Mosses as bioindicators for metal accumulation: Statistical aggregation of measurement data to exposure indices

In Germany, ectohydrical mosses were used as passive bioindicators for metal accumulation in terrestrial ecosystems in 1990, 1995 and 2000. The data quality, empirical aspects of the moss-monitoring campaigns, like the monitoring net design, moss-sampling as well as chemical analysis are described. By using the site-specific sample data on the metal accumulation, spatially valid information without geographical gaps is calculated by applying geostatistics for the whole territory of Germany. Furthermore, the metal-specific data are aggregated to statistical indices. Two aggregation procedures are used. The cluster analytical approach results in regional categories of accumulation spectra. It allows for an investigation if the emission structures remain the same over time or if they change from one campaign to the following one. The approach based on percentile statistics provides ranked or ordinal indices, which illustrate both spatial and temporal trends of metal accumulation. The respective maps show the spatial patterns of reduced metal accumulation throughout the monitoring campaigns.