Seasonal Greenhouse Gas Emissions (Methane, Carbon Dioxide, Nitrous Oxide) from Engineered Landfills: Daily, Intermediate, and Final California Cover Soils

Compared with natural ecosystems and managed agricultural systems, engineered landfills represent a highly managed soil system for which there has been no systematic quantification of emissions from coexisting daily, intermediate, and final cover materials. We quantified the seasonal variability of CH4, CO2, and N2O emissions from fresh refuse (no cover) and daily, intermediate, and final cover materials at northern and southern California landfill sites with engineered gas extraction systems. Fresh refuse fluxes (g m(-2) d(-1) [+/- SD]) averaged CH 4 0.053 (+/- 0.03), CO2 135 (+/- 117), and N2O 0.063 (+/- 0.059). Average CH4 emissions across all cover types and wet/dry seasons ranged over more than four orders of magnitude (< 0.01-100 g m(-2) d(-1)) with most cover types, including both final covers, averaging < 0.1 g m(-2) d(-1) with 10 to 40% of surface areas characterized by negative fluxes (uptake of atmospheric CH4). The northern California intermediate cover (50 cm) had the highest CH4 fluxes. For both the intermediate (50-100 cm) and final (> 200 cm) cover materials, below which methanogenesis was well established, the variability in gaseous fluxes was attributable to cover thickness, texture, density, and seasonally variable soil moisture and temperature at suboptimal conditions for CH4 oxidation. Thin daily covers (30 cm local soil) and fresh refuse generally had the highest CO2 and N2O fluxes, indicating rapid onset of aerobic and semi-aerobic processes in recently buried refuse, with rates similar to soil ecosystems and windrow composting of organic waste. This study has emphasized the need for more systematic field quantification of seasonal emissions from multiple types of engineered covers.