Detecting graves with methane

To establish whether methane (CH4) biogeochemistry could be useful in detecting graves, we measured soil–atmosphere CH4 fluxes, pore air CH4 concentrations, atmospheric CH4 concentrations near the soil surface, and soil aerobic CH4 consumption and anaerobic CH4 production potentials at a graveyard in southern Quebec, Canada, which contained cadavers of zoo animals buried at least a decade before. Soil CH4 fluxes ranged from small rates of consumption in well-drained, non-grave sites (0 to − 2 mg m− 2 d− 1) to > 30 mg m− 2 d− 1 in suspected graves and wetter sites and > 1500 mg m− 2 d− 1 at open gravesites. Pore air CH4 concentrations were sub-ambient in well-drained, non-grave soils, confirming net consumption, whereas concentrations were above ambient around graves. Sampling of air for CH4 concentration just above the soil surface after stable meteorological conditions revealed spatial patterns that were related to the occurrence of graves. There were large variations in the soil aerobic CH4 consumption and anaerobic CH4 production potentials in laboratory incubations, providing evidence of the changes in methanotrophic and methanogenic communities and substrate characteristics promoting increased rates of CH4 consumption and/or production associated with cadaver burial. These results suggest that CH4 biogeochemistry can be useful in detecting graves, though its utility will be heavily dependent on the mass, depth, age and nature of the burials as well as the local environment, such as temperature and especially soil drainage, to separate the effect of cadavers from that of the water table.

► At a zoo graveyard in southern Quebec, we tested if CH4 could detect the presence of graves.
► Fluxes of CH4 to the atmosphere were larger from grave soils than those without burials.
► Pore air CH4 concentrations were larger in soils with buried remains than without.
► Atmospheric CH4 concentrations close to the soil surface were larger around graves than non-graves.
► Potential soil CH4 consumption and CH4 production were related to the presence of buried remains.