Measurement of Permafrost Greenhouse Gas Emissions through a New Closed Chamber Automated System

English Abstract:

Over the past 30 years, the Arctic has experienced a rapid increase in surface temperatures, which has led to important consequences such as the beginning of permafrost thaw. Permafrost thaw is expected to contribute to increased emissions of greenhouse gases (GHG). Such emissions have been quantified indirectly through mathematical models and from sporadic field measurements using portable gas chambers. However, modeling still holds a lot of uncertainty and direct measurements with chambers are both labour-intensive and time-consuming.

The main objective of this project was to measure permafrost CO₂ and CH₄ emissions in a polygonal peatland located in Salluit, Nunavik. In order to assess the future impact of warming on arctic carbon fluxes, GHG emissions were measured under the current climatic conditions and inside an open-top chamber (OTC), which can reproduce the climatic conditions expected in about 50 years. In addition, the spatial variations of GHG emissions in the polygonal peatland, from dry tundra polygon centers to wet troughs where permafrost is decaying, were studied in order to determine the effects of soil water saturation on GHG emissions and composition.

This project also aimed to test a new instrumentation: a closed chamber automated system. The new system was designed and built to take precise measurements over long periods of time with low-cost gas sensors instead of using conventional ways to measure carbon concentrations, which are often expensive. In addition, the system was designed to operate autonomously and maintain the integrity of the studied sites.

Four automated closed chambers were used for the project: one chamber in natural conditions (C_n), on chamber in an OTC (C_OTC), one chamber measuring emissions on a site without vegetation (C_soil) and one chamber between two polygons where the soil is permanently water-saturated (C_sat). Two chambers were operated every day, alternating chambers each day. The chambers were closing for 30 minutes three times a day (7h30, 13h30, 19h30).

Preliminary results show that the new automated system underestimates CO₂ fluxes, but that the trends of carbon emissions are similar to a commercial system. The greatest CO₂ emissions came from C_sat, followed by C_OTC, C_n and C_soil. Emissions were most influenced by air temperature and water table depth.