Using traps and passive integrated transponder (PIT) telemetry, we investigated the effectiveness of the nature-like fishway installed at Sangju Weir on the Nakdong River, Korea. In 11 regular checks over the study period, 1474 individuals classified into 19 species belonging to 5 families were collected by the traps, representing 66% of the species inhabiting the main channel of the Nakdong River. PIT tags were applied to 1615 individuals belonging to 22 species, revealing fishway attraction and passing rates of 20.7% and 14.5%, respectively. Interspecific differences were also shown. For 63.2% of fishes, it took more than a day to pass through the fishway. Some individuals spent a longer time (>28 days) inside the fishway, suggesting the fishway was also being used for purposes other than passage. In this study, we verified species diversity of fish using a nature-like fishway installed in a large river in Korea. The results of this study provide a useful contribution to the development of fishways suitable for fish species endemic to Korea and for non-salmonid fish species worldwide.

This study analyzed the relationship between zooplankton communities and water quality characteristics, with a focus on total organic carbon (TOC), in 22 reservoirs within the Geum River basin that share similar climatic conditions but exhibit varying levels of pollution. Across all reservoirs, zooplankton community structures showed the highest correlations with TOC, suspended solids (SS), chlorophyll-a (Chl-a), and Secchi depth (SD), with stronger associations observed for rotifers and cladocerans compared to copepods. The classification of zooplankton community composition patterns, followed by an analysis of their associations with TOC concentrations, revealed relatively distinct differences between high-TOC and low-TOC reservoirs, indicating that TOC functions as a key determinant of community composition. Meanwhile, network analysis based on overall water quality characteristics indicated that patterns of water quality similarity among zooplankton-based communities differed somewhat from those based solely on TOC concentrations, suggesting that TOC may exert an independent influence on zooplankton community structure. In high-TOC reservoirs, typical eutrophic characteristics—such as elevated chlorophyll-a, total phosphorus, and suspended solids, along with reduced water transparency—were observed, accompanied by higher zooplankton abundance and a greater proportion of rotifers within the community. In contrast, low-TOC reservoirs, despite exhibiting no marked differences in other water quality variables, showed higher diversity of cladocerans alongside rotifers, further supporting the independent role of TOC in shaping zooplankton community structures. These findings highlight TOC not only as a general indicator of pollution but also as an ecologically significant factor influencing zooplankton community composition and carbon dynamics in reservoir ecosystems. They suggest that TOC should be considered a key variable in future assessments and management of lentic ecosystems.

Kellicottia bostoniensis is a rotifer species originating from North America, with numerous reports documenting its spread to Europe and South America. Meanwhile, in Asia, the occurrence of this non-native species has been scarcely documented, but its presence was recently reported in Korea in 2020. In Korea, the close geographic proximity of artificial reservoirs within a small area is expected to make the region vulnerable to the spread of K. bostoniensis. Therefore, it is deemed necessary to study the spatio-temporal distribution of K. bostoniensis, which appears to have extensively proliferated across the region, and its relationship with environmental factors. We analyzed the response of K. bostoniensis occurrence to environmental factors and aimed to compare its response patterns with those of potential competitor and predator groups, which were classified based on a functional group approach. This study, conducted on 12 small lakes located under similar climatic conditions, revealed that the response of K. bostoniensis to variables representing the trophic state of the lakes differed from those of the potential competitor and predator groups. The study sites, encompassing a wide range of trophic states from oligotrophic to hypereutrophic, across various lakes and survey periods, were well-suited for examining these relationships. Furthermore, when TSI was calculated to compare the abundance of K. bostoniensis and potential competitors across trophic conditions, the abundance of potential competitors was proportional to TSI. In contrast, K. bostoniensis exhibited higher abundances in mesotrophic and lower eutrophic environments, which distinguished it from its competitors. Our results indicate that the impact of introduced K. bostoniensis on native communities is minimal, while the resistance of native communities through the biological filter based on biological interactions is ineffective against this non-native rotifer species. This provides key evidence for explaining the widespread distribution of K. bostoniensis across continents.

In urban and agricultural streams, assessing aquatic ecosystem health is critical due to widespread pollution. Traditional methods for evaluating attached diatoms crucial for ecosystem monitoring face limitations such as species misidentification and sample damage. This study was conducted in the Miho River within the Geum River system and highlights the effectiveness of environmental DNA (eDNA) techniques for more accurate and efficient genetic-based analysis than conventional microscopic analysis methods. When eDNA-based assessments were compared with traditional microscopic methods, this study found that eDNA analysis often revealed poorer ecosystem health. Notably, eDNA assessments showed a stronger correlation with phosphorus concentrations, underlining their precision and importance in ecological studies. These findings suggest that eDNA has potential as a valuable tool for comprehensive biomonitoring. However, the use of international genetic barcode databases in eDNA analysis could lead to the identification of unrecorded species in Korea. Therefore, this study recommends developing a localized genetic barcode database and constructing eDNA information through meta-barcoding, focusing on native species. This approach is crucial for enhancing the accuracy and applicability of eDNA-based health assessments in national biomonitoring efforts.