Trends in aluminium export from a mountainous area to surface waters, from deglaciation to the recent: Effects of vegetation and soil development, atmospheric acidification, and nitrogen-saturation

We reconstructed the history of terrestrial export of aluminium (Al) to Plešné Lake (Czech Republic) since the lake origin ∼12,600 year BC, and predicted Al export for 2010–2050 on the basis of previously published and new data on mass budget studies, palaeolimnological data, and MAGIC modelling. We focused on three major Al forms; ionic Al (Ali), organically-bound Al (Alo), and particulate Al hydroxide [Al(OH)3]. In early post-glacial time, Plešné Lake received high terrestrial export of Al, but with a minor proportion of Al(OH)3 (4–25 μM), and concentrations of Ali and Alo were negligible. Since the forest and soil development (∼9900–9000 year BC), erosion has declined and soil organic acids increased export of Alo from soils. The terrestrial Alo leaching (∼7.5 μM) persisted throughout the Holocene until the industrial period. Then, Ali concentrations continuously increased (up to 28 μM in the mid-1980s) due to atmospheric acidification; the Ali leaching was mostly associated with sulphate. The proportion of Ali associated with nitrate has been increasing since the beginning of lake recovery from acidification after ∼1990 due to reduction in sulphur deposition and nitrogen-saturation of the catchment, leading to persistent nitrate leaching. Currently, nitrate has become the dominant strong acid anion and the major Ali carrier. Alo (5.5 μM) is predicted to dominate Al concentrations around 2050, but the predicted Ali concentrations (∼4 μM) are uncertain because of uncertainty associated with the future nitrate leaching and its effect on soils.