Temporal Variations in Greenhouse Gas Emissions at a Midlatitude Landfill

A field study encompassing a parallel time series of CH4, N2O, and CO2 emissions measurements was completed by using static enclosure techniques at a midlatitude landfill (northeastern Illinois) during the period of July through December 1995. The site had a pumped gas recovery system and thus a high level of engineered gas control. No net CH4 emissions to the atmosphere were measured during this study; rather, the landfill cover soils were functioning as a sink for atmospheric CH4. The net measured emissions of CO2 (dark respiration) and N2O were in ranges characteristic of natural soils and were dependent on similar controls, including temperature, moisture, and aeration status. A comparison of proximal (near gas recovery well) and distal (between wells) emissions with soil gas profiles permitted development of a conceptual biogeochemical model for gas transport and reaction through the landfill cover. This model includes a modified reduction sequence where the major zones (from ground surface downward) were a near‐surface zone of optimum CH4 oxidation; a zone of optimum CO2 production (predominantly from root zone respiration); a zone of optimum N2O production; and a deep zone dominated by transport of landfill gas (CH4 and CO2) from methanogenic production zones in the underlying refuse.