Validating modelled data on major and trace element deposition in southern Germany using Sphagnum moss

Accepted Manuscript Validating modelled data on major and trace element deposition in southern Germany using Sphagnum moss Heike Kempter, Michael Krachler, William Shotyk, Claudio Zaccone PII:

S1352-2310(17)30550-2

DOI:

10.1016/j.atmosenv.2017.08.037

Reference:

AEA 15507

To appear in:

Atmospheric Environment

Received Date: 27 April 2017 Revised Date:

11 August 2017

Accepted Date: 14 August 2017

Please cite this article as: Kempter, H., Krachler, M., Shotyk, W., Zaccone, C., Validating modelled data on major and trace element deposition in southern Germany using Sphagnum moss, Atmospheric Environment (2017), doi: 10.1016/j.atmosenv.2017.08.037. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1 2 3

Validating modelled data on major and trace element deposition in southern Germany using Sphagnum moss

4 Heike Kemptera,b*, Michael Krachlera,c, William Shotyka,d, and Claudio Zacconee

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a Institute of Earth Sciences, University of Heidelberg, INF 236, D-69120 Heidelberg, GERMANY

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b CEZ Curt Engelhorn Centre for Archaeometry, D6,3 D-68159 Mannheim, GERMANY * Author for all correspondence: [email protected]

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c European Commission, Joint Research Centre, Directorate Nuclear Safety and Security, P.O. Box 2340, D-76125 Karlsruhe, GERMANY d Department of Renewable Resources, University of Alberta, Edmonton, Alberta, T6G 2H1 CANADA

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e Department of the Sciences of Agriculture, Food and Environment, University of Foggia, Via Napoli 25, 71122 Foggia, ITALY

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Abstract

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Sphagnum mosses were collected from four ombrotrophic bogs in two regions of southern

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Germany:

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(Nordschwarzwald, NBF). Surfaces of Sphagnum carpets were marked with plastic mesh and,

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one year later, plant matter was harvested and productivity determined. Major and trace

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element concentrations (Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb, Sb, Sc, Sr,

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Th, Ti, Tl, U, V, Zn) were determined in acid digests using sector field ICP-MS. Up to 12

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samples (40 × 40 cm) were collected per site, and 6-10 sites investigated per bog. Variation in

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element accumulation rates within a bog is mostly the result of the annual production rate of

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the Sphagnum mosses which masks not only the impact of site effects, such as

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microtopography and the presence of dwarf trees, but also local and regional conditions,

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including land use in the surrounding area, topography, etc. The difference in productivity

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between peat bogs results in distinctly higher element accumulation rates at the NBF bogs

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compared to those from OB for all studied elements. The comparison with the European

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Monitoring and Evaluation Program (EMEP; wet-only and total deposition) and Modelling of

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Air Pollutants and Ecosystem Impact (MAPESI; total deposition) data shows that

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accumulation rates obtained using Sphagnum are in the same range of published values for

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direct measurements of atmospheric deposition of As, Cd, Cu, Co, Pb, and V in both regions.

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The accordance is very dependent on how atmospheric deposition rates were obtained, as

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different models to calculate the deposition rates may yield different fluxes even for the same

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region. So that, in future studies of atmospheric deposition of trace metals, both Sphagnum

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moss and deposition collectors have to be used on the same peat bog and results compared.

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Antimony, however, shows considerable discrepancy, because it is either under-estimated by

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Sphagnum moss or over-estimated by both atmospheric deposition models. Atmospheric

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deposition data obtained from sampling in open fields is unlikely to always perfectly match

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data obtained using living Sphagnum moss from bogs. In fact, plant uptake and biochemical

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utilization by living moss may affect accumulation rates of those elements that are essential

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for plant nutrition (macro and micronutrients), which is clearly seen in the data presented here

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for Mn, Fe and Zn. Furthermore, Sphagnum moss is a unique receptor, with its characteristic

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roughness and chemical complexity. These two aspects, combined with conditions found on

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the bog surface (variations in microtopography, shrubs, trees, wetness, snow cover, etc.),

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result in a unique type of interception and retention. Despite all these factors, the comparison

Bavaria

(Oberbayern,

OB)

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the

Northern

Black

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with modelled data shows that Sphagnum moss is a good indicator of atmospheric deposition

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at least in a semi-quantitative manner and certainly reflects inputs to terrestrial ecosystems.

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ACCEPTED MANUSCRIPT 1. Introduction

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Atmospheric pollution is commonly assessed by analysing concentrations of contaminants in

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ambient air or by determining atmospheric deposition to the earth’s surface (Colls and

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Tiwary, 2009). In this context, the use of mosses as passive biomonitors for atmospheric

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trace metal deposition was also intensively investigated (Shotyk et al., 2015, and refs.

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therein). Already fifty years ago, Rühling and Tyler (1968) suggested that Pb is quantitatively

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retained from precipitation by moss, and that atmospheric metal deposition rates could be

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calculated from the annual production rate of the mosses and the measured metal

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concentrations (Rühling and Tyler, 1970). More recently, other authors found that trace

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element concentrations in mosses are related to atmospheric deposition and, although they

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provide no direct quantitative measurement of deposition, these bryophytes can be used to

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estimate absolute deposition rates of metals (Berg et al., 1995; Berg and Steinnes, 1997;

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Gombert et al., 2004; Harmens et al., 2008). In fact, at the scale of the European continent, the

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total atmospheric deposition is the main factor determining both the accumulation of Cd and

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Pb in mosses and explaining their variation in concentration (Harmens et al., 2010; Schröder

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et al., 2010, 2011). Moreover, Schröder et al. (2013) stated that moss monitoring in Germany

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provides data at a high spatial resolution which can be used for the validation of modelling

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and mapping of atmospheric heavy metal deposition.

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Aboal et al. (2010, and refs. therein), on the other side, presented a critical review about

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problems occurring, when atmospheric deposition of heavy metals are estimated from their

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concentration determined in terrestrial moss. However, they admitted that, for elements like

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Pb and Cd, such estimations are reasonable, probably because they are supplied primarily by

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dry and wet deposition to forest moss. Moreover, they stated that the analysis of moss

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certainly provides information about bulk deposition, the spatial and temporal patterns of

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atmospheric inputs, and insight into element uptake by living organisms.

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Sphagnum moss growing on the surface of peat bogs is similar to forest moss. Bog mosses

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grow on an organic substrate; hence, contamination of the sample by the substrate is less

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problematic compared to forest moss. This makes Sphagnum mosses very useful for

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monitoring atmospheric deposition (Rühling and Tyler, 1971). Moreover, Sphagna have a

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particularly high cation exchange capacity (Aulio, 1985), mainly due to the abundance of

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carboxylic functional groups (Anschütz and Gessner, 1954, González and Pokrovsky, 2014).

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Compared to forest moss, Sphagnum sp. exhibits a higher density of negative surface charge

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ACCEPTED MANUSCRIPT and therefore more binding sites per unit mass, resulting in an outstanding capacity for metal

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adsorption (González and Pokrovsky, 2014).

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It is helpful to know more about the relationship between Sphagnum moss accumulation and

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atmospheric deposition of various elements. To do this, both methods have to be compared.

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However, direct measurements of atmospheric deposition of trace elements, as well as

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indirect approaches using living moss, are subject to several uncertainties. In a previous study,

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for example, we showed that metal accumulation by Sphagnum mosses were variable because

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of the influence of varying annual plant production (Kempter et al., 2010). A further point

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complicating the comparison between Sphagnum moss and atmospheric deposition is that

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total deposition on the peat bog surface might be very different from total open field

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deposition because of the special receptor which the peat bog surface represents. The

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permanent wetness (Al-Radady et al., 1993), the variable surface area and the roughness of

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the Sphagnum carpet create a micro-ecosystem analogous to a “miniature forest” resulting in

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more complex mechanisms of canopy interception. Thus, the peat bog surface could well

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represent a more efficient trap for droplets and particles than the funnels used for collecting

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precipitation data (Kempter and Frenzel, 2007).

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Concerning direct measurements of total deposition, uncertainties begin with the process of

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collecting: this alone introduces an uncertainty of a factor of two because of the different

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types of samplers used in various monitoring networks (Erisman et al., 1998; Gauger et al.,

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2000; Umweltbundesamt, 2009). Many countries and institutions operate deposition networks

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using different types of sampler even though these samplers have rarely been characterized

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with respect to efficiency of interception and retention. Moreover, an adequate number of

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replicates is needed to detect microbial transformations of collected samples or contamination

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by bird droppings. Thus, major errors in assessing bulk deposition can result from poor

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sampling properties and defective sampling strategies (Daemmgen et al., 2005). Even in

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specifically designed studies, uncertainties of up to 40% have been found, possibly because of

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the challenges presented by the sampling of dry deposition (Erisman et al., 2005). While wet

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deposition in Europe is routinely monitored in existing networks, the measurement of dry and

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cloud/fog deposition of gases and particulate matter is much more difficult. In Europe, dry

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deposition accounts for about 20% of the total deposition, with a range of 10–90% (Erisman

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et al., 1998). Deposition measurements in Germany are mainly based on monitoring systems

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conducted by the federal states and, unfortunately, methodical harmonization and quality of

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deposition measurements are not a priority (Schröder et al., 2011). Moreover, spatial density

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ACCEPTED MANUSCRIPT of measurements is often inadequate and commonly restricted to relatively short periods of

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time at single sites (Erisman et al., 1998; Gauger et al., 2000; Umweltbundesamt, 2009).

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Unfortunately, atmospheric deposition varies considerably on a very small geographic scale.

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Thus, large distances between sites where mosses and precipitation are monitored may

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account for significant differences in deposition results obtained (Aboal et al., 2010).

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Atmospheric deposition data for the studied region, which can be used to compare with our

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accumulation data obtained from Sphagnum moss, were collected within the framework of the

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European Monitoring and Evaluation Program (EMEP) where wet deposition monitoring of

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heavy metals was performed at approximately 60-70 sites across Europe. However, the spatial

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coverage was sparse; for example, in 2006 Germany was represented by only 6 stations

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recording Cd and Pb concentrations in air and precipitation (Schröder et al., 2010; 2011). One

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of these EMEP stations, i.e. “Schauinsland” (near Freiburg), is located approximately 100 km

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south of our studied bogs in the Northern Black Forest (NBF) and 200 km west of the bogs in

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Oberbayern (OB). Only the wet component of the total deposition is monitored, although the

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amount of wet deposition as a percentage of total deposition can vary considerably depending

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on the element, the orographic situation, climate, and pollution intensity. According to

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Erisman et al. (1998, 2005), the true total deposition is greater than the measured wet

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deposition. Aas et al. (2009), on the other hand, found that the wet only and bulk collectors

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(‘‘bulk bottle method’’) are comparable at wet rural sites where the total deposition arises

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mainly from precipitation. After all, wet deposition is clearly the dominant input for metals at

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background sites, such as the areas we are studying in southern Germany, while dry

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deposition becomes the dominant input at more polluted sites or in areas with greater

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roughness (e.g., more forest cover) (Erisman et al., 1998).

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More data for comparison are presented by Schröder et al. (2010, 2011, 2013); to enhance the

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spatial resolution of EMEP deposition modelling and mapping, they compared spatial trends

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with observations from the European moss survey which measures heavy metal

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concentrations in mosses. To do this, heavy metal deposition data were modelled using the

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concentrations of heavy metals in naturally growing mosses and integrating these data into a

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geographic information system. The results were validated annually with deposition

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measurements at up to 63 measurement stations within the EMEP, and mosses were collected

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at up to 7,000 sites at 5-year intervals between 1990 and 2005. Moderate to high correlations

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were found between Cd and Pb concentrations in mosses and their modelled atmospheric

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deposition. By means of multivariate decision tree analyses, it was shown that at least Cd and

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ACCEPTED MANUSCRIPT Pb concentrations in mosses were predominantly determined by the atmospheric deposition of

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these metals (Schröder et al., 2010).

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Estimated total atmospheric deposition data are given by Gauger et al. (2000, 2008) from the

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MAPESI (Modelling of Air Pollutants and Ecosystem Impact) program, and their findings can

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also be used for comparison with Sphagnum accumulation data. They used measured wet

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deposition data from German forest monitoring programs and modelled receptor-dependent

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dry deposition as well as fog and cloud-droplet deposition. According to Gauger et al. (2008),

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wet deposition is considerably greater than dry deposition, with an annually varying ratio

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between the two. On an average, this ratio is 2:1 (wet/dry) for Pb and 4.5:1 for Cd. In fact,

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modelled MAPESI data for total atmospheric deposition may reach uncertainties for Cd and

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Pb of 200 to 300%, respectively (Umweltbundesamt, 2009).

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In general, the validity of each model depends on the quality and (un)certainty of the input

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data. This applies also to emission data as well as deposition data gained in forest monitoring

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programs (Schröder et al., 2010, 2011). As our study sites in the NBF and OB are relatively

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unpolluted areas, both EMEP and MAPESI data might serve as reasonable parameters of

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comparison.

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In a previous work, we quantified variations in element concentrations within bogs, between

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bogs, as well as between regions, and compared them with a suite of major and trace elements

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obtained from terrestrial mosses growing in upland ecosystems (Kempter et al., 2017).

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Furthermore, we also demonstrated the importance of moss growth rates on Pb (and Ti)

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accumulation rates (Kempter et al., 2010). In the present paper, we focus on how the trace

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element accumulation rates obtained using Sphagnum moss compare with modelled data from

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existing monitoring programs based on directly deposition measurements.

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In fact, while Pb has been extensively investigated and its accumulation rates, obtained using

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Sphagnum, were found to be similar to regional estimates of atmospheric Pb deposition

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(Kempter et al., 2010), far fewer studies have been carried out for other elements and there is

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much less data for the less abundant, (potentially) toxic elements such as Ag, Cd, Sb, and Tl.

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Our hypothesis is that Sphagnum mosses from ombrotrophic bogs can be used to monitor

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atmospheric deposition of many elements. Our main objective is to present accumulation rates

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of an array of major and trace metals (Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb,

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Rb, Sb, Sc, Sr, Th, Ti, Tl, U, V, Zn) in living Sphagnum mosses from four southern German

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ACCEPTED MANUSCRIPT bogs and to compare them with available atmospheric deposition data: wet-only deposition of

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EMEP and modelled total deposition of MAPESI and EMEP.

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2. Experimental Procedures

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2.1 Field Study

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Four ombrotrophic, mostly undisturbed peat bogs were sampled in 2007 (Table A.1-A.3 of

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Appendix 1). Wildseemoor (WI) and Hohlohseemoor (HO) are located in the Northern Black

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Forest (NBF), whereas Gschwender Filz (GS) and Kläperfilz (KL) are located in Oberbayern

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(OB) (Appendix 2 Figure B.1). All selected peat bogs are ombrotrophic in nature and sites

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with well growing Sphagnum mosses could be selected. Plastic nets (ca. 40 × 40 cm, surface

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area 1680 cm2, 1.5 cm mesh) were positioned in April 2007 on the peat bog surface of the

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selected sites and fixed with plastic anchors to mark the surface of the mosses to be sure that

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all collected material is the same age and has been exposed to atmospheric deposition for the

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same duration. Each net represents a single sample, and up to 12 nets were installed at each

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sampling site; between 6 and 10 of these sites were established on the surface of each bog.

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Preference was given to open sites least influenced by trees, dwarf shrubs, or hummocks

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which are known from measurements of

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Moreover, focus was placed on Sphagnum lawns, whereas large hummocks and hollows were

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excluded from the study (see Kempter and Frenzel, 2007; 2008). One year later, all moss

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material above the plastic net was harvested. All sites were extensively described (e.g.,

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coordinates, parcel, and surrounding vegetation) at the beginning and at the end of the

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experiment and notes were made concerning any exceptional habits of the peat mosses or

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exceptional colours. At GS and KL the entire area of each sample (40 × 40 cm) was

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harvested, whereas at WI and HO only half this amount (40 × 20 cm) was harvested; the

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remainder was left undisturbed to allow one more year of growth and exposure; those results

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will be presented elsewhere. In total, for this study, 232 samples which had been exposed to

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atmospheric deposition during a period of one year (April 2007 to 2008) were selected for

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analysis (Table A.3). Further details about the studied peat bogs and methods used for this

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study are summarized elsewhere (Kaule, 1974; Görres, 1991; Kempter and Frenzel, 2007;

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Kempter et al., 2010).

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Pb to affect interception (Norton et al., 1997).

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ACCEPTED MANUSCRIPT 2.2 Analytical Procedures

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Selected major and trace elements - Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb,

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Sb, Sc, Sr, Th, Ti, Tl, U, V, Zn - were determined using sector field ICP-MS employing well

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established analytical procedures (Krachler et al., 2004; Rausch et al., 2005). For digestion,

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aliquots (~200 mg) of powdered peat and plant samples were dissolved in a microwave

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autoclave (ultra-CLAVE II, MLS, Leutkirch, Germany) at elevated pressure using 3 mL high

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purity HNO3 and 0.1 mL HBF4 (Krachler et al., 2003). For quality control, the certified plant

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material GBW07602 (Bush Branches and Leaves, Institute of Geophysical and Geochemical

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Exploration Langfang, China) was used. An aliquot of this material was included in each

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digestion batch of samples and provided certified values for all 23 elements investigated here,

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except for Tl (no value) and U (information value). The experimentally derived

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concentrations for all elements agreed within the standard deviation of the mean of the

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certified elemental concentrations. The reproducibility of replicate dissolutions/measurements

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of the certified reference material was better than 5% for all investigated elements. The entire

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analytical procedure is reported elsewhere (Krachler et al., 2004).

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2.3 Statistical Methods

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The median value was used in calculating representative data because it does not use tails of

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the data set, is robust and unaffected by outliers. Median values are shown in Figures 1 and 2

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as well as in Appendix 2. As the shape of the sampling distribution did not always approach a

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normal distribution, parametric methods and their non-parametric alternatives were applied.

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One-way ANOVA and Kruskal-Wallis ANOVA were used to test for differences between

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sites within a peat bog as well as between studied peat bogs and regions. In general, results

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from parametric one-way ANOVA and non-parametric Kruskal-Wallis ANOVA matched

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very well (around 95%). Results from non-parametric methods are presented here. The level

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of confidence was set to P<0.01. Statistical parameters were calculated using STATISTICA 8

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(Statsoft, 2008).

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2.4 Calculations

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2.4.1 Calculation of annual production [g m-2 a-1]

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The yield of dry plant matter from the marked surface area (ca. 1680 cm2 at GS and KL for

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the entire net area, and ca. 840 cm2 at WI and HO for only half of the net area) was

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extrapolated to one square meter as follows:

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Annual production [g m-2 a-1] = dry weight [g] x 5.95 (x 12 for WI and HO)

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Atmospheric deposition is generally expressed on an area and time basis in air pollution

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studies. Thus, if contents of various chemical elements accumulated by Sphagnum mosses

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need to be compared with atmospheric deposition, the values found in the mosses have to be

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converted into those of yearly deposition. Aaby and Jacobsen (1978) used the term ‘metal net-

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uptake’, defined as the amount of metal present in the annual layer at the time of sampling. As

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the term ‘uptake’ infers an active biological process, ‘net element accumulation’ seems more

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appropriate to differentiate from the atmospheric deposition rate which is commonly

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estimated by wet-only or bulk collectors.

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The net accumulation rate for one year was calculated as follows:

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Net accumulation rate [mg m-2 a-1] = annual production [g m-2 a-1] x element concentration

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[µg g-1]/1000

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2.5 Data on atmospheric deposition – EMEP and MAPESI

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Further information on the EMEP station “Schauinsland” (near Freiburg) located in the

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southern part of the Black Forest about 100 km to the south of NBF and more than 200 km

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west of OB, is provided in Pfeiffer and Baumbach (2008) and EMEP (European Monitoring

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and Evaluation Program http://www.emep.int). Information about the collection of data in

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German forest monitoring programs is summarized in Gauger et al. (2000).

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3. Results and Discussion

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3.1 Within-Bog Variation

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The comparison of within-site and between-site variation of element accumulation rates is

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defined as the range between the calculated minimum value and the maximum value within a

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site of a single bog, using Kruskal-Wallis ANOVA. This evaluation reveals that nearly all

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studied elements in all four peat bogs with only few exceptions were not significantly

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different between the studied sites (Figure 1, A.5-A.27 and B.2-B.5).

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Figure 1: Within-bog variation of Sb, Bi, and Th accumulation rates at the GS and WI bogs

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with individual sites indicated by Roman numerals. Each site represents 7 to 12 samples.

ACCEPTED MANUSCRIPT These findings are in contrast to elemental concentration values in Sphagnum moss (Kempter

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et al., 2017) where Kruskal-Wallis ANOVA showed that only those sampling sites within KL

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were similar for most studied elements. For GS and both the NBF peat bogs, the average

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concentrations in Sphagnum for sites within a bog were significantly different for two third of

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all studied elements (Kempter et al., 2017). As noted elsewhere, the differences in

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concentrations reflect the natural variability in the shape of growth of the mosses and a

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number of factors related to small but important differences in site conditions (Kempter et al.,

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2010).

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Concerning accumulation rates, Kempter et al. (2010) found that within-bog variation in the

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accumulation rates of Pb and Ti in Sphagnum mosses on the scale of studied sites are

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primarily a result of differences in the annual production of the Sphagnum mosses. Thus, for

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all here studied elements, it is likely too, that the strong influence of the moss production rate

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on the element accumulation rate dominated all other effects. Factors related to differences in

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site conditions become relatively unimportant once the accumulation rates have been

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calculated (Kempter et al., 2010).

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3.2 Between-Bog and Between-Region Variation

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The application of Kruskal-Wallis ANOVA revealed that Sphagnum accumulation rates

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obtained from peat bogs of the OB region and the NBF region match significantly for at least

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half of the 23 investigated elements. Again, this is also in contrast with results gained for

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element concentrations in Sphagnum showing considerable variation between both bogs of a

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studied region which was explained in terms of local conditions (Kempter et al., 2017).

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Regarding element accumulation rates, local conditions such as land use (traffic, agriculture),

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topography, elevation, exposure, shelter by extensive forests or P. mugo stands on bog

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surfaces, which all affect the deposition of atmospheric particles to the bogs, are apparently

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masked once the production rate of the mosses is considered.

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As noted earlier (Kempter et al., 2017), concentration values were significantly greater in

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Sphagnum from the NBF peat bogs compared to the OB bogs. Here, using Kruskal-Wallis

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ANOVA, we find that the same is true for element accumulation rates: the accumulation rates

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of all measured elements were significantly greater in the Sphagnum mosses of the NBF peat

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bogs compared to those of the OB peat bogs (Figures 2, 3a and 3b, A.5-A.27, B.6). This

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difference in accumulation rates reflects the significantly higher production rate of the

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Sphagnum mosses growing on the NBF peat bogs.

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Bi [µg m-2 a-1]

Bi [µg g-1]

0,08

0,04

KL

40

0,10

316

KL

GS

HO

0

WI

0,0 KL

50

GS

0,1

315

Th [µg g-1]

100

GS

0,2

GS

Sb [µg m-2 a-1]

0,4

xn ai MM rr el e i i l t s t uu se n rm OO i a e i e lr d%%nn t t e55oo ux M72NN OE

Sb [µg g-1]

ACCEPTED MANUSCRIPT

15

10

5

0 HO

WI

KL

GS

0,00

317 318

Figure 2: Between-bog variation of Sb, Bi, and Th concentration values and accumulation

319

rates.

13

ACCEPTED MANUSCRIPT In previous work, Kempter et al. (2010) showed that Sphagnum mosses in NBF bogs

321

exhibited much greater annual production rates (187 to 202 g m-2 a-1) compared to OB (71 to

322

91 g m-2 a-1) (A.4). Clearly, this difference in productivity has a strong impact on the

323

accumulation rates of trace elements (g m-2 a-1) with productive Sphagnum mosses are able to

324

accumulate more particles from the air (Kempter et al., 2010).

325

3.3 Element accumulation rates from Sphagnum compared with atmospheric deposition

326

Accumulation rates of major and trace elements obtained using Sphagnum were compared

327

with measurements of atmospheric deposition (Figures 3a and 3b). Note that EMEP data is

328

based on wet-only deposition and MAPESI data is based on modelled total deposition, but is

329

only available for Cd and Pb).

10,00

EMEP (wet-only) 2007 MAPESI (total) 2007

1.066

1,00

0,10

0.035 0.02 0.018

0.055

0,01

0,00

330 331

M AN U

11.99

NBF OB

Ag

As

Bi

Cd

5.78

1.22 0.75 0.51 0.08

0.02

TE D

Accumulation Rate [mg m-1 a-2]

100,00

SC

RI PT

320

Co

Cu

Fe

Mo

0.003

Pb

Sb

Tl

Zn

Figure 3a: Accumulation rate (mg m-2 a-1) of selected chalcophile elements obtained from

333

Sphagnum collected 2007 in OB (hollow bars; n=80) and NBF (solid bars; n=153) peat bogs.

334

These values are compared with atmospheric deposition to these regions (numerical values

335

above the bars) estimated by EMEP (2007) (http://www.emep.int (2010)) and MAPESI 2007

336

(Gauger personal information). Atmospheric deposition studies (EMEP, MAPESI) did not

337

include Ag, Bi, and Mo.

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14

ACCEPTED MANUSCRIPT NBF OB

1.48

10,00

EMEP (wet-only) 2007

1,00 0.228

0.104

0,10

0,01

0,00 Al

338

Ba

Cr

Mn

Rb

Sc

Sr

Th

RI PT

Sphagnum accumulation [mg m-1 a-2]

100,00

Ti

U

V

Figure 3b: Accumulation rate (mg m-2 a-1) of selected lithophile elements obtained from

340

Sphagnum collected 2007 in OB (hollow bars; n=80) and NBF (solid bars; n=153) peat bogs.

341

These values are compared with atmospheric deposition to these regions (numerical values

342

above the bars) estimated by EMEP (2007) (http://www.emep.int (2010)) and MAPESI 2007

343

(Gauger personal information). Atmospheric deposition studies (EMEP, MAPESI) did not

344

include Al, Ba, Rb, Sc, Sr, Th, Ti, and U.

345

At first sight, atmospheric deposition rates for the chalcophile elements As, Cu, Cd, Co, Pb

346

and Tl as well as for the lithophile element V agree quite well with the accumulation rates of

347

the peat mosses for the NBF region. Using EMEP data from the southern part of the Black

348

Forest is a compromise and might not reflect very well the deposition to the peat bogs because

349

EMEP wet-only data were collected approximately 100 km south of NBF. MAPESI data for

350

both studied regions are only available for Cd and Pb. Again, notice that the accumulation

351

rates obtained from Sphagnum mosses in the NBF region are generally higher than those from

352

the OB region (Figures 2, 3a and 3b). These regional differences are consistent with the data

353

from moss monitoring studies in Germany in 2005 for a variety of elements (Pesch et al.,

354

2007).

355

Two cautionary remarks are in order. First, in respect to the comparison of Cd and Pb

356

accumulated by Sphagnum with EMEP (wet-only), EMEP (total deposition, modelled) and

357

MAPESI (total deposition, modelled) data for different years (Tables 1and 2) it is important to

358

notice that measured wet deposition and modelled deposition values vary over the years

359

(EMEP wet only data, Appendix 1 A.28). Harmens et al. (2012) found that correlations

360

between moss concentrations and modelled deposition data were not affected by the

361

accumulation period. However, when comparing different years of element accumulation by

362

Sphagnum versus deposition measurements, inter-annual variation in deposition must be

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15

ACCEPTED MANUSCRIPT considered. While mosses used in monitoring networks may not reflect the integration of air

364

pollutants over a certain period, in our study, Sphagnum material from one year of growth

365

was used.

366

Lead and Cd deposition rates (EMEP modelled) used here were taken from a map created by

367

Schröder et al. (2011) and this appears to be one more source of inaccuracy. It happens that

368

the peat bogs included in our study were in the border area of two classifications: this affects

369

the OB peat bogs for Pb and the NBF peat bogs for Cd. Because of the challenge locating

370

these bogs on the EMEP maps, both possible locations were considered, and this explains the

371

great range in values (shown in bold in Tables 1 and 2).

2007 -2

-1

EMEP

EMEP modelled

MAPESI modelled

MAPESI modelled

(wet-only)

(total)

(total)

(total)

2005 and 2007

2005

-2

-1

[mg m a ]

[mg m a ]

GS (OB)

0.20

Data from

KL (OB)

0.34

Southern

0.89

HO (NBF)

0.78

2007 -2

-1

[mg m a ]

Black

Forest WI (NBF)

SC

Sphagnum

M AN U

Peat bog

RI PT

363

0.84 and 0.75

<0.54-0.75

1.07-1.17

-2

-1

2005

[mg m a ]

[mg m-2 a-1]

0.51

0.34

0.51

0.34

1.19

0.79

1.26

0.82

Table 1: Pb accumulation rates obtained from Sphagna compared to atmospheric deposition

373

determined by EMEP 2007 (http://www.emep.int (2010)), EMEP modelled 2005 (Schröder et

374

al., 2011) and MAPESI 2005 and 2007 (Gauger personal communication).

TE D

372

Peat bog

Sphagnum

GS (OB) KL (OB)

EMEP

(wet-only)

(total)

(total)

2005 and 2007

2005

2007

[mg m-2 a-1]

[mg m-2 a-1]

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2007

EMEP

EP

375

[mg m-2 a-1]

[mg m-2 a-1]

0.012

Data from

0.015

Southern

modelled

MAPESI modelled

0.018 Black

0.018-0.022

0.018

Forest

WI (NBF) HO (NBF)

0.027

0.028

0.023 and 0.020

0.035 0.026-0.034

0.035

376

Table 2: Cd accumulation rates obtained from Sphagna compared to atmospheric deposition

377

estimated by EMEP 2007 (http://www.emep.int (2010)), EMEP modelled 2005 (Schröder et

378

al., 2011) and MAPESI 2007 (Gauger personal communication).

16

ACCEPTED MANUSCRIPT 379

Second, we have expressed the Sphagnum moss accumulation rates as a percentage of

380

deposition rates (Table 3). Clearly, these comparisons could only be made when data for the

381

studied region were available. EMEP wet-only data were not used to compare with moss

382

accumulation rates obtained from the OB bogs. GS (OB)

KL (OB)

WI (NBF)

HO (NBF)

As (EMEP w.o.)

75.1 %

104.5 %

Cd (EMEP w.o.)

127.7 %

132.4 %

57-67 %

68-83 %

79-103 %

82-108 %

Cd (MAPESI)

51.2 %

60.9 %

73.0 %

75.6 %

Co (EMEP w.o.)

94.6 %

91.1 %

Cr (EMEP w.o.)

185.5 %

201.1 %

Cu (EMEP w.o.)

90.7 %

90.5 %

Fe (EMEP w.o.)

374.8 %

445.1 %

Mn (EMEP w.o.)

857.3 %

1009 %

96.1 %

98.2 %

76-83 %

67-73%

57.2 %

61.9 %

57.5 %

71.2 %

156.7 %

214.7 %

187.3 %

232.7 %

95.2 %

111.6 %

171.6 %

182.6 %

Pb (EMEP modelled)

>27-37 %

>45-63 %

Pb (MAPESI)

66,7 %

52,9 %

Sb (EMEP w.o.) Sr (EMEP w.o.)

V (EMEP w.o.) Zn (EMEP w.o.)

TE D

Tl (EMEP w.o.)

M AN U

Pb (EMEP w.o.)

SC

Cd (EMEP modelled)

RI PT

Element

Table 3: Element accumulation rates obtained from Sphagnum mosses compared to

384

atmospheric deposition determined by EMEP 2007 (http://www.emep.int (2010)), EMEP

385

modelled 2005 (Schröder et al., 2011) and MAPESI 2005 and 2007 (Gauger personal

386

communication) in the respective regions. Differences are expressed in percentage values.

387

EMEP (w.o.) = EMEP wet-only. Values in bold and italic indicate uncertain data because of a

388

very great range in modelled deposition rate values for Pb at OB (<0.54-0.75 mg m-2 a-1).

389

Elements such as Mn, Fe, Sr, Cr, Tl and Zn are clearly enriched in Sphagnum mosses

390

compared to atmospheric deposition (values >100 %). Iron, Mn and Zn are elements which, at

391

low concentrations, are essential for plants and are actively accumulated by Sphagnum

392

mosses. In respect to Fe and Mn, redox processes might also be involved in their enrichments

393

within the moss layer of the bogs. Strontium and Ba are biochemical analogues for Ca,

394

whereas Rb, Cs, and Tl are analogues for K. Thus, Tl uptake and recycling by the living moss

395

may profoundly affect its accumulation rates. This effect is not evident in Figure 3a but might

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17

ACCEPTED MANUSCRIPT explain the very high Tl concentration and accumulation values (A.24, B.2-B.5) found in

397

single samples. The main message here is that the accumulation rate data obtained from

398

Sphagnum, for elements which may be affected by biological processes, must be interpreted

399

with caution.

400

For many elements, including As, Cd, Cu, Co and V, the accumulation rates obtained from

401

Sphagnum are ca. 100 % of the values obtained from deposition measurements (Table 3). In

402

respect to Pb, the accordance is dependent on which atmospheric deposition data are used for

403

comparison. For example, the agreement ranges from 60 to nearly 100 % for NBF peat bogs

404

and 53 to 68 % for OB peat bogs. The same is true for Cd (73 to 132 % for NBF peat bogs

405

and 51 to 83 % for OB peat bogs). For both these elements, MAPESI data differs not only

406

from EMEP wet only data, but also from EMEP modelled data. For Cd in the NBF region, for

407

example, EMEP wet-only data are only 57 % of MAPESI data and EMEP modelled data are

408

only 74 % that of MAPESI. For Pb in the OB region, MAPESI data are only 68-75 % of

409

EMEP modelled data. The magnitude of these differences in deposition data illustrates the

410

challenge of finding a robust reference level, against which the data obtained using Sphagnum

411

moss may be compared.

412

For Sb, apparently it is either underestimated by the moss, or over-estimated by the

413

atmospheric deposition studies (Figure 3a and Table 3). In fact, the accumulation rates

414

obtained using moss, are only 70 % of the EMEP deposition values, even though dry

415

deposition was not included by EMEP. Antimony is a constituent of many plastics commonly

416

found in laboratories and concentrations in water samples may be erroneously elevated

417

because of Sb leaching from plastic (Shotyk et al., 2006). If the monitoring data are correct,

418

and if the investigated samples have not been contaminated with Sb during sampling, then a

419

part of the Sb is apparently not accumulated by the mosses. To a large extent, Sb and Pb from

420

human activities will be found in the same sub-micron aerosol fraction (Shotyk et al., 2005;

421

Shotyk and LeRoux, 2005). Lead in this fraction must be effectively retained by Sphagnum

422

because the Pb accumulation rate we obtain is in quite good agreement with direct

423

measurements of Pb deposition (EMEP wet-only around 97 %, Table 3). The agreement for

424

Sb between the two approaches is poor and an explanation might be that Sb is not well

425

retained perhaps because some dissolution of the aerosol might take place on the moss

426

surface. Moreover, Sb in the aqueous phase would be predominantly anionic (Shotyk et al.,

427

2005) and perhaps not adsorbed by the moss

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18

ACCEPTED MANUSCRIPT 4. Conclusions

429

The comparison with EMEP (wet-only and total deposition) and MAPESI (total deposition)

430

data shows that accumulation rates obtained using Sphagnum are in the same range of

431

published values for direct measurements of atmospheric deposition in both regions, at least

432

for As, Cd, Cu, Co, Pb, and V. Antimony, however, shows considerable discrepancy, because

433

it is either under-estimated by Sphagnum moss or over-estimated by both atmospheric

434

deposition models. Atmospheric deposition data obtained from sampling in open fields is

435

unlikely to perfectly match data obtained using living Sphagnum moss from bogs. In fact,

436

plant uptake and biochemical utilization by living moss may affect accumulation rates of

437

those elements that are essential for plant nutrition (macro and micronutrients), which is

438

clearly seen in the data presented here for Mn, Fe and Zn.

439

The comparison of accumulation rates obtained from moss versus data from direct deposition

440

measurements is very much dependent on how and when the atmospheric deposition rates

441

were obtained. Even if atmospheric deposition monitoring data were available at all for a

442

given study region and for a specific year, the use of different models to calculate the

443

deposition rates may yield different fluxes for the same region. It would be worthwhile to

444

study the atmospheric deposition of trace metals, using both Sphagnum moss from a given

445

peat bog as well as deposition collectors installed at the same location, so that these two very

446

different approaches could be directly compared in a comprehensive and systematic way.

447

In addition to the impact of the annual production rate of plant matter on the moss

448

accumulation rate, atmospheric deposition to a collector in an open field represents a

449

fundamentally different physical process compared to the interception experienced by the

450

surface of Sphagnum moss growing in a bog. Sphagnum has a unique surface roughness,

451

wetness and chemical composition, in addition to complications created by its surroundings

452

on the bog surface: these are perhaps best described as a mosaic of microtopographic

453

variation (ranging from pools to hummocks) and often surrounded by a canopy of dwarf

454

shrubs and trees. Despite these fundamental differences, Sphagnum mosses may serve as good

455

indicators for atmospheric deposition to plant surfaces and, in this way, help quantify

456

contaminant inputs to terrestrial ecosystems.

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457

19

ACCEPTED MANUSCRIPT Acknowledgements. The financial support of the German Research Foundation [SH 89/4-1,2]

459

is gratefully acknowledged. We thank the responsible government institutions (Regierung von

460

Oberbayern und the Regierungspräsidium Karlsruhe) for kindly allowing us to undertake our

461

studies in nature conservation areas. Thanks from H.K. to Christian Scholz, Silvia

462

Rheinberger and Nadja Salm for their tremendous help in the field and to Helen Kurzel, Nadja

463

Salm and Daniela Birkle for a large part of the lab work. We are indebted Thomas Gauger

464

(University of Stuttgart, Institute of Navigation) for quickly and kindly sharing the MAPESI

465

data.

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ACCEPTED MANUSCRIPT 466

Appendix A and Appendix B - Supplementary Data

467

Supplementary data associated with this article can be found in the online version.

468

Appendix A: Data and results of statistical parameters are presented in tables (A.1 to A.28).

469

Appendix B: Data are presented in box-and-whisker plots (B.1 to B.6).

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Pb) in acid digests of peat with ICP-SMS using

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2005/2006.

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Forschungsvorhaben

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des

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Moss-Monitoring

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ACCEPTED MANUSCRIPT Schröder W., Holy M., Pesch R., Zechmeister H., Harmens H., Ilyin I., 2011. Mapping

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atmospheric deposition of cadmium and lead in Germany based on EMEP deposition data and

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the European Moss Survey 2005. Environmental Sciences Europe 23, 19 p..

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Schröder W., Pesch R., Hertel A., Schonrock S., Harmens H., Mills G., Ilyin I., 2013.

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Correlation between atmospheric deposition of Cd, Hg and Pb and their concentrations in

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mosses specified for ecological land classes covering Europe. Atmos. Poll. Res. 4, 267‐274.

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Shotyk W., LeRoux G., 2005. Biogeochemistry and cycling of lead. Met. Ions Biol. Syst. 43,

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239-275.

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Shotyk W., Krachler M., Chen B., 2005. Anthropogenic impacts on the biogeochemistry and

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cycling of antimony. Met. Ions Biol. Syst. 44, 171-203.

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Shotyk W., Krachler M., Chen B., 2006. Contamination of Canadian and European bottled

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waters with antimony from PET containers. J. Environ. Monit. 8, 288-292.

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Shotyk W., Kempter H., Krachler M., Zaccone C., 2015. Stable (206Pb,

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Pb,

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Pb) and

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radioactive (

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ombrotrophic bogs in southern Germany: Geochemical significance and environmental

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implications. Geochim. Cosmochim. Acta 163, 101–125.

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Statsoft 2008. Statistica 8.0. Statsoft Tulsa, OK.

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Ökosysteme und die Vegetation in Deutschland und Europa (Modelling deposition loads and

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Pb) lead isotopes in 1 year of growth of Sphagnum moss from four

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Bullet Points - Highlights

Element accumulation rates in moss similar to those from direct deposition

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Accumulation rates obtained from moss affected by plant growth rates Sphagnum moss a useful bioindicator of metal deposition to “terrestrial ecosystems” Lithophile elements help understand the behaviour of chalcophile elements

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Antimony discrepancy (moss versus deposition) requires further study