Response of methane emission and dissolved organic carbons to warming and nitrogen fertilization in boreal peatlands

Sey, Albert Adu (2019) Response of methane emission and dissolved organic carbons to warming and nitrogen fertilization in boreal peatlands. Masters thesis, Memorial University of Newfoundland.

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Abstract

Although most sources of greenhouse gases (GHG) have been extensively studied, relatively little is understood about the interactive effect of warming and nitrogen addition on methane (CH₄) emissions from boreal peatland. Since methane is a considerably more potent GHG compared to carbon dioxide (CO₂), studies investigating what physical and biological factors control methane emissions in boreal peatlands are becoming increasingly important as an increase in temperature increases the rate of CH₄ emission as well as enhancing the decomposition of dissolved organic matter (DOM). In this experiment, I investigated the response of CH₄ emissions and dissolved organic carbon (DOC) concentrations and optical characteristics to warming and nitrogen fertilization in boreal peatlands as a result of global climate change at a peat bog complex in western Newfoundland, Canada. I found that climate warming increased CH₄ emission and DOC concentration at 40 cm peat depth. In contrast, nitrogen (N) addition did not increase CH₄ emission in a boreal peatland. However, the interactive effect of warming and nitrogen addition decreased the rate of CH₄ emission due to the reducing effect of N-addition which counteracted the positive effect of warming in increasing the rate of CH₄ emission from boreal peatlands. This unexpected trend suggests unforeseen factors are involved in the process of methanogenesis that were beyond the scope of this experiment. However, the interactive effect of warming and N addition synergistically increased the DOC and total nitrogen (TN) concentrations at the 40 cm depth due to root exudates favoring DOC mineralization in boreal peatlands. The results further indicate that specific ultraviolet absorbance (SUVA₂₅₄) increased peat aromaticity. Furthermore, fluorescence index (FI) indicated the peat was of microbially (1.53-1.65) processed dissolved organic matter (DOM) over vascular plant derived DOM in peatland. Humification index (HIX) values for the treatment effects ranged between 0.15-0.17, indicating the peat carbon was not highly degraded and composed of less condensed molecules, indicating a decrease in recalcitrant humified carbon production.

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