Damage to Woody Species by Anaerobic Landfill Gases

Abstract

Refuse landfills are constructed on areas of land set aside for depositing solid waste. Current practice dictates that the refuse be spread and compacted, before being covered daily with a 6in. layer of soil., for environmental protection, to save space, and to reduce the amount of settlement that will take place in the area after the landfill is completed. Soil cover is placed over the refuse to improve aesthetics; prevent papers from blowing; reduce odors; control insects, rodents and birds; reduce the hazard of fire; and reduce water infiltration into the refuse. The initial soil cover is supposed to be increased from 6 in to a 12-in-thick intermediate cover after a limited period of time, and the final soil cover for the refuse is supposed to be at least 2 ft deep. Many landfills have been completed, however, with less than 2 ft of soil over their top surface. It is in this top layer of soil cover that any vegetative cover will be planted. Although many uses have been proposed for completed landfills, experience has shown that they are generally unsuitable for excavation or for construction purposes. Open-space recreational areas, such as parks, playgrounds, picnic areas, and golf courses, therefore, are deemed to be a suitable use for such sites. In some locations attempts have been made to use the completed landfills for agricultural purposes. Depending on the composition of the fill and the environmental conditions within it, however, there are serious inherent disadvantages, not the least of which are ecological upsets due to pollution of water supplies, the production of toxic and explosive gas mixtures from anaerobic microbial decomposition of the organic matter present and surface settlement. Excessive landfill ground temperatures have also been reported. Prior to 1965 landfills were frequently operated as open-burning dumps. While this caused air pollution and vector control problems at the time of their operation, the result was that most of the material left in the landfill was nonbiodegradable, resulting in much less ultimate settlement of the landfill and much less anaerobic gas development after the landfill was closed. The present-day landfill does not permit open burning; therefore, it provides more nutrients for the microorganisms that generate the gases, mainly carbon dioxide and methane, that present problems for growing vegetation. High concentrations of carbon dioxide in the root zone of plants, have been reported to be directly toxic to vegetation (4,5). Although methane has not been reported to be phytotoxic per se, perhaps, when combined with the carbon dioxide, it can remove oxygen from the root zone of the vegetation by direct displacement, by utilization of the oxygen by methane-consuming bacteria, or by a combination of these. The end