• Economic and Environmental Geology
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• v.53 no.5
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• pp.619-629
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• 2020

The National Groundwater Monitoring Network (NGMN) in South Korea has been implemented in alluvial/ bedrock aquifers for efficient management of groundwater resources. In this study, aquifer types were reclassified with unconfined and confined aquifers based on water-level fluctuation and water quality characteristics. Principal component analysis (PCA) of water-level data from paired monitoring wells of alluvial/bedrock aquifers results in the principal components of both aquifers showing similar water-level fluctuation pattern. There was no significant difference in the rate of water-level rises responding to precipitations and in the NO₃-N concentrations between the alluvial and bedrock aquifers. In contrast, in the results classified with the hydrogeological type, the principal components of water level were different between unconfined and confined conditions. The water-level rises to precipitation events were estimated to be 4.6 (R²=0.8) in the unconfined and 2.1 (R²=0.4) in the confined aquifers, respectively, indicating less impact of precipitation recharge to the confined aquifer. The confined aquifers have the average NO₃-N concentration below 3 mg/L, implying the natural background level protected from the sources at surface. In summary, reclassification of aquifers into hydrogeological types clearly shows the differences between unconfined and confined aquifers in the water-level fluctuation pattern and NO₃-N concentrations. The hydrogeologic condition of aquifer could improve groundwater resource management by providing critical information on groundwater quantity through recharge estimation and quality for protection from potential contamination sources.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.260-263
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• 2005

Uncontrolled landfills have been a threat to surrounding environment and human health. To examine the effect of hydrogeological properties on plume migration caused by landfill leachate, two representative landfills in Cheonan and Wonju were selected. In these landfills, seven and eight groundwater wells were installed respectively to monitor water quality and waterlevel, and to perform hydraulic and tracer tests. This study reports preliminary evaluation results including site characteristics, waterlevel measurement and slug tests.

• Korean Journal of Ecology and Environment
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• v.50 no.3
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• pp.337-354
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• 2017

Cyanobacteria Aphanizomenon population is widely distributed in the world, and well known as harmful algae by producing toxins and off-flavor materials, thus belonging to one of the taxa that became more interested in the field of limnoecology. In this study, the frequency, intensity, and duration of Aphanizomenon occurrence were increased with the abnormal drawdown of water level in the winter in Boryeong Reservoir, and the spatial and temporal characteristics of them are compared with each other in the perspective of hydrometeorology (1998 to 2017) and limnology (2010 to 2017). In Korea, Aphanizomenon flourished mainly in high temperature, and the appearance in the low temperature was rare in total five times. The harmful cyanobacteria Aphanizomenon was observed in the low temperature (December to February) in Boryeong Reservoir from 2014, and then reached a maximum value of $2,160cells\;mL^{-1}$ in January 2017. In addition, the period exceeding $1,000cells\;mL^{-1}$ at this time was more than 3 months. This was simultaneously associated with abnormal water level fluctuation in the low temperature ($<10^{\circ}C$). The large drawdown of water level in the winter season has the potential to promote or amplify the germination and development of harmful algae. Also, subsequent water quality and ecological impacts(e.g., algal toxins and off-flavor substances) need to be considered carefully.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.3
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• pp.189-201
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• 2013

To study characteristics of the water quality in the Hansan-Geoje bay, we analyzed the long term monitoring data collected at the two sites during the period of 1987~2010. The trophic state of the waters in Hansan-Geoje bay was the mesotrophic level by the classification of Wasmud et al.[2001]. The water nutrients increased steadily from a wet season (Aug.), it reached the maximum concentration peak in a dry season (Nov.), and then decreased steadily to the winter, it reached at the minimum value in May in the next year. The result of factor analysis divided the waters of Hansan-Geoje bay into the five factors (nutrient, season, inflow land water, pollution, internal production) and the factors represented the 76.82% on the status of the waters. According to time series analysis, temperature, DO and bottom DIP were increased, and pH and COD were decreased during the period of 1987~2010. In particular, the fluctuation trend of DIN has been turned from oversupply to shortage by the N/P ratio since before and after 1990's. The water quality of the Hansan-Geoje bay has been recovered except DIP since 1987, despite of its geographical characteristic which is a general semi-closesd bay and a massive aqua-culture ground. To preserve the waters in Hansan-Geoje bay, we need to know on the cause of the increase or accumulation of DIP, and we should continue to study on the interrelation between the aqua-culture and water environment.

• Ecology and Resilient Infrastructure
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• v.6 no.1
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• pp.23-33
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• 2019

Naeseong Stream is a sand-bed river that flows through the northern area of Gyeongbuk province. It is characterized by dynamic sandy bedforms developed in response to the seasonal hydrological fluctuation and by its unique riverine landscape called "white river." However, changes including construction of Yeongju Dam from 2010 and the extensive vegetation establishment around 2015 occurred along the Naeseong Stream. This paper aims to analyze climate, hydrology, and water quality as factors and to examine the possibility of channel changes accordingly. The second least precipitation during the last 60 years happened in 2015, which led to the lowest peak discharge in 50 years. The sediment characteristics of Naeseong Stream were not significantly different along the upstream and downstream reaches, but it was confirmed that annual minimum water level of the stream decreased continuously regardless of the dam construction. This suggests that intermittent drought and change in water quality are likely to provide favorable conditions for riparian vegetation establishment and the resulting physical changes have affected riverbed degradation. Therefore, it is necessary to conduct diversified monitoring in connection with river vegetation change in order to analyze the causes of river changes.

• Journal of Environmental Impact Assessment
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• v.27 no.6
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• pp.674-684
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• 2018

The purpose of this study is to construct ecological pond using LID technique in order to create naturally comfortable community space in urban idle space. The specification of the ecological pond is $110m^2$ of surface area, $0.45{\pm}0.02m$ of average depth, and bed material is composed of gravel (diameter ${\leq}60mm$), sand (diameter ${\leq}2mm$) and bentonite. Rainfall and water depth monitoring were conducted to determine the annual characteristics of inflow of the water for the ecological pond, result of total rainfall was 1,287 mm and showed a seasonal imbalance that accounted for 71.3% (918 mm) during July to August, but the annual mean water depth was kept constant at $0.45{\pm}0.02m$ due to the secondary water source. Annual trends of basic water quality showed a significant changes according to the season, such as water temperature ($5.2{\sim}28.8^{\circ}C$), DO (5.0 ~ 13.8 mg/L), EC ($113{\sim}265{\mu}S/cm$). BOD, COD, TN, and TP in physicochemical water quality tended to increase after October, but the ion parameters such as $NH_3$ and $PO_4{^{3-}}$ were generally low. Phytoplankton indicators Chl-a and BGA (blue green algae) showed a sharp increase from July to August, and green algae (Selenastrum bibraianum, Pediastrum boryanum etc.) and filamentous blue green algae (Phormidium sp.) emerged as a dominant species. The ion parameters ($F^-$, $Na^+$, $K^+$, $Mg^{2+}$, $Ca^{2+}$) were strongly correlated with the $Cl^-$ as a conservative substance (R=0.70~0.97, p<0.05). Water quality was influenced by the ambient environment such as seasonal changes or rainfall, and it was closely related to fluctuation of the inflow of the water. In the future, it is necessary to consider ecological connections by referring to the characteristics surveyed in this study in order to effectively manage the water quality and biodiversity of the ecological pond in idle space.

• Journal of Aquaculture
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• v.13 no.1
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• pp.87-99
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• 2000

Field survey on the variational characteristics of water quality and chlorophyll a concentraion were carried out at the 25 stations for four seasons in Kogum-sudo(Straits) southern coast of Korean Peninsula from Feburuary to October in 1993. We made an analysis on biological factor as chlorophyll a concentraion as well as physicio-chemical factors such as water temperature salinity sigma-t transparency dissolved oxygen(DO) chemical oxygen demand(COD) nutrients (ammonia, nitrite, nitrate, phosphate, and silicate) N/P ratio and suspended solid(SS). The waters in the Kogum-sudo were not stratified due to the tidal mixing. And the high productivity in photic layer were supported by high nutrients concentration from bottom waters. The high concen-trations of suspended solid in straits had a bad influence upon marine biology of nature and cultivations. In Kogum-sudo had a sufficient nutrients for primary productivity during a year. Especially phosphate and inorganic nitrogen were high the other side silicate was very low. The source of nutrients supply depend on rather mineralization of organic matters and input of seawater from outside than input of freshwaters from lands. Phytoplankton biomass as measured by chlorphyll a concentratiion was very high all the year round and it was controlled by the combination o f several environmental factors especially of phosphate in summer and dissolved nitrogen in other seasons.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.45-56
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• 2007

Direct estimation of the pollutant load(PL) should be carried out by the data filling in the missing intervals using an appropriate method because it is impossible in which the flow discharge(water quantity) or water quality(WQ) time-series data set have the missing intervals. In this study, the several methods estimating the water quality in the missing periods are suggested and the WQ and pollutants load change patterns are compared and evaluated based on the reproducible degree of the available data change patterns. The most appropriate method is finally suggested and the contribution factor deciding the influence degree and the PL characteristics of the river estuary is also suggested. Based on the PL estimation results using the several methods, the interpolation method considering the fluctuation of the available WQ data is shown to be most efficient. The PL patterns of the Han river estuary is classified as the discharge-dominated type. The data filling process is inevitable and the WQ estimation using the efficient and effective method should be carried out in order to estimate reasonable PL.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.238-238
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• 2015

There are demands for water environmental analysis of discharge processes in paddy fields, however, it is not fully understood in nutrients discharge process for watershed modeling. As hydrological processes both surface and ground water and agricultural water managements are so complex in paddy fields, the development of lowland paddy fields watershed model is more difficult than upland watershed model. In this research, the improvement of SWAT (Soil and Water Assessment Tool) model for a paddy watershed was conducted. First, modification of surface inundated process was developed in improved pot hole option. Those modification was evaluated by monitoring data. Second, the monitoring data in river and drainage channel in lowland paddy fields from 2012 to 2014 were analyzed to understand discharge characteristics. As a case study, Imbanuma basin, Japan, was chosen as typical land and water use in Asian countries. In this basin, lowland paddy fields are irrigated from river water using small pumps that were located in distribution within the watershed. Daily hydrological fluctuation was too complex to estimate. Then, to understand surface and ground water discharge characteristics in irrigation (Apr-Aug) and non-irrigation (Sep-Mar) period, the water and material balance analysis was conducted. The analysis was composed two parts, watershed and river channel blocks. As results of model simulation, output was satisfactory in NSE, but uncertainty was large. It would be coming from discharge process in return water. The river water and ground water in paddy fields were exchanged each other in 5.7% and 10.8% to river discharge in irrigation and non-irrigation periods, respectively. Through this exchange, nutrient loads were exchanged between river and paddy fields components. It suggested that discharge from paddy fields was not only responded to rainfall but dynamically related with river water table. In general, hydrological models is assumed that a discharge process is one way from watershed to river. However, in lowland paddy fields, discharge process is dynamically changed. This function of paddy fields showed that flood was mitigated and temporally held as storage in ground water. Then, it showed that water quality was changed in mitigated function in the water exchange process in lowland paddy fields. In future, it was expected that hydrological models for lowland paddy fields would be developed with this mitigation function.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.487-492
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• 2008

In this paper, Thermocatalytic decomposition of methane in a fluidized bed reactor (FBR) was studied. The technical approach is based on a single-step decomposition of methane over carbon catalyst in air/water vapor free environment. The factors affecting methane decompostion catalyst activity in methane decomposition reactions were examined. The fluidization phenomena in a gas-fluidized bed of catalyst was determined by the analysis of pressure fluctuation properties, and the results were confirmed with characteristics of methane decomposition. The effect of parameters on the H2 yield was examined for methane decompostion. The decompstion rate was affected by the fluidization quality such as mobility, U-Umf, carbon attrition, elutriation and effectiveness density of fluidization gas.