Cycle des nutriments dans les mares d’une tourbière ombrotrophe du sud du Québec
Open-water pools are common features in northern peatlands but their nutrient biogeochemistry has seldom been studied. The goal of this thesis is to understand the nitrogen (N), phosphorus (P) and carbon (C) cycles in pools of an ombrotrophic peatland located in southern Québec and to determine the environmental factors controlling such cycles. The relationship between pool water chemistry and their physical and biological characteristics were studied. Pool characteristics significantly explained 28.2% of the variation in water chemistry. Of this, 81.9% and 14.8% were respectively explained by pool depth and the dominant vegetation type surrounding the pools. Shallow pools had higher C and N concentrations than deep pools. Organic C (OC) from pools where vegetation was dominated by coniferous trees was also more recalcitrant to decomposition than OC from pools where vegetation was mainly composed of mosses. The influence of depth on pool biogeochemistry was confirmed by a seasonal survey of pools of different sizes. Over the course of the 2016 growing season, nutrient biogeochemistry from shallow and deep pools significantly evolved differently. All summer long, P concentrations were low in all pools, indicating that ombrotrophic peatland pools are P-limited. My work has shown that water chemistry in a rain-fed peatland is not only determined by atmospheric inputs, but also by internal biogeochemical processes. This study highlights the complexity of these environments.
Biogeochemistry Open-water pools Peatlands Nutrients Nitrogen Phosphorus Carbon Limnology