• Journal of Korean Society on Water Environment
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• v.36 no.4
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• pp.284-299
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• 2020

Dam reservoirs play a particularly crucial role in processing the allochthonous and the autochthonous dissolved (DOC) and the particulate (POC) organic carbon and in the budget of global carbon cycle. However, the complex physical and biogeochemical processes make it difficult to capture the temporal and spatial dynamics of the DOC and the POC in reservoirs. The purpose of this study was to simulate the dynamics of the DOC and the POC in Daecheong Reservoir using the 3-D hydrodynamics and water quality model (AEM3D), and to quantify the mass balance through the source and sink fluxes analysis. The AEM3D model was calibrated using field data collected in 2017 and showed reasonable performance in the water temperature and the water quality simulations. The results showed that the allochthonous and autochthonous proportions of the annual total organic carbon (TOC) loads in the reservoir were 55.5% and 44.5%, respectively. In season, the allochthonous loading was the highest (72.7%) in summer, while in autumn, the autochthonous loading was the majority (77.1%) because of the basal metabolism of the phytoplankton. The amount of the DOC discharged to downstream of the dam was similar to the allochthonous load into the reservoir. However, the POC was removed by approximately 96.6% in the reservoir mainly by the sedimentation. The POC sedimentation flux was 36.21 g-C/㎡/yr. In terms of space, the contribution rate of the autochthonous organic carbon loading was high in order of the riverine zone, the transitional zone, and the lacustrine zone. The results of the study provide important information on the TOC management in the watersheds with extensive stagnant water, such as dam reservoirs and weir pools.

• Korean Journal of Ecology and Environment
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• v.51 no.1
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• pp.86-95
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• 2018

The objective of this study was to describe the development and testing of an initial ecological health assessment model, based on the index of biological integrity (IBI) using fish assemblages, before establishing the final and currently used model for ecological health assessment, conservation and management of freshwater fish in Korea. The initial fish IBI model was developed during 2004~2006 and included 10 metrics, and in 2007 the final IBI 8-metric model was established for application to streams and rivers in four major Korean watersheds. In this paper, we describe how we developed fish sampling methods, determined metric attributes and categorized tolerance guilds and trophic guilds during the development of the multi-metric model. Two of the initial metrics were removed and the initial evaluation categories were reduced from six to four (excellent, good, fair, poor) before establishing the final national fish model. In the development phase, IBI values were compared with chemical parameters (BOD and COD as indicators of organic matter pollution) and physical habitat parameters to identify differences in IBI model values between chemical and physical habitat conditions. These processes undertaken during the development of the IBI model may be helpful in understanding the modifications made and contribute to creating efficient conservation and management strategies for stream environments to be used by limnologists and fish ecologists as well as stream/watershed managers.

• Journal of Korea Water Resources Association
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• v.40 no.6 s.179
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• pp.469-483
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• 2007

Nitrate and chloride are the most common contaminants in groundwater and their concentrations increase easily due to fertilizer consumption and urbanization. The number of time series data for groundwater quality at a single site was not sufficient to analyze trends on Jeju Island. Therefore rectangle grids were drawn for the whole island and single grid was determined to be $500m{\times}500m$ after considering similar stream density, homogeneous hydraulic coefficients, geologic features of volcanic rock and low topographic slopes. All data within each lattice were collected and arranged in time series order and analyzed using Sen's method. 10.6 % of the total lattices for chloride and 22.4% for nitrate showed upward trends from the early 1990's to the early 2000's. Especially, upward trends for nitrate concentration are distinct in the low mid-mountainous areas of western and southern watersheds. Many septic tanks and much domestic waste from the urbanization of the low mid-mountainous area have produced this upward trend. Additionally, the agricultural region has dramatically increased since the 1990's and this has led to an increase of fertilizer consumption and, as a result, nitrate concentration. Therefore, the target of any management plan for groundwater quality on Jeiu Island needs to be focused on careful land use decisions in the mid-mountainous areas which are near Halla Mountain.

• Journal of Korean Society on Water Environment
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• v.28 no.3
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• pp.375-383
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• 2012

Soil erosion has been emphasized as serious environmental problem affecting water quality in the receiving waterbodies. Recently, Best Management Practices (BMPs) have been applied at a field to reduce soil erosion and its effectiveness in soil erosion reduction has been monitored with various methods. Although monitoring at fields/watershed outlets would be accurate way for these ends, it is not possible at some fields/watersheds due to various limitations in direct monitoring. Thus modeling has been suggested as an alternative way to evaluate effects of the BMPs. Most models, which have been used in evaluating hydrology and water quality at a watershed, could not reflect rainfall intensity in runoff generation and soil erosion processes. In addition, source codes of these models are not always public for modification/enhancement. Thus, runoff-sediment evaluation system using hourly rainfall data and vegetated filter strip (VFS) evaluation module at field level were developed using open source MapWindow GIS component in this study. This evaluation system was applied to Bangdongri, Chuncheonsi to evaluate its prediction ability and VFS module in this study. The NSE and $R^2$ values for runoff estimation were 0.86 and 0.91, respectively, and measured and simulated sediment yield were 15.2 kg and 16.5 kg indicating this system, developed in this study, can be used to simulate runoff and sediment yield with acceptable accuracies. Nine VFS scenarios were evaluated for effectiveness of soil erosion reduction. Reduction efficiency of the VFS was high when sediment inflow was small. As shown in this study, this evaluation system can be used for evaluation BMPs with local rainfall intensity and variations considered with ease-of-use GIS interface.

• Journal of Korean Society on Water Environment
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• v.25 no.4
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• pp.589-596
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• 2009

The spectroscopic characteristics and chemical oxygen demand (COD) oxidation efficiencies were investigated for dissolved organic matters (DOM) from diverse sources, which may indirectly affect the concentrations and the quality of DOM found in watersheds. The DOM investigated for this study showed a wide range of the percent distributions of refractory organic matter (R-OM) from 8 to 100%. Relatively high R-OM distributions were observed for the DOM with the source of head water, sediments, paddy soils, field soils, and treated sewage whereas the DOM from livestock waste, reed, weeds, algae, and attached algae exhibited lower R-OM percent distributions. The percent distribution of R-OM had positive correlations with specific UV absorbance (SUVA) and humidification indices (HIX) of DOM. The investigated DOM was classified into four different source groups (i.e., biota, vegetables, soils, sediments) by comparing the synchronous fluorescence spectra. The DOM group from biota source was characterized by a prominent presence of protein-like fluorescence (PLF) whereas fulvic-like fluorescence (FLF) was additionally observed for vegetable-source DOM. FLF became significant for the DOM from both soils and sediments although no PLF was found for soil-derived DOM. A range of COD oxidation efficiency was observed for the various DOM, ranging from 36 to 94% and from 65 to 125% for $COD_{Mn}$ and $COD_{Cr}$, respectively. The results indicate that $COD_{Cr}$ reflects the higher OM concentration than $COD_{Mn}$. However, 95% confidence intervals of the COD oxidation efficiencies were similar for the two types of COD, suggesting that $COD_{Cr}$ may not be the superior OM index to $COD_{Mn}$ in terms of the variability of the oxidation efficiency. No significant correlations were obtained between COD oxidation efficiencies and the spectroscopic characteristics of DOM for this study.

• Journal of Korea Water Resources Association
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• v.40 no.7
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• pp.555-570
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• 2007

The effects of climatic changes owing to urbanization on annual water balance have been studied. In this study, 56 meteorological stations including Seoul metropolis in South Korea have been selected, and the area of study site is $314\;km^2$. The meteorological station is centrally located in the study area with a 10 km radius. Land use status of study area was examined to estimate the urbanization extent, so that annual actual evapotranspiration could be estimated. Annual runoff was estimated by annual water balance approach using the estimated annual actual evapotranspiration and measured annual precipitation. Annual actual evapotranspiration was estimated by applying experimental equation suggested by Zhang et al, (2001) which was evaluated from 250 watersheds all over the world. Study results show that reference evapotranspiration is tending upwards due to urbanization; therefore, it seems that climatic change due to urbanization may increase the amount of annual actual evapotranspiration. However, the increase of residential area due to urbanization in study area may decrease the amount of annual actual evapotranspiration. The study results indicate that urbanization effect on annual trend of precipitation was not significant. In urban area, annual runoff is directly affected by annual precipitation, and compared with annual precipitation, annual variation of actual evapotranspiration was not significant even though it was estimated by using annual precipitation. It seems that the effect of urbanization on annual actual evapotranspiration does not influence on annual runoff significantly, and that urbanization effect on annual runoff Is not significant.

• Magazine of the Korean Society of Agricultural Engineers
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• v.23 no.1
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• pp.49-63
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• 1981

본 연구는 3개의 서로 다른 농지보전처리를 가진 시험구 및 테라스처리가 없는 목초용 Bromegrass 시험구에 있어서의 강우, 유출현상과 토양유실 관계를 규명함으로써 합리적인 농지보전 대책과 작부체계를 제시코저 하는데 그 목적이 있다. 강우, 유출 및 토양유실에 관한 분석고찰은 3개의 농지보전 시험구에서는 5년간(1972-1976년)의 자료를 그리고 Bromegrass 목초시험구에서는 3년간(1972-1974년)의 자료를 대상으로 하였다. 3개의 농지보전처리구는 첫째로 Non-terrace에 추경 춘조파형식의 관행법에 의한 비처리구와 둘째로 급역구배 테라스를 가진 초생수로에 가을 수확시 crop residue를 남겨두고 봄에 경작조파하는 Till plant system을 가진 초생수로구 그리고 마지막으로 지하배수와 함께 역구배 Terrace를 구비한 조파의 Till plant system 을 채용한 배수구를 나누어진다. Bromegrass 처리구는 Terrace나 기타 농지보전책이 없는 목초용 시험구이다. 이상의 연구에서 얻어진 결과를 요약하면 다음과 같다. 1. 시험기간대의 평균강수량은 네브라스카 링컨 지방의 76년간의 평균치, 728mm보다 66mm가 적은 662mm이였고 1974년과 1975년은 평균치보다. 300mm나 적은 극히 건조한 해 이였으며 1972년과 1976년은 거의 평균강수량에 가까웠고 1973년만은 평균치보다. 240mm나 더 많은 다우년 이었다. 2. 관행의 작부체계를 가진 비처리구에서의 연평균 유출고(2.44cm)는 역구배의 Terrace를 가지고 Till plant system을 채택한 초생수로구의 유출고(2.42cm)와 거의 유사하나 치였다. 3. 배수처리구로부터의 유출은 3개의 농지보전 처리구 중에서 5년간의 평균치가 1.57cm/year로 초생수로구와 비처리구의 유출보다 35%나 적은 가장 낮은 결과를 나타내었다. 4. Bromegrass 목초처리구에서의 유출은 방목정도에 따라서 영향되었다. 1972년의 무방축시 유출은 다른 3개 추리구로 부터의 유출으 7 내지 19%내인 0.07cm 정도였으나 1973년과 1974년의 방축년에는 조차 3개 처리구(3.4-5.18cm)에 필적되는 연평균 4.16cm로 나타났다. 5. 전체 시험구로부터으 연평균 토양유실량은 Sharpsburg 점질양토에 대한 S.C.S 한계허용치 10ton/ha/year 이내로 나타났다. 비처리구에서의 토양유실량은 평균 2.56ton/ha/year로 높게 나타난 반면 3개의 서로 다른 추리구인 비수구, 초생수로구 및 Bromegrass구에서는 각각 0.152, 0.192 및 0.290ton/ha/year로 낮은 결과를 가져왔다. 6. 평균 침전량에 대한 L.S.D. 검정 걸과 전시험구중 비처리구가 고도의 유의차를 나타낸 반면 비수구, 초생수로구 및 Bromegrass 목초구 간에는 아무런 유의차가 인정되지 않았다. 7. 농지보전 처리구인 배수구와 초생수로구는 비처리구에 비해 낮은 침두 유출량과 낮은 토양유실량을 나타내었다.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.3
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• pp.83-96
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• 2017

This study presented a surface water quality modeling framework considering the spatial resolution of pollutant load estimation to better represent stream water quality characteristics in the Saemangeum watershed which has been focused on keeping its water resources sustainable after the Saemangeum embankment construction. The watershed delineated into 804 sub-watersheds in total based on the administrative districts, which were units for pollutant load estimation and counted as 739 in the watershed, Digital Elevation Model (DEM), and agricultural structures such as drainage canal. The established model consists of 7 Mangyung (MG) sub-models, 7 Dongjin (DJ) sub-models, and 3 Reclaimed sub-models, and the sub-models were simulated in a sequence of upstream to downstream based on its connectivity. The hydrologic calibration and validation of the model were conducted from 14 flow stations for the period of 2009 and 2013 using an automatic calibration scheme. The model performance to the hydrologic stations for calibration and validation showed that the Nash-Sutcliffe coefficient (NSE) ranged from 0.66 to 0.97, PBIAS were -31.0~16.5 %, and $R^2$ were from 0.75 to 0.98, respectively in a monthly time step and therefore, the model showed its hydrological applicability to the watershed. The water quality calibration and validation were conducted based on the 29 stations with the water quality constituents of DO, BOD, TN, and TP during the same period with the flow. The water quality model were manually calibrated, and generally showed an applicability by resulting reasonable variability and seasonality, although some exceptional simulation results were identified in some upstream stations under low-flow conditions. The spatial subdivision in the model framework were compared with previous studies to assess the consideration of administrative boundaries for watershed delineation, and this study outperformed in flow, but showed a similar level of model performance in water quality. The framework presented here can be applicable in a regional scale watershed as well as in a need of fine-resolution simulation.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.1
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• pp.1-16
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• 2020

The APEX model has been developed for assessing agricultural management efforts and their effects on soil and water at the field scale as well as more complex multi-subarea landscapes, whole farms, and watersheds. Recently, a key component of APEX application, named APEX-Paddy, has been modified for simulating water quality by considering paddy rice management practices. In this study, the performance of the APEX-Paddy model was evaluated using field data at Iksan experimental paddy sites in Korea. The discharge and pollutant load data during 2013 and 2014 were used to both manually and automatically calibrate the model. The APEX auto-calibration tool (APEX-CUTE 4.1) was used for model calibration and sensitivity analysis. Results indicate that APEX-Paddy reasonably performs in predicting runoff discharge rate and nitrogen yield. However, sediment and phosphorus yield is not correctly predicted due to the limitation of model schemes. With APEX-Paddy, the performance in reproducing the discharge and nitrogen yield is found to be a satisfactory level after manual calibration. The manually calibrated model performed better than the automatically calibrated model in nearly all comparisons. For runoff, manual calibration reduced PBIAS while R² and NSE values of the automatically calibrated model were the same as the manual calibration. For T-N, NSE and PBIAS were reduced when using manual calibration, whereas R² value was the same as manual calibration. The limitation of the APEX-Paddy model for predicting sediment, as well as the phosphorous yield, was discussed in this study.

• Korean Journal of Environmental Biology
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• v.17 no.3
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• pp.345-358
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• 1999

To study the influences of thermal effluents flowing from hot spring on epilithic algal community, seasonal survey was carried out at stream and its watersheds from Seokjeong hot spring in Chollabuk-Do, Korea. Totally 7 points were divided into three regions fur sampling of water and epilithic algae, such as the direct effected, uneffected and the mixed region, respectively. At the discharging points of effluents, a dark-green cyanobacterial mat were remarkably constructed, mainly by two cyanobacteria, Oscillatoria and Phormidium. The mat formation were more obvious at low temperature than any other season, and even result in disappear with downstream and season. Totally, one hundred and fifty-three taxa of epilithic algae were classified with 15 unidentified species. Among the, diatoms occupied 58％ of total species, whereas cyanobacteria was 67% of total biomass, comparatively. In terms of stream direction, relative abundance of cyanobacteria was only limited in the upstream in cold season, and result in this pattern disappeared with season change. Although all physicochemical variables at the discharging points, was very high, compare to other points, they were quickly decreased downstream. Among them, some heavy metals were not detected or below the detection levels at downstream. Nitrate nitrogen increased with downstream, as well as phosphorus and sulfate have a similar trend throughout, while ammonia quickly decreased in the initial period of discharging effluents. This suggest that although the thermal effluent with high temperature and organic compounds could polluted the small study stream, various contributions such as flowing water, intake of uneffected streawater and collaboration of cyanobacterial mat and stream bottom gradually induces a stable water system.