Atmospheric deposition chemistry in Italian forested sites

Under the FUTMON Life+ Programme, deposition acidity and ionic content were analysed in 2009-2010 in 22 forested sites in Italy distributed over the whole national territory. Temporal trends (1998-2010) of ion concentration and precipitation amount were also evaluatedin ten sites. Finally, critical loads for nutrient nitrogen were used to calculate exceedances and identify the areas most sensitive to N enrichment.Bulk open field (BOF) and throughfall (TF) depositions were sampled weekly at all sites, using continuously exposed collectors. Permanent sites are typically located in remote areas, homogeneous for both geology and vegetation. Data validation followed the criteria of ion balance and comparison of measured and calculated conductivity. Comparisons between measured conductivities and the sum of cations and anions were also performed on the values of each plot and sample type. Departures from linearity of different sets of values were examined in the light of the completeness of the analyses and considering all the possible causes of errors.In spite of the remote location of most of the sampling sites, the atmospheric deposition contained high amounts of anthropogenic ions. Except at some high altitude sites in the Alps, bulk sulphate deposition was higher than 10 kg S ha-1 y-1. The highest ammonia deposition (10 kg N ha-1 y-1) was detected in the Po Plain (one of the most industrialized areas in Europe) and the subalpine areas of Northern Italy, while nitrate deposition was more widespread throughout the country at levels of 2-7 kg N ha-1 y-1. Significant negative trends were found for SO4 for all the plots, for both BOF and TF concentration and deposition. Significant positive trends were found for pH in some plots; a significant negative trend was also detected for calcium and magnesium, both for BOF and THF samples and for concentration and deposition data. A few stations showed significant negative trends for NH4 and NO3 concentrations in BOF samples; the number of sites with decreasing trends was higher when total nitrogen concentrations were considered (7 sites), while less significant results were obtained for depositions.Ammonium and sulphate deposition were higher in Northern Italy, particularly in the Po Plain, which is one of the most industrialised and urbanised areasin Europe. These results are in agreement with those obtained when evaluating critical loads, with most of the exceedances found in the same area. The decreasing trends of both sulphate and acidity detected at most of the sites are closely related to the decrease in SOx emissions which has occurred in Italy in the last 30 years. On the other hand, depositions of both nitrate and ammonium are still high, in agreement with emission patterns, which are constant for NH3 and only slightly decreasing for NOx.This confirms that nitrogen deposition remains an important environmental issue in Italy, and significant efforts are still needed to reduce ammonia and nitrogen oxide emissions into the atmosphere in the next few years.