Passage III

When 2 types of bacteria found in the soil of a wet-land (land having a high water table) break down organic matter, gases are generated. Aerobic bacteria, which require , generate . Anaerobic bacteria, which require little or no , generate .

Study

At the beginning of a particular summer, 3 soil sections, each 1.5 m long, 1 m wide, and 0.6 m deep, were removed intact from the surface of each of 2 wetlands—a bog and a fen—after all live plants had been removed from the sections. Each section was placed in a separate 100 L tank having sides and a lid made entirely of glass. An instrument to measure gas emissions was mounted on the underside of the lid, above the soil. All the tanks were placed at an outdoor site near the wetlands.

Different amounts of water were added to the 3 tanks containing bog soil sections to produce a water table (WT) 1 cm above the surface (+1 cm) of the first soil section, a WT 10 cm below the surface (-10 cm) of the second soil section, and a WT 20 cm below the surface (-20 cm) of the third soil section. This procedure was repeated for the 3 tanks containing fen soil sections. All the lids were then closed.

Over the next 3 months, gas emissions from each soil section were measured, in moles of carbon per square meter (mol C/m²). Throughout this period, the temperature inside the tanks was kept the same as the outdoor temperature. Figure 1 shows the total emission of and the total emission of from each bog soil section due to bacterial activity; Figure 2 does the same for each fen soil section.