## 4 Discussion  
The concentration of organic and inorganic pollutants in the soil can be used as a chemical fingerprint to identify the historical pollution of the NFSI plots by anthropogenic influences. The results of the present study make clear that inorganic pollutants in the mineral top soil depend to a large extent on the respective current soil chemical properties, which significantly influence their binding and mobilization behavior. The pollutant concentrations in the humus layer, however, show relationships that suggest common sources of input. The close relationship between low molecular weight PAH and the elements As and Cr is particularly noticeable. It confirms that the low molecular weight PAHs in particular were released on a large scale through the combustion of coal, as is also assumed for As [55, 56]. [PERSON] et al. [57] associate high levels of low molecular weight PAHs (especially naphthalene and phenanthrene) with coal mining. In the Germany-wide analysis of NFSI data, [PERSON] et al. [37] found relationships between high concentrations of two- and three-ring PAHs in the soil and the emissions released from lignite opencast mining and (brown) coal-fired power plants, especially in eastern Germany. In the second half of the last century, the entire forest area of Brandenburg was heavily affected by atmospheric emissions from flue gases and fly ash from lignite combustion. In  
Figure 8: Box plots of the contents of As, Cd, Cr, Ci, Ni, Pb and Zn in the humus layers of pine stands differentiated according to stand age and crown condition (percentage needle loss). southern Brandenburg, even at the time of the second NFSI (2007-2009), the Brandenburg-wide highest base cation stocks were found in naturally nutrient-poor early Pleistocene sandy soils, which can be attributed to the cumulative input of basic (i.e., Ca, Mg, K-containing) dusts from the atmospheric deposition [27; 38; 58]. It can be assumed that, together with these nutrients, which had a rather beneficial effect on the trees' growth, a wide variety of pollutants, such as heavy metals and organic pollutants, were also deposited with the fly ash [59]. In the long term, these have changed the properties of the affected soils and might have had a destabilizing effect on the forest ecosystems [60]. The principal component analyses (PCA) is particularly suitable for the characterization of pollutants in the soil with regard to their origin and historical allocation [61]. Inorganic and persistent organic pollutants in soils or sediments were also evaluated by [PERSON] et al. [12], [PERSON] [62] and [PERSON] et al. [63] with the help of the PCA and by [PERSON] and [PERSON] [64] additionally with geostatic methods in order to analyze correlation patterns, to group sites according to the degree of their overall pollution and to identify regional emission sources. Overall, close relationships between the organic and inorganic substance groups could always be observed in these studies, which suggests common origins. In the present study, both principle component 1 and principle component 2 represent the influence of technologically induced inputs into the soil. The principle component 1 shows, that specific organic substances, such as polycyclic aromatic hydrocarbons and the compound hexachlorobenzene, which can be attributed to emissions [37], are closely associated with As and Cr. This component thus expresses the technogenic pollutant inputs, as they result above all from the burning of lignite and possibly other industrial plants. The element As in the humus layer seems to be suitable for indicating depositions from the former lignite combustion. Due to the anionic occurrence, the fixation of As to the soil colloids increases with a decreasing pH-value, so that due to the predominantly acidic soil conditions, the element apparently remained stably integrated in the humus for decades and still shows regionally differentiated the influence of lignite combustion in the 1970s and 1980s.