[Show abstract][Hide abstract] ABSTRACT: Elevated atmospheric deposition of reactive nitrogen species, mainly nitrate (NO3
−) and ammonium (NH4
+), may negatively affect peatland carbon balance and thus contribute to climatic warming. It is difficult to take an accurate inventory of atmospheric N inputs into Sphagnum-dominated bogs, due to uncertainties in estimating horizontal deposition. At two mountain-top peat bogs (Czech Republic, Central Europe), we modelled N interception by replacing S. cuspidatum capitula with polyethylene (PE) strands of an identical surface area. After a 12-week exposure of the samplers to frequent spring and autumn fogs, we compared the amount of N captured by the PE strands (nitrate, ammonium, and organic N) with vertical N deposition via rainfall. Horizontal deposition added 35–69 % N to rainfall N input. The more polluted site exhibited a significantly higher horizontal N deposition than the less polluted site. We scaled our S. cuspidatum data to S. capillifolium, a species common in boreal regions in the form of densely packed carpets. Assuming a proportional decrease in N interception with decreasing Sphagnum surface, we estimated that horizontal deposition in S. capillifolium would add 12–45 % N to rainfall N input. Our data will help to close the N mass balance in peat bogs studies.
[Show abstract][Hide abstract] ABSTRACT: Measurements of nitrogen isotope ratios (δ15N) along vertical porewater profiles are instrumental in localizing sources and sinks of nitrous oxide (N2O) in wetland ecosystems. We present the first N2O concentration and isotope data for porewaters of ombrotrophic, mountain-top bogs. Our two study sites, situated in the Czech Republic at elevations higher than 1000 m, have been affected by atmospheric N pollution for more than 100 years. In recent decades, the northeastern site KB received over 30 kg N ha-1 yr-1 via atmospheric deposition, the southwestern site BS was 3 times less polluted. Both peat bogs were surrounded by defoliated, dead spruce stands. We hypothesized that elevated nitrate (NO3-) inputs in rain-fed bogs may cause sizeable N2O emissions. Porewater N2O concentrations in the studied ombrotrophic bogs were 400 to 800 times higher, compared to fens in nearby Bavaria (Germany). The highest N2O concentrations and the lowest δ15N-N2O values were found at the bottom of the sampled porewater profiles, 40 to 60 cm below surface. Low δ15N-N2O values resulted from a N isotope fractionation associated with denitrification. The site with the lower historical N pollution, BS, exhibited up to 7 times higher porewater N2O concentrations than KB, possibly due to a higher denitrification potential determined as abundance of nirK and nirS genes. Upcore, N2O abundance decreased and δ15N-N2O increased, indicating N2O reduction. Processes of N2O formation and consumption at different depths were integrated by measuring N2O fluxes across the peat – atmosphere interface. These fluxes were minute (< 0.02 µmol N2O m-2 h-1). We even observed scavenging of air-borne N2O by the bog substrate. Nitrogen pollution of ombrotrophic bogs led to vigorous N cycling, manifested by extremely high peat porewater N2O concentrations. However, effective in-situ consumption of the produced N2O greatly reduced its warming potential.
Soil Biology and Biochemistry 11/2014; in press. DOI:10.1016/j.soilbio.2014.10.021 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There are fears that global warming will lead to degradation of peatlands, higher emissions of greenhouse gases from peat, and accelerated warming. Anaerobic decomposition of organic soils produces methane (CH4), a potent greenhouse gas. Two peat bogs differing in mean annual temperature, Velke Darko (VD, Czech Republic, 7.2 °C), and Stor Åmyran (SA, Sweden, 4.0 °C), were selected for a comparative study of how organic soils in different climatic zones will respond to warmer and drier conditions. Twenty peat cores from each bog were incubated in growth chambers. Under present-day summer conditions, VD produced 14 times more CH4 than SA. Two different warming scenarios were used. Peat-core replicates were kept at temperatures of 11 versus 16 °C, and 11 versus 22 °C. From 11 to 16 °C, the CH4 production slightly decreased at SA, and slightly increased at VD. From 11 to 22 °C, the CH4 production increased 9 times at SA, but slightly decreased at VD. After an 8-month incubation, peat cores under drying conditions (water table at −14 cm) were compared to samples with original water table (−2 cm). Drying conditions led to a steeper reduction in CH4 production at VD, compared to SA. The CH4 production decreased more than 100 times at VD. Then, the combined effect of simultaneous warming and drying at 11 and 22 °C was studied. We did not find any significant effect of interactions between increasing temperature and decreasing water table level. Overall, the warmer site VD responded more strongly to the simulated climate change than the colder site SA.
Mitigation and Adaptation Strategies for Global Change 10/2014; 19(7). DOI:10.1007/s11027-013-9456-0 · 2.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have measured pollen, aluminum, and lead abundances in a Czech peat bog at Bozi Dar in order to investigate the environmental impact of Holocene climate changes and mining activities in Central Europe. The pollen record shows a continuous vegetal cover since 13 kyr BP. Aluminum and pollen deposition characterize the Younger Dryas (YD) cold event at 12.3-11.0 kyr BP, within its expected time frame in Northern Europe. Aluminum fluxes reveal four other significant dust events with significant Asian and Saharan sources, as shown with variations in stable Pb-204, Pb-206, and Pb-207 isotopes. Recurrent Asian incursions are seen at Bozi Dar during the YD and Mid-Holocene dust events (at 7.1, 6.5, and 5.9 kyr BP). These Asian imprints are also observed by Le Roux and colleagues during the YD in the nearest Holocene-long geochemical peat record from Switzerland (Etang de la Gru re). We do not see at Bozi Dar the distinct western European volcanic inputs identified in the Swiss peat by Shotyk and colleagues. However, isotopic ratios characteristics of Mediterranean airflows are evident at both locations during the Mid-and Late Holocene. The occurrence of these various air mass sources in Switzerland and the Czech Republic substantiates Holocene atmospheric circulation models in Central Europe with dominating zonal airflows during the Early Holocene, followed by a governing meridian dispersion during the Mid-and Late Holocene. Lead inputs at 5.1-4.3 and 1.9 kyr BP cannot be explained by increased dust deposition only. The 1.9 kyr event fits local Bohemian ore isotopic imprints of which isotopic signatures are seen as early as 2.2 kyr BP in our core, hence revealing the oldest ever environmental record of mining-related activities in the Czech Republic. Relatively elevated Pb deposition at 5.1 and 4.3 kyr BP are tentatively attributed to contamination that may be from local sources and/or long-range transport.
The Holocene 07/2014; 24(8):919-931. DOI:10.1177/0959683614534746 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Isotopic evidence for nitrogen mobility in peat bogs, Geochimica et Cosmochimica Acta (2014), doi: 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.
[Show abstract][Hide abstract] ABSTRACT: Carcinogenic effects of hexavalent chromium in waters are of concern in many countries worldwide. We explored Cr isotope systematics at 11 sites in the Czech Republic and Poland. Geogenic Cr pollution was associated with serpentinite bodies at former convergent plate margins, while anthropogenic Cr pollution resulted from electroplating, tanning, and chemical industry. Cr(VI) concentration in geogenic waters was less than 40 ppb. Anthropogenic waters contained up to 127,000 ppb Cr(VI). At both geogenic and anthropogenic sites, where known, the source of pollution had a low δ53Cr (<1‰). δ53Cr of geogenic and anthropogenic waters was up to 3.9 and 5.8‰, respectively. At both serpentinite-dominated and industrial sites, δ53Cr(VI)aq was shifted toward higher values, compared to the pollution source. At the industrial sites, this positive δ53Cr shift was related to Cr(VI) reduction, a process known to fractionate Cr isotopes. At geogenic sites, the origin of high δ53Cr(VI)aq is tentatively ascribed to preferential release of 53Cr during oxidation of soil Cr(III) and its mobilization to water. δ53Cr(VI) of industrially contaminated waters was significantly higher (p<0.001) compared to δ53Cr of waters carrying geogenic Cr (VI), implying that either the effective fractionation factor or process extent were greater for Cr(VI) reduction than for Cr(III) oxidation.
[Show abstract][Hide abstract] ABSTRACT: Soils in polluted regions are generally regarded as a delayed, long-lasting source for Pb contamination of aquatic systems. Lead deposited on topsoil is slowly transported downward with particulate and colloidal organic matter, driven by infiltrating precipitation. Then, Pb is tightly retained in mineral soil. Lead export from catchments is extremely low and de-coupled from the atmospheric input. We tested this hypothesis in 11 small catchments, differing in pollution levels. Input/ouput Pb fluxes were monitored for 14-15 years in an era of decreasing industrial Pb emission rates. Between 1996/1997 and 2010, Pb deposition fluxes decreased significantly, on average by 80 %. At the beginning of the monitoring, Pb export constituted 2 to 58 % of Pb input. At the end of the monitoring, Pb export constituted 2 to 95 % of Pb input. Highly polluted sites in the northeast exported significantly more Pb than less polluted sites further south. The 206Pb/207Pb isotope ratios of runoff (1.16) were identical to those of topsoil and present-day deposition, and different from mineral soil and bedrock. Lead isotope systematics and between-site flux comparisons indicated that a portion of the incoming Pb had a relatively short residence time in the catchments, on the order of decades.
[Show abstract][Hide abstract] ABSTRACT: Soil is a complex natural resource that is considered non-renewable in policy frameworks, and it plays a key role in maintaining a variety of ecosystem services (ES) and life-sustaining material cycles within the Earth's Critical Zone (CZ). However, currently, the ability of soil to deliver these services is being drastically reduced in many locations, and global loss of soil ecosystem services is estimated to increase each year as a result of many different threats, such as erosion and soil carbon loss. The European Union Thematic Strategy for Soil Protection alerts policy makers of the need to protect soil and proposes measures to mitigate soil degradation. In this context, the European Commission-funded research project on Soil Transformations in European Catchments (SoilTrEC) aims to quantify the processes that deliver soil ecosystem services in the Earth's Critical Zone and to quantify the impacts of environmental change on key soil functions. This is achieved by integrating the research results into decision-support tools and applying methods of economic valuation to soil ecosystem services. In this paper, we provide an overview of the SoilTrEC project, its organization, partnerships and implementation.
Environmental Science and Pollution Research 12/2013; 21(4). DOI:10.1007/s11356-013-2346-x · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we report chromium isotope compositions, expressed as δ53/52Cr in per mil (‰) relative to NIST 979, measured in selected Cr-rich minerals and rocks formed by the primary magmatic as well as the secondary metamorphic and weathering processes. The main objectives of this study were: (i) to further constrain the isotope composition of the Earth’s mantle Cr inventory and its possible variation during geological history, based on the analysis of globally distributed and stratigraphically constrained mantle-derived chromites; and (ii) to investigate the magnitude and systematics of Cr isotope fractionation during oxidative weathering and secondary alteration (i.e., hydration, serpentinization) of the magmatic Cr sources. Specifically, we analyzed δ53/52Cr in a set of globally distributed mantle-derived chromites (FeMgCr2O4, n = 30) collected from various locations in Europe, Asia, Africa and South America, and our results confirm that a chromite-hosted Earth’s mantle Cr inventory is uniform at −0.079 ± 0.129‰ (2SD), which we named here as a ‘canonical’ mantle δ53/52Cr signature. Furthermore our dataset of stratigraphically constrained chromites, whose crystallization ages cover most of the Earth’s geological history, indicate that the bulk Cr isotope composition of the chromite-hosted mantle inventory has remained uniform, within about ±0.100‰, since at least the Early Archean times (∼3500 million years ago, Ma).
[Show abstract][Hide abstract] ABSTRACT: In recent years, routine application of the stable isotope determination of chromium (Cr) in environmental and health protection research has led to the search for simpler chromite decomposition techniques. As the range of Cr isotope abundance ratios in nature is very narrow, conventional chromite decomposition techniques are no longer suitable, due to the relatively high risk of contamination during laboratory procedures. We have developed a protocol for the decomposition of chromites based on oxidation by bromic acid at room temperature. The procedure takes 15 d and requires two doses of bromic acid during the reaction period (day 1 and 8), due to the limited stability of the reagent. Chromium extracted by alkaline oxidative fusion and by bromic acid decomposition yielded statistically indistinguishable delta Cr-53 values, measured by multi-collector inductively coupled plasma-mass spectrometry following addition of a Cr-50-Cr-54 double-spike.
Geostandards and Geoanalytical Research 09/2013; 38(1). DOI:10.1111/j.1751-908X.2013.00229.x · 3.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, used brewers draff was investigated as a novel sorbent for Cr(VI) and compared with other biosorbents (grape waste, peat moss, and sawdust). FTIR-ATR, BET analysis, and pH determination were used to characterize the sorbents. Kinetic and equilibrium experiments were performed, and two empirical models, Langmuir and Freundlich, were used to describe Cr adsorption. Additionally, packed bed column experiments were also performed. In order to identify possible reduction processes, ion exchange separation on the AG1-X8 resin was used to separate the anionic Cr(VI) and the reduced cationic Cr(III) from the aqueous phase after biosorption. Cr(VI) removal was pH-dependent and fitted well both the Langmuir and the Freundlich isotherm models. The ion exchange separation showed that Cr(VI) reduction had occurred in the solution during biosorption. The efficiency of draff as a biosorbent was comparable (or even higher) to highly organic materials (e.g., composted peat), showing its potential application for Cr(VI) decontamination.
Journal of Colloid and Interface Science 04/2013; 396:227-33. DOI:10.1016/j.jcis.2013.01.029 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitrogen belongs to chemical elements whose biogeochemical cycles are
most heavily disturbed by human activities, and large regions worlwide
experience elevated depositions of reactive N (NO3-, NH4+). Peatlands
contain as much as 15 % of the world's soil N. It it is unclear whether
fertilizing by anthopogenic N will lead to higher storage of C in
wetlands. Elevated N input may lead to both higher net primary
productivity, but will also augment microbial decomposition. Here we
discuss two aspects of N cycling in Sphagnum-dominated bogs in the Czech
Republic, an area characterized by a steep north-south pollution
gradient and high annual N deposition (60 kg ha-1). These two aspects
are N inventory in 210Pb-dated peat cores, and post-depositional
mobility of N in peat. We compared the N inventory in two Czech bogs,
differing in pollution, with cumulative atmospheric N input. We
hypothesized that the total amount of N in the peat cores would be
smaller than the cumulative N input (leaching of excess N from the bog,
denitrification). The two bogs were VJ (industrial north) and CB (rural
south). The investigated period was 1885-2002. The total amount of N was
4020 kg ha-1 at VJ and 1530 kg ha-1 at CB. Peat in the north contained
2.6 times more N than in the south. Historical rates of N deposition in
the Czech Republic are well known (numerous papers by Kopacek). To
estimate cumulative N inputs into the bogs, we also used the monthly N
depositions between 1994 and 2002, measured in two nearby catchments.
The estimated cumulative atmospheric N input was 1350 kg ha-1 at VJ, and
530 kg ha-1 at CB. In both cases, the amount of N found in peat was 3
times higher than the estimated atmospheric N input. Such high storage
of N in peat is surprising. Post-depositional mobility of N may help to
explain the discrepancies between atmospheric N inputs and N storage in
peat. We found two-fold evidence for post-depositional mobility of N.
Maximum N concentrations at VJ were observed in layers dated at 1950,
whereas pollution level increased up to 1980, and dropped thereafter. At
the end of an 18-month reciprocal peat transplant experiment between VJ
and CB, we found that N isotope ratios N converged to the host site. The
magnitude of the isotope change was 3 per mil, the affected depth was 10
cm. Our results are consistent with the concept of Lamers et al. (2000)
in that both ^15N and the found shift in N peaks downcore confirmed
removal of N from surface moss under high N depositions. On the other
hand, the excess of stored N relative to the cumulative N input remains
unexplained, and merits further study.
[Show abstract][Hide abstract] ABSTRACT: Growth in human population and demand for wealth creates ever-increasing pressure on global soils, leading to soil losses and degradation worldwide. Critical Zone science studies the impact linkages between these pressures, the resulting environmental state of soils, and potential interventions to protect soil and reverse degradation. New research on soil processes is being driven by the scientific hypothesis that soil processes can be described along a life cycle of soil development. This begins with formation of new soil from parent material, development of the soil profile, and potential loss of the developed soil functions and the soil itself under overly intensive anthropogenic land use, thus closing the cycle. Four Critical Zone Observatories in Europe have been selected focusing research at sites that represent key stages along the hypothetical soil life cycle; incipient soil formation, productive use of soil for farming and forestry, and decline of soil due to longstanding intensive agriculture. Initial results from the research show that soil develops important biogeochemical properties on the time scale of decades and that soil carbon and the development of favourable soil structure takes place over similar time scales. A new mathematical model of soil aggregate formation and degradation predicts that set-aside land at the most degraded site studied can develop substantially improved soil structure with the accumulation of soil carbon over a period of several years. Further results demonstrate the rapid dynamics of soil carbon; how quickly it can be lost, and also demonstrate how data from the CZOs can be used to determine parameter values for models at catchment scale. A structure for a new integrated Critical Zone model is proposed that combines process descriptions of carbon and nutrient flows, a simplified description of the soil food web, and reactive transport; all coupled with a dynamic model for soil structure and soil aggregation. This approach is proposed as a methodology to analyse data along the soil life cycle and test how soil processes and rates vary within, and between, the CZOs representing different life cycle stages. In addition, frameworks are discussed that will help to communicate the results of this science into a more policy relevant format using ecosystem service approaches.
[Show abstract][Hide abstract] ABSTRACT: Little is known about atmospheric input of beryllium (Be) into ecosystems, despite its highly toxic behavior. For three consecutive winters (2009-2011), we measured Be concentrations in horizontal deposition (rime) and vertical deposition (snow) at 10 remote mountain-top locations in the Czech Republic, Central Europe. Beryllium was determined both in filtered waters, and in HF digests of insoluble particles. Across the sites, soluble Be concentrations in rime were 7 times higher, compared to snow (6.1 vs. 0.9ng·L(-1)). Rime scavenged the pollution-rich lower segments of clouds. The lowest Be concentrations were detected in the soluble fraction of snow. Across the sites, 34% of total Be deposition occurred in the form of soluble (bioavailable) Be, the rest were insoluble particles. Beryllium fluxes decreased in the order: vertical dry deposition insoluble>vertical dry deposition soluble>horizontal deposition soluble>vertical wet deposition insoluble>vertical wet deposition soluble>horizontal deposition insoluble. The average contributions of these Be forms to total deposition were 56, 21, 8, 7, 5 and 3%, respectively. Sites in the northeast were more Be-polluted than the rest of the country with sources of pollution in industrial Silesia.
Science of The Total Environment 10/2012; 439C:26-34. DOI:10.1016/j.scitotenv.2012.08.089 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Slightly elevated concentrations of toxic species in waters sampled in the surroundings of a leaky landfill may be both a sign of an approaching contaminant plume, or a result of water-rock interaction. Isotopes can be instrumental in distinguishing between anthropogenic and geogenic species in groundwater. We studied sulfur and lead isotope ratios at an abandoned industrial-waste landfill, located in a densely populated part of Central Europe. Stable isotope variability in space and time was used to follow the movement of a groundwater plume, contaminated with toxic metals (Cd, Cr, Be), in fractured granitoids. Toxic metals had been mobilized from industrial waste by a strong pulse of sulfuric acid, also deposited in the landfill. Both tracers exhibited a wide range of values (δ(34)S between +2.6 and +18.9‰; (206)Pb/(207)Pb between 1.16 and 1.39), which facilitated identification of mixing end-members, and made it possible to assess the sources of the studied species. In situ fractionations did not hinder source apportionment. Influx of contaminated groundwater was observed neither in irrigation wells in a nearby village, nor at distances greater than 300m from the landfill. Combination of stable isotope tracers can be used as part of an early-warning system in landscapes affected by landfills.
[Show abstract][Hide abstract] ABSTRACT: Here we report chromium isotope compositions, expressed as δ53Cr
relative to NIST 979, measured in selected Cr-bearing geological
materials formed by igneous, hydrothermal and metamorphic processes. The
δ53Cr variations were determined by MC-ICP-MS (NEPTUNE and
Isoprobe P) using a double spike enriched in 50Cr and 54Cr.
Specifically, we analyzed δ53Cr in chromite deposits sampled from
mafic/ultramafic igneous complexes in Europe (Norway, Austria, Poland,
Cyprus, Turkey), Russia (Ural), Kazakhstan (Chromtau), New Caledonia
(Tiebaghi), Cuba (Rio Cayo Guam), and South Africa (Bushveld Complex).
These globally distributed chromite deposits share a uniform Cr isotope
composition with an average δ53Cr of 0.050±0.182% (2SD, n =
19), with respect to the NIST 979 that yielded -0.006±0.172% (n =
32). Considering that most of the Cr used in industry is produced from
these large chromite deposits, their bulk δ53Cr signature of ~0%
thus represents an important reference point for the environmental
studies investigating Cr contamination related to industrial sources. In
contrast, samples of hydrothermal lead chromates, i.e. crocoites
(PbCrO4), collected in Germany (Calenberg), Russia (Beresovsk), Brazil
(Minas Gerais), and Tasmania (Dundas), yielded heavier δ53Cr
signatures spanning from 0.115±0.181% up to 2.071±0.151%.
The heavy Cr isotope enrichment found in crocoites is in agreement with
the results of Schoenberg et al. (2008, Chem. Geol. 249, 294-306).
Interestingly, a crocoite specimen from 'Beresovsk' analyzed by the
latter study gave δ53Cr of 1.007±0.049%, which is identical
with our analysis of a crocoite from the same locality that yielded
δ53/52Cr of 1.046±0.086%. As to the alteration products of
mafic/ultramafic rocks, a sample of serpentinite from Slovakia (Dobsina)
showed slightly heavier δ53Cr signature of 0.248±0.055%,
compared to a 'primary' mantle-derived chromium (δ53Cr ≈ 0%),
suggesting that metamorphism and aqueous alteration can induce a
considerable Cr isotope fractionation. This seems to be corroborated by
the analysis of other post-metamorphic/hydrothermal Cr-rich minerals,
such as chrome-tremolite and chrome-diopside (Finland), which both gave
heavy δ53Cr values of 0.250±0.119% and 0.608±0.010%,
respectively. A similarly heavy δ53Cr value of 0.515±0.122%
was measured in a sample of chrome chalcedony from an ultramafic
intrusion in Western Australia (Newman). On the other hand, a sample of
stichtite (Morocco, Bou Azzer), which is formed as an alteration product
in serpentines, gave a 'mantle-like' δ53Cr signature of
0.038±0.123%. One possible explanation for the heavy isotope
enrichments of Cr-bearing minerals from metamorphic-hydrothermal
systems, is that a portion of the dissolved Cr present in a
mineral-forming fluid was reduced to Cr (III), prior to the formation of
a mineral, causing a shift of the residual Cr in the fluid towards
heavier δ53Cr (cf. Schoenberg et al. 2008). Alternatively, the
δ53Cr of the metamorphic-hydrothermal fluid was already heavy at
the time of the fluid formation, due to preferential partitioning of the
isotopically heavy Cr(VI) into the fluid at the mineral-water interface.
[Show abstract][Hide abstract] ABSTRACT: Plant-available reserves of major base cations, Ca2+ and Mg2+, decreased markedly in soils over the past century, thus posing a potential threat to forest ecosystem health. Trees are thought to obtain dissolved Ca2+ ions mainly from an easily accessible soil–water reservoir also termed the ‘exchangeable cation pool’. The status of Ca reserves in this soil pool is sensitive to anthropogenic perturbations such as soil acidification induced by acid rain and/or excessive timber harvesting. Here we show that in a base-poor forest of the northeastern USA (i.e. Wachusett Mountain, Massachusetts) the ‘exchangeable Ca pool’ of deeper mineral soils has a unique isotope signature that is significantly enriched in the radiogenic 40Ca, due to the dissolution of K-rich silicate minerals such as biotite. Using a simple isotope mass balance, and assuming that the input of Ca from biotite has a εCa signature of ∼16, the results of our calculation indicate that the weathering of biotite may supply a sizeable fraction, up to 25%, of Ca2+ ions into the ‘exchangeable cation pool’ of deeper mineral soils. Importantly, samples of local vegetation (i.e. woody tissues of red oak) show no detectable excess of the radiogenic 40Ca, and based on our model the upper limit of a possible biotite-derived Ca contribution in vegetation is estimated at ∼5%. We also found no evidence of the radiogenic 40Ca signal in the samples of forest floor and the uppermost organic-rich soils (0–15cm depth), which in turn suggest that over the long-term development of the forest and its organic matter accumulation, the vegetation growth must have also relied primarily on the non-radiogenic Ca sources. Based on our experimental data, such sources may include (i) wet atmospheric deposition, (ii) the organically-complexed Ca in topsoil horizons, and (iii) chemical weathering and/or fungal-mediated dissolution of apatite and Ca-rich plagioclase. Hence, our stable and radiogenic Ca isotope data indicate that the studied base-poor forest is able to bypass the ‘exchangeable cation pool’ of deeper (i.e. below 15cm) mineral soils, and still manages to meet its nutritional requirements with respect to Ca. Another important implication of this study is that the organically-complexed Ca in the topsoil horizon (0–15cm depth) has to be tightly bound to the ion exchange sites, otherwise the large radiogenic 40Ca signatures present in the ‘exchangeable cation pool’ of deep mineral soils would be swamped by the downward gravitational flux of non-radiogenic Ca from the decaying organic matter and litterfall. Hence, the limited mobility of the organically-complexed Ca in soils and its tight biological cycling could explain the lack of a significant impact of vegetation on the Ca isotope systematics observed in large rivers.
[Show abstract][Hide abstract] ABSTRACT: The biogeochemical cycles of most toxic metals have been significantly altered by anthropogenic activities. Anaerobic, rain-fed organic soils are believed to record historical changes in atmospheric pollution. Suspected postdepositional mobility of trace elements, however, hinders the usefulness of peat bogs as pollution archives. To lower this uncertainty, we quantified the mobility of six trace metals in peat during an 18-month field manipulation. A replicated, reciprocal peat transplant experiment was conducted between a heavily polluted and a relatively unpolluted peatland, located 200 km apart in the Czech Republic (Central Europe). Both peatlands were Sphagnum-derived, lawn-dominated, and had water table close to the surface. A strikingly different behavior was observed for two groups of elements. Elements of group I, Fe and Mn, adjusted their abundances and vertical patterns to the host site, showing an extremely high degree of mobility. In contrast, elements of group II, Pb, Cu, Zn, and Ti, preserved their original vertical patterns at the host site, showing a high degree of immobility. Our experimental results suggest that not just lead, but also copper and zinc concentration profiles in peat are a reliable archive of temporal pollution changes within a wide pH range (2.5-5.8).