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Thesis (Master's)

Agricultural University of Iceland > Náttúra og skógur > Meistaraprófsritgerðir >

Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/44383

  • Phenology Effects on Carbon and Water Dynamics in a Pristine Boreal Fen A multi-decadal analysis from 2005-2007 & 2014-2022
  • Master's
  • Boreal peatlands are major constituents of the global carbon (C) and water cycles and therefore important climate regulators. These cycle dynamics are strongly determined by plant phenology (e.g.,vascular plant photosynthesis and seasonality) and evapotranspiration (ET), next to other abiotic factors. While it is evident that climate change affects these networks of interactions, it is only poorly understood to what extent, as site-specific empirical evidence over multiple decades is lacking. This study investigates the role of phenology (leaf area index: LAI) for peatland C (net ecosystem exchange: NEE) and water fluxes (ET and water table: WT) by combining inter-annual and seasonal observations at the ecosystem level, in Siikaneva fen, Finland (2005-2007, 2014-2022). Interactions
    with temperature (T), vapor pressure deficit (VPD), photosynthetically active radiation (PAR) and rain were included and tested with various statistical methods (trend- and correlation-analysis, commonality
    analysis, time lag testing, stepwise multiple-regression, and structural equation modelling).
    Significant trends were found for LAI (increasing) and WT (decreasing), suggesting ongoing changes in the ecosystem (climate change signal). Within this system LAI provided substantial effects on NEE, less
    so on ET. These relationships differed seasonally: the greenup season showed the strongest effects of LAI on NEE and ET (and other interactions). However, e.g., PAR and VPD became more relevant for NEE and ET in the later seasons. A time lag analysis suggested that effects (e.g., LAI on NEE) can be delayed at the scale of weeks. Inconclusive evidence was found for the LAI effect on ET and WT (via ET). It is assumed that ET is a limited measure to differentiate between evaporation (E) and transpiration (T) by leaves or the ground, as they might cancel each other out. A shading of increasing LAI over the season might shade moss-ET (and photosynthesis).
    The applied methods provided complementary information with differing suitability to reveal certain parts of complex network dynamics. A consistent, while seasonally changing, importance of plant phenology
    for peatland NEE can be concluded. Phenology showed clear correlation with ET, however, the effect size could not be quantified conclusively. Future studies should partition E and T or incorporate the
    contribution of mosses to both ET and NEE for a more comprehensive understanding. Collectively, this study highlights the role of phenology for peatland C and water fluxes and provides evidence for climate
    change induced alterations of biotic-abiotic interactions at the ecosystem scale.

  • Thesis approved in partial fulfillment of a double Nordic Master MSc degree in environmental changes at higher latitudes (EnCHiL), from University of Helsinki and Agricultural University of Iceland.
  • May 22, 2023
  • http://hdl.handle.net/1946/44383

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