Passage III

A study examined the production and consumption of methane (CH₄) by soil bacteria in 4 areas of a particular forest: an area of healthy black spruce trees, an area of burned black spruce trees, an area of healthy jack pine trees, and an area of burned jack pine trees.

Study

On May 15, 4 identical soil gas collection cylinders were placed in the forest, one in each area. Each cylinder had an open end and a closed end; its open end was pushed into the soil, and then its aboveground surface was covered with shiny foil (see Figure 1). That same day, a gas sample was taken from each cylinder by inserting the needle of a50 cm³ syringe into the closed end (through an airtight seal). The CH₄ content of each gas sample was determined. Likewise, on the 15th day of June, July, August, and September, a gas sample was taken from each cylinder and its CH₄ content was determined.

The difference in the CH₄ contents of consecutive samples (for example, the samples taken on May 15 and June 15) from a cylinder indicated whether there had been a net production of CH₄ (more CH₄ had been produced than consumed) or a net consumption of CH₄ (more CH₄ had been consumed than produced) in the area over the month between the 2 sampling dates. From these differences, the average rate of CH₄ production or consumption was calculated, in milligrams per square meter per day (mg/m²/day), for each area over each month (see Figure 2).

Figure 2 adapted from Sami Ullah et al. , "Greenhouse Gas Fluxes from Boreal Forest Soils during the Snow-Free Period in Quebec, Canada." ©2009 by NRC Research Press.