Browsing by Subject "carbon dynamics"
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Hydrological changes in subarctic Russian peatlands during the last millennia due to climate change (2021)Abstract: Northern boreal peatlands form one of the biggest carbon pools in the biosphere, thus having great potential to cause major changes to the global carbon cycle. The ongoing recent warming may affect the carbon dynamics though factors, such as, vegetation, hydrology and permafrost balance. As the future is still uncertain there are no definitive answers on how the peatlands will react in the future. Fortunately, moisture sensitive organisms such as, bryophytes and testate amoeba is preserved in the peat and can therefore be used to reconstruct past climatic shifts. In this thesis I studied palaeohydrology and peat accumulation over the last two millennia, from three peat cores originating in a permafrost peatland in Rogovaya, Russia. I used testate amoeba as a proxy of past moisture conditions and plotted the taxa composition of each core against 14C and 210Pb dated samples, to reconstruct past moisture shifts. The results were also supplemented by plant macrofossil and carbon accumulation data for more robust results. Of the three cores, Rog11 provided the oldest testate amoeba dataset by reaching the Dark Ages Cold Period. During this period there were indications of dry moisture conditions followed by a wet Medieval Warm Period. The Little Ice Age gave indications of a drying trend, while toward the end of the LIA Rog8 indicated opposite moisture conditions. From the end of the LIA onwards a general trend of drying and increased carbon accumulated is noted. Yet, during the last decade the trend has turned. The wet shift might indicate that the threshold for the peatland has been reached and the amount of melting permafrost has exceeded the evapotranspiration rate. As a conclusion my result indicates that the dynamics of both hydrology and carbon are complicated processes affected by both autogenic and allogenic factors, therefore causing large variability even on a local scale. The absence of widely spread observations of the most recent wet shift also indicates that the response of the peatland to the recent warming might be unequal. To rectify this situation, continued research is crucial, so that we can increase our understanding of climate-peatland interactions.
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(2020)Northern peatlands have a major role in the global carbon cycle due to their carbon stocks and fluxes of carbon dioxide (CO2) and methane (CH4). Anthropogenic climate change may affect peatland carbon dynamics through changes in e.g. primary production, hydrology, and permafrost dynamics. It is uncertain whether these changes will lead to northern peatlands becoming significant sources of carbon to the atmosphere. Changes in moisture conditions especially can be an important factor in determining the carbon sink potential of northern peatlands. In this thesis I examine the palaeohydrology and peat accumulation over the past centuries in a permafrost peatland complex in Lovozero, Kola Peninsula, Russia. I used testate amoebae as a proxy of past changes in moisture conditions. Other study methods used here are detrended correspondence analysis (DCA) and 14C and 210Pb dating. The results were also supplemented with plant macrofossil and carbon accumulation data provided by other members of the research team. The results show varying responses of the peatland hydrology and peat accumulation to the past climatic shifts, suggesting that the changes have been driven more by autogenic factors rather than climate. However, all three sites indicated a drying trend and an increased peat accumulation for the last century. Yet, the last decade is charachterised by a wet shift. The wet shifts suggest that the peatlands may have crossed a threshold where increased evapotranspiration is exceeded by increased moisture due to thawing permfrost. The surface peat layers of all three sites were dominated by mixotrophic testate amoebae, which may have contributed to the high peat accumulation. The inconsistency of past successional pathways identified at Lovozero peatlands and the drying trend over the past century correspond to the previous studies from northern peatlands elsewhere. However, the most recent surface wetting during the last decade differs from what has been reported for the other northern sites. This suggests that the response mechanisms of peatlands to the anthropogenic climate change may not be uniform. Thus, further research is inevitably needed to increase our understanding of peatland-climate intercations.
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