Mapping atmospheric depositions of cadmium and lead in Germany based on EMEP deposition data and the European Moss Survey 2005
Authors: Schröder Winfried , Holy Marcel , Pesch Roland , Zechmeister Harald , Harmens Harry , Ilyin Ilia 
Published: May 2011

Abstract

Background
Every five years since 1990, the European Heavy Metals in Mosses Survey provided data on atmospheric heavy metal bioaccumulations in mosses throughout Europe at a high spatial resolution. The moss data show the effectiveness of air quality control policies: for Germany the metal bioaccumulations decreased between 1990 and 2000, whilst they increased from 2000 to 2005. This investigation is intended to show how the moss data could be used to map atmospheric depositions of Cd and Pb, which later on might serve for the calculation of Critical Loads Exceedances. In addition, we compared how much heavy metal concentrations in mosses in Germany deviate from background data observed in Greenland.

Methods
Mapping heavy metals with a high spatial resolution for the German territory was conducted according to the following methodology: EMEP deposition maps (50 km by 50 km spatial resolution) were intersected within a GIS with Kriging maps on Cd and Pb accumulations in mosses (EMEP (European Monitoring and Evaluation Programme) is a scientifically based and politically driven programme under the Convention on Long-range Transboundary Air Pollution for international co-operation to solve transboundary air pollution problems). Subsequently, the statistical relations between the EMEP modelled depositions and the bioaccumulations in mosses were quantified by using regression analysis. The regression functions were used to transform the moss concentration maps into deposition maps. The resulting maps on Cd and Pb depositions have a spatial resolution of 5 km by 5 km and were added to the respective map on the residuals of the regression functions (Regression Kriging). Finally, the territory of Germany was extracted from the European maps on Cd and Pb depositions and the legends were adjusted accordingly in terms of n standard deviations from the German mean value. The concentrations of Al, As, Cd, Cr, Cu, Mo, Pb, Sb, Sn, and Zn in the mosses sampled in 1990, 1995, 2000 and 2005 in Germany were compared with background values derived from mosses sampled in north-eastern Greenland (Zackenberg Background Values). The differences between heavy metal concentrations in mosses in Germany and Greenland were calculated for the 16 federal states of Germany and mapped for Pb.

Results and discussion
The regression models corroborate that the Cd concentration in mosses is correlated with the EMEP modelled total Cd deposition across Europe (regression coefficient according to Pearson, r

p
= 0.67; regression coefficient according to Spearman, r

s
= 0.69). The coefficient of determination is r

2
= 0.44. The same is true for Pb with r

p
= 0.76 and r

s
= 0.77 and r

2
= 0.58. Based on the regression models and the respective residuals, maps on the total deposition of Cd and Pb were calculated for the year 2005. The German mean value of total Cd and Pb deposition was 0.342 g/ha/a (standard deviation 0.08 g/ha/a and 8.6 g/ha/a (standard deviation 2.1 g/ha/a) respectively. The maps depict the spatial patterns of the total Cd and Pb deposition in terms of n standard deviations from the respective German wide mean value. The spatial resolution of the maps is 5 km × 5 km and reflects the mesh size of the moss monitoring net. Even today, the bioaccumulation of several metals in Germany still exceeds the background values observed in Greenland. This is true especially for Cd, Cr, Cu, Mo, Pb, Sb, Sn and Zn. Comparing the results of this investigation with those from other methods it can be concluded that the mean values calculated for the total Cd and Pb deposition for Germany differ from such assessed by deposition measurements and models. The latter are used to calculate Critical Loads Exceedances, which complement the ecotoxicological endpoint 'accumulation'. The deposition measurements in Germany are mainly based on monitoring systems conducted by the federal states. When trying to use deposition measurements from the ICP Forests level II programme for the validation of the EMEP deposition modelling, problems arose due to a lack of methodical harmonization and the quality of the depositions measurements. That is why in this investigation the quality controlled and spatially high resolved moss data were used to empirically validate EMEP modelled deposition maps.

Conclusions
In Germany, the moss measurement data provide a valuable tool at a high spatial resolution for the validation of modelling and mapping of atmospheric heavy metal deposition and should as such be used for this purpose. The comparison of the metal concentrations in mosses in Germany with the values found in Greenland indicate that atmospheric deposition of heavy metals in Germany is still considerably higher than the natural background deposition.