Balancing preservation of material and the need for analytical accuracy: Mass requirements of Sphagnum moss from herbarium collections for trace element analysis

<p><em>Sphagnum</em> mosses have been used in some of the earliest works in biomonitoring of atmospheric deposition of trace elements (TEs). Since their adoption into the field the Sphagnaceae have become one of the foremost biomonitors. When taken as contemporary samples, these mosses have allowed us to identify spatial variations as well as trends and major changes in atmospheric deposition due to changing policy, technology, industry, and land use. While long term monitoring programs, such as the European Moss Survey, allow us to track these changes through time, these ongoing studies only reach as far back as their start dates. In the case of the European Moss Survey this was 1990. The use of materials already collected and archived in herbaria provides a low-cost method for retrospective analysis of atmospheric deposition of TEs. The critical advantage of herbarium specimens over other historical monitoring method is their high temporal resolution, as their exact collection date is known. Once collected, stored, and protected from atmospheric dust, the concentrations of non-volatile TEs present remain effectively unchanged. The oldest herbarium records can predate industrialisation, but most have records from the beginning of industrialisation, with the frequency of collection increasing in the modern era. Using only the top 2 cm of herbarium specimens of<em> Sphagnum</em> mosses (<em>S. fuscum, S. angustifolium, S. capillifolium, S. magellanicum</em>) found in Canadian ombrotrophic bogs, we will be creating historical reconstructions of atmospheric deposition in northern Alberta since the 1940s and southern Ontario since 1860’s. The first objective is to determine how best to balance preservation of the limited herbarium material available while also using sufficient material to achieve suitable levels of analytical accuracy. As TE analyses using ICP-MS are destructive and some specimens have immeasurable value from a natural history perspective, as little material as possible should be taken for analysis. Grinding of the sample was avoided, to minimize sample loss and the risk of contamination. We compared the measured concentrations obtained with ICP-MS as a function of the mass of <em>Sphagnum</em> digested, using selected herbarium samples as well as two certified, Standard Reference Materials (NIST 1515 and HB36-M2). These analyses allow us to determine the optimal amount of material necessary to balance the analytical accuracy and preservation of material of 4 species of <em>Sphagnum</em> mosses from Alberta over the last 80 years. The results will be compared with the data already available for TE concentrations in age-dated peat cores from the same region.</p>

Estimating Background Values of Potentially Toxic Elements Accumulated in Moss: A Case Study from Switzerland

Although the use of moss as biomonitor of air pollution is relatively simple, the interpretation of the data needs reference values. Background values for Cd, Cu, Pb, and Zn accumulated in moss samples from Switzerland, collected every five years from 1995 to 2015 in the framework of the European Moss Survey, were statistically estimated. These background values can be used as reference for the assessment of spatial and temporal trends, to be expressed in terms of bioaccumulation ratios with actual values. The use of annual background values is of great importance to identify spatial trends, while period-wide background values identify temporal trends. The latter are consistent with those reported in other comprehensive similar biomonitoring studies in Europe and are required to be updated in time, possibly every five years. The use of cutoff values to be used as benchmark for bioaccumulation ratios is invaluable in having a scale for assessing ecological quality.

Moss species-specific accumulation of atmospheric deposition?

Background This article presents statistical analyses of elements concentrations in mosses collected in two monitoring programmes: 1. The German moss monitoring as part of the European Moss Survey conducted in 1990, 1995, 2000, 2005 and 2015 at 592, 1026, 1028, 726 and 400 sites across Germany, respectively, and chemically analysed according to harmonised methods throughout Europe; and 2. The moss surveys additionally performed throughout Bavaria, federal state of Germany. The evaluations of the present study are intended to examine indications whether the element accumulations are specific to moss species and whether, therefore, conversion factors should be used. Such observations and recommendations have so far been limited to spatially confined areas and relatively few moss samples and were derived from different studies without a common methodology. Therefore, the objective of this investigation was to analyse large and long-term datasets from moss surveys for differences in element concentrations in different moss species. This analysis was based on data derived from several moss species collected across Germany and specimens of only one moss species collected in the monitoring programme performed by the environmental authority of Bavaria. So far, the presented investigation is the most comprehensive one in terms of running time, spatial density of the measurement network and method harmonisation. Results The present study does neither verify nor falsify the hypothesis of moss species-specific element accumulations in mosses. This, like the other studies, is not possible because of its empirical design, since that would require strictly controlled laboratory experiments. However, this investigation yielded hints, that the differences in element accumulation in several moss species across German surveys between 1990 and 2015 are in the range of the intra- and inter-specific variance reported. Conclusion It is, therefore, advisable to continue dispensing with conversion factors so far.

Heavy metals and radionuclides concentrations in mosses from the region of Northern Greece

Mosses can be used as biomonitors for investigating the atmospheric deposition of radionuclides and heavy metals. They receive most of their nutrients directly from wet and dry deposition. During the 2015/2016 European moss survey, ninety-five samples of Hypnum cupressiformeHedw. were collected in Northern Greece. They were analyzed to the content of heavy metals using INAA. The concentrations of 137Cs,40K, 7Be and 210Pb radionuclides were determined using gamma spectrometry. Differences have been observed in the activity concentrations between mosses collected from ground surface, rocks, branches and near roots. Finally, a high sampling density was achieved, providing information for the elemental and radionuclides deposition from the atmosphere to terrestrial systems over the region of Northern Greece.

Entwicklung der Schwermetall- und Stickstoffkonzentrationen in Moosen in Deutschland

Development of heavy metals and nitrogen concentrations in moss throughout Germany Under the Convention on Long-range Transboundary Air Pollution, moss samples have been collected in Europe every five years since 1990 and evaluated for the concentration of heavy metals (since 1990) and nitrogen (since 2005). This article uses the data of this European Moss Survey to geostatistically evaluate and map the spatial distribution and temporal development of the heavy metals cadmium (Cd), lead (Pb) and mercury (Hg) as well as nitrogen (N) for Germany. Since the year of first sampling in Germany (Cd, Pb: 1990, Hg: 1995), heavy metal concentrations in moss tissue have decreased, while nitrogen concentrations have been remaining at almost the same level since 2005. Since 1990, Cd and Pb have shown a consistent hotspot of bioaccumulation within a broad band from North Rhine-Westphalia to Saxony, while for the other regions and with regard to Hg for most regions of Germany the geostatistical analyses corroborate that the spatial patterns of element concentrations in moss are changing across time. With regard to N, North Rhine-Westphalia and Mecklenburg-West Pomerania (2005–2015), as well as northwestern Germany (2015), proved to be a hotspot of nitrogen accumulation in moss. By contrast, the N concentration in mosses has decreased significantly in the southern German states, especially in Bavaria and Baden-Württemberg.