Methane oxidation potential of boreal landfill cover materials: The governing factors and enhancement by nutrient manipulation

Methanotrophs inhabiting landfill covers are in a crucial role in mitigating CH4 emissions, but the characteristics of the cover material or ambient temperature do not always enable the maximal CH4 oxidation potential (MOP). This study aimed at identifying the factors governing MOPs of different materials used for constructing biocovers and other cover structures. We also tested whether the activity of methanotrophs could be enhanced at cold temperature (4 and 12 degrees C) by improving the nutrient content (NO3-, PO43-, trace elements) of the cover material. Compost samples from biocovers designed to support CH4 oxidation were exhibiting the highest MOPs (4.16 pmol CH4 g h(-1)), but also the soil samples collected from other cover structures were oxidising CH4 (0.41 mol CH4 ga-j, h(-1)). The best predictors for the MOPs were the NOi content and activity of heterotrophic bacteria at 72.8%, which were higher in the corimost samples than in the soil samples. The depletion of NOT from the landfill cover material limiting the activity of methanotrophs could not be confirmed by the nutrient manipulation assay at 4 degrees C as the addition of nitrogen decreased the MOPs from 0.090 gmol CH4 g(dw)(-1)h(-1) to <0.085 pino1 CH4 g11-1. At 12 degrees C, all nutrient additions reduced the MOPs. The inhibition was believed to result from high ionic concentration caused by nutrient addition. At 4 degrees C, the addition of trace elements increased the MOPs (>0.096 mu mol CH4 g(-1), h(-1)) suggesting that this was attributable to stimulation of the enzymatic activity of the psychrotolerant methanotrophs. (C) 2015 Elsevier Ltd. All rights reserved.