Lakes are one of major sources of methane gas due to anaerobic decomposition of organic matter in sediments. Since methane released from lakes is a greenhouse gas, it is necessary to investigate factors affecting methane production of lakes. This study conducted field and incubation experiments in Lake Asan in August and October to determine effects of thermal stratification and sediment organic matter characteristics on methane production. Field experiments measured temperature and dissolved oxygen to determine the formation of thermal stratification of lakes. Methane and organic matter characteristics were analyzed using gas chromatography, Total Organic Carbon (TOC) analyzers, and fluorescence spectroscopy. Incubation experiments under anaerobic conditions used sediment and water samples from the same site. Field results showed higher methane fluxes in August and increased Dissolved Organic Carbon (DOC) concentration closer to Asan Bay seawall. Elevated methane fluxes and DOC concentration resulted from intensified anaerobic decomposition formed by thermal stratification. Incubation results indicated that sediment organic matter characteristics influenced methane flux between sites. Statistical analysis revealed that thermal stratification could be a primary factor affecting methane production of lakes. Characteristics of sediment organic matter with respect to quantity and quality could be factors influencing methane production of lakes. Results of this study can serve as fundamental data for predicting methane emissions from lakes due to climate change and for mitigating lake's contributions to global warming.

This study investigated water quality characteristics and influencing factors of park drinking fountains having directly piped water systems by analyzing stagnation water (first draw) and water after a 10-minute flush (flushed water). First draws exhibited significant variations in residual chlorine, heavy metals, bacteria, and turbidity, which were largely influenced by usage frequency and external environmental contamination. However, water quality stabilized after flushing. A seasonal analysis indicated that the greatest difference in residual chlorine between first draws and flushed water occurred in spring, followed by that in winter when drinking fountains were discontinued, accompanied by increased zinc concentrations in stagnation water. A comparative analysis of water quality variability by faucet type revealed that push-button faucets exhibited greater variabilities in copper, zinc, and nickel levels than screw-down faucets, likely due to corrosive by-products generated from water hammer effects. Additionally, an analysis based on exterior material indicated that metal fountains experienced higher temperature increases and elevated zinc concentrations in first draws than stone fountains. Regarding installation environments, drinking fountains exposed to direct sunlight or partial shade had higher concentrations of copper, zinc, and nickel in first draws than those installed in constant shade. Overall, these findings suggest that frequent use or flushing can help maintain stable water quality with the exception of push-button faucets.

Although lakes are an important part of freshwater, research on biological methods for assessing ecological integrity of Korean lakes is insufficient. Therefore, this study aimed to develop Lakes Benthic Macroinvertebrates Multi-Metric Index (LBMMI) to assess the ecological integrity of lakes in Korea to further understand Korean lake's ecosystem. We used biological data from 388 sampling units of national lake monitoring programs from 2022 to 2023 and water quality data from Water Environment Information System (WEIS). As a result, firstly, reference points and disturbed points were selected through Principal Component Analysis (PCA). Secondly, six core metric elements (Pielou's Evenness index (J), Total number of taxa (To.t), Percent of taxa in insecta (% I.t), Percent of individuals in Oligochaeta and chironomidae(tuble) (% OliCht.i), Percent of taxa in Predator (% Pe.t), and Percent of taxa in Clingers (% CL.t) were selected through discriminant analysis and relationship-test. Lastly, LBMMI was calculated for each sampling point by scoring using core metric elements and five grades were assigned for LBMMI scores using a Beta probability distribution model, with the suitability of LBMMI reviewed by comparing it with TSI_KO. LBMMI developed in this study is expected to appropriately assess ecological integrity of Korean lakes and provide a basis for further research on lake environment conservation.