BOOK OF ABSTRACTS 99 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL46 Shifting Drivers of DOM in Boreal Waters: From Acidification Recovery to Climate Forcing Rolf D. Vogt, Marianne Stave Sekkenes, Magnus D. Norling, Kari Austnes, Heleen A. de Wit and Øyvind Kaste Norwegian Institute for Water Research, 0855 Oslo, Norway Substantial declines in acidifying emissions across Europe have led to pronounced chemical recovery of Norwegian surface waters. In recent decades, however, changes in water chemistry have increasingly coincided with climate change, complicating the attribution of observed trends to individual drivers. This study assesses whether ongoing climate change has produced detectable effects on freshwater chemistry in Norway and how these effects vary among catchments with differing sensitivities to acidification. The Model of Acidification of Groundwater In Catchments (MAGIC), which is based on current understanding of the processes governing acid-base chemistry in soils and waters, was used to simulate the effects of declining acid deposition. Deviations between observed and modelled water chemistry were provisionally interpreted as climaterelated effects. The analysis draws on long-term monitoring data (1986–2022) from 59 acid-sensitive Trend Lakes distributed across Norway, together with four Field Research Stations (1986–2020) representing contrasting hydroclimatic and biogeochemical conditions. Temporal trends were evaluated using the Mann-Kendall test and Sen’s slope estimator, while relationships between inferred climate effects and climatic variables were examined using Pearson correlation analysis. Across the Trend Lakes, inferred climate effects were predominantly positive for acid-neutralising capacity (ANC) and base cations, suggesting that climate change may contribute to accelerated chemical recovery, particularly in catchments less sensitive to acidification. Inferred climate effects varied substantially among the Field Research Stations. Higher temperatures were generally associated with enhanced recovery, possibly through intensified silicate weathering, whereas increased precipitation and runoff appeared to dampen recovery. Overall, the results suggest that climate change exerts a measurable influence on freshwater chemistry in Norway, although the magnitude and direction of the response are strongly modulated by catchmentspecific characteristics. Quantitative attempts to separate climate-related and acid-deposition-related effects across a large number of acid-sensitive catchments remain rare. Here, we use deviations between observed water chemistry and MAGIC simulations of acid deposition recovery as a screening
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