Research project description
Volatile organic compounds in aquatic systems of the ice-wedge polygonal landscape
Introduction
Terrestrial biomass in the Arctic is low compared to boreal, temperate and other ecosystems. Aquatic habitats therefore play an essential role in carbon metabolism. VOCs are an overlooked but important component of carbon metabolism, as they are made up of carbon and are produced and consumed by many organisms. In addition, VOCs can increase the lifetime of methane in the atmosphere or influence cloud formation, which has a direct impact on the positive feedback loops of global warming. With permafrost thawing underway and the changing dynamics of the Arctic, data generated on VOCs produced and emitted by thermokarst ponds and lakes will feed coupled carbon-climate models and provide a better understanding of future climate dynamics.
Objectives
Chapter 1: Investigate the quantity and composition of VOCs in ice wedge trough ponds and polygonal tundra lakes during summer and explore their links with geomorphological and limnological properties.
Chapter 2: Identify relationships between VOC assemblages, microbial diversity and function by characterizing (i) bacterial and archaeal communities, (ii) phytoplankton and zooplankton communities, and (iii) plant dominance in ponds.
Chapter 3: Identify the main processes behind VOC production in ice wedge ponds, identifying the influence of various factors such as biotic communities and light. To this end, the net production of VOCs from different zones within the ponds will be measured by incubation experiments, and the diurnal cycle of VOC concentrations will be monitored over 48 hours.
Chapter 4: Quantifying and characterizing net VOC production (and potentially fluxes) from tundra ponds during the spring thaw period for comparison with summer net production (Chapter 1).
Study Sites
The study site is in the Qarlikturvik Valley on Bylot Island, Nunavut, Canada, in Sirmilik National Park (73°08' N, 80°00' W). This valley is home to thousands of biologically active aquatic systems, ranging from small puddles of a few square meters to proglacial lakes of less than 0.2 square kilometers. The abiotic and biotic properties of these water bodies are strongly influenced by permafrost degradation, organic matter inputs and climatic processes.
Material and methods
Through the four chapters of my PhD, we will study the volatile organic compounds produced in tundra ponds and lakes, with an emphasis on ice wedge ponds. The first chapter consists of a reconnaissance study to compare the quantity and composition of VOCs produced in different types of polygonal tundra aquatic systems. In Chap. 2, we study the links between communities of microorganisms and the diversity of VOCs produced, involving collaboration with Jérôme Comte's team. Chap. 3 consists of an experiment on the production of VOCs by different zones of erosive and stable ponds, as well as measurements of concentrations and fluxes during a diurnal cycle, with fluxes measured by a collaborator from the U. of Copenhagen. Finally, Chap. 4 compares the production of VOCs in summer with that in spring, when the ice melts. VOCs are extracted in thermal desorption tubes and analyzed by gas chromatography at the U. of Copenhagen. We also collect physicochemical and biotic data at each sampling.
Expected results
We already know that erosive ponds produce a significantly higher quantity of VOCs than other types of ponds (Field 2024). We also expect the diversity of VOCs produced to vary according to the type of aquatic system, production zone (pelagic vs. littoral, abiotic vs. biotic) and season (spring vs. summer). Lastly, we anticipate that the production of certain VOCs shows cyclical variations over the course of the day, due to its dependence on primary production and/or exposure to UV radiation (abiotic photoproduction), which respond to diurnal variations despite the absence of darkness in summer. However, VOCs dependent solely on heterotrophic bacterial production may show less pronounced, or even absent, cyclicity.
