Landfill site restoration: the inimical challenges of ethylene and methane.

Vertically migrating landfill gases pose inimical challenges to site revegetation strategies. Laboratory studies were made to examine the efficacy of ectomycorrhizae and soil cover to obviate the challenges of ethylene and methane. In the presence of ethylene concentrations </= 640 ppm the mean colony radial extension rates of the fungal isolates Laccaria proxima, Paxillus involutus and Hebeloma crustuliniforme were comparable with the non-ethylene controls. H. crustuliniforme afforded no protection to Betula pendula (Silver Birch) seedlings. Methane removal by the soil cover may be important to minimise the indirect phytotoxic effects of methane on tree seedlings. In closed culture enrichments with refuse as inoculum source material methanogenesis consistently exceeded methanotrophy even after major oxygen perturbations. With subsoil and topsoil, however, net methane concentrations decreased, thus emphasising the importance of these cover materials in site restoration strategies.