Climate effects on water chemistry in acid sensitive catchments

Summary

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 increasingly coincide with climate change, complicating attribution of observed trends to drivers. This study assesses whether ongoing climate change has produced detectable effects on freshwater chemistry in Norway and how such effects vary among catchments with differing sensitivity to acidification. The Model of Acidification of Groundwater In Catchments (MAGIC) was used to simulate the effects of declining acid deposition. Deviations between observed and modelled water chemistry were tentatively interpreted as climate-related effects. Analyses were based on long-term monitoring data (1986–2022) from 59 acid-sensitive Trend Lakes distributed across Norway and four Field Research Stations representing contrasting hydroclimatic and biogeochemical conditions. Temporal trends were evaluated using Pearson correlation. Their relationships with climatic variables and their Mann-Kendall significant Sen’s time slopes were examined using regression and multivariate analyses. Across the Trend Lakes, climate effects were predominantly positive for acid neutralising capacity (ANC) and base cations, suggesting that climate change contributes to accelerated chemical recovery, at least in the less acidification-sensitive catchments. Climate effects varied substantially between the Field Research Stations, with increased temperature generally enhancing recovery, possibly through intensified weathering. In contrast, increased precipitation and runoff reduced recovery rates. Overall, the results suggest that climate change exerts a measurable influence on freshwater chemistry in Norway, strongly modulated by catchment characteristics.