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The main objectives of this study were to analyze the spatiotemporal variations of water quality, fish ecological guilds and longitudinal connectivity in the weirs of Musim Stream. Fish were collected at 44 sites during spring and fall seasons for the analysis of trophic guilds, tolerance guilds, and the ecological stream health, based on FAI model. Total 33 species were observed in the stream and the dominant species were Zacco platypus and Squalidus qracilis majimae. Mean values of BOD and COD, as an indicator of organic matter pollution, showed high in the drought spring and low in fall (post-monsoon season). Also, TP showed same pattern with the BOD and COD pattern. The hierarchical clustering, based on the fish compositions, classified as three groups (up-stream, mid-stream and the down-stream). Based on the NMDS (Non-metric Multidimensional Scaling) analysis of fish abundance, high similarity was observed between S1-S5 sites, which were consistent with the results of hierarchical cluster analysis. Fish ecological guilds in the upper stream showed a high similarity between the insectivore and sensitive species, while in the middle and lower reaches, high similarity was found between the omnivore and intermediate species. Evaluations of longitudinal connectivity, based on the structural and hydrological characteristics of the weir, indicated all disconnections by the weirs, except for S15, in the spring. Stream ecological health, based on the FAI model, was significantly (p < 0.05, n=37) influenced by the height of overflow (Hu1). Overall, our study suggests that the longitudinal connectivity, based on the weir structures, flow regime and fish swimming capacity, were blocked off by the weirs in the stream. The results provide valuable insights for securing river management strategies and served as the fundamental data for stream restoration in the future.

This study analyzed spatiotemporal variation and long-term trends in water quality indicators and trophic state conditions in an Asian temperate reservoir, Juam Reservoir (JR), and developed models that forecast algal chlorophyll (CHL-a) over a period of 30 years, 1993–2022. The analysis revealed that there were longitudinal gradients in water quality indicators along the reservoir, with notable influences from tributaries and seasonal variations in nutrient regimes and suspended solids. The empirical model showed phosphorus was found to be the key determinant of algal biomass, while suspended solids played a significant role in regulating water transparency. The trophic state indices indicated varying levels of trophic status, ranging from mesotrophic to eutrophic. Eutrophic states were particularly observed in zones after the summer monsoons, indicating a heightened risk of algal blooms, which were more prevalent in flood years. The analysis of trophic state index deviation suggested that phosphorus availability strongly influences the reservoir trophic status, with several episodes of non-algal turbidity at each site during Mon. Increases in non-algal turbidity were more prevalent during the monsoon in flood years. This study also highlighted overall long-term trends in certain water quality parameters, albeit with indications of shifting pollution sources towards non-biodegradable organic matter. According to the machine learning tests, a random forest (RF) model strongly predicted CHL-a (R2 = 0.72, p 60 μg/L), compared to all other models. Overall, our research suggests that CHL-a and trophic variation are primarily regulated by the monsoon intensity and predicted well by the machine learning RF model.

This study focused on the longitudinal connectivity analysis, based on fish communities in the aspect of spatial variations of 34 sites from upstream to downstream. The Fish Assessment Index (FAI), based on ecological guilds and species composition, was applied to compare the ecological health among the sampling sites. The total number of 35 fish species, were sampled during the study period with dominant species of Zacco platypus (35.4%) and Zacco koreanus (11.8%). Cluster analysis showed that all sites were categorized as 4 distinct group communities (A, B, C, D). Non-metric multidimensional scaling analysis showed distinct difference between upstream (A, B) and downstream groups (C, D). Indicator Value Analysis (IndVal method), conducted to identify indicator species within each group, indicated that the species favoring upstream environments Rhynchocypris oxycephalus for the Group A and Iksookimia koreensis for the Group B. In contrast, the analysis indicated that the species with a preference for downstream habitats Pseudogobio esocinus for the Group C and Carassius auratus for the Group D. Ecological health, based on the FAI scores, showed a declining pattern toward the downstream, along with an increasing proportion of tolerant species and omnivores within the fish community. Overall these findings suggest the compositions of fish communities, as four groups, were modified by the weir structures and organic matter, nutrient pollutions.

The main objectives of this study were to evaluate biological integrity analysis and longitudinal connectivity assessment in Tan Stream. The research included the analysis of chemical water quality, ecological health assessment based on fish, and a comparison of aquatic ecosystem health before and after restoration, following the removal of two weirs (Baekgung weir and Baekhyeon weir) among the nine weirs with five fishways. Additionally, an assessment of longitudinal connectivity is being conducted. Dissolved oxygen (DO), biological oxygen demand (BOD), total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and suspended solids (SS) concentrations were not high based on the criteria of the Ministry of Environment, Korea. The ecological health assessment based on fish showed an average health grade of “Fair (C)”, indicating a partial deterioration of ecological health, with Zacco platypus as the dominant species. The results of the regression analysis showed that there was no significant correlation between water quality and ecological health (p > 0.05). After the removal of Baekgung weir, the health of the aquatic ecosystem (FAI) improved slightly, increasing from “50” to “56.25”. And after the removal of Baekhyeon weir, the value remained the same as before the removal (“56.25”). However, it was found that the overall improvement effect on the entire Tan Stream was minimal. The evaluation of longitudinal connectivity revealed, three continuities, two partial continuities and two discontinuities at the artificial weir unit level, while at the stream unit level, it was evaluated as “continuous (52.8%)”. Further comprehensive research is needed to investigate the potential impact of artificial structures on the integrity of the aquatic ecosystem.

Elucidating the responses of aquatic communities to environmental (e.g., chemical, habitat, and flow regime) and biological disturbances is essential to the maintenance and restoration of healthy ecosystems. This study investigated the interactions between environmental and biological disturbance factors and functional indicators of ecological health in 99 sampling sites along a temperate river. Variance tests and multivariate statistical tools, such as non-metric multidimensional scaling (NMDS) and generalized linear models (GLMs), were employed to evaluate the responses of functional indicator guilds and ecological river health to various in-stream chemical, physical, habitat, and land-use pattern factors along with the biological impact of invasive alien species (IAS). Variance testing revealed significant variation (χ2 > 6.2 and p

The aim of this study was to predict the distribution of a potential invasive alien species, smallmouth bass (Micropterus dolomieu), in South Korea using a life-history-based habitat suitability model. Environmental data (air temperature, water temperature, and fish occurrence) at present (2011–2020) were collected from 160 representative sites across the five river basins (Han, Nakdong, Guem, Seomjin, and Yeongsan). Future predictions were conducted under the representative concentration pathway 8.5 scenario in the 2050s (2046–2055) and the 2080s (2076–2085). Two spawning scenarios were implemented in the future, where smallmouth bass will not change the spawning season in the non-adaptive scenario and change the season in the adaptive scenario. The life-history habitat suitability (LHS) of smallmouth bass was evaluated using the geometric mean of the annual habitat suitability indices (HSIs) for each life stage (adult, juvenile, fry, and spawner). The LHS model was validated using the occurrence data of largemouth bass (Micropterus salmoides), which shares most of its habitats with smallmouth bass. The average LHS of smallmouth bass in South Korea was predicted to be 0.519 at present and expected to be 0.491 and 0.541 in the 2080s under non-adaptive and adaptive scenarios, respectively. Considering that the period for spawner fish may change in the future under climate change, the adaptive scenario seems to be more reasonable. The potential presence rate of smallmouth bass in South Korea was 100% at present, except for the Han River Basin (66%) which was expected to increase to 86% in the 2080s under the adaptive scenarios. The LHS model predicted that smallmouth bass could inhabit South Korea, and its distribution may expand under global warming, requiring urgent preventive measures.

Trait-based functional studies are widely used to elucidate the relationships between ecological indicators and environmental parameters as well as to predict functional change in aquatic biota in response to various types of human disturbance. Clarifying how functional traits of aquatic organisms depend on environmental conditions can facilitate aquatic conservation and management, but determining the importance of these traits to ecological river health requires further investigation. As fish play a key role in the assessment of ecological conditions, we examined the relevance of the functional diversity of lotic fish to the river health assessment using multi-metric models of water pollution (mWPI) and fish-based biological integrity (mIBI). Twelve fish traits related to food acquisition, environmental stability, and mobility were used for the functional analyses. Chemical river health was highly sensitive to downstream organic matter and nutrient pollution according to mWPI. Based on the present gradient of chemical health and water chemical variables, we identified three water quality groups (G-I, G-II, and G-III). G-I, G-II, and G-III showed low, intermediate, and high levels of water quality degradation, respectively. Spatially significant differences among these groups were observed for both the taxonomic and functional structures of lotic fish as well as ecological river health based on mIBI. The dominance of sensitive species was high in G-I, whereas tolerant and exotic species contributed strongly to the species compositions of G-II and G-III. Functional richness and dispersal were significantly reduced in G-III, and their decreases correlated with ecological health and the loss of species that are insectivorous, rheophilic, and sensitive to water pollution. Regarding redundancy analyses, both the models of functional trait metrics (F = 8.06, p < 0.001) and mIBI metrics (F = 4.88, p < 0.01) indicated good performance in terms of the variation in water quality and chemical river health parameters. Overall, the functional trait-based diversity of lotic fish is significant to the assessment of ecological river health and reflects water chemical quality. This association arises because niche occupation in functional space by all species, along with their abundance distribution, is highly responsive to the loss of species with sensitive traits due to water pollution.

River water pollution is one of the biggest environmental challenges in the world. Therefore, it is imperative to assess the spatial and temporal variability of surface water quality to manage water resources from pollution. This study aimed to identify spatio-temporal variations of Geum River surface water quality and the factors that influence it. Summer monsoon, land-use land-cover (LULC), and weirs are dominant factors determining the dynamics of river water quality. Empirical analysis showed that total phosphorus (TP), total nitrogen (TN), biological oxygen demand (BOD), and chemical oxygen demand (COD) had positive linear functional relations with the agricultural and built-up cover but negative linear relations with forest cover. The results showed that the total suspended solids (TSS), chlorophyll-a (CHL-a), TP, and COD levels were higher in the summer than in any other season. On the other hand, total nitrogen (TN) and electrical conductivity (EC) levels were lower during summer in the river due to the dilution effect. Pollutant-transport theory shows that TSS acts as a TP carrier (R2 = 0.83, p

Under pressure from existing and emerging contaminants, lotic ecosystems are becoming increasingly susceptible to ecological deterioration. Therefore, investigations of the impacts of persistent organic pollutants (POPs) and heavy metals on riverine fish health, water quality, and biotic integrity are critical. We examined the effects of 52 POPs and heavy metals on ecological health and land use, based on the monitoring of fish assemblages and river water quality from 2007 to 2014. Among the 52 chemical species, 35 were present in water and fish tissues, including eight heavy metals. The concentrations of these POPs and heavy metals in 12 fish species are presented. Most POPs were either undetected or present at negligible levels in fish tissues, although a few polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs; dichlorodiphenyltrichloroethanes and heptachlor epoxide) were detected above the screening values (SVs). Hg, As, and Cd were detected in most water samples and fish species at concentrations above their SVs. Among the fish species in the investigated trophic guild, heavy metal contents were in the order of Zn < Cr < Cu < Pb < Se, while trophic levels were in the order of insectivorous < omnivorous < carnivorous. Agricultural cover showed an association with endosulfan II (R2 = 0.50, r = 0.70), followed by alachlor (R2 = 0.43, r = 0.66). For PAHs, all detected substances showed significant relationships with forest cover. Ecological health assessment revealed that most river sites are in poor condition, indicating the direct impacts of pollutants. In conclusion, of the 28 POPs detected, 16 PAHs and 3 OCPs (hexachlorobenzene, lindane, and heptachlor epoxide) were of significant concern, such that action is needed to curb their inflow to the riverine environment. The studied river basin is under substantial threat from harmful POPs that endanger ecological health and fish biodiversity.

Predicting the shift of invasive species distribution in response to climate change is essential for ecological risk assessment. In this study, the distribution of invasive largemouth bass (Micropterus salmoides) was predicted from 2016 to 2085 in the Han River basin of South Korea using HadGEM3-RA based climate change scenarios (representative concentration pathway [RCP] 4.5 and 8.5 scenarios). A random forest model was developed using largemouth bass occurrence data and environmental variables (temperature, precipitation, flow rate, water quality, elevation, and slope) for five years (2011–2015). The annual mean temperature was the second most contributing variable after elevation. The occurrence of largemouth bass in the Han River basin was expected to increase in the future with increasing annual mean temperature, especially after the 2060 s (2056–2065) in the RCP 8.5 scenario. The latitudinal, longitudinal, and altitudinal shifts of largemouth bass distribution were expected to be −1.76 km, 4.19 km, and 9.07 m per 10 years under the RCP 8.5 scenario, respectively, indicating a gradual southeastward shift to higher locations. Given that invasive fish can disturb the habitat of endemic species, three-dimensional distribution shift under climate change should be considered for the ecological risk assessment of invasive species.

Despite the extensive usage of synthetic musk compounds (SMCs) and siloxanes in various personal care products (PCPs), trophic magnification of such chemicals in aquatic environments remains unexplored. In June and September 2020, eleven SMCs and nineteen siloxanes were measured in water, sediments, and biota. Samples were collected from two sites where levels were expected to be influenced by the distance from the wastewater treatment plant (WWTP) in the Geum River, Republic of Korea, were expected. High concentrations of SMCs and siloxanes entered through WWTP were measured in water, sediment, and biota at the both sites and both seasons. The δ15N of amino acids provided a high-resolution food web and accurate trophic position (TP), which is an important factor for determining the trophic magnification factor (TMF). Among 24 TMFs, 19 of them were

The key objectives of this research were to establish fish monitoring methodologies and sampling efficiency strategies through the analysis of relations between fish species (compositions) and different kinds of sampling gear for lentic ecosystem health assessments. During the study, 81 species of fish and 53,792 individuals were sampled from the thirty reservoirs. When we tested the efficiency of combinations of multiple sampling gears, the combination of the cast net (CN) and kick net (KN) was most cost-effective, based on the sampling time elapsed and total cost of the sampling. This combination (1st choice method) sampled 74 fish species and 21,321 individuals and showed even better results than the combination of four types of gear (2nd choice method), which included the CN, fyke net (FN), trammel net (TN), KN, although 80 species and 52,242 individuals were sampled from the 2nd method. Overall, our preliminary data suggest that the lentic ecosystem health assessment (LEHA) model developed for national-level surveys may be used as an efficient tool for LEHA and the combined use of the CN and KN was more cost-effective than the 2nd choice method of four types of sampling gear (CN, FN, TN, and KN). Keywords: Fish sampling gear, Lentic ecosystem health assessment, Sampling efficiency

Land-use patterns influence water quality in lotic ecosystems worldwide; consequently, deteriorating water quality affects fish communities and composition and the ecological health of water bodies. This study aimed to evaluate how land use, stream order, and elevation regulate water quality and ecological health in 64 streams based on the following four land cover types: namely, forest, agriculture, urban upstream, and urban downstream regions. Spatial analysis revealed that urban downstream areas had higher nutrient concentrations [total phosphorus (TP) as follows: 117 µg/L; total nitrogen (TN): 5.57 mg/L] and organic pollutants [chemical oxygen demand (COD): 7.71] than other regions. Empirical analysis indicated that TP (R2 = 0.46) had a high relation with chlorophyll-a (Chl-a) compared to TN (R2 = 0.23) and TN:TP (R2 = 0.20). Elevation, stream order, and monsoon season significantly impact nutrients, organic matter, suspended particles, ionic content, and algal chlorophyll concentrations. The index of biotic integrity (IBI) was significantly positively correlated with elevation (R2 = 0.387), indicating that forest streams (high elevation) had better water quality and ecological health than lower-elevation streams. The proportion of insectivore species shows a significant negative relationship with biological oxygen demand (BOD) (R2 = 0.123) and TP (R2 = 0.155). The multi-metric index of biotic integrity (IBI) model suggested that the ecological health of forest streams was in fair condition. In contrast, agricultural streams were in poor condition, and urban upstream and downstream were in very poor conditions. The outcomes of this study indicated that land-use patterns and elevation largely regulate the water quality and ecological health of the streams.

The ecological integrity of lotic ecosystems is influenced by land cover type and human activity throughout the watershed. This study evaluated Nakdong River conditions in 2016 using two multi-metric models, the index of biotic integrity (IBI) and the water pollution index (WPI), and compared model outputs for four land cover types: predominantly urban, forest, barren land, and agricultural. The primary objective of this study was to determine whether the land cover type and human disturbance metrics effectively regulate water quality, fish communities, and ecological integrity in the Nakdong River basin. Predominantly forest sites had low nutrient, organic matter, suspended solids, ion, and algal chlorophyll concentrations. In contrast, these concentrations were higher in predominantly agricultural, urban, and barren land areas. Concentrations of nutrients, organic matter, ions, suspended particle loadings, and algal growth regulated by the intensity of the Asian summer monsoon. Model outputs indicated that total phosphorus (TP) was the most important factor in algal growth in agricultural (R2 = 0.25) and barren land (R2 = 0.35) sites, and evidence of P limitation was found, with TN:TP ratios >17 in ambient water. Fish community analysis indicated that tolerant species dominated the fish community in the agricultural (52%), barren land (85%), and urban sites (53%), and sensitive species were dominant in the forest sites (56%). Fish composition analysis indicated that two exotic species (Lepomis macrochirus (3.99%) and Micropterus salmoides (3.92%)) were identified as the fifth and seventh most abundant fish species in the watershed and labeled as “ecologically disturbing species” in Korea. Nutrient enrichment, organic pollution, and algal blooms enhanced the mean relative abundance of omnivorous and tolerant fish species. Mean WPI and IBI scores indicated fair or poor conditions in the agricultural (WPI: 22, IBI: 16), barren land (WPI: 21, IBI: 14), and urban (WPI: 21, IBI: 17) sites and good or fair conditions in forest (WPI: 28, IBI: 21) sites. The chemical (r = −0.34) and biological (r = −0.21) health of the river basin were negatively related to human disturbance metrics. The findings suggested that regional land cover, summer monsoon intensity, and human disturbance are important drivers of water quality, fish community, and ecological health. The resulting information suggested that agricultural diffuse pollution control, cutting-edge wastewater treatment technologies, and reducing the degrees of human disturbance could improve the Nakdong River’s ecological integrity.

Largemouth bass (Micropterus salmoides) is one of the world’s most notorious fish species, rapidly invaded in the aquatic ecosystems because of high fecundity and recruitment rate across the world, including South Korea, and is a major threat to native fish biodiversity and ecosystems. Knowledge about invasion range of largemouth bass has immense importance for conservation and management of native fish species. This study was conducted to predict a potential spatial spread in the future for the national-level risk assessments and successful management of largemouth bass in Korea. Using the MaxEnt (Maximum Entropy) model, 1109 streams and rivers of largemouth bass along with 24 climatic environmental variables of Korea were used to predict the future spatial distribution patterns and habitat suitability area. The precision of the MaxEnt model was highly significant, with an area under the curve value of 0.854 and 0.829 in 2050 and 2100, respectively. Overall, our study suggested that the output of MaxEnt model is useful for understanding how climatic variables affect the distribution range of invasive alien fish species and generating a map of potential risk. Keywords: Geographical distribution, Invasive alien species, Largemouth bass, Maximum entropy model, South Korea

River water quality degradation is one of the hottest environmental issues worldwide. Therefore, monitoring water quality longitudinally and temporally is crucial for effective water management and contamination control. The main aim of this study was to assess the longitudinal variations in water quality in the mainstream of the Han River, Korea, from 2015 to 2019. The trophic state classification (TSC), microbial pollution indicator (MPI), and river pollution index (RPI) were calculated to characterize river water quality and revealed more serious pollution toward the downstream zone (Dz) due to agricultural and urban-dominated areas. The biodegradability index (BI) indicated that non-biodegradable organic pollutants are increasing in the water body from the urban and animal wastewater treatment plants. Nutrients, organic matter contents, total suspended solids, ionic factors, and algal chlorophyll were higher in the Dz than in any other zones and were markedly influenced by the summer monsoon. Empirical analysis showed that nutrients and organic matter had positive linear functional relations with agricultural and urban coverage and negative linear relations with forest coverage. The pollutant-transport function suggested that suspended solids act as TP and TN carriers. Regression analysis indicated that TP (R2 = 0.47) has more positive functional relations with algal growth than TN (R2 = 0.22). Our findings suggest that a combination of empirical models and pollution indices might be utilized to assess river water quality and that the resulting information could aid policymakers in managing the Han River.

The main theme of the study was to determine long-term temporal and spatial patterns of the nutrient regime [total phosphorus (TP) and total nitrogen (TN)], chlorophyll dynamics (CHL), suspended solids, biological oxygen demand, chemical oxygen demand, total organic carbon, and electrical conductivity in Yeongsan watershed, based on the data set of 10 years (2007–2016) and then to develop the nutrient–chlorophyll empirical models. Summer monsoon is the key determinant which regulates the nutrient concentrations and algal growth of the watershed. The nutrient concentrations (TP and TN) were greater in headwater zone (Hz) compared to midwater zone (Mz) and downwater zone (Dz) because of high flushing rate during monsoon season. TP (R2 = 0.23, p

Invasive alien fish species (IAFS) influence recipient ecosystems in multiple ways, from altered native fish communities to poor ecological health and higher economic losses to control and eradication. We tested key drivers and connections between an IAFS (Micropterus salmoides) presence, absence, geomorphological, hydro-chemical, physical habitat, native fish assemblages, and large river basins biotic integrity during 2016–2019. A total number of 62,121 individuals (TNI) representing 74 fish species were observed, out of which 68 species (45,677 TNI) belonged to the Geum River (GR) basin, while 63 species (16,444 TNI) were from the Mankyong/Dongjin River (MDR) basin. The results illustrated a significant contrast based on stream order, catchment area, altitude, stream gradient, and width among the sites with and without largemouth bass. However, fluctuations in nutrients (nitrogen and phosphorus) were not affected by variations in pH, dissolved oxygen, conductivity, suspended solids, and river flow. The largemouth bass has emerged as the 8th largest fish population in the GR and swiftly occupies the MDR basin with a constancy value of 45.5. Native sensitive (r = −0.38), insectivore (r = −0.252), carnivores (r = −0.085), and TNI (r = −0.512) displayed a negative correlation with increasing largemouth bass abundance. Largemouth bass induced significant regime transformation in the carnivore species. A significant difference (p < 0.01) of biotic integrity was illustrated among the largemouth bass population sites. A conspicuous interplay between ‘poor’ ecological health (r = 0.33, p = 0.038, n = 41) sites and ‘fair–excellent’ (r = −0.38, p < 0.001, n = 622) sites as compared to the overall ecological health linked with largemouth bass abundance (r = −0.397, p < 0.001, n = 663) alluded to stronger impact of the IAFS. In conclusion, the largemouth bass has potentially altered the native fish assemblage and ecological health. Further, we conclude that rapidly shifting flow patterns supported by the expanding anthropogenic interventions (weirs and dam) are the most approving factors of impending fish invasions.

Water quality degradation is one of the most pressing environmental challenges in reservoirs around the world and makes the trophic status assessment of reservoirs essential for their restoration and sustainable use. The main aims of this study were to determine the spatial variations in water quality and trophic state of 204 South Korean reservoirs at different altitude levels. The results demonstrated mean total phosphorus (TP), chlorophyll-a (CHL-a), total suspended solids (TSS), organic matter indicators (chemical oxygen demand: COD; total organic carbon: TOC), water temperature (WT), and electrical conductivity (EC) remain consistently higher in the very lowland reservoirs (VLLR) than those in other altitudes, due to sedimentary or alluvial watersheds. The average TP and CHL-a levels in VLLR crossed the limit of the eutrophic water, symptomizing a moderate risk of cyanobacterial blooms. Empirical models were developed to identify critical variables controlling algal biomass and water clarity in reservoirs. The empirical analyses of all reservoir categories illustrated TP as a better predictor of CHL-a (R2 = 0.44, p < 0.01) than TN (R2 = 0.02, p < 0.05) as well as showed strong P-limitation based on TN:TP ratios. The algal productivity of VLLR (R2 = 0.61, p < 0.01) was limited by phosphorus, while highland reservoirs (HLR) were phosphorus (R2 = 0.23, p < 0.03) and light-limited (R2 = 0.31, p < 0.01). However, TSS showed a highly significant influence on water clarity compared to TP and algal CHL-a in all reservoirs. TP and TSS explained 47% and 34% of the variance in non-algal turbidity (NAT) in HLR. In contrast, the TP and TSS variances were 18% and 29% in midland reservoirs (MLR) and 32% and 20% in LLR. The trophic state index (TSI) of selected reservoirs varied between mesotrophic to eutrophic states as per TSI (TP), TSI (CHL-a), and TSI (SD). Mean TSI (CHL-a) indicated all reservoirs as eutrophic. Trophic state index deviation (TSID) assessment also complemented the phosphorus limitation characterized by the blue-green algae (BGA) domination in all reservoirs. Overall, reservoirs at varying altitudes reflect the multiplying impacts of anthropogenic factors on water quality, which can provide valuable insights into reservoir water quality management.

Due to rapid eutrophication, sustainable water quality management and supply are essential in drinking water sources and aquatic biota in large reservoirs. We evaluated the potentially crucial factors influencing the algal chlorophyll (CHL-a), nutrients, and the links between the rainfall and other vital elements in a large multipurpose reservoir (Yongdam Reservoir) during 2013–2019. We developed the empirical models on algal CHL-a, total phosphorus (TP), total nitrogen (TN), and TN:TP’s ambient ratios considering the maneuvering influence of Asian monsoons. The intensive rainfall during the monsoon months strongly impacted the nutrient regime and other vital factors. The seasonal patterns of algal CHL-a varied in response to the nutrient contents (TN, TP), suspended solids, and ambient N:P ratios along the longitudinal gradient. The conditional plot analysis, empirical modeling, and observations supported an overall P-limitation scenario, as was evident from the magnitude of N:P ratios (R2 = 0.36, F = 24.9, p < 0.001). Furthermore, the reservoir’s trophic status alluded to the larger particles and blue-green algae during the monsoon and postmonsoon months. The correlation analysis, Mann–Kendall trend test, and principal component analysis illustrated compelling links between CHL-a, TP, and rainfall regime. The outcomes suggested the reservoir was primarily controlled by phosphorus limitation, with an increasing CHL-a tendency along with nitrogen dilution. However, a slight decline in phosphorus was also detected. The Yongdam Reservoir is under the threat of recurrent eutrophication events that could jeopardize this vital drinking water facility due to increasing agricultural and anthropic activities.

The main objective of this study was to develop empirical models from Landsat 5 TM data to monitor nutrient (total phosphorus: TP), organic matter (biological oxygen demand: BOD), and algal chlorophyll (chlorophyll-a: CHL-a). Instead of traditional monitoring techniques, such models could be substituted for water quality assessment in aquatic systems. A set of models were generated relating surface reflectance values of four bands of Landsat 5 TM and in-situ data by multiple linear regression analysis. Radiometric and atmospheric corrections improved the satellite image quality. A total of 32 compositions of different bands of Landsat 5 TM images were considered to find the correlation coefficient (r) with in-situ measurement of TP, BOD, and CHL-a levels collected from five sampling sites in 2001, 2006, and 2010. The results showed that TP, BOD, and CHL-a correlate well with Landsat 5 TM band reflectance values. TP (r = −0.79) and CHL-a (r = −0.79) showed the strongest relations with B1 (Blue). In contrast, BOD showed the highest correlation with B1 (Blue) (r = −0.75) and B1*B3/B4 (Blue*Red/Near-infrared) (r = −0.76). Considering the r values, significant bands and their compositions were identified and used to generate linear equations. Such equations for Landsat 5 TM could detect TP, BOD, and CHL-a with accuracies of 67%, 65%, and 72%, respectively. The developed empirical models were then applied to all study sites on the Paldang Reservoir to monitor spatio-temporal distributions of TP, BOD, and CHL-a for the month of September using Landsat 5 TM images of the year 2001, 2006, and 2010. The results showed that TP, BOD, and CHL-a decreased from 2001 to 2006 and 2010. However, S3 and S4 still have water quality issues and are influenced by climatic and anthropogenic factors, which could significantly affect reservoir drinking water quality. Overall, the present study suggested that the Landsat 5 TM may be appropriate for estimating and monitoring water quality parameters in the reservoir.

The objectives of this study were to determine tolerance ranges and trophic gradients of two fish populations of Zacco koreanus (Zk) and Zacco platypus (Zp) in relation to chemical water quality and ecological stream health, based on the biological integrity metric (BIM) model. Seventy-six streams and rivers were sampled for the analysis. The population of Zk had a narrow chemical tolerance with a low phosphorus limit (

The main objectives of this study were to determine how Asian monsoon influences nutrient regime, suspended solids, and algal chlorophyll (CHL) in 182 agricultural reservoirs, and then to develop the empirical models of nutrients-chlorophyll. The intensity of summer monsoon directly determined the ambient concentrations of nitrogen (N) and phosphorus (P). Regression analysis of empirical model showed that CHL had a high linear relation (R2 = 0.716, p < 0.01) with total phosphorus but a weak relation (R2 = 0.041, p < 0.01) with total nitrogen. Seasonal empirical models of TP-CHL showed that the regression coefficients in premonsoon (R2 = 0.605) and postmonsoon (R2 = 0.554) were greater than that of the monsoon. Values of trophic state index (TSI) implied that phosphorus limitation was severe in the Korean agricultural reservoirs. Overall, our study of 182 reservoirs suggested that phosphorus was key nutrient regulating the phytoplankton growth. This phenomenon was supported by the analysis of trophic state index deviation relations of “TSI (CHL)−TSI (SD) < TSI (CHL) – TSI (TP)”.

This study was carried out to analyze the difference in fish fauna, ecological indicator characteristics, biological status of other fish populations, and fish community structures between two groups of reservoir ecosystems along with the invasion of an introduced species, Micropterus salmoides. Six reservoirs were selected and divided into two groups: reservoirs noninvaded and invaded by M. salmoides were RNIv and RIv, respectively. A total of 11,519 individuals of 28 species were sampled in RNIv, whereas 1925 individuals of 19 species were sampled in RIv. Korean endemic fish population dominates in RNIv, exotic fish species, especially M. salmoides, dominate in RIv. Sensitive species dominate in RNIv, whereas tolerant species and carnivore species dominate in RIv. The analysis of total length size distribution showed some difference, particularly in species size group between RNIv and RIv. Also, the analysis of total fish biomass showed a significant difference in accordance with M. salmoides inhabitation. According to the fish community analysis results, as M. salmoides proportion increased, species richness and diversity decreased. Overall data suggest that the dominant distribution of M. salmoides may influence simplification of the fish fauna, species composition, as well as community structure, and affect the length distribution and biomass of other fish population negatively.

The key objective of this study was to analyze the sampling efficiency of various fish sampling gears for a lentic ecosystem health assessment. A fish survey for the lentic ecosystem health assessment model was sampled twice from 30 reservoirs during 2008–2012. During the study, fishes of 81 species comprising 53,792 individuals were sampled from 30 reservoirs. A comparison of sampling gears showed that casting nets were the best sampling gear with high species richness (69 species), whereas minnow traps were the worst gear with low richness (16 species). Fish sampling efficiency, based on the number of individual catch per unit effort, was best in fyke nets (28,028 individuals) and worst in minnow traps (352 individuals). When we compared trammel nets and kick nets versus fyke nets and casting nets, the former were useful in terms of the number of fish individuals but not in terms of the number of fish species.

The incidence and dispersal of invasive alien fish species (IAFS) have ecological impacts on biodiversity and environmental health at regional to global scales. We identified links between the presence of largemouth bass (Lb) and bluegill (Bg), and selected indicators of environmental water quality, trophic and tolerance guilds, ecological health factors, and stream order. We used the data collected from national biomonitoring study sites in four major rivers of South Korea. IAFS occurred in eutrophic waters (Lb = total phosphorus: 140 ± 170 µg/L, chlorophyll a: 16.7 ± 27.5 µg/L; Bg = total phosphorus: 160 ± 190 µg/L, chlorophyll a: 19.43 ± 28.05 µg/L) and dominated at higher ambient ratios of total nitrogen to total phosphorus (TN:TP). At TN:TP ≤ 100, the relative abundance of Lb and Bg was highest (95.3% and 96.0%, respectively). Concerning tolerance guilds, Lb (R2 = 0.78, p < 0.0001) and Bg (R2 = 0.59, p < 0.0001) had positive relationships with tolerant species in all four river watersheds and negative relationships with the percentages of insectivores and omnivores. This indicates the harmful impacts of IAFS on the aquatic food web. These invasive fish species also influenced stream health, particularly in the Nakdong and Yeongsan/Seomjin rivers. Our findings suggest that assessing chemical water quality can help identify the optimal and suboptimal survival and spread ranges of IAFS (Lb and Bg), as they directly influence tolerance and trophic guilds in the aquatic food web. In conclusion, these IAFS could be a major factor in the deteriorating ecosystem health, which had negative relationships with the abundance and occurrence of IAFS. Therefore, approaches that use appropriate water chemistry factors and species tolerance may provide critical insights into the efficient management of river health that has been perturbed by the presence of IAFS.