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Atmospheric deposition of acidifying compounds (e.g. S), nitrogen (N) as a nutrient and base cations (e.g. Ca) to forests is a major driver for many processes in forests. In Europe, various measures have been taken to reduce S and N deposition since the late 1980ties. Trend analyses are regularly performed based on measurement in open field by EMEP and in forests by ICPForests. However, various trend analyses techniques are in use. In this study the trends of bulk and throughfall N and S deposition on ICP-Forests level II sites have been investigated. Sulphur deposition showed a decreasing trend from 2001 to 2010 that has been identified to be significant for the majority of the about 50 sites with continuous data (linear regression, 95% sign. Level). The mean thoughfall of theses sites decreased from about 12 kg S ha-1 a-1 in 2001 to about 6 kg S ha-1 a-1 (about 6% a-1). For N this value decreased from about 15 kg N ha-1 a-1 to about 12 kg N ha-1 a-1 (about 2.5% a-1), however, decreasing trends were identified to be significant for much fewer sites. In order to estimate the minimal detectable trend, p-values were plotted against the relative slope. Most p-values were in a similar bell-shaped band for time series with the same length for most ions. For time series with 10 years S deposition data, the band falls below 0.05 at relative slope larger than about 3% a-1. With 6 years of data, relative slopes need to be larger to reliably attain p

The chemical composition of solution samples can vary over time due to biological activity in the sample, exchanges and adsorption on the walls of the storage vessel, abiotic particle formation or dissolution. Factors influencing these processes include the initial composition of the sample, e.g. pH, temperature and light conditions, which directly determine the activity of microorganisms such as nitrifiers, storage duration (in the field or the laboratory), cleaning of the storage vessels, and pre-treatment of the samples before analysis (e.g. filtering, acidification). Precipitation, throughfall and soil water regularly sampled in forest monitoring needs to be protected toward possible alterations. A range of storage experiments have been performed both in forests and in laboratories to check the quality of samples when they are stored under different conditions and situations. The first objective was to examine the change in temperature and light along with possible change in chemistry of soil solution, precipitation and throughfall samples during the period they are collected in the forest and whenstockpiled in the laboratory before analysis. The second objective was to recommend methods and storage that diminish possible chemical transformations in solution samples. Depending on the sampling design, solution samples collected in the forest were to various extents subject to ambient air temperature fluctuations during the day and high light exposure. In the summertime the temperature in samples could get unfavorably high whensamples were not protected properly. Our storage experiments showed changes in chemical composition in samples stored for longer periods both in the laboratory and the forest; however, the results suggested that it is most important to reduce the duration of sampling period (i.e. weekly samples instead of bi-weekly or monthly sampling) in the forest.