IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 212 Poster Session / NOM and Aquatic Systems Hall A P3.3 Analysis of Baltic Coastal Waters Dissolved Organic Matter by HPLC Viia Lepane1, Karin Elliku2 1,2 Tallinn University of Technology, Institute of Chemistry and Biotechnology, Akadeemia tee 15, EE-12618 Tallinn, Estonia, viia.lepane@taltech.ee There is an important general objective nowadays to improve the quality of water in water bodies. The dissolved organic matter (DOM) is present in all natural waters but the chemical composition, quality and quantity can be very different. In Baltic region, near Estonian coastline, the DOM is derived from land and is transported into the sea by rivers. The other source of DOM in this area waters is leaching from sediments. A strong seasonal dependence of DOM composition and transformation has been evident. Cold winters result to inflow of terrestrial refractory humic substances from rivers. Spring time is characterized by labile DOM inflow and an increase of proteinlike DOM that is continuing in summer period (June to August). Autumn DOM contains again more humic-like and less protein-like DOM. In present study the intention was to study DOM characteristics by using HPLC-DAD size-exclusion (SEC) and reversed-phase (RP) modes. Detailed characterization of DOM was carried out in order to identify the sources of organic matter that has entered the water. Molecular and optical characteristics of coastline seawater near Tallinn, Estonia area were monitored at 5 stations during spring-time (April to May). In addition one sampling point at River Pirita was also added to reveal the terrestrial input of DOM. RP- HPLC analysis of data indicated two different types of DOM chromatograms. That means some samples were characterized by similar DOM compounds polarity, with only one peak. Second type had two peaks, representing DOM fractions with differing polarity. The study showed that the twopeak chromatograms were present in all samples from the Pirita River. HPLC-SEC method provided data as 3D fingerprint chromatograms of DOM, that were further processed to extract absorption curves, reveal peak identity according to IHSS standard materials, calculate absorption ratios, concentrations and to assess the heterogeneity of DOM. HPLC-SEC data analysis revealed the molecular masses of DOM were between 1500 to 2100. The concentrations of DOM were highest in River Pirita water 25-80 mg L-1 (DOC 13-22 mg L-1). All analysed water samples contained material that originated from land. Cluster and factor analyses were carried out to reveal the differences between DOM characteristics between the sampling points and seasonally.
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