Bioakkumulation von Metallen und Stickstoff zwischen 1990 und 2005 in Niedersachsen

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 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 Lower 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. Materials and methods The bioaccumulation of up to 40 trace elements and nitrogen in mosses was determined according to a Europe-wide harmonised methodology. The according experimental protocol regulates the selection of sampling sites and moss species, the chemical analysis and quality control and the classification of the measured values for mapping spatial patterns. In Lower Saxony 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 MMI_1990–2005 was calculated for As, Cd, Cr, Cu, Fe, Ni, Pb, Ti, V and Zn. The statistical association of the metal and nitrogen 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 shows a significant decrease of the metal bioaccumulation in Germany from 1990 to 2000 for all elements but Zn. From 2000 to 2005 a further significant decrease can be stated for Cd, Hg and Pb, to most parts non significant increases can be observed for Cr, Cu, Fe, Sb and Zn. Cr thereby exhibits the highest accumulation in 2005 when compared to the results of 1990, 1995 and 2000. The MMI illustrates the temporal trend of the metal bioaccumulation as a whole: From 1990 to 2000 a continuous significant decrease can be observed. From 2000 to 2005 the median of the MMI increases, again significantly, from 3.4 to 4. The N concentration in mosses in Lower Saxony reaches from 1.1 to 1.9?% in dry mass. High N concentrations were detected in agriculturally intensively used areas. Highly significant bivariate correlations between the metal bioaccumulation and land use in the surroundings of the sampling sites were found reaching from 0.3 to 0.5. Other location criteria with similar correlation coefficients/Cramér’s V are moss species, altitude, distance to the North and Baltic Sea and the distance of the sampling site to the nearest tree crown. N only shows negative correlations to urban land use and the distance to the nearest tree. Exemplified for Sb multivariate correlations were furthermore detected by CART. It could be shown that the Sb bioaccumulation interacts with the moss species and the ratio of agriculture, forests and urban areas around the sampling site. Discussion The decrease of the continuously decrease of heavy metals reflects the improving air quality in the past 15 years. Compared to other environmental monitoring and modelling programmes the moss surveys registered increasing concentrations of toxic metal elements between 1990 and 2005, e.?g. Cr. High Cr loads in mosses were also registered in other European countries like in Switzerland. Further investigations are therefore necessary to investigate whether this is due to different emission conditions or biogenic effects (e.?g. as a result of increasing nitrogen depositions). 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. As, Al, Hg, Sb, V). Due to its ecotoxicological relevance nitrogen was monitored in the European moss survey 2005 for the first time. Compared to the metals regionally high emissions of nitrogen compounds into the atmosphere can be detected in Lower Saxony. 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 should correlate to a high degree with measured or modelled depositions is not appropriate since these approaches are considering different biological or physical receptors. Nevertheless, the accumulation of air pollutants in terricolous mosses reflects the degree of air pollution which is permanently deposited and affects the system of plants and soils. 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. Conclusions The moss surveys contribute to the heavy metal and the multi-component-model of CLRTAP because they prove on different spatial scales how air pollution control influences the accumulation of emitted substances in environmental subjects of protection like vegetation incl. arable crops. If environmental monitoring is seen as a continuous task and the applied methodology works well as an early warning system then environmental policy is enabled to act in preventative sense and to pursue unexpected developments. No other environmental monitoring programme provides such a wide range of ecotoxicologically relevant elements measured as spatially dense as the case for the moss surveys. The spatial distribution of environmental information is an essential criterion for their usability in terms of political measures for the federal states and the federation. Recommendations and perspectives 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). In Germany the harmonised and quality controlled moss data are made available via a WebGIS portal. Therefore the moss data may easily be accessed for environmental monitoring purposes and the control of environmental political actions. Hence, the continuous task of environmental monitoring can be met and carried on in the future.