Metalle und Stickstoff angereichert in Moosen Sachsens. [Metals and nitrogen accumulated in mosses Saxony]

Background, aim and scope Since 1990 the UN ECE Heavy Metals in Mosses Surveys provide data inventories of the atmospheric heavy metal bioaccumulation across Europe. In the survey 2005 the nitrogen (N) accumulation was measured for the first time in most of the participating countries. In Germany, the surveys were conducted in close cooperation of the relevant authorities of both the Federal Republic and the sixteen states. Therefore, statistical evaluations of the moss survey data with regard to the whole German territory and single federal states are of interest. This article concentrates on Saxony, dealing with the mapping of the spatiotemporal trends of metal accumulation from 1990 to 2005, the spatial patterns of nitrogen accumulation in 2005, and the spatial variability of bioaccumulation due to characteristics of the sampling sites and their surroundings. Exemplified for Cadmium (Cd), Mercury (Hg) and Lead (Pb) the metal loads in mosses are furthermore related to modelled deposition data provided from the European Monitoring and Evaluation Programme (EMEP). Materials and methods In Saxony Pleurozium schreberi (1990, 1995 most frequent moss species, thereafter second most), Hypnum cupressiforme (1990, 1995 second most, thereafter most frequent moss species), Scleropodium purum and Brachytecium rutabulum (1995, 2000) were sampled at up to 83 sites. All sampling sites were described with regard to topographical and ecological characteristics and several criteria to be fulfilled according to the guideline. Together with the measurements this metadata was combined with other information regarding land use in the surroundings of the sampling sites in the WebGIS MossMet. The spatial structure of the metal bioaccumulation was analysed and modelled by variogram analyses and then mapped by applying different kriging techniques. Furthermore, multi metal indices (MMI) were derived for both the sampling sites and raster maps with help of percentile statistics: The MMI1990–2005 was calculated for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), lead (Pb), titanium (Ti), vanadium (V) and zinc (Zn). The statistical association of the metal bioaccumulation, site specific characteristics as well as information on land use and emissions was analysed by bivariate nonparametric correlation analysis, contingency tables and Classification and Regression Trees (CART). Results The results of the quality controlled chemical analyses show a decrease of the metal bioaccumulation in Saxony from 1990 to 2000. From 2000 to 2005 a significant increase can be stated for As, Cr, Cu, Fe, Ti and V. The element loads of Cd, Hg, Pb and Sb show a decreasing, although non significant, tendency. The MMI1990–2005 decreased significantly from 1990 to 2000 and increased significantly from 2000 to 2005. The N concentration in mosses in Saxony reaches from 1.36 to 1.96 % in dry mass showing significant correlations to the agriculture density (+), the height of the surrounding trees (+), altitude (–) and the precipitation sum for the accumulation period (–). The ratios of forests around the monitoring sites show a negative correlation to all elements but for Pb, Sb and V. Unlike Cd the moss loads of As, Cr, Cu, Fe, Hg, Ni, Pb, Ti and V are positively correlated to the density of urban areas calculated from the Corine Landcover map 2000. The same holds true for Cr, Cu Fe and Ni regarding traffic density and Cd, Cu, Hg and Ni regarding agricultural density. The precipitation sum within the accumulation period is positively correlated with As, Cd, Cr (1990–2000), Ni, Pb, Sb und V, negatively with Cr (2005), Cu, Fe and Zn. Regarding altitude a similar tendency can be observed. The slope gradient shows significant association to Cd, Cu, Ni and Pb. Regarding the canopy effect negative correlation coefficients were calculated for As, Pb and Sb regarding the distance of the sampling site to the nearest tree crowns and positive correlations were calculated for Cd, Cr, Fe and Sb with respect to the height of the surrounding trees. The distance of the moss site to human settlements is significantly related to As, Cd, Cr, Hg, Ni, Pb and Sb. The impact of traffic becomes apparent for As, Cr, Cu, Ni, Pb, Sb, V and Zn which are all negatively correlated with the distance of the moss site to the nearest road. The multivariate statistical CART analysis identifies the urban land use density in a radius of 5 km around the sampling site as well as the height of surrounding trees as the statistically most significant factors for the Cu concentrations in mosses sampled in 2005. The modelled total deposition of Cd, Hg and Pb (EMEP) and the respective concentrations in Saxon mosses are correlated significantly (1995 Hg: r s = 0.62, p = 0.004; 2005 Cd: r s = 0.43, p = 0.07, Hg: r s = 0.44, p = 0.06, Pb: r s = 0.39, p = 0,099). Discussion Unlike in e. g. Baden-Württemberg the metal accumulation in mosses in Saxony increased between 2000 and 2005, Cr thereby increased dramatically. For Cd, Hg and Pb it could be shown that the metal loads in mosses are significantly correlated to the modelled total deposition provided by EMEP. Nevertheless, this does not hold true for all elements in all campaigns. Taking this into account, it can be verified that positive relationships between the metal bioaccumulation and the deposition for Saxony exist. Conclusions Contrary to deposition measurements that exhibit a higher temporal resolution the moss surveys provide measurement data on a wide range of elements. Some of these elements are important with regard to human-toxicological aspects (e. g. Al, As, Hg, Sb, V). The standardised biomonitoring of atmospheric pollution with mosses is an important link between the technical acquisition of depositions and the accumulation in biological material. To claim that the element concentrations in mosses and in the deposition should correlate to a high degree is not appropriate since both approaches are physically related but are not identical. The degree of correlation thereby depends on the boundary conditions of the physical processes, like regional and site-specific meteorological conditions within the accumulation period, the vertical and horizontal vegetation structure or land use conditions. Recommendations and perspectives The Heavy Metals in Mosses Surveys are a positive example for environmental monitoring activities reaching across three spatial and administrative levels: regional (e. g. federal state or natural landscape), nation wide (e. g. Germany) and continental (e. g. Europe). It can therefore be claimed that the moss survey is the only environmental monitoring network that provides high density and surface covering information on the metal and N exposition of near-natural and agricultural ecosystems. The correlations of the metal bioaccumulation and the modelled deposition should therefore be used to complement the deposition measurement activities across Europe