Browsing by Author "Arnkil, Sini"

The atmospheric nitrogen (N) deposition has increased in industrialized and densely populated areas, which according to previous studies may cause changes in the vegetation, microtopography, and carbon (C) cycling of peatlands. Knowing the effects of nutrient deposition is important, because a significant amount of C is stored in boreal nutrient-limited ombrotrophic bogs, which are also a significant natural source of methane (CH4). The aim of this study was to investigate how elevated N deposition affects the CH4 fluxes and vegetation in an ombrotrophic bog. This study was conducted at a long-term fertilization experiment at Mer Bleue, a Sphagnum moss and evergreen shrub dominated ombrotrophic bog in Ottawa, Southern Ontario. The experiment consisted of nine nutrient treatments, each with three replicate 3 x 3 m plots. In the summer of 2015, the plots had been fertilized for 11–16 years with 1.6, 3.2, and 6.4 g N m-2 with or without phosphorus (P) and potassium (K) and control plots received distilled water. Methane fluxes were measured weekly from the beginning of May to the end of August using closed chamber method. Peat temperature, water table level, and volumetric soil water content were also measured. The changes in vegetation abundance and species composition were monitored monthly using point-intercept method. The results show that instantaneous CH4 fluxes at the bog are typically small (0–0.2 mmol m-2 h-1). The seasonal average CH4 emissions from N only treatments are equal to controls. However, the average CH4 emissions have increased after 15–16 years of fertilization from the highest NPK treatments compared to unfertilized control due to nutrient induced changes in vegetation, microtopography, and peat characteristics. The changes in vegetation include the loss of Sphagnum mosses and new deciduous species in the area. Due to the loss of moss cover, the peat has subsided and it has become wetter, which may explain the increased CH4 emissions. Direct effects of fertilization on the microbial communities may also be a factor. The results of this study indicate that elevated atmospheric deposition of nutrients may increase loss of C as CH4 in peatlands through a complex suite of feedbacks and interactions among vegetation, microclimate, and microbial communities.