Korean Streams Research Articles

Heavy metal bioaccumulation based on seasonal monsoon impact in benthic macroinvertebrates of Korean streams.

This study investigates the influence of seasonal monsoon flooding on heavy metal contamination and bioaccumulation in benthic macroinvertebrate communities within a stream ecosystem. We analyzed sediment and benthic macroinvertebrate samples for eight heavy metals [zinc (Zn), chromium (Cr), nickel (Ni), lead (Pb), copper (Cu), arsenic (As), cadmium (Cd), and mercury (Hg)] ) before (BF) and after (AF) a major flooding event. Significant spatial and temporal variations in heavy metal concentrations were observed, with generally higher levels detected after the flood. Chironomidae consistently exhibited high bioaccumulation factors (BAFs) for several metals, highlighting their role as bioindicators. Notably, elevated Cu accumulation was observed in multiple species, including Radix auricularia (R. auricularia), Cipangopaludina chinensis malleata (C. c. malleata), and Palaemon spp. Non-metric multidimensional scaling (NMDS) analysis revealed shifting correlations between environmental variables and bioaccumulation patterns before and after flooding. Pre-flood, total nitrogen (TN) showed a strong positive correlation with Hg bioaccumulation, while post-flood, large sand content emerged as a more influential factor for Zn, Cr, Ni, and Pb bioaccumulation. Our findings emphasize the complex interplay between seasonal flooding, environmental factors, and heavy metal dynamics, with potential implications for ecological risk assessment and water quality management.

Development of a link extrapolation-based food web model adapted to Korean stream ecosystems

Development of a link extrapolation-based food web model adapted to Korean stream ecosystems

Functional trait dataset of benthic macroinvertebrates in South Korean streams

Functional traits are the result of evolution and adaptation, providing important ecological insights into how organisms interact with their environment. Benthic macroinvertebrates, in particular, have garnered attention as biomonitoring indicators for freshwater ecosystems. This study presents a functional trait dataset for benthic macroinvertebrates, comprising 447 taxa (393 at genus level, 53 at family level and one at class level) from five phyla (Annelida, Arthropoda, Mollusca, Nematomorpha, and Platyhelmenthes), categorized into nine traits related to life history, morphology, and habit. To account for variation in available trait information, we assigned confidence levels to each taxon and functional trait based on the level of evidence using fuzzy coding. Our dataset provides an important resource for understanding the ecology of benthic macroinvertebrates in South Korea, serving as a valuable baseline dataset for studying their biodiversity, conservation, and biomonitoring in freshwater ecosystems.

Development and Testing of a RIVPACS-type Model to Assess the Ecosystem Health in Korean Streams: A Preliminary Study

Development and Testing of a RIVPACS-type Model to Assess the Ecosystem Health in Korean Streams: A Preliminary Study

Distribution patterns and vulnerability of stoneflies (Plecoptera: Insecta) in South Korean streams with conservation perspectives

Biodiversity loss and conservation are major issues at global and regional scales. Plecopteran species have limited distribution areas and are vulnerable to environmental changes. In this study, we evaluated the distribution patterns and environmental characteristics of plecopteran assemblages in South Korean streams to consider the conservation of plecopteran diversity. We used plecopteran assemblage data with environmental data including 32 environmental variables in six categories (geography, meteorology, land use, substrate composition, hydrology, and water quality) surveyed at 412 sampling sites distributed on a nationwide scale in South Korean streams. Self-organizing map classified sampling sites into seven clusters according to the similarities of assemblages. Non-metric multidimensional scaling (NMDS) was used to characterize the relationship between assemblages and abiotic environmental variables. The abundance of 32 plecopteran taxa recorded in the dataset displayed a positive relationship with the number of their occurrence sites, and most species, including the dominant ones, had low abundances in limited distribution areas. More than 78% (25 out of 32) of the recorded plecopteran species were listed in the Korean Red List of Threatened Species, including 17 taxa in the least concern category. The NMDS results presented the habitat preference of species, and the major influential factors from six environmental categories were elevation, maximum temperature in July, proportion of forest in land-use type, proportion of cobbles in substrate, proportion of riffle in flow condition, and turbidity in physicochemical water quality. The results revealed that plecopteran species were diverse and abundant in cold and undisturbed running water on rocky substrates near mountain forests. The dominant species generally displayed similar habitat conditions. However, their habitat preferences varied depending on the species, with different sensitivities and responses to temperature and hydrological flow conditions. Finally, our results revealed that the plecopteran species in South Korea are mostly vulnerable and endangered, and extensive protection policies covering the stream channel and the surrounding areas are required to preserve their biodiversity.

Integrating Deep Learning and Machine Translation for Understanding Unrefined Languages

In the field of natural language processing (NLP), the advancement of neural machine translation has paved the way for cross-lingual research. Yet, most studies in NLP have evaluated the proposed language models on well-refined datasets. We investigate whether a machine translation approach is suitable for multilingual analysis of unrefined datasets, particularly, chat messages in Twitch. In order to address it, we collected the dataset, which included 7,066,854 and 3,365,569 chat messages from English and Korean streams, respectively. We employed several machine learning classifiers and neural networks with two different types of embedding: word-sequence embedding and the final layer of a pre-trained language model. The results of the employed models indicate that the accuracy difference between English, and English to Korean was relatively high, ranging from 3% to 12%. For Korean data (Korean, and Korean to English), it ranged from 0% to 2%. Therefore, the results imply that translation from a low-resource language (e.g., Korean) into a high-resource language (e.g., English) shows higher performance, in contrast to vice versa. Several implications and limitations of the presented results are also discussed. For instance, we suggest the feasibility of translation from resource-poor languages for using the tools of resource-rich languages in further analysis.

Development of a predictive model for benthic macroinvertebrates by using environmental variables for the biological assessment of Korean streams

Predictive models for benthic macroinvertebrates based on changes in environmental variables can assess the biological integrity of streams by comparing observed biotic communities with those expected at reference sites. To develop a predictive model of the abiotic community, we used benthic macroinvertebrates and environmental variables collected from 2,700 sites from 2010 to 2019. First, we selected 357 reference sites by using the 5-day biochemical oxygen demand, ammonia nitrogen, total phosphorus, turbidity, and coarse particle percentage. Then, we used Two-Way Indicator Species Analysis to classify the reference sites into six groups based on benthic macroinvertebrates. Reference sites classified by biological characteristics were linked to environmental variables by multi-discriminant analysis. The relative influences environmental variables on the classified groups were in decreasing order of catchment area, latitude, velocity, water depth, altitude, and longitude. To develop the predictive model, we combined (1) identification level, (2) grouping method, and (3) probability of capture, and then used the normalized root mean square error (NRMSE) to check the fit of each model. The higher the probability of capture was at the family level compared to the species level, the lower was the NRMSE. The grouping method was not as consistent as the identification level and probability of capture because the NRMSE for the number of taxa was low when used as a weighted average. The NRMSE was also low for the Benthic Macroinvertebrates Index and the Benthic Macroinvertebrates Family-level Biotic Index (BMFI) when used for assignment to the group with the highest probability. We selected the predictive model which used family level, weighted average, and BMFI-proposed indicator taxa as the final assessment model due to its sensitivity and fit. This model was the most reasonable choice, but we had to reduce the error of the model and revise it elaborately by securing additional environmental variables.

Challenges and Achievements beyond Decision-Making Power of Planners: How Are Decisions on Planning for Stream Restoration Made in South Korea?

This research covers existing planning theory and possible ways to improve the decision-making process in Korean stream restoration. First, it attempts to recognize what extent the Korean stream restoration case follows Western environmental decision-making models. Additionally, key concepts and factors of environmental decision-making are discussed to build a foundation of planning theory. This research reveals key works in the broad and changing field of stream restoration that provides the foundation for understanding Korean water resource planning. To recognize the challenges and achievements of this planning, this paper first notes that, while technical perspectives of the engineering field have historically dominated stream restoration, current thinking recognizes the much greater complexity of stream restoration requires more than only engineering perspectives. After reviewing the literature in related areas, this research considers what the planning field has to offer. In the conclusion, this author argues that the application of citizen-oriented decision-making approaches could lead to better water resource management. Admittedly, this may still be hindered by political uncertainty and power conflicts caused by science-dominant environmental planning.

A multimetric diatom index for biological integrity assessment of Korean streams

A multimetric diatom index for biological integrity assessment of Korean streams

Development Necessity of Diatom Indices for the Integrated Assessment of Water Quality and Aquatic Ecosystem of Korean Streams.

River water quality and organisms have a very close relationship with the human living environment and health, so it is very important to ensure and maintain the ecological integrity of the aquatic ecosystem. In that sense, benthic diatoms have relatively little mobility, can explain the effects of long-term exposed pollution sources, and are very suitable indicator organisms for river ecosystem evaluation. Diatom ecologists have been developed various diatom indices to assess water quality and stream ecosystem over the world. However, they so far have insufficient identification of taxa, are strongly regional, and are difficult to apply as they are domestically. Unfortunately, there has not been developed an independent diatom index suitable for the Korean stream. Therefore, management of water quality and aquatic ecosystem suitable for domestic rivers can be made, and development or improvement of comprehensive multivariate diatom index for the integrated assessment of water quality and aquatic ecosystem is urgently needed.

Korean stream types based on benthic macroinvertebrate communities according to stream size and altitude

ABSTRACTType-specific stream assessment systems based on biotic indicators are considered a main focus of future stream assessment in many European countries. However, there is a lack of information on type-specific differences of freshwater eco-regions in South Korea. We aimed to classify the stream types characterized by stream size and altitude. Analyzing the relationship between physical environmental variables and benthic macroinvertebrates collected between 2008 and 2015 at 1,020 sites (i.e. 13,366 samples) on a national scale in South Korea, we classified a total of five Korean stream types. All streams were divided into wadeable and non-wadeable streams using stream order and width. Wadeable streams were classified as mountain, highland, or lowland wadeable streams based on altitude. Non-wadeable streams were divided into lowland non-wadeable streams or rivers based on width. Mountain and highland streams significantly correlated with altitude, whereas others were distinctly related to stream order and width. We selected 25 indicator species sensitive to stream size and altitude. These assessments will provide preliminary information for development of a future biotic stream assessment system based on stream typology.

Spatial Distribution of Benthic Macroinvertebrate Assemblages in Relation to Environmental Variables in Korean Nationwide Streams

Conserving and enhancing freshwater biodiversity are global issues to ensure ecosystem integrity and sustainability. To meet this, it is critical to understand how the biological assemblages are determined by environmental gradients in different spatial scales. Nevertheless, information on their large-scale environmental relationships remains scarce in Korea. We aimed to understand nationwide spatial distribution patterns of benthic macroinvertebrates and important environmental factors affecting their distribution in 388 streams and rivers across Korea. A total of 340 taxa, belonging to 113 families in 23 orders of five phyla, were identified. Assemblage composition in most Korean streams included a few predominant colonizers and a majority of rare taxa. Cluster analysis based on benthic macroinvertebrates classified a total of 720 sampling sites into five clusters according to the pollution levels from fast-flowing less polluted streams with low electrical conductivity to moderately or severely polluted streams with high electrical conductivity and slow water velocity. Canonical correspondence analysis revealed that altitude, water velocity and streambed composition were the most important determinants, rather than watershed and water chemistry variables, for explaining the variation in macroinvertebrate assemblage patterns. The results provide basic information for establishing the conservation and restoration strategies of macroinvertebrate biodiversity against anthropogenic disturbances and developing more confident bio-assessment tools for diagnosing stream ecosystem integrity.

남강에 대한 하천분류체계의 적용 연구

하천은 구간에 따라 하도의 지형학적인 특성이 다양하기 때문에 수리 및 하도 특성 평가를 위해서는 하천의 유형을 분류할 필요가 있다. 또한 하도 특성에 대한 정량적 평가체계는 하천 유형의 특성이 반영되어야 한다. 따라서, 본 연구에서는 하천분류체계의 한국 하천에 대한 적용성을 검토하기 위하여 Rosgen의 하천분류체계와 Yamamoto의 하천분류체계를 비교, 분석하였고, 남강을 사례로 그 적용성을 검토하였다. 하천 지형학적인 측면에서 우리나라의 지방 및 국가하천의 평균하상경사와 종적 연속성을 고려하기 위해서는 하천 지형학적인 측면에서 Yamamoto의 하천분류체계가 적용성이 높은 것으로 판단된다. 또한, 하상재료의 측면에서 Rosgen 분류체계가 Yamamoto의 분류체계보다는 하상경사와의 상관성이 낮게 나타났다. 반면에 Yamamoto의 분류체계는 하상경사에 따른 토사분급 (수리분급)을 반영할 수 있는 것으로 확인되었다. 남강에 대하여 얻어진 결과에 의하면, Rosgen의 분류체계로서는 하상경사와 하상재료의 관계로서 하천유형을 분류할 수 없으나, Yamamoto 분류체계는 그 상관성을 입증할 수 있었다. 다만, 자연하천에 대하여 추가적인 적용성 검토가 필요하다. 하도 특성 평가체계에 적용할 수 있는 3개의 하천유형을 결정하여 제시하였다. Because streams have a great diversity of morphological features according to their reaches, it is necessary to classify the types of streams in order to assess their characteristics of channel. In addition, a quantitative assessment system for channel characteristics should be reflected in the stream type properties. Therefore, this study compares two stream classification system (Rosgen's and Yamamoto's) to review their applicability on Korean streams, and the two classification systems were applied on the Nam River. In order for the mean bed slope and the longitudinal connectivity of the provincial and national streams to be reflected in the assessment system of channel characteristics, the Yamamoto system is considered highly adaptable in the stream geomorphology side. In addition, it has been found the Rosgen system has a low correlation of bed slope compared to the Yamamoto system in the view of bed materials. On the other hand, the Yamamoto system was found to be capable of reflecting sediment sorting (hydraulic sorting) of the bed slope. According to the results obtained at the Nam River, the Rosgen system could not classify a type of stream by relationship between bed material and bed slope, but the Yamamoto system can verify the correlation of stream type. However, further review is needed with respect to the applicability of natural rivers. Three types of stream that can be applied to the assessment system of channel characteristics were proposed.

Ecological conservation and the restoration of freshwater environments in Korea

Freshwater ecosystems worldwide are subjected to a variety of anthropogenic threats (Malmqvist and Rundle 2002). Inappropriate land use practices, pollutants, overexploitation, and overpopulation have simplified/fragmented aquatic habitats and degraded biodiversity and water quality. In fluvial systems, human threats result from relatively slight use, such as, sports activities (e.g., canoeing and rafting), to severe pollution of water quality (inflow of nutrient-enriched sewage and a large amount of nonpoint source pollution loads), and damage to stream morphology (e.g., channelization and straightening) and the flow continuum (e.g., impoundment by large dams and weirs). Thus, conserving and reviving freshwater health and biodiversity are increasingly becoming global aims to ensure ecosystem integrity and freshwater ecosystem sustainability. Freshwater is a crucial resource for nature and man, and a biodiversity hotspot, which supports almost 10 % of all known animal species (Strayer and Dudgeon 2010), but they are much more vulnerable to disturbances than other ecosystems (Cushing and Allan 2001). Nevertheless, despite global attention on biodiversity imperilment in freshwater ecosystems for decades, increasing human pressures will accelerate species loss. Dudgeon et al. (2006) apprehended the extinction of freshwater animal species at a rate of 4 % per decade in North America, which exceeded by several fold that is expected of terrestrial species. In the case of Korean freshwater fishes, 63 of the 215 species (29.3 %) are endemic and 26 (12.1 %) are designated as ‘Critically Endangered,’ ‘Endangered,’ or ‘Vulnerable’ based on the IUCN (International Union for the Conservation of Nature and Natural Resources) red list, which portends a consistent decrease in their numbers (MOE/NIBR 2012). Intensive human-centered land use practices, such as, agricultural activities and urbanization, over decades have severely altered most stream and river ecosystems in Korea through excessive water use, which threatens water security and biodiversity (Jeong et al. 2010). Consequently, very few Korean streams and rivers remain undisturbed, and currently these compose only 5 % of reference streams listed in the National Aquatic Ecological Monitoring Program (NAEMP) database (Jun et al. 2012). ‘‘Restoration of the ecological integrity of the nation’s water’’ is one of the most important objectives of legislation concerning water environment management and conservation and related policies in many countries (e.g., US EPA 2011). This is also the case in Korea, where the Water Quality and Aquatic Ecosystem Conservation Act, and water environment management programs declare the importance of the health and integrity of aquatic ecosystems (MOE 2007). Given the implementation of national investment in water infrastructure and regulation, much work has been done to restore aquatic ecosystems, particularly rivers and streams. However, although major water quality improvements have been achieved (e.g., BOD) over the past three decades, many environmental challenges remain, such as, loss and destruction of habitat, altered S.-J. Hwang (&) Department of Environmental Health Science, Konkuk University, Seoul 143-701, Republic of Korea e-mail: sjhwang@konkuk.ac.kr

선진 하천환경 평가체계의 사례검토

본 연구는 독일과 호주 등 선진국의 하천환경 평가체계의 개념적 틀과 평가체계의 발달과정 및 평가기법에 대한 종합적인 검토결과를 바탕으로 한국형 하천환경 평가체계 정립의 기본방향을 제시하기 위하여 수행되었으며, 연구를 통해 얻은 결론은 다음과 같다. 일차적으로 하천환경 평가체계는 하천공간의 위계에 기초한 지질 지형학적 구조 및 화학적 질과 생물학적 다양성이 시공간적으로 긴밀한 상호관계를 이룬다는 사실이 전제되고 있다는 점이다. 따라서 우리나라 고유의 하천환경 체계와 특성, 그리고 실제적인 하천관리 여건 등을 충분히 고려한 평가체계의 구축이 요구된다는 점이다. 한편으로 선진국의 표준화된 하천환경 평가체계가 다년간의 하천관리의 경험적 측면과 학제적 지식 및 기술을 바탕으로 이루어졌으며, 또한 각국의 하천환경의 특성이 반영된 하천환경의 유형화 및 계층적 위계, 평가목적, 평가지표 및 방법, 참조하천의 설정 및 기준의 정립측면에서 논리적 일관성을 확보하고 있다는 사실이다. 따라서 우리나라의 하천환경 평가체계 구축도 선진국 평가체계에서 나타난 기본원칙과 과정 및 방법 등을 최대한 고려하되 우리의 현실적인 여건에 적합한 과학적이면서 통합적인 평가체계를 지향해야 할 것으로 판단되었다. This study was carried out to suggest principles & guidelines necessary for setting up of the assessment system applied in Korean stream. The work was based on the review and discussion of advanced stream assessment techniques and its adjustment for Korean stream condition and management status. The results obtained from this study were summarized as follows: Firstly, stream assessment system has been developed from the fact that geomorphological structures and chemical qualities forming stream system in the hierarchy, were closely correlated to the biological diversity through temporal and spatial scales. Therefore, Korean stream assessment system must be developed with a sufficient consideration on the characteristics of stream conditions as well as actual status of stream management. The other side, those advanced and standardized assessment system, which has been originated from a long experienced lessons on stream management, interdisciplinary knowledge and techniques, represented much logic consistence in view of basic components such as aims for assessment, establishment of assesment indicators and criteria, selection of reference conditions. Accordingly, our assessment system must be also progressed towards scientifically oriented and integrated system which reflects our real stream surroundings and also includes some principles and process and techniques reviewed in advanced system.

Natural and anthropogenic sources and processes affecting water chemistry in two South Korean streams

Acid mine drainage (AMD) in a watershed provides potential sources of pollutants for surface and subsurface waters that can deteriorate water quality. Between March and early August 2011, water samples were collected from two streams in South Korea, one dominantly draining a watershed with carbonate bedrock affected by coal mines and another draining a watershed with silicate bedrock and a relatively undisturbed catchment area. The objective of the study was to identify the sources and processes controlling water chemistry, which was dependent on bedrock and land use. In the Odae stream (OS), the stream in the silicate-dominated catchment, Ca, Na, and HCO3 were the dominant ions and total dissolved solids (TDS) was low (26.1–165mg/L). In the Jijang stream (JS), in the carbonate-dominated watershed, TDS (224–434mg/L) and ion concentrations were typically higher, and Ca and SO4 were the dominant ions due to carbonate weathering and oxidation of pyrite exposed at coal mines. Dual isotopic compositions of sulfate (δ34SSO4 and δ18OSO4) verified that the SO4 in JS is derived mainly from sulfide mineral oxidation in coal mines. Cl in JS was highest upstream and decreased progressively downstream, which implies that pollutants from recreational facilities in the uppermost part of the catchment are the major source governing Cl concentrations within the discharge basin. Dual isotopic compositions of nitrate (δ15NNO3 and δ18ONO3) indicated that NO3 in JS is attributable to nitrification of soil organic matter but that NO3 in OS is derived mostly from manure. Additionally, the contributions of potential anthropogenic sources to the two streams were estimated in more detail by using a plot of δ34SSO4 and δ15NNO3. This study suggests that the dual isotope approach for sulfate and nitrate is an excellent additional tool for elucidating the sources and processes controlling the water chemistry of streams draining watersheds having different lithologies and land-use patterns.

Modification of SWAT model for simulation of organic matter in Korean watersheds

The focus of water quality modeling of Korean streams needs to be shifted from dissolved oxygen to algae or organic matter. In particular, the structure of water quality models should be modified to simulate the biochemical oxygen demand (BOD), which is a key factor in calculating total maximum daily loads (TMDLs) in Korea, using 5-day BOD determined in the laboratory (Bottle BOD(5)). Considering the limitations in simulating organic matter under domestic conditions, we attempted to model total organic carbon (TOC) as well as BOD by using a watershed model. For this purpose, the Soil and Water Assessment Tool (SWAT) model was modified and extended to achieve better correspondence between the measured and simulated BOD and TOC concentrations. For simulated BOD in the period 2004-2008, the Nash-Sutcliffe model efficiency coefficient increased from a value of -2.54 to 0.61. Another indicator of organic matter, namely, the simulated TOC concentration showed that the modified SWAT adequately reflected the observed values. The improved model can be used to predict organic matter and hence, may be a potential decision-making tool for TMDLs. However, it needs further testing for longer simulation periods and other catchments.

A multimetric benthic macroinvertebrate index for the assessment of stream biotic integrity in Korea.

At a time when anthropogenic activities are increasingly disturbing the overall ecological integrity of freshwater ecosystems, monitoring of biological communities is central to assessing the health and function of streams. This study aimed to use a large nation-wide database to develop a multimetric index (the Korean Benthic macroinvertebrate Index of Biological Integrity—KB-IBI) applicable to the biological assessment of Korean streams. Reference and impaired conditions were determined based on watershed, chemical and physical criteria. Eight of an initial 34 candidate metrics were selected using a stepwise procedure that evaluated metric variability, redundancy, sensitivity and responsiveness to environmental gradients. The selected metrics were number of taxa, percent Ephemeroptera-Plecoptera-Trichoptera (EPT) individuals, percent of a dominant taxon, percent taxa abundance without Chironomidae, Shannon’s diversity index, percent gatherer individuals, ratio of filterers and scrapers, and the Korean saprobic index. Our multimetric index successfully distinguished reference from impaired conditions. A scoring system was established for each core metric using its quartile range and response to anthropogenic disturbances. The multimetric index was classified by aggregating the individual metric ..scores and the value range was quadrisected to provide a narrative criterion (Poor, Fair, Good and Excellent) to describe the biological integrity of the streams in the study. A validation procedure showed that the index is an effective method for evaluating stream conditions, and thus is appropriate for use in future studies measuring the long-term status of streams, and the effectiveness of restoration methods.

Effects of low-head dam removal on benthic macroinvertebrate communities in a Korean stream

This study was conducted to examine how a low-head dam removal (partial removal) could affect benthic macroinvertebrate communities in a stream. Benthic macroinvertebrates and substrates were seasonally sampled before and after dam removal (March 2006–April 2007). Benthic macroinvertebrates and substrates were quantitatively sampled from immediately upstream (upper: pool) and downstream (lower: riffle) sites, the location of the dam itself (middle), and immediately above the impoundment (control: riffle). After the removal, species richness and density of benthic macroinvertebrates as well as the EPT group (Ephemeroptera, Plecoptera and Trichoptera) increased to higher levels than those before the removal, while functional feeding groups and habitat orientation groups changed more heterogeneously at the upper site. At the lower site, species richness and density decreased somewhat immediately after dam removal, which was associated with an increase of silt and sand, but recovered after monsoon floods which helped to enhance substrate diversity at the upper site. Decreased dominance index and increased diversity index in both the upper and lower sites are evidence of positive effects from the dam removal. In conclusion, we suggest that even a partial removal of a dam, resulting in increased substrate diversity in the upper site, could sufficiently help rehabilitate lost ecological integrity of streams without major habitat changes.

Impact of flood intensity on aquatic insect communities in a Korean stream under monsoonal climate

As a consequence of climate change, localized torrential rainfall has increased in intensity and frequency in Northeast Asia under the influence of the monsoonal climate. The purpose of this study was to evaluate the impact of flood intensity on aquatic insect communities in a Korean stream, where the summer monsoonal flood is normal. Quantitative sampling was conducted according to stream reaches (upstream, midstream, and downstream sites) in Gapyeong stream, located in the central Korean peninsula, during July 2008–October 2009. Sampling was conducted within 48 hours after every rain event during the rainy season, and flood intensity was evaluated using the total amount of precipitation for 3 days before sampling. Precipitation was categorized in 100 mm increments. Water velocity and Froude number (Fr) were measured, and mean species abundance and species richness were determined. Habitat orientation groups (HOGs) were analyzed. Data were analyzed using nonmetric multidimensional scaling (NMS) ordination and two‐way analyses of variance .As a result, the velocity increased as precipitation increased at all sites, and the Fr at the upstream and midstream sites were below critical flow for all precipitation categories. The EPT‐group (Ephemeroptera, Plecoptera, and Trichoptera) together with Diptera were >90% in abundance at all study sites. The mean abundance of some major taxa (i.e., Ephemeroptera and Plecoptera) decreased significantly as precipitation increased, particularly, at the downstream site. The mean abundance of all HOGs was more influenced by the relatively large amount of precipitation (e.g., >200 mm) at all sites. According to NMS ordination, the amount of precipitation was the major factor determining the composition of aquatic insect communities in the study stream. In conclusion, aquatic insect communities in the Gapyeng stream were significantly influenced by the intensity of precipitation, and the impact was intensified at the downstream site.