Atmospheric deposition in European Forests in 2016

Studying the effects of atmospheric pollution to forest ecosystems requires an evaluation of air quality and of the amount of pollutants carried to the forests by atmospheric deposition. Pollutant flux towards ecosystems through deposition mainly follows two pathways: wet deposition of compounds dissolved in rain and snow and dry deposition of particulate matter through gravity or filtration, for example by forest canopy. Pollutant deposition shows a relatively high local variability, related to the distribution of pollutant sources and the local topography, and in-situ measurement is needed to obtain accurate evaluations and to validate model estimates. In 2016, the chemical composition of atmospheric deposition was measured in 276 Level II permanent plots. In this report, we focus on acidifying, buffering, and eutrophying compounds. High throughfall deposition of nitrate was mainly found in central Europe (Germany, Switzerland), Denmark, and Belgium, while for ammonium high deposition was also found in northern Italy. The area of high deposition is smaller for sulphate, including some plots in Germany and Poland. High values were also measured in Belgium, but they are partially due to deposition of marine aerosol, and they are less evident after sea-salt correction. High deposition in southern Italy may be related to local anthropogenic sources and to volcanic contribution. Calcium, potassium, and magnesium deposition can buffer the acidifying effect of atmospheric deposition. High values of calcium throughfall deposition were reported for southern Europe, where it is often related to the deposition of Saharan dust, and for Eastern Europe. The correction for the marine contribution does not affect its spatial pattern. On the contrary, for magnesium, the number of sites with the highest values is markedly reduced by the sea salt correction.