Feasibility in using historical data to perceive changes in peatlands : Changes in peatland's structure and vegetation over the past 91 years
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Energy shortages in the early 20th century sparked an intensive survey of peatlands fromsouthern to middle Sweden. In this study a survey of peatlands northeast of Uppsala wasconducted that aimed to determine the feasibility of using diaries from the surveys in the early 20th century to assess possible changes in peat structure and vegetation over the last 90 years. Despite differences in the assessments of both determination of peat and vegetation, comparisons of the two surveys indicated a general change to drier and more nutrient-richconditions in surveyed peatlands. Furthermore, peatland thickness had reduced during the past 90 years most likely because of changes in hydrology caused by wetland drainage. Althoughthe method here was unable to compare coring sites within peatlands at both time periods it did give indications of general changes of peatlands over time. Results suggest that studies ofthe peatlands in Sweden can be linked to surveys from the early 20th century and providefurther information in understanding recent changes in peatlands.Keywords:
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Climate is the most important determinant of the distribution and character of peatlands,and its variation determines the location,typology and biodiversity of peatlands through the world;peatlands preserve,in the constantly accumulating peat,a unique record of their own development as well as of past climate changes,and are good geological archives of variation in climate and regional environment.Based on the discussion of peat deposition process and the development characteristics of different types of mires,this paper systematically reviewed international paleoclimatic studies about peat sediments from the two perspectives of the common climatic proxies and the carbon records in peatlands.The scopes of application as well as merits and demerits of six common climatic proxies including peat humification,peat macrofossils,testate amoebae,biomarker compounds,stable isotopes and pollen are analysed in detail,and the recent hot issues on carbon accumulation and carbon cycles in peatlands are also involved.Finally,the important research fields and contents in peatlands and climate changes are summarized based on four aspects:past climate variability reconstructed from peatlands,impacts of recent global climate variations on peatlands,potential feedbacks mechanisms of peatlands to climate change,and current direct observations and measurements on climatic and ecological conditions in peatlands.
Macrofossil
Testate amoebae
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The principal aim of the PhD work presented here is to explore how geochemistry and palynological approaches on peatlands, particularly when considered together, can help in the understanding of Holocene (the last ~11600 years) environmental changes. To achieve this general aim, different types of peatlands (ombrotrophic and minerothrophic), environments (boreal and temperate zones) and Holocene chronological intervals (although with special attention to the Late Holocene) have been studied. The focus has been on gaining insights into how different environmental stressors –such as climate and human activities– influenced past environments. In particular, the following processes have been addressed: 1) natural- and human-induced soil erosion and its relation with forest evolution and hydrological changes on wetlands; 2) changes in past climate and its relation with peat organic matter decomposition, vegetation and other aspects of the environment, including human activity, and paying special attention to the Little Ice Age period, and 3) trends in past atmospheric metal pollution and its possible link with changes in the tree cover. Within geochemistry, both physical (loss on ignition and density of the peat) and chemical (elemental composition, carbon and nitrogen stable isotope ratios, lead isotope ratios, peat humification and infrared spectroscopy) analyses were applied, whereas within palynology both pollen and non-pollen palynomorphs were considered. Because the inherent complexity in the functioning of natural systems is behind the interaction among different compartments of ecosystems (i.e., biosphere, lithosphere, hydrosphere and atmosphere), the combined use of geochemistry and palynology enabled us to obtain a more integrated overview of past environmental changes beyond what would have been possible by any of these disciplines independently. Knowing the past evolution of ecosystems at large enough temporal scales is crucial to understand their dynamic and functioning, hence, this knowledge should be considered when implementing present-day environmental policies.
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Testate amoebae
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Peatlands provide a widespread terrestrial archive of Holocene environmental change. The taphon omy of peat is relatively simple, the range of evidence and proxies is wide, and dating methods have become more accurate and precise, such that the potential temporal resolution of records is high. Although long estab lished, the use of peatlands as archives of Holocene change has undergone phases of decline and resurgence. Here, the variable exploitation of the peat archive is explored, and recent developments in peatland science as applied to Holocene records are reviewed with reference to the collection of papers in this Special Issue of The Holocene, which are arranged in four key themes: (1) records of Holocene climatic change; (2) peatland dynamics; (3) carbon accumulation; and (4) implications for conservation and management. The changing acceptance of peatlands as archives of Holocene climatic change is attributed to developments in understanding of the peatland system and geographical differences in the history of Holocene research. Recent developments in biological and geochemical proxies combined with improvements in chronological techniques have resulted in renewed interest in peatland palaeoclimate records. Peatlands are an important global carbon pool and it is clear that climate has influenced the efficiency of long-term carbon sequestration by these systems. Climate has also had an impact on the biodiversity and condition of peatlands, which creates problems in discerning cause and effect in sites affected by human activities, and in targeting remedial management. It is concluded that particular strengths of the archive are the current diversity of peat-based palaeoenvironmental research and the potential for multiproxy analyses to be applied to a range of research issues. Mire-based investigations can complement research in other realms, and are deserving of greater attention from researchers of other archives.
Environmental change
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Organic carbon concentrations have increased in surface waters across parts of Europe and North America during the past decades, but the main drivers causing this phenomenon are still debated. A lack of observations beyond the last few decades inhibits a better mechanistic understanding of this process and thus a reliable prediction of future changes. Here we present past lake-water organic carbon trends inferred from sediment records across central Sweden that allow us to assess the observed increase on a centennial to millennial time scale. Our data show the recent increase in lake-water carbon but also that this increase was preceded by a landscape-wide, long-term decrease beginning already A.D. 1450-1600. Geochemical and biological proxies reveal that these dynamics coincided with an intensification of human catchment disturbance that decreased over the past century. Catchment disturbance was driven by the expansion and later cessation of widespread summer forest grazing and farming across central Scandinavia. Our findings demonstrate that early land use strongly affected past organic carbon dynamics and suggest that the influence of historical landscape utilization on contemporary changes in lake-water carbon levels has thus far been underestimated. We propose that past changes in land use are also a strong contributing factor in ongoing organic carbon trends in other regions that underwent similar comprehensive changes due to early cultivation and grazing over centuries to millennia.
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Permafrost dynamics play an important role in the surface hydrology and carbon balance of northern peatlands. Plant macrofossil analysis with radiocarbon dating has been widely used in detecting past permafrost dynamics in peatlands; however, there is a lack of permafrost‐specific plant indicator species, which makes it challenging to determine the exact timing of historical permafrost aggradation. We investigated the indicator value of oribatid mites in determining past permafrost dynamics in sub‐Arctic peatlands. Analyses of subfossil oribatid mite assemblages of Holocene peat profiles from two mires, one in northern Finland and one in northeastern European Russia, were carried out and interpreted using modern calibration data from the same study areas. The results were compared with previously published reconstructions of permafrost history based on plant macrofossil analyses from the same locations. The results suggest that the oribatid mites Carabodes labyrinthicus , Chamobates borealis and Neoribates aurantiacus are promising indicator species to detect past permafrost occurrence in peatlands. In addition, N. aurantiacus is clearly associated with the presence of lichens, which is particularly useful because lichen remains are rarely preserved in peat deposits. Results are in accordance with earlier studies showing that oribatid mites are useful indicators of past environmental change.
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Mire
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Peatlands are globally important ecosystems that serve as archives of past environmental change. Peatlands form over thousands of years from the accumulation of decaying plants and hold water, or in some cases, purely rainwater. Therefore, external processes, such as climate, as well as internal processes, such as the rates of peat growth and decay, control the water table in peatlands. However, throughout the previous century and particularly over the past decade, paleoclimatologists have increasingly relied on reconstructions of the water table in rain‐fed peatlands to infer changes in rainfall through the Holocene period (the past ∼12,000 years), ignoring the potentially important role of internal processes.
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Rainwater Harvesting
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We investigated the developmental and hydrological history of a Sphagnum -dominated, kettle peatland in Upper Michigan using testate amoebae, plant macrofossils, and pollen. Our primary objective was to determine if the paleohydrological record of the peatland represents a record of past climate variability at subcentennial to millennial time scales. To assess the role of millennial-scale climate variability on peatland paleohydrology, we compared the timing of peatland and upland vegetation changes. To investigate the role of higher-frequency climate variability on peatland paleohydrology, we used testate amoebae to reconstruct a high-resolution, hydrologic history of the peatland for the past 5100 years, and compared this record to other regional records of paleoclimate and vegetation. Comparisons revealed coherent patterns of hydrological, vegetational, and climatic changes, suggesting that peatland paleohydrology responded to climate variability at millennial to sub-centennial time scales. Although ombrotrophic peatlands have been the focus of most high-resolution peatland paleoclimate research, paleohydrological records from Sphagnum -dominated, closed-basin peatlands record high-frequency and low-magnitude climatic changes and thus represent a significant source of unexplored paleoclimate data.
Ombrotrophic
Testate amoebae
Macrofossil
Paleoclimatology
Paleoecology
Sphagnum
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Holocene climatic optimum
Paleoclimatology
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Sphagnum
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