Atmospheric mineral dust not only interacts with the climate system by scattering incoming solar radiation and affecting atmospheric photochemistry, but also contributes critical nutrients to marine ...and terrestrial ecosystems. In a high-resolution analysis of paleodust deposition, peat development and soil dust sources, we assess the interplay between dust deposition and bog development of the Davidsmosse bog in south-western Sweden. Analyses of the 5400-year record (458 cm) included radiocarbon dating, bulk density, ash content, chemical and mineralogical composition and carbon stable isotopes, subsequently explored using principal component analysis. Fourteen dust events (DEs) were recorded (cal BP) in the peat sequence: 3580–3490; 3280; 3140; 3010–2840; 2740; 2610; 2480; 2340; 2240–2130; 1690; 1240; 960, 890–760, and 620–360. The majority of the DEs were coupled to increases in peat accumulation rates and increased nutrient content (N, P and K) suggesting that the DEs contributed with nutrients to the bog ecosystem, promoting increased accumulation. We also analyzed the chemical and mineral composition of potential mineral source deposits (separated into 6 grain-size fractions) from sites within a 4 km radius as well as aeolian dunes closer to the coast (25 km). The composition deposited on the present-day bog surface indicates that the bulk of the contemporary minerals have a local origin (<1.5 km), but the DEs may be of a more distant origin. The results also indicate that quartz and plagioclase feldspar content consistently increase with increasing grain-size, both in the source samples as well as in the peat sequence, and that the Si/Al ratio can be used to infer grain size changes in the peat. Two longer phases saw numerous DEs, between 2800 and 2130 cal BP and a stepwise increase from 960 towards 360 cal BP. The episodic character of the events, together with the inferred coarse grain size, suggest that the particles were deposited by (winter) storms. Future studies should include grain size analysis as well as a more in-depth comparison with regional paleo dust and storm records to increase knowledge on both transport processes (creep, saltation, suspension) and the climate processes driving late Holocene dust and storm events in Scandinavia.
The composition of sediment organic matter (OM) exerts a strong control on biogeochemical processes in lakes, such as those involved in the fate of carbon, nutrients and trace metals. While ...between-lake spatial variability of OM quality is increasingly investigated, we explored in this study how the molecular composition of sediment OM varies spatially within a single lake and related this variability to physical parameters and elemental geochemistry. Surface sediment samples (0–10 cm) from 42 locations in Härsvatten – a small boreal forest lake with a complex basin morphometry – were analyzed for OM molecular composition using pyrolysis gas chromatography mass spectrometry for the contents of 23 major and trace elements and biogenic silica. We identified 162 organic compounds belonging to different biochemical classes of OM (e.g., carbohydrates, lignin and lipids). Close relationships were found between the spatial patterns of sediment OM molecular composition and elemental geochemistry. Differences in the source types of OM (i.e., terrestrial, aquatic plant and algal) were linked to the individual basin morphometries and chemical status of the lake. The variability in OM molecular composition was further driven by the degradation status of these different source pools, which appeared to be related to sedimentary physicochemical parameters (e.g., redox conditions) and to the molecular structure of the organic compounds. Given the high spatial variation in OM molecular composition within Härsvatten and its close relationship with elemental geochemistry, the potential for large spatial variability across lakes should be considered when studying biogeochemical processes involved in the cycling of carbon, nutrients and trace elements or when assessing lake budgets.
•Depth records of C/N, markers for lignin, cellulose and sphagnum acid are compared for peat cores.•Their relation to bog hydrology is established in five peatlands from different climatic ...zones.•Under aerobic conditions polyphenols degrade faster than polysaccharides in Sphagnum peat.•4-Isopropenylphenol reflects past hydrological conditions in Sphagnum peat.•Interpretation of vegetation and decomposition proxies in Sphagnum peat is site-dependent.
The net accumulation of remains of Sphagnum spp. is fundamental to the development of many peatlands. The effect of polyphenols from Sphagnum on decomposition processes is frequently cited but has barely been studied. The central area of the Rödmossamyran peatland (Sweden) is an open lawn that consists mostly of Sphagnum spp. with a very low contribution from vascular plants. In order to determine the effects of decay on sphagnum phenols, 53 samples of a 2.7m deep core from this lawn were analysed with pyrolysis gas chromatography–mass spectrometry (pyrolysis-GC–MS) and compared with more traditional decomposition proxies such as C/N ratio, UV light transmission of alkaline peat extracts, and bulk density. Factor analysis of 72 quantified pyrolysis products suggested that the variation in 4-isopropenylphenol was largely determined by aerobic decomposition instead of Sphagnum abundance. In order to evaluate the effects of aerobic decay in Sphagnum peat, down-core records from different climatic regions were compared using molecular markers for plant biopolymers and C/N ratio. These included markers for lignin from vascular plants ((di)methoxyphenols), polyphenols from Sphagnum spp. (4-isopropenylphenol), and cellulose (levoglucosan). Our results indicate that polyphenols from Sphagnum are preferentially degraded over polysaccharides; consequently the variability of the marker for sphagnum acid, 4-isopropenylphenol, was found indicative of decomposition instead of reflecting the abundance of Sphagnum remains. The fact that 4-isopropenylphenol is aerobically degraded in combination with its specificity for Sphagnum spp. makes it a consistent indicator of past hydrological conditions in Sphagnum-dominated peat. In contrast, the variability of C/N records in Sphagnum-dominated peat was influenced by both vegetation shifts and decomposition, and the dominant effect differed between the studied peatlands. Our results provide direction for modelling studies that try to predict possible feedback mechanisms between peatlands and future climate change, and indicate that the focus in Sphagnum decay studies should be on carbohydrates rather than on phenolic compounds.
Lake burial of carbon has increased threefold over the last 150 years in response to human disruption of global nutrient cycles.
Lakes have a disproportionate effect on the global carbon (C) cycle ...relative to their area, mediating C transfer from land to atmosphere, and burying organic-C in their sediments. The magnitude and temporal variability of C burial is, however, poorly constrained, and the degree to which humans have influenced lake C cycling through landscape alteration has not been systematically assessed. Here, we report global and biome specific trajectories of lake C sequestration based on 516 lakes and show that some lake C burial rates (i.e., those in tropical forest and grassland biomes) have quadrupled over the last 100 years. Global lake C-sequestration (~0.12 Pg year
−1
) has increased by ~72 Tg year
−1
since 1900, offsetting 20% of annual CO
2
freshwater emissions rising to ~30% if reservoirs are included and contributing to the residual continental C sink. Nutrient availability explains ~70% of the observed increase, while rising temperatures have a minimal effect.
We compare lead concentration and stable lead isotope analyses from three peat bog and three lake sediment records in Sweden. Radiocarbon dated stratigraphies give evidence that trends in the ...concentration of Pb in the peat and sediment cores are very similar, and follow the general outline of historical global Pb production over several thousand years. Due to the large difference in the 206Pb/207Pb ratio between Sweden, about 1.5, and continental Europe (excluding Fennoscandia), ,1.2, it is possible to distinguish external sources of Pb to Sweden. In the lake sediments, profiles of 206Pb/207Pb ratio mirror the Pb concentration until 1000 AD; increasing concentration is accompanied by decreasing ratios. After 1000 AD the ratio varies little at about 1.2 in sediments, because of the near total dominance of pollutant Pb. There is a further decline in the Pb ratio to about 1.14 in this century as a result of the addition of alkyl-Pb in petrol. The Pb concentration profiles in the peat match the lakes, but the isotope profiles do not. During the fen-to-bog transition there is a rapid decline in the 206Pb/207Pb ratio from >1.3 to about 1.2, and the ratio continues to decline to the present. We hypothesise that this is because externally-derived Pb from long-range transport of soil dust and atmospheric pollution has always been more important in the ombrotrophic peat than in lakes, which have a greater influx of catchment-derived Pb.
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•We studied copper (Cu) and silver (Ag) deposition in lake sediment.•Two sediment cores from Lake Titicaca provide a ∼2400 years history of metallurgy.•Pb isotopic fingerprinting ...allowed identifying ore sources in the central Andes.•Tiwanaku copper mining was performed by smelting of local ores.•Late intermediate, Inca and Colonial mining was performed in the Potosi region.
Copper, silver, and gold exploitation has been a foundation of economic and socio-cultural development of Andean societies, at least for the last three millennia. The main centers of pre-colonial metallurgy are well-known from archeological artifacts, but temporal gaps inherent in this record handicap a finer understanding of the modalities of ore exploitation by succeeding civilizations. A continuous record over time of trace metals emitted during ore smelting operations make lake sediments excellent candidates to fill those gaps. Two millennia of metallurgy were reconstructed from atmospherically derived metals together with lead (Pb) isotope ratios in two dated sediment cores from Lake Titicaca. The first evidence for metallurgy is found during the apogee of the Tiwanaku state (AD 800–1150), with a higher copper (Cu) accumulation that can be attributed to the smelting of local Cu ores, based on Pb isotopic fingerprinting. During the Late Intermediate Period (AD 1150–1450), recorded peaks in metal deposition that persisted for ∼ twenty years show that mining activities were intensive but discontinuous. Pb isotope ratios suggest diversified extractive activities, mainly located in the southern part of the central Altiplano. Finally, the most intense mining epoch began during the Inca Empire (ca. AD 1500) and lasted until the end of the Colonial Period (AD 1830), with unprecedented metal deposition over this interval. Pb isotope fingerprinting shows that mining operations occurred mainly in the Lake Titicaca and Potosi areas and were responsible for metal emissions recorded in the entire Altiplano, as evidenced by other studies.
Metal pollution is viewed as a modern problem that began in the 19th century and accelerated through the 20th century; however, in many parts of the globe this view is wrong. Here, we studied past ...waterborne metal pollution in lake sediments from the Bergslagen region in central Sweden, one of many historically important mining regions in Europe. With a focus on lead (including isotopes), we trace mining impacts from a local scale, through a 120-km-long river system draining into Mälaren – Sweden's third largest lake, and finally also the Baltic Sea. Comparison of sediment and peat records shows that pollution from Swedish mining was largely waterborne and that atmospheric deposition was dominated by long-range transport from other regions. Swedish ore lead is detectable from the 10th century, but the greatest impact occurred during the 16th–18th centuries with improvements occurring over recent centuries, i.e., historical pollution
>
modern industrial pollution.
Pollution in Sweden during AD 900–1900 was often greater than modern industrial pollution.
Recent research has recognized the utility of the peat record in ombrotrophic bogs to reconstruct past changes in the atmospheric deposition of, for example, lead and mercury. Frequently, these ...reconstructions rely only on single peat records to make assessments of regional deposition rates. The surface of a bog is not a uniform feature; rather, vegetation and micro‐topography vary over small spatial scales, which can affect the interception and retention of atmospheric deposition, and over relatively short timescales. Analyses of nine hummock cores collected from a 2000 m2 area on one bog, Store Mosse, show that concentrations and cumulative inventories (past 110 years) of lead and mercury vary by a factor of 2 for lead (0.75 to 1.40 g Pb m−2, three cores) and 4 for mercury (0.85 to 3.4 mg Hg m−2, nine cores). The range of values within Store Mosse is greater than the difference between any one core and the metal inventories from either Dumme Mosse (0.95 g Pb m−2 and 2.0 mg Hg m−2) or Trollsmosse (1.6 mg Hg m−2), each about 60 km distant. Although the general temporal trends are similar in all cores, our data indicate that single reconstructions do not necessarily provide a representative flux for the bog as a whole. To overcome the potential constraints of single records, we suggest incorporating data from multiple sites or at least multiple cores in order to scale up to regionally valid models of past metal deposition.
Knowledge about the natural atmospheric background deposition rate of lead (Pb) prior to anthropogenic pollution is critical in the understanding of present‐day pollution and for establishing ...realistic goals for the reduction of atmospheric Pb. We utilize stable Pb isotopes (206Pb and 207Pb) in radiocarbon‐dated peat cores from three ombrotrophic bogs from south Sweden, to calculate fluxes and to survey atmospheric Pb trends prior 3500 BP (the so far known onset of large‐scale anthropogenic pollution). The estimated atmospheric Pb deposition rate was between 1 and 10 μg Pb m2 yr−1 between 5900 and 3700 calendar years BP, which is 100 to 1000 times lower than present‐day deposition rates. The majority of the samples older than 3500 calendar years BP had 206Pb/207Pb ratios ≤1.20, which is significantly lower than unpolluted Swedish mineral soils (206Pb/207Pb > 1.30), suggesting that even the natural atmospheric deposition of Pb was dominated by long‐range transport, rather than local inputs from soil dust. Low 206Pb/207Pb ratios (1.16–1.18) of several samples indicate that this distant transport originated at least partly from early pollution sources. A possible climatic connection with the observed Pb deposition trends is suggested.
Knowledge about the residence time of lead in the organic horizon (mor layer; O-horizon) overlaying forest mineral soils is important for the prediction of past and future lead levels in the boreal ...environment. To estimate the mean residence time (MRT) of lead in the mor layer, we use in this study from Northern Sweden three different approaches: (1) lead-210 is applied as a tracer of lead migration; (2) estimations of loss rates of stable lead (concentrations and ²⁰⁶Pb/²⁰⁷Pb ratios) from the mor layer at an undisturbed forest setting, and (3) a study of lead in a soil series with sites of different age (a chronosequence of 20-220 years). In the last two approaches we compared measured inventories in the soil with estimated inventories derived using analyses of lake sediments. The results suggested a MRT of about 250 years in the mor layer in the mature forest and in the older parts of the chronosequence it was at least >170 years. The agreement between the three different approaches gives good credibility to this estimate. It is also supported by a modeling of trends in the ²⁰⁶Pb/²⁰⁷Pb ratio both between single cores and with depth in the mor layer. Our results suggest that it will take centuries for the deeper parts of the mor layer of undisturbed boreal forest soils to fully respond to decreased atmospheric lead pollution. However, data from the chronosequence indicate that the response could be much faster (MRT< 50 years) in the mor layer at early stages of forest succession where graminoid and broadleaved litter fall dominates over conifer litter.
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