IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 30 Analysis and Characterization Monday, 24 August 2026 / Hall B+C SL9 Quantitative Size Fractionation of Dissolved Organic Matter in a Large Lake Using Ultrafiltration– Nanofiltration with Diafiltration Correction Kazuhide Hayakawa1, Yasuhiko T. Yamaguchi1, Yasuro Fuse2, Koichi Shimotori3, Shin-ichi Nakano4 1 Lake Biwa Environmental Research Institute, 5-34 Yanagasaki, Otsu, Shiga 520-0022, Japan; hayakawa-k@lberi.jp 2 Department of Molecular Chemistry and Engineering, Kyoto Institute of Technology, Japan 3 National Institute for Environmental Studies, Japan 4 Center for Ecological Research, Kyoto University, Japan Introduction Dissolved organic matter (DOM) in aquatic environments is a complex mixture spanning a wide range of molecular sizes, and its biodegradability and chemical reactivity are highly dependent on molecular size. Therefore, accurate characterization of DOM based on size-dependent properties is essential for understanding its biogeochemical functions. Several studies have reported that highmolecular-weight (HMW) DOM in oceans contains biopolymers such as polysaccharides and proteins, whereas humic-like substances in the low- to intermediate-MW range may exist as assemblages of smaller molecules [1,2]. However, conventional size fractionation using ultrafiltration (UF), typically based on a binary classification (HMW/LMW), may not adequately represent the true size distribution of DOM, due to its limited resolution in the low-molecularweight (LMW) range, which can be complemented by nanofiltration (NF). In this study, we developed an approach to evaluate the relationship between DOM size and chemical properties, using water samples from Lake Biwa, the largest lake in Japan as the model for both marine and freshwater systems. This approach combines optimized membrane MW cut-offs with ultrafiltration and nanofiltration coupled with diafiltration (UF-NF-DF) to enhance the purity of size fractions. In addition, a permeation model was applied to correct fractionation biases and improve the estimation of DOM size distribution. Materials and Methods A cross-flow ultrafiltration system equipped with a flat-sheet membrane cell and a peristaltic pump was employed. Surface water samples (5 m depth) were collected from the northern basin of Lake Biwa, Japan, between 2022 and 2023, filtered through a 0.1 µm membrane, and subjected to sequential size fractionation. DOM characterization was conducted using TOC analysis,
RkJQdWJsaXNoZXIy NDA4Mjc=