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Andersson, S. & Schoning, K. 2010: Surface wetness and mire development during the late Holocene in central Sweden. Boreas, Vol. 39, pp. 749–760. 10.1111/j.1502‐3885.2010.00157.x. ISSN 0300‐9483. Late Holocene mire development and surface wetness changes have been studied in a small mixed mire located in central Sweden. Today the mire is characterized by a mainly ombrotrophic centre dominated by Sphagnum mosses, with Carex content increasing towards the more minerotrophic mire margins. Two peat sequences extracted from the central ombrotrophic part were investigated for stratigraphy, humification, testate amoebae analysis, C/N ratio and δ13C and δ15N stable isotopes. Three main stages of mire development are identified, with the first stage, between c. 4200 and 2600 cal. yr BP, characterized by water‐logged conditions, suggesting a minerotrophic fen stage. The second stage, between c. 2600 and 1000 cal. yr BP, is characterized by more ombrotrophic conditions and Sphagnum‐dominated vegetation. The onset of the prominent change at c. 2600 cal. yr BP could have been initiated by climate change coincident with a change in solar activity. The last stage, between c. 1000 and 50 cal. yr BP, is dominated by more ombrotrophic conditions, suggesting increased precipitation. This study shows that the response of hydrological proxies in a mixed mire during its development towards more ombrotrophic conditions might result in conflicting results, a finding that needs to be considered in palaeoenvironmental reconstructions from mires that change between ombrotrophic and minerotrophic settings.  相似文献   

3.
Paleoenvironmental interpretation of proxy data derived from peatlands is largely based upon an evolutionary model for ombrotrophic bogs, in which peat accumulates in still environments. Reports on proxies obtained from minerotrophic fens, where hydrologic inputs are variable, are less common. In this study, a highland peatland in southern Brazil is presented through ground penetrating radar (GPR) and sedimentological, palynological and geochronologic data. The radar stratigraphic interpretation suggests a relatively complex history of erosion and deposition at the site since the beginning of Marine Isotope Stage 3 (MIS 3) interstadial period. In spite of this, radar stratigraphic and palynologic interpretations converge. Electromagnetic reflections tend to group in clusters that show lateral coherence and correlate with different sediment types, while pollen grains abound and are well preserved. As a result, the study of minerotrophic fens provides a source of proxies, suggesting that ombrotrophic bogs are not the only reliable source of data in wetlands for palynological analysis.  相似文献   

4.
Wetlands are exceptional ecosystems that contribute to biodiversity and play a key role in the hydrological and carbon cycles. Knowledge of their long-term ecology is essential for a proper understanding of these valuable ecosystems. We present the application of multi-proxy analyses to a 115 cm-thick core from La Molina mire (Alto de la Espina) located in NW Iberia, with a chronology spanning since ～500 BC. The mire is located in an area intensively mined for gold during the Roman period, and close to a water-canalization system used for mining operations at that time. Our aim was to get insights into the development of the wetland by combining palynological records of hydro-hygrophytes, non-pollen palynomorphs and geochemical analyses, supported by 14C datings and multivariate statistics. The results indicate a complex pattern of ecological succession. During the local Iron Age the wetland was minerotrophic. Since ～20 AD it was subjected to dramatic hydrological changes due to a rise of the water-table, fluctuating between the presence of open water and phases of drawdown. Finally, by ～745 AD, the wetland experienced a rapid evolution towards ombrotrophic conditions. High grazing pressure was detected for the last decades. The significant change occurred during Early Roman Empire seems to have been the consequence of the direct use of the wetland as a water-reservoir of the canalisation system used for gold-mining. Thus, the current nature of the mire may be the result of human impact, although multiple human- and climate-induced causes were potentially linked to the detected shifts. However, the system seems to have been resilient, successfully buffering the changes without substantial alterations of its functioning. Our investigation shows that palaeoecological research is necessary to understand modifications in the structure of wetland ecosystems, their long-term ecology and the role of human-induced changes.  相似文献   

5.
Numerous palaeoecological studies have used testate amoeba analysis to reconstruct Holocene hydrological change in peatlands, and thereby past climatic change. Current studies have been almost exclusively restricted to ombrotrophic bogs and the period since the fen–bog transition. Although the critical link between peatland surface wetness and climate is less direct in minerotrophic peatlands, such records may still be of value where there are few others, particularly if multiple records can be derived and inter‐compared. Expanding the temporal and spatial scope of testate amoeba‐based palaeohydrology to minerotrophic peatlands requires studies to establish the primacy of hydrology and the efficacy of transfer functions across a range of sites. This study analyses testate amoeba data from wetlands spanning the trophic gradient in the eastern Mediterranean region. Results demonstrate that different types of wetlands have distinctly different amoeba communities, but hydrology remains the most important environmental control (despite water table depth being measured at different times for different sites). Interestingly, Zn and Fe emerge as significant environmental variables in a subset of sites with geochemical data. Testate amoeba–hydrology transfer functions perform well in cross‐validation but frequently perform poorly when applied to other sites, particularly with sites of a different nutrient status. It may be valid to use testate amoebae to reconstruct hydrological change from minerotrophic peatlands with an applicable transfer function; however, it may not be appropriate to use testate amoebae to reconstruct hydrological change through periods of ecosystem evolution, particularly the fen–bog transition. In practice, the preservation of amoeba shells is likely to be a key problem for palaeoecological reconstruction from fens. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

6.
Quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the North York Moors in northeast England (May Moss). Testate amoebae, plant macrofossil and humification analyses were carried out for six peat profiles. Transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy, which complement the semi‐quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis. 14C dates provide the chronology for the stratigraphy. Differences were encountered between AMS 14C dates on pure Sphagnum remains and radiometric dates on bulk peat from the same horizon, which perhaps arise from the heterogeneity of peat. Replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies, and reveals a strong agreement between the water table level proxies. The record of hydrological changes at sites across May Moss are in synchrony, and so climate change is the most likely cause of the moisture fluctuations. Changes to a wetter or cooler climate were identified cal. ad 260–540, ca. ad 550–650, cal. ad 670–980, ca. ad 1350–1450, cal. ad 1400–1620 and ca. ad 1700–1800. Periods with a drier or warmer climate precede all of these wet shifts, with particularly dry periods between cal. ad 650–860 and 690–980 and between cal. ad 1290–1410 and 1400–1620. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

7.
We present the first testate amoeba‐based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present‐day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral‐rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run‐off. More ecohydrological work on sub‐alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
In general, mires develop by autogenic succession from more groundwater‐fed to more rainwater‐fed. This study from a calcareous mire in the West Carpathians (Slovakia) describes a similar development in the Early Holocene, followed by a reverse development in the Middle and Late Holocene. Pollen, macrofossil and testate amoeba analyses show that the site started as a minerotrophic open fen woodland. After 10 700 cal a BP autogenic succession led to the accumulation of at least 1 m of Sphagnum fuscum peat. Around 9000 cal a BP, as climate could no longer sustain a stable water regime, the bog desiccated and a fire broke out. The fire removed part of the peat layer and as a consequence relative water levels rose, leading to the establishment of a wet minerotrophic swamp carr with Thelypteris palustris, Equisetum sp. and Alnus sp. with extremely slow peat accumulation. After 600 cal a BP, rapid peat accumulation with calcareous tufa formation resumed as a result of anthropogenic deforestation and hydrological changes in the catchment and resulting increased groundwater discharge. At present the mire still hosts a wealth of relict and endangered plant and animal species typical of calcareous fens and fen meadows. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

9.
A brief review of the genesis of blanket peats is presented, together with detailed analyses of basal peats from northern Scotland. Particular attention is paid to local factors affecting peat growth and the problems of sampling and interpretation arising from them. Macrofossil and loss-on-ignition analyses of four peat-mineral interfaces solve many of the terminological problems of such profiles and indicate that interpretations based on field stratigraphy alone are uncertain. Pollen analyses of two profiles from contrasting microtopographic situations show well-defined vegetational change associated with early peat development. Fully organic ombrotrophic peat is present from 6805 ± 50 BP at one site, following anthropogenic burning from c . 7500 BP and partial recovery of the open birch woodland. A change from birch woodland to Calluna heath occurs at approximately the same time on a more freely drained site with much later peat development, following further burning from 4890 ± 65 BP. Anthropogenic activity is clearly associated with changes in soil and vegetation preceding peat formation, and the role of climatic factors remains equivocal.  相似文献   

10.
Palaeoenvironmental reconstructions from peat are strongly focused on ombrotrophic mires, but this study demonstrates that eutrophic mires can also be used. A multi-proxy approach was applied to a eutrophic mire on a floodplain terrace in the southern taiga of West Siberia. The results of the reconstruction were considered in the wide geographic context of the surrounding regions, including Siberia and Central Asia. Different palaeoecological proxies (analysis of plant macrofossils, testate amoebae, oribatid mites, molluscs, peat humification, ash content and spectral characteristics of humic acids) were used in this study. The results of different proxies showed a high level of consistency among themselves, which allowed for a robust interpretation of Holocene mire development. Throughout the ~7800 years history of the mire, there was a high level of surface wetness. The presence of mineral matter in the peat between 7800 and 5100 cal. a BP indicates regular flooding caused by the intensive fluvial activity, apparently resulting from increased precipitation. This was followed by a trend towards a gradual decrease in surface wetness from conditions of high surface moisture (stagnant water) between 5100 and 3000 cal. a BP to present day conditions of moderate surface moisture with a water table slightly below the mire surface. This pattern is consistent with the well-documented long-term trend from palaeoecological records throughout the taiga and arctic zones in West Siberia and central arid Asia. Our data further support the idea that the westerlies were the dominant driver of climate for the southern taiga of West Siberia during the Middle to Late Holocene.  相似文献   

11.
Stratigraphical studies, pollen analyses and radiocarbon dating of peat cores from two blanket mire areas, Mannen and Hestevollane, on the central mountain plateau of the hat-shaped island of Haramsøy in the Nordøyane archipelago indicate that blanket mire formation here dates back about 3,000 years and was primarily caused by human activity, namely regular burning to provide or improve grazing areas. Corresponding investigations of peat cores from two strandfiat sites on either side of the island demonstrate that a population existed on the strandfiat at least 6,800 years ago and gradually converted the original vegetation of the strandfiat into pastures and fields. The human influence increased further about 3,000 years ago when the activity was extended to the mountain plateau where grazing and regular burning, in addition to deteriorating climatic conditions, resulted in blanket mire formation.  相似文献   

12.
A review is made of earlier work and theories on a formation of string mires, together with a report on detailed investigations carried out over seven years on a small string ( aapa ) mire in eastern Finland, to determine the applicability of earlier hypotheses on the explanation of string and pool patterning. Attention is paid to the topography of the surface and bottom of the mire and to the peat and pollen stratigraphy. Results are presented of year-round temperature measurements and long sequences of snow and frost depth readings from both pools and strings. Snow depth is shown to be a decisive factor in ground frost formation. The strings are shown by a series of repeated Geodimeter measurements to move partly upslope, partly downslope and partly in a sideways direction. The maximum cumulative movement recorded was about 1 m in seven years. Some of the pools remained unfrozen even in midwinter because of groundwater flow. Uneven retention and discharge of the surface water causes the strings to be in a labile state and promotes their movement. The initial formation of the string and pool topography is dated to 2,000–3,000 radiocarbon years B.P. and attributed to a rise in the groundwater table due to climatic change. The resulting fluviodynamics of the mire surface led to the accumulation of loose material into ramparts at the spring flood season and led in time to differential peat formation conditions, progressive peat accumulation on the strings, and regressive peat degradation in the pools. Thus the strings became higher and the pools deeper. The authors believe the importance of frost action, ice expansion and solifluction on the development of string and pool patterns is frequently overestimated.  相似文献   

13.
More than 3800 coal thickness measurements, proximate analyses from 97 localities, and stratigraphic and sedimentological analyses from more than 300 outcrops and cores were used in conjunction with previously reported palynological and petrographic studies to map individual benches of the coal and document bench-scale variability in the Fire Clay (Hazard No. 4) coal bed across a 1860 km2 area of the Eastern Kentucky Coal Field. The bench architecture of the Fire Clay coal bed consists of uncommon leader benches, a persistent but variable lower bench, a widespread, and generally thick upper bench, and local, variable rider benches. Rheotrophic conditions are inferred for the leader benches and lower bench based on sedimentological associations, mixed palynomorph assemblages, locally common cannel coal layers, and generally high ash yields. The lower bench consistently exhibits vertical variability in petrography and palynology that reflects changing trophic conditions as topographic depressions infilled. Infilling also led to unconfined flooding and ultimately the drowning of the lower bench mire. The drowned mire was covered by an air-fall volcanic-ash deposit, which produced the characteristic flint clay parting. The extent and uniform thickness of the parting suggests that the ash layer was deposited in water on a relatively flat surface without a thick canopy or extensive standing vegetation across most of the study area. Ash deposits led to regional ponding and establishment of a second planar mire. Because the topography had become a broadly uniform, nutrient-rich surface, upper-bench peats became widespread with large areas of the mire distant to clastic sources. Vertical sections of thick (>70 cm), low-ash yield, upper coal bench show a common palynomorph change from arborescent lycopod dominance upward to fern and densospore-producing, small lycopod dominance, inferred as a shift from planar to ombrotrophic mire phases. Domed mires appear to have been surrounded by wide areas of planar mires, where the coal was thinner (<70 cm), higher in ash yield, and dominated by arborescent lycopods. Rectangular thickness trends suggest that syndepositional faulting influenced peat accumulation, and possibly the position of the domed mire phase. Faulting also influenced post-depositional clastic environments of deposition, resulting in sandstone channels with angular changes in orientation. Channnels and lateral facies were locally draped by high-ash-yield rider coal benches, which sometimes merged with the upper coal bench. These arborescent-lycopod dominant rider coal benches were profoundly controlled by paleotopography, much like the leader coal benches. Each of the benches of coal documented here represent distinctly different mires that came together to form the Fire Clay coal bed, rather than a single mire periodically split by clastic influx. This is significant as each bench of the coal has its own characteristics, which contribute to the total coal characteristics. The large data set allows interpretation of both vertical and lateral limits to postulated domed phases in the upper coal bench, and to the delineation of subtle tectonic structures that allow for meaningful thickness projections beyond the limits of present mining.  相似文献   

14.
Climate change is expected to have substantial impacts on flow regime in the Upper Yellow River (UYR) basin that is one of the most important biodiversity hotspots in the world. These impacts will most possibly exert negative effects on the habitat availability for riverine species. Thus, it is necessary to understand the alteration of river flow regime under climate scenarios. In this paper, we use the modified hydrological model HBV in conjunction with three general circulation models under three representative concentration pathways (RCP 2.6, 4.5, and 8.5) to address changes in flow regime under climate change for the UYR basin in the mid-term (2050s) and end-term (2080s) of the twenty-first century. Flow regime is quantified using the Indicators of hydrological alteration approach. Thereafter, the potential threats to riverine ecosystem in the UYR basin are identified based on the projected alterations of various flow characteristics and their ecological influences. The results showed that the magnitude of monthly flow would increase during the dry period. The date of the annual 1-day minimum streamflow will likely shift toward earlier time under different scenarios, and significant increases in magnitude of annual minimum flow of different durations were detected under both RCP 4.5 and 8.5 scenarios in the 2080s. In addition, assessments of the modification degree of the overall flow regime revealed that climate change would remarkably modify (medium level) the overall flow regime in the UYR basin, particularly by the end of the twenty-first century or under the high emission scenarios. Besides, destruction of habitat and reduced availability of food induced by substantially increased hydrological instability in the 2080s would make two endangered fishes more vulnerable in the UYR basin. These findings provide insights into potential adaptive countermeasures for water resource management and environmental system restoration in the Upper Yellow River.  相似文献   

15.
The Sunnyside Member of the Upper Cretaceous Blackhawk Formation in the Book Cliffs of eastern Utah is composed of coal-bearing coastal-plain strata and wave-dominated shoreface deposits. The member includes a thick (up to 6 m), laterally extensive coal seam, which formed in a large ombrotrophic raised mire, parallel to the shoreline of the Western Interior Seaway. The petrographic composition of the Sunnyside coal was investigated by means of maceral analysis and telovitrinite reflectance determinations of closely spaced samples taken from seven vertical sections through the seam. Sampling was carried out in a combination of outcrop and underground mine sites, using lithotype logging to determine sample spacing. The excellent exposure in the study area enables accurate stratigraphic correlation between sampling localities, which are spread over more than 30 km of depositional dip and 50 km of depositional strike. The correlation of petrographic trends between the seven sampled sections demonstrates the reproducibility of the results and suggests that they represent regional-scale accommodation changes, as opposed to localised variation in the mire. On this basis, we are able to identify a high-resolution record of accommodation change throughout the deposition of the Sunnyside coal, spanning two cycles of increasing and decreasing accommodation. We are also able to identify a marine flooding surface within the coal, which can be traced down depositional dip into the time-equivalent shallow-marine strata, where it represents a parasequence boundary. The proportion of detrital minerals is used as the main discriminator of accommodation trends within the coal. Other useful indicators of conditions in the mire include semifusinite, pyrite, and isometamorphic variations in telovitrinite reflectance.  相似文献   

16.
Niinemets, E., Pensa, M. & Charman, D. J. 2010: Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands. Boreas, 10.1111/j.1502‐3885.2010.00188.x. ISSN 0300‐9483. Local variability in decadal water‐table changes on an ombrotrophic peatland was explored using testate amoebae analysis of near‐surface peats in an Estonian raised bog. The distribution of testate amoebae assemblages was studied along the gradient from hummock to hollow in the upper 30‐cm layer of peat. As expected, testate amoebae assemblages in different micro‐ecotypes from hummock to hollow, even as close as 10 m apart, are distinctly different. Past water‐table change was reconstructed by applying a transfer function based on modern samples from throughout Europe. Results show a decline in water level from the mid‐late 20th century on Selisoo bog in all profiles from the different micro‐ecotypes. However, the absolute water‐table depths and amplitudes of fluctuations vary between reconstructions from different sampling micro‐ecotypes. Cores were correlated using changes in non‐mire pollen concentrations down‐core, but it was not possible to correlate minor changes in water‐table owing to non‐contiguous sampling and variable accumulation rates. We conclude that different microtopes show the same decadal trends in relative water‐table change but that the absolute magnitude of change may be more variable locally. It is important that reconstructed palaeohydrological changes in bogs consider changes in bog micro‐ecotypes, and their variation over time, as this may alter the sensitivity of an individual record to drivers such as climate change. Comparison and compilation of data from parallel cores from different micro‐ecotypes and/or different sites are likely to provide more robust reconstructions.  相似文献   

17.
A palsa mire in Finnish Lapland is studied by means of plant macrofossil analysis, physico-chemical analysis and AMS radiocarbon dating of peat deposits in order to reconstruct its development. Emphasis was on permafrost dynamics during the Holocene. Mire initiation recorded at four studied sites took place between 8240 and 5210 yr BP, first through terrestrialization of a pond and, beginning from 6780 yr BP, through paludification of birch-dominated uplands. Slow lateral expansion of the mire suggests relatively dry conditions in the region. Rich wet fens prevailed until the late Holocene, when changes connected with permafrost development occurred. First permafrost aggradation is recorded in a high palsa site at c. 2460 yr BP. The pathway of permafrost formation possibly points to a climate cooler than today. Permafrost aggradation in a ridge palsa site is dated to c. 645 yr BP, indicating an early Little Ice Age date. The long-time average carbon accumulation rate in the four peat profiles is 16 gC/m2yr. In the older, high palsa, carbon accumulation during the palsa stage has been low (9 gC/m2yr), while in the younger, ridge palsa site it has been very high (73 gC/m2yr).  相似文献   

18.
A wide range of palaeoenvironmental evidence from the Holocene has suggested periodicities in the Earth's climate of 10s to 1000s of years. Identifying these millennial‐, century‐ and decadal periodicities, and their impacts, is critical in developing a fuller understanding of natural climate variability. Any solar‐induced climatic change needs to be distinguished from other causes of natural climate variability and from short‐term catastrophic events induced either by external or internal processes. Such events might themselves generate a periodicity, or in combination with other forcing factors they may contribute towards a periodicity (and so spuriously imply a universal and continuing periodicity in the climate record), or they may resonate with a solar‐induced periodicity. Here, evidence from peat records for periodicity in climate change over the mid to late Holocene is reviewed and this is followed by a test of the replicability of claimed periodicities using blanket peat data covering the past 2000 yr from four sites in the British Isles. Results suggest that the mires studied do go through phases of being responsive to periodic forcing factors, with ca. 200, ca. 80 and 60–50 yr wavelengths reflected in some data sets. However, the patterns shown are not consistent. This could be the result of local conditions at individual mires (human impact, sensitivity and vegetation succession) or of changes in the strength or nature of global forcing factors. Assessing a solar–mire link remains difficult because the century‐scale variations of the Sun show different intervals between solar minima, the durations of which are themselves unequal, and because the proxy‐climate data‐sets from peat profiles may themselves not be dated with sufficient precision and/or accuracy. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

19.
The creation of anthropic sediments, traditionally referred to under the blanket term midden, through the utilization of settlement waste materials in domestic settlement construction was first recognized during early excavations at the Orcadian Neolithic site of Skara Brae (V.G. Childe, 1931a; 1931b). Prior to the present study there has been no systematic attempt to identify the nature of these sediments at Skara Brae, whose likely occupation dates between ˜3100 and 2500 B.C., or to assess whether different materials were incorporated into construction or varied with different phases of site formation. The opportunity to begin addressing these issues arose with the location of undisturbed sediment samples held in storage since the last site excavations of 1972–1973 (D.V. Clarke, 1976). Ten thin sections were manufactured from these samples, representing earlier and later phases of Neolithic settlement at Skara Brae. Observations using thin‐section micromorphology, supported by total phosphorus and particle‐size distribution analyses, suggest that both earlier and later settlement phases show accumulation of household waste dominated by fuel residues. These wastes may have been used to help stabilize wind‐blown sand deposits during the later settlement phases. In addition, the use of clay material tempered with household waste is associated with wall construction. Animal manures are only evident in anthropic deposits on the edge of the main settlement site where composting may have been taking place, and there is no evidence for their use in site construction. The authors conclude by drawing attention to possible diverse uses of anthropic sediments in settlement construction at other Neolithic settlements in Orkney. © 2006 Wiley Periodicals, Inc.  相似文献   

20.
The Holocene development of a treed palsa bog and a peat plateau bog, located near the railroad to Churchill in the Hudson Bay Lowlands of northeastern Manitoba, was traced using peat macrofossil and radiocarbon analyses. Both sites first developed as wet rich fens through paludification of forested uplands around 6800 cal. yr BP. Results show a 20th-century age for the palsa formation and repeated periods of permafrost aggradation and collapse at the peat plateau site during the late Holocene. This timing of permafrost dynamics corroborates well with that inferred from previous studies on other permafrost peatlands in the same region. The developmental history of the palsa and peat plateau bogs is similar to that of adjacent permafrost-free fens, except for the specific frost heave and collapse features associated with permafrost dynamics. Permafrost aggradation and degradation is ascribed to regional climatic, local autogenic and other factors. Particularly the very recent palsa development can be assessed in terms of climatic changes as inferred from meteorological data and surface hydrological changes related to construction of the railroad. The results indicate that cold years with limited snowfall as well as altered drainage patterns associated with infrastructure development may have contributed to the recent palsa formation.  相似文献   

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