Bioindication and modelling of atmospheric deposition in forests enable exposure and effect monitoring at high spatial density across scales

Key message

Moss surveys provide spatially dense data on environmental concentrations of heavy metals and nitrogen which, together with other biomonitoring and modelling data, can be used for indicating deposition to terrestrial ecosystems and related effects across time and areas of different spatial extension.

Context

For enhancing the spatial resolution of measuring and mapping atmospheric deposition by technical devices and by modelling, moss is used complementarily as bio-monitor.

Aims

This paper investigated whether nitrogen and heavy metal concentrations derived by biomonitoring of atmospheric deposition are statistically meaningful in terms of compliance with minimum sample size across several spatial levels (objective 1), whether this is also true in terms of geostatistical criteria such as spatial auto-correlation and, by this, estimated values for unsampled locations (objective 2) and whether moss indicates atmospheric deposition in a similar way as modelled deposition, tree foliage and natural surface soil at the European and country level, and whether they indicate site-specific variance due to canopy drip (objective 3).

Methods

Data from modelling and biomonitoring atmospheric deposition were statistically analysed by means of minimum sample size calculation, by geostatistics as well as by bivariate correlation analyses and by multivariate correlation analyses using the Classification and Regression Tree approach and the Random Forests method.

Results

It was found that the compliance of measurements with the minimum sample size varies by spatial scale and element measured. For unsampled locations, estimation could be derived. Statistically significant correlations between concentrations of heavy metals and nitrogen in moss and modelled atmospheric deposition, and concentrations in leaves, needles and soil were found. Significant influence of canopy drip on nitrogen concentration in moss was proven.

Conclusion

Moss surveys should complement modelled atmospheric deposition data as well as other biomonitoring approaches and offer a great potential for various terrestrial monitoring programmes dealing with exposure and effects.

     

Are cadmium, lead and mercury concentrations in mosses across Europe primarily determined by atmospheric deposition of these metals?

Purpose

This study aimed at investigating correlations between heavy metal concentrations in mosses and modelled deposition values as well as other site-specific and regional characteristics to determine which factors primarily affect cadmium, lead and mercury concentrations in mosses. The resulting relationships could potentially be used to enhance the spatial resolution of heavy metal deposition maps across Europe.

Materials and methods

Modelled heavy metal deposition data and data on the concentration of heavy metals in naturally growing mosses were integrated into a geographic information system and analysed by means of bivariate rank correlation analysis and multivariate decision trees. Modelled deposition data were validated annually with deposition measurements at up to 63 EMEP measurement stations within the European Monitoring and Evaluation Programme (EMEP), and mosses were collected at up to 7,000 sites at 5-year intervals between 1990 and 2005.

Results and discussion

Moderate to high correlations were found between cadmium and lead concentrations in mosses and modelled atmospheric deposition of these metals: Spearman rank correlation coefficients were between 0.62 and 0.67, and 0.67 and 0.73 for cadmium and lead, respectively (p?<?0.001). Multivariate decision tree analyses showed that cadmium and lead concentrations in mosses were primarily determined by the atmospheric deposition of these metals, followed by emissions of the metals. Low to very low correlations were observed between mercury concentrations in mosses and modelled atmospheric deposition of mercury. According to the multivariate analyses, spatial variations of the mercury concentration in mosses was primarily associated with the sampled moss species and not with the modelled deposition, but regional differences in the atmospheric chemistry of mercury and corresponding interactions with the moss may also be involved.

Conclusions

At least for cadmium and lead, concentrations in mosses are a valuable tool in determining and mapping the spatial variation in atmospheric deposition across Europe at a high spatial resolution. For mercury, more studies are needed to elucidate interactions of different chemical species with the moss.     

Trace Metals in Soil and Plants Subjected to Strong Chemical Pollution

The total concentrations of ten elements (Ag, As, Co, Cs, Fe, Ir, Ni, Rb, Sb, and Sc) were determined in soil and vegetation samples from the surroundings of a Cu-Ni smelter in Monchegorsk, Northwest Russia, and a background area in Naruska, North Finland. The samples were analysed by epithermal neutron activation analysis (ENAA). Elements emitted from the smelter (Ag, As, Co, Ir, Ni, and Sb) were mostly accumulated in the topsoil. Some elements also appeared to contaminate deeper soil layers. In both soil and vegetation the metal concentrations decreased with increasing distance from the smelter. The most significant contributor to the high concentrations of Fe and Sc near the smelter was probably damaged ground vegetation and subsequent wind erosion. Possibly high geochemical abundance of Fe and Sc may also have been a contributing factor. Concentrations of Cs and Rb in soil and vegetation generally increased with increasing distance from the pollution source. High negative correlations were evident between these elements and the elements emitted from the smelter, suggesting that cation exchange of Cs and Rb by the elements supplied from the smelter was likely occurring in the surface soil.