Lake Paldang Research Articles

Analysis of microplastic behaviors in river-type lakes using a quasi-three-dimensional microplastic transport model

Paldang Lake in South Korea is a river-type lake characterized by weak temperature stratification and a short water residence time. It exhibits complex flow structures resulting from the convergence of two major rivers, the North Han River (NHR) and the South Han River (SHR), and one small river, the Gyeongan Stream. Analyzing the spatio-temporal variations in microplastic (MP) concentration in Paldang Lake is important because of its significance as a water supply source for the metropolitan area. In this study, a quasi-three-dimensional MP transport model (MPT-Q3D) based on the Lagrangian particle-tracking technique was developed to analyze the trajectory and concentration distribution of MPs driven by shear dispersion in river-type lakes. Using the simulation results of MPT-Q3D, which were validated with MP monitoring data and EFDC simulations, we investigated the spatio-temporal variations in MP concentration during both low-flow and flood-flow periods. Simulation results showed that horizontal transport by shear flow contributed more to MP transport than vertical transport, including settling movements based on MP density. Thus, the MP transport during the low-flow period was significantly influenced by the recirculating flow induced by hydropeaking of the NHR, as well as flow blockage caused by the strong inflow momentum from the SHR. During the flood-flow period, flood discharge from the three tributary rivers had an equal influence on MP transport and the variation in MP concentrations around the water intake facilities. Furthermore, the MP residence time was primarily affected by variations in the flow characteristics of the inflowing tributaries rather than the properties of the MP types. Analysis of the influx and efflux of MPs in Paldang Lake revealed that polypropylene was the predominant constituent, accounting for 53.9 % and 75.2 % of all residual MPs during the low-flow and flood-flow periods, respectively.

Seasonal Variations in the Thermal Stratification Responses and Water Quality of the Paldang Lake

We evaluated the thermal and chemical stratifications of Paldang Lake using Schmidt’s stability index (SSI) and the chemical stratification index (IC-i) with weekly data from 2013 to 2022. The temporal trends of stratification were analyzed alongside correlations with meteorological, hydrological, and water quality variables. Thermal stratification intensified with rising air temperature and sunshine duration, while hydrological factors like discharge and retention time affected SSI during periods with less than five days of water retention. During summer, fewer occurrences of intense rainfall or early rainfall before August led to stronger stratification. In fall, nutrient influx from external sources during summer stimulated algal growth, increasing Chlorophyll-α (Chl-α) concentrations. Summer rainfall had a significant impact on the strength and duration of stratification in Paldang Lake. Annual rainfall patterns and subsequent changes in discharge were key factors affecting the physical environment of the lake, which in turn determined water quality and the extent of algal blooms. We provide insights into the seasonal stratification and water quality variations in temperate river-type reservoirs like Paldang Lake. SSI and IC-i from this research can be applied to understand stratification and mixing dynamics in other lakes.

Effect of Culture Temperature on 2-Methylisoborneol Production and Gene Expression in Two Strains of Pseudanabaena sp.

The presence of the odorant 2-methylisoborneol (2-MIB) in drinking water sources is undesirable. Although 2-MIB production is known to be influenced by temperature, its regulation at the gene level and its relationship with Chlorophyll-a (Chl-a) at different temperatures remain unclear. This study investigates the impact of temperature on 2-MIB production and related gene expression in Pseudanabaena strains PD34 and PD35 isolated from Lake Paldang, South Korea. The strains were cultured at three temperatures (15, 25, and 30 °C) to examine cell growth, 2-MIB production, and mic gene expression levels. 2-MIB production per cell increased with higher temperatures, whereas mic gene expression levels were higher at lower temperatures, indicating a complex regulatory mechanism involving post-transcriptional and enzyme kinetics factors. Additionally, the relationship between Chl-a and 2-MIB involved in metabolic competition was analyzed, suggesting that high temperatures appear to favor 2-MIB synthesis more than Chl-a synthesis. The distinct difference in the total amount of the two products and the proportion of 2-MIB between the two strains partially explains the variations in 2-MIB production. These findings highlight the significant effect of temperature on 2-MIB biosynthesis in Pseudanabaena and provide a valuable background for gene data-based approaches to manage issues regarding 2-MIB in aquatic environments.

Microplastic accumulation dynamics in Han river headwaters: Sediment interactions and environmental implication

The prevalence of microplastic (MP) contamination has become a significant environmental concern due to its pervasive nature and persistent effects. While sediments are considered major repositories for MPs, information on their spatial distribution within these matrices is insufficient. This research examined both the horizontal and vertical presence of MPs in the sediments surrounding Lake Paldang in South Korea, alongside a comprehensive evaluation of the physicochemical characteristics of the samples obtained. The total content of MPs varied from 2.15 to 122.2 particles g−1. The average contents of MPs on surface sediments were 40.47, 34.14, 5.01, and 8.19 particles g−1 in north mainstream (NM), south mainstream (SM), tributary (TB), and Tributary catchment (TC) based on Sonae Island, Gyeongan stream, respectively. The most abundant MP types were polyethylene (PE), polytetrafluoroethylene (PTFE), and polypropylene (PP), accounting for more than 70% of the total MPs. The most abundant sizes of MPs were within 45–100 µm. At all sediment depths, polymers were distributed in the order PE, PP, and polyester in NM, SM, and TC, respectively, whereas PTFE mainly occurred in the surface layer. MPs distribution also exhibited seasonal variation as larger inflows and flow rates varied with season.

Innovative interpretable AI-guided water quality evaluation with risk adversarial analysis in river streams considering spatial-temporal effects

Water security remains a critical issue given the looming threats of industrial pollution, necessitating comprehensive assessments of water quality to address seasonal fluctuations and influential factors while formulating effective strategies for decision makers. This study introduces a novel approach for evaluating water quality within a complex riverine zone in South Korea: Han River that encompasses five river streams situated at each junction of North and South streams (including Gyeongan Stream) that ultimately leading towards Paldang Lake. By utilizing the monthly water characteristic data from the year 2013–2022 across 14 different locations, the significant seasonal trends and potential influences on water quality are identified. The water quality here is calculated with the proposed method of sub-index water quality index (s-WQI). A combinatorial prediction approach of s-WQI for each location is conducted through a collective of data preprocessing approaches including Hampel filtering and feature selection in prior to the machine learning predictions. In return, light gradient boosting (LGB) is the most accurate predictor by outperforming other prediction algorithms, especially through LGB-Pearson and LGB-Spearman combinations for North and South stream intersections, and LGB-Pearson for Paldang Lake. To further evaluate the robustness of this evaluation and extending the results to a foreseeable scenario, a seasonal based Monte-Carlo Simulation with 10,000 attempts targeting the water characteristic distributions obtained from each location considered are carried out to identify the risk bounds within. The results are further interpreted with SHAP analysis on identifying the contributions of each water characteristics towards the water quality through local and global spectrum. This research yields practical implications, offering tailored strategies for water quality enhancement and early warning systems. The integration of AI-based prediction and feature selection underscores the transformative potential of computational techniques in advancing data-driven water quality assessments, shaping the future of environmental science research.

Effects of hydropeaking by an upstream dam on thermal mixing in a riverine lake

The hydropeaking operations of a hydropower dam can significantly affect the flow and thermal regimes in riverine reservoirs, and this effect is very complex, both in space and time. In this study, we used a 3D hydrodynamic model, calibrated with field datasets, to investigate the thermal mixing resulting from hydropeaking within Paldang Lake (PL) in South Korea. The spatiotemporal temperature patterns revealed that density currents critically affected thermal mixing in the reservoir and developed differently based on upstream dam operations and flooding events. Notably, the confluence of the North Han River (NHR) and South Han River (SHR) played a key role in shaping the thermal regime. During the hydropeaking release from the upstream dam in the NHR, the colder water of the NHR from the deep-water discharge of the upstream dam plunged beneath the warmer water of the SHR, leading to three-dimensional mixing. Consequently, the thermal mixing patterns varied depending on the discharge patterns from the upstream dam. Additionally, diurnal variations in the dam discharge frequently affected areas of the reservoir exhibiting high Schmidt stability. During the non-operation period of the upstream dam, the SHR flow backflowed into the downstream section of the NHR, resulting in the confluent area exhibiting the poorest vertical mixing. Secondary currents also played a crucial role in influencing the flow and thermal regimes, with the intensity of the secondary flow varying along the longitudinal mainstream of the reservoir. The thermal mixing state was predominantly weakened to partial mixing within a curved reach owing to the secondary current. Overall, this study demonstrates that the complexity of flow and thermal processes in the PL is significantly influenced by hydropeaking events. These findings emphasize the importance of understanding density currents and secondary flows according to dam operation in managing riverine reservoirs for enhanced ecological health and sustainable water resource management.

Study of the cause of the generation of odor compounds (geosmin and 2-methylisoborneol) in the Han River system, the drinking water source, Republic of Korea

Abstract Paldang Lake in the Han River system is an important source for supplying drinking water. Recently, the occurrence of odor compounds geosmin and 2-methylisoborneol (2-MIB), in Lake Paldang has adversely affected the drinking water supply. The causative organisms of odor compounds have not been identified. Thus, this study analyzed the correlation between odor compounds and microorganisms and identified the odor-producing microorganisms in the Han River system. Odor compounds were primarily detected in the Bukhan River system but not in the Namhan River system. Geosmin was detected at high concentrations in summer, whereas 2-MIB was detected at high concentrations in summer and autumn. Microorganisms that appeared at the time of geosmin occurrence were actinobacteria (0.317, p < 0.01) and Dolichospermum (0.326, p < 0.01) among cyanobacteria, and the correlation was significant. The occurrence of 2-MIB mainly coincided with actinobacteria (0.745, p < 0.01) and Pseudanabaena (0.321, p < 0.01) among cyanobacteria, and the correlation was significant. Therefore, to manage the odor compounds in Lake Paldang, which is a drinking water source, it is important to control the appearance of actinobacteria and cyanobacteria in the Bukhan River system.

A Study on Paldang Reservoir Water Quality Improvement Effect by Pollutant Source Location Regulation Using Watershed-Reservoir Integrated Prediction

Objectives:Since the enactment of the 「Han-River Watershed Act」, comprehensive analysis about direct and indirect contributions and effects of various environmental policies and water quality improvement projects for the preservation of water quality in the Han-River watershed is insufficient. Especially, effect of pollutant source location regulation should be inferred and estimated through model prediction because it does not exist unregulated conditions. As development pressure in non-urban areas near the metropolitan area is increasing, it is necessary to analyze the effects of pollutant source location regulation.Methods:In this study, average pollutant density of Gangwon-do, Gyeonggi-do, and Chungcheongbuk-do, where the regulation areas located, and average pollutant density of water source management areas were compared and analyzed. After that changes in pollutant sources in regulation areas were estimated by assuming load of pollutant sources in unregulated areas that load of pollutant sources in regulation areas. Since many reservoirs are located in Han-river watershed, it is difficult to simulate the water quality of Paldang reservoir using only watershed model, BASINS/WinHSPF and EFDC-WASP were linked. Through this, change in water quality of Paldang Lake was tried to predict when the pollutant location regulation was not implemented, and to analyze the effect of the pollutant location regulation.Results and Discussion:Water quality improvement of Paldang reservoir was evaluated by applying the discharge load when the pollution source location regulation was not implemented to the calibrated model. As a result of the pollution source location regulation, discharge load in the location regulation area was analyzed to reduce by 53.90% and T-P by 48.58%, and the BOD and T-P improvement effect of Paldang Dam was analyzed 6.77% and T-P 6.62%. Since the water quality improvement effect of Paldang Lake is accumulated to the entire upstream, it is evaluated relatively less than pollutant load reducing effect.Conclusion:It was analyzed that pollutiont source location regulation has water quality improvement effect, despite the small area which only located in near Paldang reservoir compared to the total area of the Han-River watershed.

팔당호의 호소 부영양화 관리를 위한 수질인자 분석

It is necessary to comprehensively understand about lake water quality, environmental factors to successfully manage environmental problems such as eutrophication and mass propagation of phytoplankton in lakes. When it comes to a method of eutrophication evaluation, Carlson’s trophic state index (TSI) has been used so far but was not suitable for artificial lakes in Korea. Accordingly, a new Korean trophic state index (TSIKO), was developed and utilized by National Institute of Environmental Research. The purpose of this research is to identify current situation of water quality in the six spots of artificial lakes, to measure eutrophication through Korean TSIKO, to finally provide information on lake eutrophication management. As a result, Chl-a (Chlorophyll a) of KAC9 showed higher than others. According to Korean TSIKO, nutritional status by lake In 2016 showed that Paldang Lake was mesotrophic·eutrophic In the long-term from 2008 to 2016, Korean TSIKO of Paldang Lake ranged from 44 to 50 and it was assessed mesotrophic·eutrophic as well. To conclude, in the Han River That is why going downstream and increasing inflow link to increasing retention time in the lake as well as an increase of algae, nutrients and so on, it could be reasons of eutrophication and needs management continuously with nonpoint pollution. This paper could be applied a basic resource for comprehensive management of lake eutrophication by types of lake.

Morphological and Molecular Studies of Three New Diatom Species from Mountain Streams in South Korea

In January 2019, epilithic diatoms were collected from two streams on Mount Gumdan and Mount Yongma near Lake Paldang in central South Korea. A total of 16 diatoms were isolated and classified by molecular and morphological analysis. Morphology was studied by LM and SEM, while the molecular study focused on small subunit (SSU) rRNA and ribulose bisphosphate carboxylase (rbcL) genes. Molecular analysis showed that the three species had clear differences in phylogenetic distance. Based on these findings, we studied the ultrastructure of three species. Among the morphological characteristics, Hannaea librata is longer but narrower and always has conical spines, while the similar species H. pamirensis has bifurcated spines in the central region and conical spines near the pole. Gomphonema seminulum is wider in the axial–central area than G. pumilium. Nitzschia inclinata has a bended valve apex, while N. oligotraphenta has a straight apex.

Effects of Long-Term Increases in Water Temperature and Stratification on Large Artificial Water-Source Lakes in South Korea

Long-term changes in air and water temperatures and the resulted stratification phenomena were observed for Soyang Lake (SY), Paldang Lake (PD), Chungju Lake (CJ), and Daecheong Lake (DC) in South Korea. Non-parametric seasonal Kendall and Mann-Kendall tests, Sen slope estimator, and potential energy anomaly (PEA) were applied. The lake surface water temperatures (LSWTs) of SY and DC increased at the same rate (0.125 °C/y), followed by those of CJ (0.071 °C/y) and PD (0.06 °C/y). Seasonally, the LSWT increase rates for all lakes, except PD, were 2–3 times higher than the air temperature increase rates. The lake stratification intensity order was similar to those of the LSWT increases and correlations. SY and DC displayed significant correlations between LSWT (0.99) and PEA (0.91). Thus, the LSWT significantly affected stratification when the water temperature increased. PD demonstrated the lowest correlation between LSWT and PEA. Inflow, outflow, rainfall, wind speed, and retention time were significantly correlated, which varied within and between lakes depending on lake topographical, hydraulic, and hydrological factors. Thus, hydraulic problems and nutrients should be managed to minimize their effects on lake water quality and aquatic ecosystems because lake cyanobacteria can increase as localized water temperatures increase.

Influence of Zooplankton and Environmental Factors on Clear-Water Phase in Lake Paldang, South Korea.

Lake Paldang is a complex water system with both fluvial and lacustrine characteristics and the largest artificial dam lake in South Korea. In this study, the different occurrence patterns and causes of the clear-water phase (CWP) were investigated using water quality and hydrological factors at four sites in Lake Paldang. Among the environmental and other factors associated with CWP occurrence, secchi depth and turbidity exhibited significant correlations with precipitation, hydraulic retention time (HRT), and individual and relative abundance (RA) of zooplankton (Cladocera) (p < 0.01). Hence, a change in the HRT because of precipitation could alter the CWP. The Cladocera individuals and RA showed significant correlations with the water temperature, indicating that the emergence of Cladocera in spring as the water temperature rises could cause the CWP. Sensitivity assessments conducted using Bayesian models demonstrated different CWP occurrence sensitivity relationships for the river-type, lake-type, and shallow and deep sites. Turbidity, secchi depth, and zooplankton factors also showed sensitive relationships with CWP occurrence for all sites. The sensitivity to precipitation and HRT was higher in the river-type sites. The lake-type sites, with common Cladocera emergence and long HRT, favored CWP occurrence. Thus, CWP occurrence was dependent on the site characteristics and climate conditions.

Long-term relationship between air and water temperatures in Lake Paldang, South Korea

A long-term investigation into the relationship between air and water temperatures was conducted in Lake Paldang, which is the largest water source in South Korea, by studying hysteresis. From 1973 to 2018, the annual mean air temperature increased by 0.05°C/yr (seasonal Sen’s slope). The results of a numerical model (R &gt; 0.86) showed that the ratios of the air and water temperatures increased (0.71‒0.77) in the rising limb and decreased (0.70‒0.76) in the falling limb. However, the intercept values were 0.13–3.52 and 6.62–7.78 in the rising and falling limbs, respectively, and hence there was a 4–5°C increase in temperature. In particular, in 2015, 2016, and 2018, the intercept values in the falling limb were ≥ 7, exhibiting hysteresis, whereby high water temperatures were slow to decline. Lake Paldang showed stronger water temperature hysteresis than its influent rivers and stream. The rising and falling limbs did not show a large difference in the extent of water temperature change (slope). However, the water temperature did not decrease rapidly, and the decrease continued for longer due to hysteresis, which is a type of inertia where the elevated temperature persists if the summer air temperature is significantly increased.

Evaluation of optimal size of illite adsorbent for 137Cs removal in contaminated artificial lake

Since the Chernobyl and the Fukushima Daiichi disasters, contamination caused by radioactive accidents has attracted increasing attention. The present study evaluated immediate cleanup of 137Cs dissolved in surface water reservoir using an illite adsorbent, simulating an event of 137Cs contamination at Lake Paldang, South Korea. The study was conducted in two parts: (1) calculation of the residence time (tr) of illite adsorbent, and (2) evaluation of the adsorption time (ta) of illite adsorbent. tr was calculated based on physical properties (e.g., density, diameter, shape, and roughness) of the illite adsorbent at designated depth of surface water. Subsequently, ta was measured for 4 illite adsorbents (Korea01-Illite, Korea02-Illite, USA-Illite, and China-Illite) at 100 and 100,000 μg/L Cs, via kinetic adsorption experiment. Upon spraying of illite adsorbents with 50–150 μm diameter to locations where lake depth was between 6.5 m and 25.5 m, tr ranged from 0.132 to 3.300 h ta of 4 illite adsorbents was shorter than 0.6 and 2.5 h, for respective tests using 100 and 100,000 μg/L Cs. Based on the two characteristic times (tr and ta), the optimal particle diameter for the 4 illite adsorbents were evaluated at available lake depths in Lake Paldang. The study revealed that the USA-Illite is the efficient adsorbent at 100 μg/L Cs; in contrast, China-Illite could serve as the effective adsorbent at 100,000 μg/L Cs. Also, it was suggested that adsorbent efficiency had seasonal variations; tr was 2 h longer in winter than summer. In general, the study suggests that in the event of 137Cs contamination at Lake Paldang, Korea01-Illite is likely the best adsorbent to remove 137Cs due to its removal efficiency and accessibility from the illite deposit in Korea.

Cyanobacterial occurrence and geosmin dynamics in Paldang Lake watershed, South Korea

AbstractWe investigated the relationship between cyanobacteria and geosmin occurrence in the Paldang Lake watershed, South Korea, by examining samples from the Bukhan and Namhan Rivers weekly from 2011 to 2015. Cyanobacteria were detected in summer, when water temperatures reached 20°C or more.Merismopedia, non‐nitrogen‐fixing cyanobacteria, dominated the Namhan River, which had high nitrogen concentrations. In the Bukhan River,Dolichospermum, nitrogen‐fixing cyanobacteria, was dominant. Temporary nitrogen inflow into the Bukhan River due to rainfall transformed the cyanobacterial community from one dominated by nitrogen‐fixing cyanobacteria (Dolichospermum) to one dominated by non‐nitrogen‐fixing cyanobacteria (Microcystis). Geosmin was highly correlated withDolichospermumin the Bukhan River (r = 0.947,P &lt; 0.01) and its concentration changed in accordance withDolichospermumcell counts. In theMerismopedia‐dominated Namhan River, geosmin concentrations were low, suggesting that the cyanobacterial community composition affects geosmin levels.

Algal Contribution to the Occurrence of Refractory Organic Matter in Lake Paldang, South Korea: Inferred from Dual Stable Isotope (&lt;sup&gt;13&lt;/sup&gt;C and &lt;sup&gt;15&lt;/sup&gt;N) Tracer Experiment.

Algal Contribution to the Occurrence of Refractory Organic Matter in Lake Paldang, South Korea: Inferred from Dual Stable Isotope (&lt;sup&gt;13&lt;/sup&gt;C and &lt;sup&gt;15&lt;/sup&gt;N) Tracer Experiment.

Spatial and Temporal Distribution of Zooplankton Communities in Lake Paldang

Spatial and Temporal Distribution of Zooplankton Communities in Lake Paldang

Effect Analysis Regarding Different Scenarios to Improve Water Quality of the Lake Paldang Basin in Korea

The object of this research is to analyze the water quality improvement of Lake Paldang by implementing Integrated Lake Basin Management (ILBM). To establish ILBM, the basin environment database was built as well as water environment management support system for monitoring present conditions, and predicting changes in basin environment. The major contaminants in Lake Paldang Basin are from domestic pollution, agricultural land, and livestock. Scenarios for reducing contaminants were targeting the increase percentage of sewered population, agricultural and livestock contaminants reduction to analyze the water quality improvement effects. This study applied the SWAT model to Lake Paldang Basin using the basin environment database to improve the water quality of Lake Paldang in Korea. The results of calibration and validation of flow rate, Suspended Solids (SS), Total Nitrogen (TN) and Total Phosphorus (TP) showed that the measurement values and simulation values turned out to be similar, and that it is possible to apply the SWAT model to Lake Paldang Basin. The reduction efficiency of SS by scenario was 11-45%, TN 8-37%, and TP 7-35% and this shows that water quality was significantly improved prior to application. Therefore, to improve the water quality of Lake Paldang, it is recommended to implement the ILBM which is considered to play an important role in making water quality management policy in Korea.

Changes in the Water Environment Based on the Statistical Data in the Lake Paldang

Changes in the Water Environment Based on the Statistical Data in the Lake Paldang

Water quality improvement through the interaction of biotic and abiotic variables within the rhizospheric zone of an artificial floating vegetation island

ABSTRACTDemands for water quality improvement and reduction of harmful algal blooms in Korean lakes and rivers due to eutrophication and climate change have been increasing. As an environmentally friendly measure to mitigate the eutrophication and phytoplankton growth, a full-scale artificial floating vegetation island (AFVI) was installed in Lake Paldang, a large on-river reservoir. This study investigated the detailed mechanisms for improving water quality and reducing the phytoplankton growth of the AFVI by comparing the biotic and abiotic environmental factors between the AFVI and the adjacent pelagic part of the lake. Much lower chlorophyll a concentration, much higher zooplankton biomass, especially large crustacean zooplankton, and a higher proportion of active bacteria in total bacteria in the AFVI indicate an effective reduction of phytoplankton growth and vigorous decomposition of organic matter. The major mechanisms for improving water quality of the AFVI are shown to be inhibition of phytoplankton growth by attenuating light and top-down control by zooplankton grazing. Active microbial decomposition of organic matters and nitrate reduction in the hypoxic rhizospheric zone also would be a major mechanism for improving water quality, even though it is difficult to quantify in the open water system.