Browsing by Subject "peatlands"
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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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(2009)Lately the need to increase the amount of domestic logging has grown. That has been caused by a decrease in raw wood import. A big part of the extra logging potential is located on peatlands. Wintertime harvesting on peatlands cannot be increased since the logging equipment at that time of the year is already fully employed. That creates a need to be able to operate on peatlands year-round if the logging amounts are expected to grow significantly. With the existing average machinery and traditional equipment this is not possible. The traditional equipment for peatlands is only to mount wide steel tracks around the wheels. With this kind of equipment logging from soils with lowest bearing capacities is practically impossible if low amount of harvesting damages is expected. For logging on peatlands during the period of unfrozen ground new technical innovations are needed to decrease the surface pressure that a machine produces to the ground and to decrease its rut formation. For low rut formation there have been special machines for peatlands already for a long time but their productivity is too low for profitable logging. Since the use of special machines has been proven to be expensive, it seemed rational to focus on equipping a standard machine to perform better on peatlands and other soft soils. The main problem is to combine low rut formation and good productivity into the same machine. This is possible by adding low rut formation due to the new track system to the good productivity of a basic machine. The study was done by using constructive research method. The aim of the study was to find a good track system for a forwarder regarding low rut formation and other important properties for operating on low bearing capacity soils. First all the existing constructions were gathered and some new possible constructions were also brainstormed. From these constructions the one that seemed most potential was chosen for field testing. Support for the choice was sought by making an expert interview round. The results supported the arguments on which the choice was based on. In the field tests the test machine with the new track system and the comparison machine with the traditional track system both drove their own testing sectors which were estimated to be equal by conditions. The field test area was located in Ilomantsi and was a normal thinning site. The idea was to compare the rut formation of the track systems in real harvesting conditions that were mathematically equalized. The known factors that effect the bearing capacity were measured and their effect on the results was minimized by standardizing them mathematically. The calculations were executed by using multifactor regression analysis. The test machine caused less rut formation but the difference between the machines was quite small. There were some minor faults in the test machines properties and reliability but those are likely to be rather easily solved with some modifications to the track system.
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(2023)Non-growing season carbon fluxes can contribute to a significant amount of the full-year ecosystem carbon balance. Year-round net ecosystem exchange (NEE) data from 17 years was used to analyse the non-growing season carbon dioxide (CO2) fluxes together with environmental and meteorological variables at Siikaneva fen in Southern Finland. Generally, the fen acted as a sink of CO2 with a mean annual carbon balance of -50.9 (± 39.4) g C m-2. On average, the CO2 emissions during non-growing seasons offset 57% of the following growing seasons CO2 uptake. Two years from the 17-year dataset were a consistent net source of CO2, 2018 and 2016. In 2016, a strong respiration release during the winter-spring transition period turned the annual balance of CO2 to positive, resulting in the highest emission of CO2 during the entire study period. The period of anomalous respiration alone offset 38% of the following growing seasons CO2 uptake. Since the biological activity during non-growing season is low, the CO2 fluxes likely composed mainly of heterotrophic respiration, and thus were likely driven by soil temperature. The relative importance of air and soil temperature, vapor pressure deficit, water table depth, and photosynthetically active radiation (PAR) on NEE of CO2 was analyzed with a random forest algorithm. PAR and soil temperature were the most important drivers during non-growing season, growing season and year-round periods. PAR had the highest importance during growing season while during non-growing seasons, PAR and soil temperature had an equal relative importance. A wavelet coherence analysis further revealed that the mean annual cycles of NEE and soil temperature were coherent during the summer months across the diurnal scale. For instance, NEE correlated positively (decreasing the net carbon sink) with soil temperature and lagged the response to temperature by 4-6 hours. There was no coherence between the annual cycles of soil temperature and NEE during winter. The results emerging from this thesis stress the importance of studying what controls the interannual variation in soil temperature and the possible accumulation of CO2 in soil during non-growing season, but also how they contribute to spring-time CO2 releases like the one observed in spring 2016.
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(2019)In nutrient poor boreal peatlands, a significant proportion of photosynthesis-derived carbon of mycorrhizal plants is allocated to their fungal symbionts in exchange for nutrients. The soil carbon cycle is intertwined and affected by inputs of e.g. nitrogen and sulfur, whose amounts both in the soil and atmosphere have increased since the Industrial Revolution. In addition, as stated in the recent Global Warming of 1.5 °C -report (IPCC 2018) global warming is likely to reach 1.5 °C above pre-industrial levels before 2052. In this study, data from ericoid mycorrhizal fungi (ErMF) abundance, enzyme activities and the fungal taxa associated with them under increased warming and nutrient depositions were connected. This thesis is part of the Nitro-Erica -project of Natural Resources Institute Finland (LUKE) and it has been funded by the Academy of Finland (SA286731). Root fragments of Vaccinium oxycoccos L. and Andromeda polifolia L. were observed under a light microscope to determine the abundance of all root associated fungi, ErMF and dark septate endophytes (DSE). Fluorometric and photometric assays were used to study the ability of the fungi to degrade organic material and scavenge nutrients. Finally, direct PCR and Sanger sequencing were used to learn the dominant fungal taxa in the roots. A decrease in the abundance of ErMF and DSE was observed, indicating the possibility of a reduction in the carbon sink potential of peatlands through a decrease in the number of fungi. An increase in acid phosphatase activity under nitrogen deposition was observed in the two plants, which was expected as boreal peatlands are often nitrogen limited. In contrast, sulfur deposition suppressed the activity of all carbon acquiring enzymes which we concluded was likely to be the result of the sulfur inhibiting the growth of two parasitic fungi that greatly contributed to the overall high activity of carbon acquiring enzymes. More research is needed to gain a comprehensive understanding of the fungal abundance, communities and their functioning in peatlands under the changing environmental conditions.
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