NWT RESEARCH DATABASE

Tags: physical sciences, permafrost, greenhouse gases, organic matter, soil chemistry, forest fire, methane, carbon, biogeochemistry

Objective(s): To clarify how soil organic matter quality, fire intensity and time since fire are affecting the microbial biomass and biochemical processes driven by microbes (e.g. greenhouse gas fluxes and carbon turnover).

Project Description: The field work in Trail Valley Creek and Inuvik aims to study: 1) how catchment characteristics, such as vegetation and soil properties, control the amount and quality of aquatic dissolved organic matter (DOM) and its microbial degradability, and 2) how these factors further regulate greenhouse gas fluxes (carbon dioxide CO2, methane CH4, nitrous oxide N2O) from Arctic lakes. At the Dempster highway, the aim is to study the long-term effects of different fire intensities on the decomposition of soil organic matter in northern boreal forests under changing fire regimes. The objectives are to explore the long-term effects of forest fires on: 1) above- and belowground biomasses, 2) above- and below ground temperatures, 3) vegetation succession and 4) quantity, quality and decomposition of soil organic matter, 5) to clarify how soil organic matter quality, fire intensity and time since fire are affecting the microbial biomass and biochemical processes driven by microbes (e.g. greenhouse gas fluxes and carbon turnover). To study the factors controlling the amount and quality of aquatic DOM in the Canadian Arctic tundra, water and soil samples will be collected and analyzed for their chemical composition of DOM (FT-ICR-MS) in the Trail Valley Creek and Inuvik. Detailed measurements of lacustrine greenhouse gas flux dynamics will be performed using the floating chamber (FC) technique. The long-term effects of fire will be studied based on chronosequence, where forest stands with similar soil type, but different fire history will be compared to study biogeochemical changes following the fire. The study areas for this part of the project are located in northern boreal forests with continuous permafrost, in Northwest Territories and in Yukon, Canada. The study areas were created in summer of 2015 (in project financed by Academy of Finland) and consists of 4 age classes: fires in years 2012, 1990, 1969, control area with last fire more than a hundred years ago (in total of thirty-six sample plots). The study sites of the project in NWT are located between Inuvik and Tsiigehtchic, along the Dempster Highway. The research team have conducted intensive field measurement campaigns at the fire chronosequence sites in 2015 and 2018 to study soil C and N stocks, soil CO2, CH4 and N2O fluxes, soil permafrost depth, soil temperature profiles and soil chemical and microbiological properties, vegetation changes, albedo, tree biomass and leaf area changes. The team will use the field samplings for parameterizing process based soil organic matter decomposition and ecosystem C cycle model to estimate the long term effects of fire on soil and tree carbon stocks on a stand level. The team study the effects of fire on soil organic matter quality on soil carbon turnover by measuring the decomposition rates of soil organic matter by incubating soil samples collected from different soil depths between the permafrost and soil surface. The samples were taken from sample plots in the 2015 campaign and incubated in the laboratory. Soil carbon turnover time will be calculated from soil incubation measurements and soil temperature profile measurements conducted at the field sites. In the summer 2019, the team will measure the soil temperature profiles and active layer depths at the same sites as were studied in 2015 and 2018 campaigns. At the same time, the team will also conduct vegetation biomass and greenhouse gas flux measurements at the sites. The research team is working with the effects of soil properties and vegetation on the greenhouse gas emissions from lakes. Thus, different educational opportunities for local involvement are possible – seminars, lectures, collaboration in scientific data processing and writing. Scientific papers will be sent to Western Arctic Research Centre (our host in Inuvik, NWT). The results will be also sent to Government of the Northwest Territories (GNWT) Environment and Natural Resources. The fieldwork for this study will be conducted from May 27, 2019 to July 9, 2019.