• Journal of Korea Water Resources Association
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• v.54 no.10
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• pp.779-793
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• 2021

Water stress and environmental drivers are important factors to explain the variance of gross primary production (GPP). Environmental drivers are used to generate GPP in Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm and process-based model. However, MODIS algorithm only consider the vapor pressure deficit (VPD) data while the process-based biogeochemical model also uses limited data to express water stress. We compared the relationship between environmental drivers and GPP from eddy covariance method, MODIS algorithm, and Community Land Model 4 (CLM 4) simulation in normal years and drought years. To consider water stress specifically, we used VPD and evaporative fraction (EF). We evaluated the effects from environmental drivers and EF towards GPP products using the structural equation modeling (SEM) in South Korea. We found that GPP products from MODIS algorithm and model simulation results were not restricted from VPD data if VPD was underestimated. We also found that in the cropland area, irrigation effects can relieve VPD effects to GPP. However, GPP products derived from MODIS and CLM 4 had limitation to explain the irrigation effects to GPP. Overall, these results will enhance the understanding of GPP products derived from MODIS and CLM 4.

• Journal of the Korean GEO-environmental Society
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• v.9 no.6
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• pp.43-51
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• 2008

This study is to evaluate the NPP (Net Primary Production) distribution in the Geum River basin from NOAA/AVHRR satellite imagery data. It is supposed that the natural vegetation condition and the NPP has the linear relationship. The NPP from natural vegetation increases proportional to the annual net radiation (Rn), where radiative dryness index (RDI) is a proportional constant connecting net radiation to NPP. Normalized Difference Vegetation Index (NDVI) is used for monitoring vegetation change, and iNDVI (integrated NDVI) for annual analysis. The iNDVI has a close relation to Rn and NPP, which can be used effectively for estimating NPP distribution of where the meteorological data is unavailable. The purpose of this study is to propose a simple method to get NPP in the Geum river basin.

• Korean Journal of Remote Sensing
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• v.36 no.2_2
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• pp.237-247
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• 2020

Here, we generated maps of primary production in the coastal waters of the East Sea using sea surface chlorophyll-a concentrations (CHL), photosynthetically available radiation (PAR), euphotic depth induced by GOCI along with sea surface temperature (SST) from satellites of foreign countries as input parameters, and carried out a sensitivity analysis for each parameters. On 25th of July in 2013 when a wide cold waters appeared and on 13th of August in 2013 when a big harmful algal bloom existed in the study area, it shows high productivities with averages 1,012 and 1,945 mg C m^-2 d^-1, respectively. On August 25, 2013, when the cold waters and red tide retreated, it showed an average of 778 m^-2 d^-1, similar to the results of the previous analysis. As a result of the sensitivity analysis, PAR did not significantly affect the results of the primary production, but the euphotic depth and CHL showed aboveaverage sensitivity. In particular, SST had a large influence to the results, thus we could imply that an error in SST could lead to a large error in the primary production. This study showed that GOCI data was available for primary production study, and the accuracy of input parameters might be improved by applying GOCI, which can acquire images 8 times a day, making it more accurate than foreign polar orbit satellites and consequently, it is possible to estimate highly accurately primary production.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.127-127
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• 2011

본 연구에서는 RHESSys (Regional Hydro-Ecologic Simulation System) 모형을 이용하여 산림 유역의 생태수문학적 거동을 평가하고자 한다. 설마천 유역($8.48\;km^2$)을 대상으로 2007~2009년의 관측 일유출량을 이용하여 유출량을 검 보정하였고, 증발산량 및 토양수분은 신뢰할 만한 실측자료를 바탕으로 모형의 보정(2007-2008)및 검증(2009)을 실시하였다. 또한 지구의 탄소순환을 규명할 수 있는 식생의 순광합성량과 총일차생산량에 대한 모형의 검 보정은 Terra 위성의 MODIS (Moderate Resolution Imaging Spectroradiometer) 센서를 이용한 산출물인 순광합성량과 총일차생산량 자료를 바탕으로 모형의 보정(2007)및 검증(2008)을 실시하였다. 모형의 최적의 수문, 생리생태학, 토양의 매개변수를 선정하여 검증한 결과, 유출량에 대한 Nash-Sutcliffe 모형효율은 0.84, 증발산, 토양수분, 총일차생산량, 순광합성량의 결정계수는 0.49, 0.18, 0.38, 0.93 이었다.

• Journal of the Korean GEO-environmental Society
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• v.22 no.3
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• pp.15-29
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• 2021

The purpose of this study is to establish an ecosystem model that can predict ecosystem fluctuations in the Nakdong estuary, and use this model to calculate total primary production and respiration. AQUATOX model was used as the ecosystem model, and the model was calibrated and verified using the measured data. For the calibration of the model, chlorophyll-a data measured at the Nakdong estuary were used, and the model verification was performed using DO, TN, and TP data. In general, the total primary production and respiration volume vary greatly depending on the season, but the total primary production and respiration in the Nakdong estuary were greatly influenced by the amount of water discharged from Nakdong estuary bank. When the amount of effluent increased, photosynthesis could not be performed due to the loss of phytoplankton living in the lower area, and the total primary production amounted to zero, whereas the respiration increased sharply due to the inflow of organic substances contained in the effluent. The increase in the inflow water means the inflow of organic substances contained in the inflow water, and the organic substances are decomposed by oxidation, reducing dissolved oxygen. Compared with other countries' estuaries, the Nakdong estuary shows the lowest total primary production and because the respiration is larger than the total primary production, the dissolved oxygen is depleted by the oxidation of organic matter.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.218-218
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• 2023

일차생산은 화학합성 또는 광합성에 의하여 무기탄소가 유기물질로 전환되는 것을 의미한다. 한강은 하류로 갈수록 유속이 느리지만 수심이 깊어져 부착조류가 서식하기 쉽지 않은 환경이기에 대부분의 일차생산자는 식물플랑크톤이다. 선행연구와 비교 결과, 한강 본류의 부영양화가 여름철에 발생하고 있으며 팔당댐 방류량과 지류의 유입에 의한 유기물 증가로 하천 내 1차 생산의 기여도가 증가하고 있고, 이는 유기물 근원을 판정하여 수질오염에 대한 처리대책을 위해 지속적으로 연구가 필요하다. 따라서 본 연구는 한강본류에서 식물플랑크톤의 일차생산력을 조사하고, 유기물의 분해속도를 측정하여 당해 유역의 유기물 수지를 추정하여 한강 고유의 특성과 지류에서 기인할 수 있는 부영양화 기여도를 파악하여 부영양화에 의한 유기물 증가로 발생할 수 있는 수질오염을 예측하고자 한다. 조사유역은 한강의 팔당댐 방류구로부터 신곡수중보까지 전 구역 중 총 12개의 지점을 선정하였다. 기간은 2021년 5월부터 2022년 3월까지 계절별 2회로 총 8회 조사를 실시하였으며, 한강본류에서는 식물플랑크톤의 산소소비법을 통해 일차생산력과 유기물 분해속도를 조사하여 내부기원 유기물을 측정하였고, 한강본류로 유입되는 4개의 유입하천에서는 COD를 조사하여 외부기원 유기물을 측정하여 한강에서 발생하는 총유기물량을 산정하였다. 연구 결과, 하류 지점으로 갈수록 일차생산량이 점차 중가하였으며 지천이 유입되는 안양천, 탄천지점에서 유기물분해 속도가 빠르게 나타났다. 이는 수온 상승으로 인한 미생물 활성도가 높아져 식물플랑크톤의 일차생산량이 증가한 것으로 사료된다. 또한 여름 조사 전 강우에 의한 팔당댐 방류량 증가로 인해 식물플랑크톤 현존량이 다른계절에 비해 비교적 낮았지만, 호수의 부영양호 기준보다 높게 나타나 부영양한 수체로 판단하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.481-481
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• 2022

본 연구에서는 기후 변화 완화에 대한 잠재력을 평가하기 위해 국내에서 가장 우세한 소나무 종인 Pinus densiflora의 기후변화에 대한 반응을 평가하였다. 기후변화의 시나리오로 4가지 대표 농도경로(RCP)에 기반 하여 CO₂, 강수량, 온도의 변화를 개별 및 조합하였다. 생태수문학적 및 지구화학적 모델인 ecosys를 활용 및 보완하여 광릉 시험림에 적용하였다. 본 연구에서는 대기 중 CO₂ 증가가 총일차생산량(GPP)과 순일차생산량(NPP)에 미치는 긍정적인 영향이 강수량과 기온 변화로 인한 부정적인 영향보다 더 큰 것으로 나타났다. 특히, 기준 시나리오와 비교하여 각각 RCP2.6, 4.5, 6.5, 8.5에서 3.79%, 13.44%, 18.26%, 28.91%의 NPP 개선이 모의되었다. 또한, 본 연구에서는 지표하 질소 유출과 지표 N₂O 플럭스가 기후 변화가 심해짐에 따라 소나무 생장 향상 및 토양 수분 저하로 인하여 토양 질소 손실 감소가 모의되었다. 기후변화의 강도가 증가함에 따라 증발산량이 증가하였지만, 기공 감소는 토양에서 흡수하는 물이용 및 광합성 효율 증진을 가져왔다. 이러한 결과는 소나무가 기후 변화를 완화하는 환경 친화적인 선택으로 작용할 수 있는 잠재성을 나타낸다.

• Korean Journal of Remote Sensing
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• v.35 no.6_2
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• pp.1117-1132
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• 2019

Forest covers 30% of the Earth's land area and plays an important role in global carbon flux through its ability to store much greater amounts of carbon than other terrestrial ecosystems. The Gross Primary Production (GPP) represents the productivity of forest ecosystems according to climate change and its effect on the phenology, health, and carbon cycle. In this study, we estimated the daily GPP for a forest ecosystem using remote-sensed data from Moderate Resolution Imaging Spectroradiometer (MODIS) and machine learning algorithms Support Vector Machine (SVM). MODIS products were employed to train the SVM model from 75% to 80% data of the total study period and validated using eddy covariance measurement (EC) data at the six flux tower sites. We also compare the GPP derived from EC and MODIS (MYD17). The MODIS products made use of two data sets: one for Processed MODIS that included calculated by combined products (e.g., Vapor Pressure Deficit), another one for Unprocessed MODIS that used MODIS products without any combined calculation. Statistical analyses, including Pearson correlation coefficient (R), mean squared error (MSE), and root mean square error (RMSE) were used to evaluate the outcomes of the model. In general, the SVM model trained by the Unprocessed MODIS (R = 0.77 - 0.94, p < 0.001) derived from the multi-sites outperformed those trained at a single-site (R = 0.75 - 0.95, p < 0.001). These results show better performance trained by the data including various events and suggest the possibility of using remote-sensed data without complex processes to estimate GPP such as non-stationary ecological processes.

• 한국해양학회지
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• v.21 no.2
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• pp.73-84
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• 1986

Photometric Winkler titration provides high precision enough to use the oxygen method in moderately productive waters In short incubation (2-4hr), about $2{\mu\textrm{g}}C/\ell/h$ can be differentiated by the photometric titration. The oxygen and $^{14}C$ methods resulted in good agreement with each other in the diurnal primary production measurements. Despite small descrepancies the severe underestimation of $^{14}C-technique$ was not observed in short-term incubation. Size-fractionated production studies indicated the importance of nanoplanktonic production in the coastal water (62-88%). Bacterial respiration may lead to significant underestimation in estimating net photosynthesis in the oxygen method. In spite of some problems associated with the ecological application of antibiotics, it seems feasible to use Gentamycin in separating planktonic respiration from that of total community.

• Journal of Korea Water Resources Association
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• v.45 no.12
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• pp.1293-1307
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• 2012

This study is to evaluate the RHESSys (Regional Hydro-Ecological Simulation System) simulated streamflow (Q), evapotranspiration (ET), soil moisture (SM), gross primary productivity (GPP) and photosynthetic productivity (PSNnet) with the measured data. The RHESSys is a hydro-ecological model designed to simulate integrated water, carbon, and nutrient cycling and transport over spatially variable terrain. A 8.5 $km^2$ Seolma-cheon catchment located in the northwest of South Korea was adopted. The catchment covers 90.0% forest and the dominant soil is sandy loam. The model was calibrated with 2 years (2007-2008) daily Q at the watershed outlet and MODIS (Moderate Resolution Imaging Spectroradiometer) GPP, PSNnet and 3 year (2007～2009) daily ET data measured at flux tower using the eddy-covariance technique. The coefficient of determination ($R^2$) and the Nash-Sutcliffe model efficiency (ME) for Q were 0.74 and 0.63, and the average $R^2$ for ET and GPP were 0.54 and 0.93 respectively. The model was validated with 1 year (2009) Q and GPP. The $R^2$ and the ME for Q were 0.92 and 0.84, the $R^2$ for GPP were 0.93.