Physicochemical and biological parameters (temperature, salinity, pH, dissolved inorganic nutrients, and chlorophyll-a) were analyzed to evaluate the effects of precipitation variability associated with climate change on the water quality in the Nakdong River Estuary, South Korea. Multi-year monitoring data (2016–2021) were collected seasonally (February, May, August, and November) throughout the study period. Extreme rainfall events caused pronounced estuarine freshening (salinity < 1) and sharply enhanced riverine nutrient fluxes, with wet-to-dry season increases of 4–70 times for dissolved inorganic nitrogen, 4–36 times for phosphorus, and 9–740 times for silicate, showing strong positive correlations with precipitation (r² = 0.76–0.82, p < 0.001). Time-series and self-organizing map classifications revealed estuarine that the water quality was strongly controlled by seasonal precipitation and river discharge, whereas offshore waters exhibited weaker but detectable responses. Notably, extreme rainfall events altered the chlorophyll-a distribution, suppressing phytoplankton accumulation in the estuary because of dilution and flushing, while enhancing chlorophyll-a concentrations in offshore waters through nutrient-enriched river plume dispersion. These results demonstrated that extreme rainfall driven by climate change can enhance the terrestrial nutrient input into coastal waters, thereby increasing the potential for eutrophication and harmful algal blooms.

A Gram-stain-negative, strictly aerobic and motile rod, designated strain SyP6RT, was isolated from the freshwater alga Synura petersenii in Nakdong River, Republic of Korea, representing a niche expansion of Methylobacterium to the algae. Colonies were pink-coloured, convex and circular on Reasoner's 2A agar. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain SyP6RT formed a distinct phyletic lineage within the genus Methylobacterium, showing the highest similarity to Methylobacterium platani PMB02T (98.9%). Genomic G+C content was 69.6 mol%, and phylogenomic analysis supported its distinct phyletic lineage. The average nucleotide identity values (89.2-89.6%) and digital DNA-DNA hybridization values (36.3-38.2%) with the closely related taxa were clearly below the species delineation thresholds. Notably, strain SyP6RT possesses biosynthetic genes for B vitamins, including thiamine, riboflavin, pantothenate and folate, highlighting its potential ecological role as a vitamin-supplying symbiont. Strain SyP6RT was oxidase-positive and catalase-negative, growing optimally at 30 °C and pH 7.0 and 0.25% (w/v) NaCl. Strain SyP6RT possessed ubiquinone-10 as the sole respiratory quinone and C16:0, summed feature 5 (comprising C18:0 ante and/or C18:2 ω6,9c), C18:0, summed feature 3 (comprising C16:1 ω7c and/or C16:1 ω6c) and summed feature 8 (comprising C18:1 ω7c and/or C18:1 ω6c) as the major cellular fatty acids (>5%). The predominant polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified aminolipid. Based on polyphasic evidence, strain SyP6RT represents a novel species of the genus Methylobacterium, for which the name Methylobacterium synurae sp. nov. is proposed. The type strain is SyP6RT (=KACC 19923T=JCM 33308T).

Comparative evaluation of limit-of-detection-based and K-nearest-neighbors-based classification approaches for detecting effluent contamination using fluorescence-derived water quality parameters.

This paper discusses the process by which the polities of Late Gaya emerged following the dissolution of Early Gaya. The Late Gaya polities—such as Ara, Bihwa, Dara, Gara, Seongsan, and SoGaya—did not emerge simultaneously but were established sequentially as they moved upstream along the Nakdong River.I propose naming this phenomenon the “Nakdong River Upstream Theory.” Although this study takes a general approach, its main arguments are based on a comprehensive synthesis of my previous research on tomb, horse harness, armour, pottery, chronology, and related topics. The key to this line of reasoning lies in identifying the founding periods of each small polity by determining the earliest royal tombs. Representative examples include Tomb No. 45 at Malyisan in Haman for Ara, Tomb No. 23 at Okjeon in Hapcheon for Dara, and Tomb No. 73 at Jisan-dong in Goryeong for Gara. For Bihwa, Seongsan, and SoGaya, materials that can either be considered their earliest royal tombs or are otherwise comparable have been selected. From Ara to Dara, these small polities emerged before the appearance of the high-mounded tomb tradition. By contrast, Gara and Seongsan were established as Late Gaya small polities with the advent of high-mounded tombs. Another important implication of the formation of Late Gaya is that this period marks the beginning of full-scale development in the western Gyeongnam region, centered on the Nakdong River. Consequently, at the time these polities emerged, population concentration became possible along two major routes: the Geumho River corridor—including Gyeongju, Gyeongsan, and Daegu— and the Nakdong River corridor, encompassing Busan, Gimhae, Haman, Changnyeong, Hapcheon, and Goryeong, where the Late Gaya polities were located.

Short-term microbial community reassembly and sediment-driven water quality pulses following a managed weir opening in the Nakdong River

Accurate information regarding species boundaries is essential for ecological research and conservation planning. This information is particularly difficult to obtain but essential for cryptic amphibian species. The distribution and potential dispersal corridors of two cryptic salamander species, the Korean clawed (Onychodactylus koreanus) and the Yangsan clawed (O. sillanus) salamanders, were investigated using integrated approaches for high-resolution species distribution modeling (SDM), genetic species identification, and habitat connectivity analysis. The SDM results showed high habitat suitability in mid- and high-mountainous areas, but very low suitability in riverine areas for both species. Genetic species identification of the 25 populations delimited the distribution boundary between the two species along the Nakdong and Geumho rivers. Dispersal corridors of the two species commonly involved a detour around the major rivers and produced only one possible dispersal route, where both species moved into the opposite species’ habitat along the east side of the mountainous areas of the Geumho River. The findings not only clarify the distribution range of two cryptic Onychodactylus species in the Republic of Korea but also highlight the importance of the unique dispersal route for studying species interactions and maintaining ecological connectivity.

Seasonally different toxicity drivers in a river system revealed by insights from POCIS, bioassays, and suspect screening.

This study developed analytical methods for quantifying 39 per- and polyfluoroalkyl substances (PFAS) and 23 pharmaceuticals in water samples using direct injection and online solid-phase extraction (online SPE) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). The performance of the online SPE method was compared with that of direct injection. For PFAS, online SPE achieved lower method detection limits (MDLs; 0.1794.72 ng/L) than direct injection (3.2731.3 ng/L). Similarly, for pharmaceuticals, MDLs obtained with online SPE (0.0590.314 ng/L) were lower than those from direct injection (1.0956.8 ng/L). Both methods met established analytical criteria, showing acceptable accuracy (70130%) and precision (≤20%). The optimized method was applied to water samples from the Nakdong River in Korea. Among the 39 PFAS, only one compound was detected via direct injection, whereas eight compounds were identified using online SPE. For pharmaceuticals, direct injection detected 10 compounds, while online SPE identified 15. Additionally, the detection frequency across sampling sites was similar to or higher than that of online SPE compared to direct injection. Overall, online SPE proved more effective for detecting PFAS and pharmaceuticals in river water than direct injection, offering additional advantages in labor efficiency, cost-effectiveness, and suitability for routine water quality monitoring programs.

The water treatment plant is a key facility to remove pathogenic microorganisms in order to supply safe tap water to the people, and due to its efficiency, economy, and persistence, a disinfection process using chlorine-based disinfectants is widely used. However, chlorine-based disinfectants react with organic substances during the chlorine disinfection process to produce disinfection by-products that are harmful to the human body, and these substances are strictly managed internationally. The Nakdong River basin has a characteristic that the concentration of disinfection by-products is higher than that of other watersheds due to high contamination load and enhanced chlorine treatment. Therefore, in this study, 91 water treatment plants in the Daegu and Gyeongbuk region were classified according to water supply and analyzed the generated concentration of disinfection by-products (THMs, HAAs, and HANs). Using the data from the national water supply information system, changes by year and month were identified, and the difference in the occurrence of disinfection by-products was compared according to whether or not an advanced treatment process was introduced. In addition, based on the data from the Meteorological Administration, the correlation between temperature and the concentration of disinfection by-products was evaluated through the Pearson correlation coefficient. As a result of the analysis of water treatment plants in Daegu and Gyeongbuk from 2011 to 2024, THMs, HAAs, and HANs all showed high concentrations in water treatment plants using river water and lake water as raw water, and were relatively low in groundwater and riverbed water. THMs showed a positive correlation with rising temperature (r = 0.4357), whereas HANs exhibited no correlation. HAAs tended to show increased variability and higher median values with increasing temperature, but no statistically significant correlation was observed. In addition, it was confirmed that the concentration of all disinfection by-products was lower in the water treatment plant that introduced the advanced water treatment process compared to the standard water treatment process. For safe supply of tap water, it is essential to comply with the appropriate concentration of disinfectant injection by seasonal, and in order to effectively remove precursors that may generate disinfectant by-products depending on the water source, it is effective to introduce advanced treatment processes such as ozone and activated carbon.

During the Three Kingdoms period, the Namhan River's flow from east to northwest, reaching the western sea, proved beneficial to Silla. It was a geographic structure that allowed Silla to maintain control of the Han River basin. After Silla took control of the Han River basin in 553, military supplies produced in Danyang, Jecheon, Chungju, and Wonju were distributed downstream. While Goguryeo and Baekje simultaneously attacked the Han River basin from both north and south, Silla's fortresses there remained intact. The Han River waterway was also utilized during the Silla-Tang War and the development of Paegangjin after unification. Of course, the people of the lower reaches of the Han River and the fortresses along the west coast did more than simply consume goods. One-way traffic diminished the sustainability of the flow. They were the guardians of the waterways that carried goods produced on the west coast upstream to the middle and upper reaches of the Han River, the overseers of the salt farms, and the primary agents of replenishing ships' stalls with seaborne produce. Passing vessels always sought a full cargo. Something had to be filled, and salt, with its widespread consumption, would have made up a large portion of the cargo on ships traveling up the Han River. His filled the salt warehouses of Wonju, Chungju, Jecheon, and Danyang, and to meet the demands of the Silla capital, salt flowed over the pass and into the Nakdong River basin. The salt that crossed Gyeripnyeong Pass likely traveled down the Nakdong River before entering its tributary, the Geumho River, where it was unloaded at Bongmu-dong in Daegu. It would then travel further upstream during the water-boosting period, where it was unloaded at Dodong in Yeongcheon City, and then overland to fill the salt warehouses of the capital. King Sinmun, feeling the burden of overland transportation between Daegu and the capital, attempted to relocate the capital to Daegu in 689, but was unable to achieve his goal. The Silla people were obsessed with residing in the royal capital. In the capital, which existed for a thousand years, the bone rank system, a typical caste system, emerged, and this system was limited to those living in the capital. For them, leaving the capital and moving their base to the provinces typically meant a decline in social status, as it meant being separated from the intermarriage rights of the capital residents. The bone rank system itself was a structure that concentrated the upper class in the royal capital. According to the Samguk Yusa (Memorabilia of the Three Kingdoms), 178,936 households lived in the royal capital, bringing the population close to one million. Even if one does not believe this, it is clear that the royal capital was overcrowded and overpopulated. The royal capital, with its high-ranking class, likely accounted for more than half of the nation's consumption. This doesn't mean the upper class consumed more salt. The number of nobles, along with the number of subordinates supporting them, increased, leading to a population concentration in the capital, spurring consumption. The massive demand for the capital demanded an influx of goods from the provinces. The Salt Way(鹽池通) weren't the only route for salt supply. The Samguk Yusa records the influx of salt from Gimhae to Gyeongju. This region was a salt-producing region. First, there was the sea second, the countless reeds and brushwood in the marshlands of the Nakdong River estuary provided fuel for boiling seawater in pots and third, the river provided a useful route for transporting salt inland. Salt was also produced in Pohang and Ulsan. Most importantly, they were close to the capital, a major consumer.

This study compares the performance of empirical and hybrid deep learning (DL) models in estimating daily potential evapotranspiration (PET) in the Nakdong River Basin (NRB), South Korea, with the FAO-56 Penman–Monteith (PM) method as a reference. Two empirical models, Priestley–Taylor (P-T) and Hargreaves–Samani (H-S), and two DL models, a standalone Long Short-Term Memory (LSTM) network and a hybrid Convolutional Neural Network Bidirectional LSTM with an attention mechanism, were trained on a meteorological dataset (1973–2024) across 13 meteorological stations. Four input combinations (C1, C2, C3, and C4) were tested to assess the model’s robustness under varying data availability conditions. The results indicate that empirical models performed poorly, with a basin-wide RMSE of 5.04–5.79 mm/day and negative NSE (−10.37 to −13.99), and are therefore poorly suited to NRB. In contrast, DL models achieved significant improvements in accuracy. The hybrid CNN-BiLSTM Attention Mechanism (C1) produced the highest performance, with R2 = 0.820, RMSE = 0.672 mm/day, NSE = 0.820, and KGE = 0.880, which was better than the standalone LSTM (R2 = 0.756; RMSE = 0.782 mm/day). The generalization of heterogeneous climates was also verified through spatial analysis, in which the NSE at the station level consistently exceeded 0.70. The hybrid DL model was found to be highly accurate in representing the temporal variability and seasonal patterns of PET and is therefore more suitable for operational hydrological modeling and water-resource planning in the NRB.

This study presents an explainable artificial intelligence (XAI)-based explainable planning management (EPM) framework designed to provide interpretable prediction-driven insights for water quality management. Although deep learning models such as the multi-layer perceptron (MLP) effectively predict water quality indicators, they have limited interpretability and practical use. To address this limitation, Shapley additive explanations (SHAP) were applied to quantify each input feature’s contribution to model-predicted chlorophyll-a (Chl-a) values and to support the construction of scenario-based analyses. The proposed framework was applied at the Dasan water quality observation station in the Nakdong river basin, Republic of Korea. Daily water quality data from 2014 to 2023 were used for model training, and 2024 data were used for prediction. The model excluding turbidity achieved the lowest root mean squared error (RMSE) of 7.3922. Scenario analyses were performed by varying Chl-a(t−1) and major variables in 10% increments, guided by influence identified through SHAP analysis. Results indicated that pH, which had the highest Shapley value excluding Chl-a(t−1), was the most influential variable, reducing algal bloom warning occurrences by up to 34%. These results demonstrate that the proposed EPM framework enhances interpretability and supports the exploration of prediction-based planning strategies, without implying causal or mechanistic relationships among water quality variables.

Abstract Per- and polyfluoroalkyl substances (PFAS) are persistent and potentially toxic compounds increasingly detected in aquatic environments, yet their occurrence, sources, and health risks in major watersheds remain under-characterized. This study provides a comprehensive assessment of PFAS contamination in the Nakdong River Basin, South Korea, through integrated analysis of spatial distribution, source apportionment, mass fluxes, and age-stratified human health risks. Surface water samples were collected from 23 sites across the mainstem and major tributaries during high-flow conditions. A total of 11 PFAS compounds were detected, with ΣPFAS concentrations (sum of PFAS) ranging from 9.28 to 171.40 ng/L. Concentrations of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) exceeded the United State environmental protection agency (USEPA) maximum contaminant levels at several sites. Land-use analysis revealed that industrial and wastewater treatment plant (WWTP) affected tributaries showed the highest PFAS levels and detection frequencies. Positive matrix factorization (PMF) modeling identified four source profiles linked to domestic wastewater, industrial discharge, electronics manufacturing, and secondary re-entry. Mass flux calculations indicated that tributaries such as GA-3 and IG-3 contribute disproportionately to basin wide PFAS transport. Human health risk assessment using mixture hazard quotients (HQ mix ) showed that children (0–5 years) exceeded the precautionary risk threshold of 0.1 at six sites, despite all values remaining below 1.0. These findings highlight the need for integrated monitoring and land-use-informed management strategies to mitigate PFAS exposure, especially in vulnerable populations. The study provides critical insights for targeted regulation and sustainable watershed protection in PFAS impacted regions.

Corrigendum to: Random Forest Model for Salinity Prediction in the Nakdong River Estuary Reflecting Spatio-temporal Lag Effects

Corrigendum to: Optimization of Input Variables for Salinity Modeling in the Nakdong River Estuary Using Exploratory Data Analysis

This study developed an algorithm to predict algal blooms in river systems by integrating the two-dimensional CE-QUAL-W2 water quality model with optimization techniques. The study area was the Nakdong River system in South Korea, and the model was constructed for eight multipurpose weir sections. Sensitivity analysis was used to identify key parameters influencing algal concentrations, and an optimization algorithm was developed using the bagging ensemble method. The algorithm aimed to minimize the relative error (%Difference) between simulated and observed chlorophyll-a concentrations, which served as the target variable. The model achieved a "Very Good" rating in the overall efficiency assessment across all target weir sections. Furthermore, A separate evaluation of temporal algal trends was conducted, which showed that while some sections received a 'Poor' rating during low-concentration periods, most sections achieved a 'Good' or higher rating overall. In addition, the model effectively captured temporal patterns and spatial heterogeneity, demonstrating its adaptability to complex hydrodynamic conditions. By integrating machine learning techniques into the physically-based modeling framework, the proposed algorithm is expected to enhance model reliability and improve optimization efficiency. These improvements are applicable to water quality prediction and management systems.

Assessment of the role of estuarine barrage operational management in enhancing glass eel (Anguilla japonica) migration in a closed estuary.

At the Gangjeong-Goryeong site on the Nakdong River, cyanobacterial cell counts increased approximately 45-fold within a short span, underscoring the need to address algal blooms not just as a water quality issue, but also as a disaster management priority. This study examined how algal bloom driving factors vary by river type, focusing on chlorophyll-a (Chl-a), as a representative indicator of algal biomass. The Miho River, a smaller tributary and the Nakdong River, a large mainstem river, served as study sites. Various scenarios were constructed based on the hydrological and biochemical parameters. Predictive models for Chl-a concentration were developed using machine learning techniques such as Random Forest and XGBoost. The variable importance was derived for each model, and the prediction performance was evaluated separately. Results showed water temperature as the dominant driver in the Miho River, while biochemical factors like BOD and COD were more influential at the Gangjeong-Goryeong site. These results support the development of river -specific algal bloom prediction systems and targeted disaster response strategies.

Comparison of Forecasting Systems to Reflect the Characteristics of Tidal Deformation Outside Nakdong River Estuary Dam : A Long-term Harmonic Analysis Method Using Utide

Abstract We investigated fossil planktonic foraminifera from cores ND‐02 (Nakdong River delta) and PC‐11 (inner shelf off southeast Korea), to assess millennial‐scale variations in the surface oceanography. The coiling ratio of Neogloboquadrina pachyderma shows five millennial‐scale near‐cyclic variations (∼8.7–8.3, ∼7.5–6.2, ∼4.7, ∼2.8 and ∼0.5 ka) since ∼9 ka. These variations are similar to warm‐water diatom variations at the Oki Ridge where a cyclicity of ∼1.6 kyr is present, possibly associated with a Bond event. By contrast, the near‐cyclic variations in our planktonic foraminiferal record were not fully consistent with the reported intensity variations of the Tsushima Warm Current in the East Asian margin and the warm Kuroshio Current in the Northwest Pacific. Our records from southeast Korea seem to reflect the more regional oceanographic variations in the marginal seas of East Asia. We suggest that the coastal upwelling of subsurface cold water along the southeast coast of Korea plays an important role in generating near‐cyclic variations of warm‐water biota. These variations may have a connection to Bond event periodicity in the North Atlantic Ocean.