Peat Geochemistry Research Articles

Steady and ebullitive methane fluxes from active, restored and unrestored horticultural peatlands

Peatlands used for horticultural peat extraction lose their ecological function of carbon accumulation. While their restoration has been shown to increase methane (CH4) flux compared to unrestored sites, the time required for CH4 balance to recover and the factors affecting the recovery remain unclear. We quantified CH4 emissions from restored sites with different time since restoration efforts began (5, 8 and 25 years prior to the study), an unrestored post-extraction (Unrestored) and actively extracted (Active) sites, and compared them to CH4 emission from a natural boreal bog (Natural). All study sites were located within one horticulture peatland complex in central Alberta, Canada. Both steady (diffusive and steady ebullitive) fluxes and abrupt ebullitive events were determined using manual chambers and a portable greenhouse gas analyzer. Methane emissions were greater at the restored sites than at the Natural, Unrestored, and Active sites. Abrupt ebullition occurred only at two restored sites that were flooded/water saturated, dominated by vascular plants, and had the highest steady fluxes. Ebullition accounted for 7% of total CH4 emission at the site restored in 1991 (25–26 years post-restoration), and 6% at the site restored in 2012 (4–5 years post-restoration). Despite shallow water table and dense sedge cover, the third restored site (7–8 years post-restoration), showed no abrupt ebullition and mean steady flux lower than at the Natural site, likely caused by peat geochemistry. At sites where it occurred, ebullition was significantly positively but weakly correlated with CH4 flux, concentration of CH4 in pore water, soil temperature, water table (WT), gross ecosystem production , and percentage cover of moss. Steady CH4 fluxes were higher when soil temperature at 20 cm depth was higher, WT shallow, and with greater plant productivity and cover of graminoids, but lower with higher shrub cover. Peat chemical characteristics can supersede these environmental factors and suppress CH4 emission even in restored, wet, and sedge-dominated sites. Restored sites with more fen-like conditions (wet and sedge-dominated) are likely to have abrupt ebullition events and higher CH4 fluxes than undisturbed bogs, with local controls seemingly more important than time since restoration on resulting CH4 emission.

Influence of transboundary transport of trace elements on mountain peat geochemistry (Sudetes, Central Europe)

Mountain ombrotrophic peatlands in Central Europe are an important stock of transboundary contamination both of natural and anthropogenic origin. The Śnieżka Mountain (West Sudetes) forms a significant orographic barrier and receives aerosols from broadly-recognized anthropogenic sources (production and use of stainless steel, processing of uranium, coal combustion, nuclear weapon tests, and Chernobyl accident). The main objective of the study was to assess the pattern of distribution and origin of trace elements and to distinguish the long-range transport vs. local signals in two 210Pb and 14C – dated peat cores from the highest summit of the Karkonosze (West Sudetes) spanning the last 280 years.Maximum values and accumulations of almost all investigated elements (Pb, Zn, Cu, Ni, Cr, Ti, Al, U, Sc, and REE) were identified around the 1970s. The analysis of peat using scanning electron microscopy (SEM) confirmed the occurrence of spheroidal aluminosilicate fly ash particles (SAP) in the topmost 40 cm (from AD 1938) together with a maximum of mullite (3Al2O3·2SiO2), an anthropogenic marker originating from coal-based power plants. The overall 206Pb/207Pb signature ranges from 1.160 to 1.173, indicating a predominant contribution of anthropogenic Pb. Human activities promote the release of mobile 234U, due to the weaker bonds to mineral structure, and cause the radiogenic disequilibrium between 238U and its daughter 234U.

Runoff events and related rainfall variability in the Southern Carpathians during the last 2000 years

The occurrence of heavy rainfall events is expected to undergo significant changes under increasing anthropogenic forcing. South-eastern Europe is reacting rapidly to such changes, therefore understanding and forecasting of precipitation variability is vital to better comprehending environmental changes in this area. Here we present a sub-decadal reconstruction of enhanced rainfall events for the past 2000 years from the Southern Carpathians, Romania using peat geochemistry. Five clear periods of enhanced rainfall are identified at 125–250, 600–900, 1050–1300, 1400–1575 and 1725–1980 CE. Significant runoff is observed during the second half of the Medieval Warm Period, whilst the Little Ice Age was characterised by significant variability. The North Atlantic Oscillation appears to be the main control on regional precipitation, but changes in solar irradiance also seem to play a significant role, together with the Siberian High. Comparison of the data presented here with model outputs confirms the ability of models to predict general trends, and major shifts, but highlights the complexity of the region’s hydrological history.

Predominance of methanogens over methanotrophs in rewetted fens characterized by high methane emissions

Abstract. The rewetting of drained peatlands alters peat geochemistry and often leads to sustained elevated methane emission. Although this methane is produced entirely by microbial activity, the distribution and abundance of methane-cycling microbes in rewetted peatlands, especially in fens, is rarely described. In this study, we compare the community composition and abundance of methane-cycling microbes in relation to peat porewater geochemistry in two rewetted fens in northeastern Germany, a coastal brackish fen and a freshwater riparian fen, with known high methane fluxes. We utilized 16S rRNA high-throughput sequencing and quantitative polymerase chain reaction (qPCR) on 16S rRNA, mcrA, and pmoA genes to determine microbial community composition and the abundance of total bacteria, methanogens, and methanotrophs. Electrical conductivity (EC) was more than 3 times higher in the coastal fen than in the riparian fen, averaging 5.3 and 1.5 mS cm−1, respectively. Porewater concentrations of terminal electron acceptors (TEAs) varied within and among the fens. This was also reflected in similarly high intra- and inter-site variations of microbial community composition. Despite these differences in environmental conditions and electron acceptor availability, we found a low abundance of methanotrophs and a high abundance of methanogens, represented in particular by Methanosaetaceae, in both fens. This suggests that rapid (re)establishment of methanogens and slow (re)establishment of methanotrophs contributes to prolonged increased methane emissions following rewetting.

Effects of warming and increased nitrogen and sulfur deposition on boreal mire geochemistry

Boreal mire ecosystems are predicted to experience warmer air temperatures as well as changed deposition loads of nitrogen and sulfur during the coming century. In this study, we hypothesized that vegetation changes that accompany these new environmental conditions alter the chemical composition of peat. To test this hypothesis, we quantified changes in peat geochemistry (Al, Ca, Fe, Mg, Na, P, Pb, and Zn) that have occurred in field manipulation plots exposed to 12 years of warming and nitrogen and sulfur additions in a nutrient-poor boreal mire. In contrast to non-nutrients with a mainly atmospheric origin (i.e. Pb), Al-normalized inventories of micronutrients (Zn and Fe) and macronutrients (P and Ca) were significantly (P < 0.05) higher as a result of warming. For P and Ca, enrichments were also induced by nitrogen additions alone. These results suggest that mires evolving under increasing temperatures and availability of nitrogen are around two times more effective in storing nutrients in the accumulating peat. Our study provides the first empirical evidence that predicted changes in climate and nitrogen deposition scenarios will increase the retention of Ca, Fe, P, and Zn in surface peat of boreal mires in the near future, which may cause a depletion of nutrients released to inland waters dependent on mire inputs.

A Geochemical Signal from a Mesolithic Intertidal Archaeological Site: A Proof‐of‐Concept Study from Clachan Harbor, Scotland

This paper presents the results of multielemental mapping conducted on peat samples taken from a presumed Mesolithic coastal activity zone at the intertidal site of Clachan Harbor, Scotland. The aim of the study was to use peat geochemical analysis to assess possible evidence for an anthropogenic chemical signal within the peat that might be linked to the use of the site during the Mesolithic. Spatial changes in peat geochemistry revealed a “change point” within the peat bed that may reflect the former boundary between the human activity zone and the coastline. Enhanced dating of events was achieved by integrating the chemical dataset with an existing relative sea‐level curve available for the site. The research demonstrates the advantages of using a multielemental method ahead of a single‐element (e.g., phosphorous‐only) approach when attempting to characterize and trace chemical evidence for past human activity in the intertidal zone. This paper will hopefully lead to the adoption of an improved methodology that can help us to better understand the development of coastal sites within an archaeological context.

Postglacial shifts in lake trophic status based on a multiproxy study of a humic lake

The long-term development of a humic lake ecosystem in Poland was investigated via palaeoecological analyses of age-dated sediment cores. Peat and lacustrine deposit records spanning approximately 12,000 years of lake history were analysed with regard to palynomorphs, plant macrofossils, degree of peat decomposition, Cladocera and geochemistry. Our study demonstrated the difficulty of classifying sediments deposited in humic lakes. We considered it inadequate to classify dy sediment exclusively using macroscopic criteria in the absence of geochemical parameters. Our study of the palaeoecology of the humic lake suggested three primary shifts in its trophic status: from oligotrophy to mesotrophy (Allerød-Boreal), to eutrophy (Atlantic), and to humotrophy (from the Sub-Boreal to the present). The results indicated that shifts in the trophic status occurred in response to climatic changes and factors linked to the catchment. The transformation from a clearwater lake of high trophic status to a humic lake was possible, such that the latter may originate not only from an oligotrophic lake. As a result of our pioneering study, we determined that a humic water body may even develop because of transformation of a eutrophic lake.

Environmental processes in Rano Aroi (Easter Island) peat geochemistry forced by climate variability during the last 70 kyr

We analyze the geochemistry of Rano Aroi mire record (Easter Island) using bulk peat composition (C, N, S) and stable isotopes (δ13C, δ15N, δ34S) and major, minor and trace elemental compositions obtained by ICP-AES (Al, Ti, Zr, Sc, V, Y, Fe, Mn, Th, Ba, Ca, Mg and Sr). Peat geochemistry and the pollen record are used to reconstruct the environmental changes during the last 70kyr BP. Principal component analysis on ICP-AES data revealed that three main components account for the chemical signatures of the peat. The first component, characterized by lithogenic elements (combined signal of V, Al, Sc, Y, Cr, Cd, Ti, Zr and Cu), evidences long-term changes in the basal fluxes of mineral material into the mire. This component, in combination with stable isotopes and pollen data suggests a link between soil erosion and vegetation cover changes in the Rano Aroi watershed. The second component is identified by the signal of Fe, Mn, Th, Ba, Zr and Ti, and is indicative of strong runoff events during enhanced precipitation periods. The third component (tied mainly to Ca, Sr and Mg) reflects a strong peat oxidation event that occurred during an arid period with more frequent droughts, sometime between 39 and 31kyr BP. Correlation coefficients and a multiple regression model (PCR analysis) between peat organic chemistry and the principal components of ICP-AES analysis were calculated. Isotope chemistry of the peat organic matter further contributes to define Rano Aroi environmental history: δ13C data corroborates a vegetation shift documented by the palynological record from C4 to C3 between 55 and 45calkyr BP; the δ15N record identifies periods of changes in mire productivity and denitrification processes, while the δ34S peat signature indicates a marine origin of S and significant diagenetic cycling. The geochemical and environmental evolution of Rano Aroi mire is coherent with the regional climatic variability and suggests that climate was the main forcing in mire evolution during the last 70kyr BP. The coupling of geochemical and biological proxies improves our ability to decipher depositional processes in tropical and subtropical peatlands and to use these sequences for paleoenvironmental and paleoclimate reconstructions.

Exploitation of peat geochemistry to reconstruct past hydrological and biogeochemical variations during the late Holocene

Exploitation of peat geochemistry to reconstruct past hydrological and biogeochemical variations during the late Holocene

An integrated geochemical and palynological study of human impacts, soil erosion and storminess from southern Greenland since c. AD 1000

An integrated pollen-analytical and geochemical study is presented from Qinngua Kangilleq, southwest Greenland. This site was formerly one of the largest farms in the Eastern Settlement of Norse Greenland. The study is the first to determine what link, if any, exists between Norse landnám (early settlement), vegetation change, soil erosion, climate change and peat geochemistry. The data suggest that fluxes in lithogenic elements supplied to a peat column by terrestrial sources and atmospheric deposition were coupled to the pattern of local Norse settlement beginning ∼ cal. AD 1020. A severe phase of soil erosion is indicated which is coincident with the landnám horizon. This may represent proxy evidence for the stripping of turf for the construction of turf-and-stone buildings at the farm. Radiocarbon dates suggest the presence of a hiatus in the sediment column spanning ∼ cal. AD 1380–1950. Following the recommencement of sediment accumulation, the geochemical data indicate a critical change in site conditions which may be consistent with the well-known change in Northern Hemisphere atmospheric circulation that started between c. AD 1400 and 1420. Bromine (Br) and chlorine (Cl) concentrations are demonstrably higher in the sediments dating to the 20th century relative to the pre-15th century deposits. Rising halogen concentrations at Qinngua appear to be correlated with increased levels of Na +(sea salt sodium) precipitation in the GISP2 ice core which earlier studies have interpreted as indicative of increased North Atlantic storminess.

Long term mobilisation of chemical elements in tephra-rich peat (NE Iceland)

This paper presents geochemical profiles of a tephra-bearing minerotrophic peat column from NE-Iceland obtained using various elemental analyses of the solid phase and the pore water. The influence of tephra grain size, thickness and composition of each tephra on the peat geochemistry was investigated. Interpretations are supported by a statistical approach, in particular by autocorrelation, and by microscopy observations. Minerotrophic peat geochemistry may be strongly dependent upon post-depositional mobilization and possible leaching of elements as demonstrated by Fe and trace metal concentration profiles. Chemical elements, and more specifically potentially harmful metals, can be slowly leached out of volcanic falls during their weathering and re-accumulate downwards. It is emphasised that a tephra deposit can act as an active geochemical barrier, blocking downward elemental movements and leading to the formation of enriched layers. In this study, the formation of poorly amorphous Fe phases above the Hekla 3 tephra is shown. These poorly crystalline Fe phases scavenged Ni.

The Geochemistry of Ombrotrophic Sphagnum Species Growing in Different Microhabitats Of Eight German and Belgian Peat Bogs and the Regional Atmospheric Deposition

Comparing today’s atmospheric deposition records with the elemental concentration and the net-uptake rates of ombrotrophic Sphagnum mosses from eight German and Belgian peat bogs revealed that most of all the quality and number of regularly obtained deposition monitoring data is not satisfactory. Moreover, it seems likely that the deposition rate, determined by Sphagnum mosses, does not reliably reflect the record of the total open field deposition indicated by the deposition monitoring data. The moss data, too, show a distinct spatial variability possibly because the geochemistry of peat mosses differs according to the annual growth in height, the total surface area and the surface roughness of the receptor ‘peat moss’ (special interception deposition). Increased Ti concentration values, for example, combined with a high annual growth rate in height at the hollow moss S. cuspidatum resulted in generally high Ti net-uptake rates and a high Ti inventory (total Ti in sample). We, therefore, suggest that productive Sphagnum species might be able to fix more Ti particles on their larger surface area than less productive species do. Moreover, the results demonstrate that for reliably calculating Sphagnum elemental net-uptake rates, as well as for all quantification of Sphagnum or peat geochemistry on a time and area basis, an accurate knowledge of the period the collected samples were exposed to atmospheric deposition is required. In particular, to do reliable reconstructions of past atmospheric deposition rates using peat deposits, further studies are needed to precisely specify the spatial variability in the geochemistry of living Sphagnum mosses.

Mired in the past — looking to the future: Geochemistry of peat and the analysis of past environmental changes

Peat cores from ombrotrophic bogs have been used as a valuable archive to study environmental change for over a century. Much of this focus on the peat record has been on biological proxies of environmental change, such as pollen and peat-forming macrofossils, but there is growing interest in the geochemical record to study environmental changes. Several studies of long-term peat records in Europe have reconstructed past changes in atmospheric lead pollution, for example, and the general cohesiveness of the results and their agreement with known historical trends in metal production exemplify the best potential of peat geochemistry as an environmental archive. Based on the success with lead, a current emphasis in peat reconstructions is to assess the record of past mercury deposition and results thus far show generally consistent trends, e.g., a pre-anthropogenic mercury accumulation rate of about 0.5–1.5 μg Hg m − 2 year − 1 . Despite this general consistency there is increasing concern that there may be diagenetic effects on the quantitative record of some metals, which can be inferred based on a strong relationship between mercury and other organically bound elements and proxies for peat decomposition (C/N ratio). However, it is possible that changes in decomposition and the alteration of some metal records could provide climatic information. A few recent studies show that closer examination of the geochemical matrix, in some cases along with biological proxies, can provide valuable information on landscape changes and climate; for example, partitioning metals into different weight fractions and source regions can be applied to climate studies. The best interpretations of the peat geochemical record in the context of environmental and climate change will likely come when geochemical and biological records are considered simultaneously.

Contrasting the sorption of Zn by oxyhydroxides of Mn and Fe, and organic matter along a mineral-poor to mineral-rich fen gradient

The geochemistry of Mn and Fe in surface pools, pore-waters and surface peats and the sorption of Zn by the surface peats was contrasted among 15 peatlands sampled along a mineral-poor to mineral-rich fen gradient. Sorption of Zn by surficial peats was compared via distribution coefficients, both total (K DT) and partial (K DERMn, K DRFe and K DORG), where ER Mn, R Fe and ORG are amounts of Zn recovered from the easily reducible Mn oxides, reducible Fe oxides, and organic components of peat, respectively. Apparent stability constants (K As) for Zn sorption onto oxides of Fe recovered from the surface peats were also calculated and compared along the same gradient. Peat geochemistry was peatland dependent; mineral-poor fens had less easily reducible Mn and greater amounts of organic matter (%Loss on Ignition; LOI) versus mineral-rich fens (range of 0.66–8.6 mm kg −1 for ER Mn and 20–88% LOI for organic matter). Reducible Fe also varied among peatlands (range 51–315 mm kg −1) but was independent of the mineral-poor to mineral-rich fen gradient. Comparison of partial K Ds for amounts of Zn sorped onto the ER Mn, R Fe and ORG components of peat indicated that sorption was dominated by R Fe in all peatlands. K DTs ranged from 0.54–2.00. In contrast to other aquatic systems, however, the range in K DTs was not related to either surface or pore-water pH. K As ranged from 0.36 to 3.06 and were also independent of surface or pore-water pH. However, average K As (but not K DTs), were greater for mineral-poor fens ( P<0.02), suggesting greater Zn binding by surface peats of mineral-poor fens versus either the moderately poor or mineral-rich peatlands. Other water chemistry variables, such as pore-water base cation concentrations, weakly correlated to Zn partitioning onto R Fe ( r=−0.35, P=0.05), but did not fully explain differences in Zn partitioning among peatlands. Greater average K As for the mineral-poor peatlands may in part be due to the presence of strong metal-organic matter-Fe oxide complexes in the Sphagnum dominated peatlands as well as lower pore-water base cation concentrations that occur in the mineral-poor peatland as compared to the more mineral-rich fens.

Elemental Distribution and Pyrite Occurrence in a Freshwater Peatland, Alberta

A continental minerotrophic peatland in Alberta was studied for its botanical, petrographical, mineralogical and geochemical characteristics. Changes in peat stratigraphy and mineralogy are related, and development toward oligotrophic conditions is recorded. Elemental concentration and distribution vary in the peat profile, reflecting the influence of natural and anthropogenic factors on peat geochemistry. Many elements (Al, As, Ba, Co, Cr, Fe, Mn, Th, V) accumulate in the zone of water table fluctuation as a result of changes in redox chemistry. The relative elemental concentration at the surface and near-surface (e.g., As, Cr, Sb, Th, Ti, V) may also be attributed to atmospheric deposition related to anthropogenic activity. Chemical analysis (Al, Fe, Mg, Na, Si, Ti) also reveals the presence of a non-visible volcanic-ash-rich layer near the base of the peat profile, possibly Mazama tephra. This study provides evidence of pyrite formation in a freshwater peat-forming environment, associated with high-sulphur peats.

Geochemical and petrographical characteristics of a domed bog, Nova Scotia: a modern analogue for temperate coal deposits

A freshwater domed bog in Nova Scotia, Canada, was investigated for its petrographic, mineralogical and geochemical characteristics. Three cores were taken from the lagg zone, margin and centre, to examine different stages of evolution in a fen to domed bog sequence. Based on this study, a model was developed, which shows the relationship between factors controlling peat geochemistry and petrography, all of them being dependent on trophic conditions. The bog may represent a modern analogue for temperate coal deposits, and thus can be used to help understand spatial variability within coal beds. Rheotrophic conditions in the early stages of mire development result in the formation of high-ash, highly humified Carex-dominated peat, while the evolution toward ombrotrophic conditions is reflected in a progressive replacement by low-ash and well-preserved Sphagnum-dominated peat. The associated decrease in pH reflects a decrease of groundwater influence, which is also supported by the mineralogical assemblage and petrographic data (decrease in reflectance and change in maceral composition). Except for Cl, Br, I and Se, which are associated with the organic fraction, variations in elemental composition can be explained in terms of mineral matter abundance, i.e. decrease upward and with increasing distance from the margin. Sea spray is the most probable origin for halogen enrichment in the peat.

Metal concentrations in chrionomids in relation to peatland geochemistry

Concentrations of Zn, Cu, Al, Fe, and Mn were determined in Chironomidae (Diptera) larvae sampled from three sites within eight peatlands, located in south-central Ontario, Canada. The eight peatlands displayed a range in pH and alkalinity and were classified abiotically (i.e., chemically, hydrologically) and biotically (i.e., dominant vegetation present) as mineral-poor, moderately poor, or as mineral-rich fen. Surface peats of mineral-poor fens were distinct from those of moderately poor and mineral-rich fens; mineral-poor fens contained higher concentrations of organic matter with low concentrations of easily reducible Mn vs. the moderately poor and mineral rich fens. A one-way nested ANOVA indicated that chironomid metal concentrations were peatland dependent (P<0.05). To determine if differences in chironomid metal concentrations among the peatlands could be related to peat geochemistry, an R2 MAX procedure using peat geochemistry as the independent variable and chironomid metal concentrations as the dependent variable was applied. Peat geochemistry was defined as concentrations of peat organic matter, reducible Fe (Fe oxides), reducible Mn (Mn oxides) and easily reducible metal (where metal = Zn, Cu, Al, Mn and Fe), and reducible metal and organically bound metal. Chironomids from mineralrich peatlands, i.e., peatlands low in organic matter with high concentrations of reducible Mn and Fe or easily extractable metal contained greater concentrations of Zn, Mn, and Fe vs. chironomids sampled from mineral poor peatlands, i.e., peatlands with high concentrations of peat organic matter and low concentrations of reducible Mn or easily extractable metal. In contrast, Cu concentrations were greatest in larvae sampled from mineral-poor vs. mineral-rich peatlands. Aluminum larvae concentrations were independent of peat geochemistry. We suggest that bioavailability of metals such as Zn, Fe, and Mn will be greater to invertebrates inhabiting mineral rich vs. mineral poor fens, whereas greater chironomid Cu concentrations will be found in chironomids sampled from mineral poor fens. Differences in metal availability to invertebrates among peatland types has important implications when comparing the impact of contaminant transfer to higher trophic levels among different types of peatlands.

Relationship between peat geochemistry and depositional environments, Cranberry Island, Maine

The Heath, Great Cranberry Island, Maine, offers a unique locality for studying lateral and vertical relationships between radically different peat types within 1 km 2. The majority of The Heath is a Sphagnum moss-dominated raised bog. Surrounding the raised bog is a swamp/marsh complex containing grass, sedge, Sphagnum moss, alder, tamarack, and skunk cabbage. Swamp/ marsh-deposited peat occurs both around the margins of The Heath and under Sphagnum-dominated peat, which was deposited within the raised bog. A third peat type, dominated by herbaceous aquatics, is present underlying the swamp/marsh-dominated peat but is not present as a dominant botanical community of The Heath. The three peat types have major differences in petrographic characteristics, ash contents, and associated minerals. Sulfur contents range from a low of 0.19 wt.% (dry) within the raised bog to a high of 4.44 wt% (dry) near the west end of The Heath, where swamp/marsh peat occurring directly behind a storm beach berm has been influenced by marine waters. The presence of major geochemical variations within a 1-km 2 peat deposit suggests the need for in-depth characterization of potential peat resources prior to use.