\mu}g/L$ ), the Okdong ($0.2\~69{\mu}g/L$) and the Gubong ($0.5\~101{\mu}g/L$) mine areas contained high As concentration to cause the arsenicosis in these areas. In As speciation, the concentration ratios of As(III) to As(total) present up to $75\%$ and $100\%$ in stream waters from the Okdong and the Songcheon mines, and $70\%$ in groundwaters from the Okdong and the Dongjung mines. Arsenic concentration decreases downstream from the tailing dump correlatively with pH and Fe concentration. Highly elevated As concentrations are found in the dry season (such as April and March) than in the wet season (September) due to the dilution effect by heavy rain during summer in stream waters from the Dongil and the Songcheon mine areas.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.319-319
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• 2017

Methane is the main greenhouse gas released from rice paddy field. Methane from paddy fields accounts for 11 % of the global total methane emission. The global warming potential (GWP) of methane is 25 times more than that of carbon dioxide on a mass basis. It is well known that most effective practice to mitigate methane in paddy is related to the water management during rice growing season and the use of organic matters. This study was conducted to investigate the effects of tillage and cultivation method on methane emission in paddy. Tillage (tillage and no-tillage) and cultivation methods (transplanting and direct seeding) were combined tillage-transplanting (T-T), tillage-wet hill seeding (T-W), tillage-dry seeding (T-D) and no-till dry seeding (NT-D) to evaluate methane mitigation efficiency. Daily methane emission was decreased on seeding treatments (T-W, T-D, NT-D) than transplanting treatment (T-T). Amount of methane emission during rice growing season is highest in T-T ($411.7CH_4\;kg\;ha^{-1}y^{-1}$) and lowest in NT-D treatment (89.7). In T-W and T-D treatments, methane emissions were significantly decreased by 36 and 51 % respectively compared with T-T. Methane emissions were highly correlated with the dry weight of whole rice plant ($R^2=0.62{\sim}0.93$). T-T treatment showed highest $R^2$ (0.93) among the four treatments. Rice grain yields did not significantly differ with the tillage and cultivation methods used. These results suggest that direct seeding practice in rice production could mitigate the methane emissions without loss in grain yield.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.977-986
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• 1996

The uncertainty of rains at the onset of wet season (WS) and the drought risk involved hinder growing more than one rainfed lwoland rice crop per year. Establishing transplanted rice well into the WS leaves insufficient moisture in the soil for subsequent crop. Rice establishment early in the season gives the farmer better opportunities to grow a crop after rice. An experiment was conducted startign in 1993 to evaluate dry seeding of rice through slit soil seeding. It is done utilizing the vertical metering slit seeder for conserving soil moisture coming from the first rains in the early WS to sustain germination and establishment of the seeding at least until the succeeding rains under therainfed lowland (RL) environment. The treatment consisted of slit-seeding the PSBRc 14 into the tilled and nontilled plots at 100kg/ha and at depths of <10 mm (shallow seeding) and 60-70m (deep seeding). The control treatment was broadcast seeded on tilled soil and harrow to cover the seeds The superior crop establishment observed in 1995 WS experiment on nontilled, slit-seeded plots confirmed the results observed in 1993 WS and 1994 WS experiments. Emergence in deep seeding was not significantly different from shallow seeding in nontilled plots giving an average yield of 2.1 t/ha in all slit-seeded plots. This offers an advantage of reduced energy in put in nontilled shallow seeding. However, heavy weed infestation has to be addressed at the early stage of rice in nontilled soil to get the full advantage from slit seeding. The consistently better crop establishment observed in slit seeding over that of broadcast seeding in the WS of 1993, 1994 and 1995 also demonstrates that the slit seeding technology can be adopted with confidence in the rainfed lowland field condition to reduce the risks involved in broadcast seeding.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.856-864
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• 2006

For estimating the minimum discharge to maintain a river, low flow analysis is required and long term runoff records are needed for the analysis. However, runoff data should be estimated to run a hydrologic model for ungaged river basin. For the reason, parameter estimation is crucial to simulate rainfall-runoff events for those basins using Tank model. In this study, only runoff data recorded for dry season are used for parameter estimation, which is different to other methods based on runoff data recorded for wet and dry seasons. The Harmony Search algorithm is used to determine the optimum parameters for Tank model. The coefficient of determination ($R^2$) is served as the objective function in the Harmony Search. In cases that recorded data are insufficient, the recording interval is changed and Empirical CDF is adopted to analyze the estimated parameters. The suggested method is applied to Yongdam dam, Soyanggang dam, Chungju dam and Seomjingang dam basins. As results, the higher $R^2s$ are obtained when the shorter recording interval, the better recorded data quality, and the more rainfall events recorded along with certain rainfall amount is. Moreover, when the total rainfall is higher than the certain amount, $R^2$ is high. Considering the facts found from this study for the low flow analysis, it is possible to estimate the parameters for Tank model properly with the desired confidence level.

• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.173-184
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• 2004

The objective of this study is to examine the usefulness of climate model simulations (GCM) in Korea water resource management. The methods are based on probabilistic measures of the effectiveness of GCM simulations of an indicator variable for discriminating high versus low regional observations of a target variable. The formulation uses the significance probability of the Kolmogorov-Smirnov test for detecting differences between two variables. AMIP-II(Atmospheric Model Intercomparison Project-II) type GCM simulation done by ECMWF(European Centre for Medium-Range Weather Forecasts) was used for indicator variable and observed mean average precipitation(MAP) values on 7 major river basins were used as target variable. Monte Carlo simulation is used to establish the significance of the estimator values. The results show that GCM simulations done by ECMWF are skillful in discriminating the high from the low of the observed MAP for wet season in all seven basins of Korea, but not enough for dry season.

• Animal cells and systems
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• v.16 no.2
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• pp.162-171
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• 2012

We investigated food webs of a $Salix$ $subfragilis$-dominated wetland in the Janghang wetland in the Hangang estuary, which is very close to the Demilitarized Zone, along the west coast of Korea. Our study focused on understanding sesarmine crab ($Sesarma$ $dehaani$)-related food webs in a $S.$ $subfragilis$ forest. For our study, we used carbon and nitrogen stable isotopes and fatty acid biomarkers. We collected samples of plants, animals, and detrital sediment from four quadrats ($5{\times}5m^2$) set in the $S.$ $subfragilis$ community. Samples were collected from September 2006 to June 2009, except during the winter hibernation period of $S.$ $dehaani$. In the wet season, the sediment showed relatively high ${\delta}^{13}C$ and low ${\delta}^{15}N$ signatures compared with relatively low ${\delta}13C$ and high ${\delta}15N$ signatures in the dry season. Mature $S.$ $dehaani$ appeared to feed on fresh leaves and other carbon sources, such as immature individuals or fish, in addition to detrital sediment, which appeared to be the main carbon source for immature crabs. Principal component analysis of fatty acid biomarkers of $S.$ $dehaani$ showed a clear difference between immature individuals (10-30 mm) and mature ones (larger than 30 mm), indicating that the main food source for immature crabs was detrital sediment, whereas mature crabs foraged plants in addition to consuming detrital sediment. On the basis of our results from stable isotope and fatty acid analyses, mature $S.$ $dehaani$ appeared to feed on detrital sediment and fresh leaves of $S.$ $subfragilis$ in summer in addition to engaging in cannibalism of immature individuals.

• Environmental Engineering Research
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• v.13 no.3
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• pp.147-154
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• 2008

The purpose of this study was, as a preliminary step for understanding the whole aspects of the impacts of a weir on the ecosystems in upper and lower streams, to find out the impacts of the weirs with and without a fish-way. A survey on the aquatic ecosystem of upper and lower streams of weirs in Ham-an Stream was carried out from June to October, 2006. Results of the investigation showed that some meaningful effects on the ecosystems had occurred by the weirs. The fish fauna in upper stream of the weir with a fish-way appeared to include 3 families, 8 species, and 184 individuals, while that in the lower stream of the weir appeared to include 5 families, 14 species, and 664 individuals. The fish fauna in the upper stream of the weir without a fish-way appeared to include 3 families, 9 species, 107 individuals, while that in the lower stream of the weir appeared to include 9 families, 19 species, 520 individuals, disclosing that, no matter with or without a fish-way, fish fauna species diversity and size of population were more abundant and bigger in the lower stream than in the upper stream, but that difference of fish fauna species diversities between upper and lower streams of the weirs appeared to be bigger for the weir with a fish-way than for the weir without a fish-way. Benthos species diversity and size of population were found to be more abundant and bigger in lower stream than in upper stream, and in wet season than in dry season.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.25 no.3
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• pp.97-111
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• 2022

This study was conducted as restoration work to improve the discharge in forested wetlands where there is a concern of damage and observed changes in the discharge and groundwater level. The monthly changes showed that during the wet season, the amount of discharge decreased after restoration and GWL increased. It showed that during the dry season, the GWL and discharge increased. The increased discharge after restoration seems to be the difference in the number of days with no rainfall duration. The change in discharge for each unit of rainfall showed a tendency to increase the baseflow and decrease the direct discharge after restoration. The recharge ratio of GWL showed a decreasing tendency as rainfall was higher. After restoration, it showed a higher tendency under rainfall with less than 20mm. It has been confirmed that the restoration implemented by the study caused such an effect as the increased baseflow and increased GWL. It would be an effective restoration method to maintain water resources in forested wetlands. In the initial rainfall, it demonstrated a certain level of effect, but it is necessary to develop a restoration technology that can decrease the amount of water discharged after the end of rainfall or during the period of no rainfall to protect and maintain the forested wetlands. Streamflow should be identified by each type of terrain of wetlands and a proper restoration countermeasure should be devised for the site where the discharge frequently occurs.

• Fisheries and Aquatic Sciences
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• v.26 no.8
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• pp.491-499
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• 2023

Lake Tinisu Abaya is home to some fish species. The lake's native fish species include Barbus and Tilapia zilli. Tilapia fish (Oreochromis niloticus L.) were stocked in Lake Tinishu Aabaya in 1997. This study aimed to investigate the feeding behaviors of O. niloticus in Lake Tinishu Abaya to develop an appropriate fisheries management approach in the lake. 428 O. niloticus fish samples (2.5 to 30.9 cm and 1.1 to 475 g) were collected to calculate the diet composition. Out of the total of 428 gut contents examined, 55 (12.85%) were found to be empty and 373 (87.15%) to be containing one or more food items. The diet behavior of the stocked fish in the study lake revealed that phytoplankton (39.5% by volume) and macrophytes (25.81% by volume) were the most noteworthy food items followed by detritus (14.39%) and zooplankton (12.95%). With increasing fish size, the importance of phytoplankton, macrophytes, and detritus increased while the contribution of zooplankton, insects, and other foods with an animal origin decreased. Seasonal variation in the diet composition of fish was evident (t-test; p < 0.05). Macrophytes, zooplankton, and detritus were the dominating food items during the wet season, while phytoplankton predominated during the dry season. This study demonstrated that O. niloticus had phytoplanktivores that primarily consumed phytoplankton and that the seasons and fish size had a significant impact on their feeding preferences. The diet of O. niloticus in Lake Tinishu Abaya comprised foods with both plant and animal origins. It concludes that the dietary habit of O. niloticus in the lake is, generally, the omnivorous type.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.516-516
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• 2022

Agricultural reservoirs are critical water resources structures to ensure continuous water supplies for rice cultivation in Korea. Climate change has increased the risk of reservoir failure by exacerbating discrepancies in upstream runoff generation, downstream irrigation water demands, and evaporation losses. In this study, the variations in water balance components of 400 major reservoirs during 1973-2017 were examined to identify the reservoirs with reliable storage capacities and resilience. A conceptual lumped hydrological model was used to transform the incident rainfall into the inflows entering the reservoirs and the paddy water balance model was used to estimate the irrigation water demand. Historical climate data analysis showed a sharp warming gradient during the last 45 years that was particularly evident in the central and southern regions of the country, which were also the main agricultural areas with high reservoir density. We noted a country-wide progressive increase in average annual cumulative rainfall, but the forcing mechanism of the rainfall increment and its spatial-temporal trends were not fully understood. Climate warming resulted in a significant increase in irrigation water demand, while heavy rains increased runoff generation in the reservoir watersheds. Most reservoirs had reliable storage capacities to meet the demands of a 10-year return frequency drought but the resilience of reservoirs gradually declined over time. This suggests that the recovery time of reservoirs from the failure state had increased which also signifies that the duration of the dry season has been prolonged while the wet season has become shorter and/or more intense. The watershed-irrigated area ratio (W-I_ratio) was critical and the results showed that a slight disruption in reservoir water balance under the influence of future climate change would seriously compromise the performance of reservoirs with W-I_ratio< 5.