This page outlines the observations being done by the University of Leeds in support of MOYA.

The attribution of methane sources and sinks using CH4 concetration measurements alone is difficult as concentrations do not provide any indiction of origin. However, sources of CH4 have differing isotopic signatures, as a result measurements of isotopic concentrations and knowledge of emissions/sink signitures can provide insight into the trends in atmospheric CH4, both globally and locally. Not only do isotopic signatures vary between source and sink types, but they also vary within the same type. For example, temperate wetlands may yield different isotopic signatures than tropical wetlands. Currently, the largest gaps in measurements of the δ13CH4 isotopic signature is in tropical wetlands.

Work carried out by the University of Leeds intends to increase the number of observations made to better understand the Amazon wetland δ13CH4 values. This will be done using isotopic fingerprinting. Air samples will be collected at a range of distances from the source (in this case the wetland), these will then be sent for δ13CH4 analysis at Royal Holloway. Keeling plot analysis will then be performed to determine the isotopic signature of the source.

To investigate the suitablity of the bag sampling method outlined above we performed a pilot study at a local landfill site. Using a landfill site as a pilot offered the advantage of a more concentrated source of CH4. The Welbeck Landfill, located on the outskirts of Wakefield, West Yorkshire, was chosen as a suitable pilot study site. The site has been in operation for over 10 years and receives ~600,000 tonnes of non-hazardous waste per year.

The Welbeck Landfill site on the edge of Wakefield, West Yorkshire.

Keeling plot analysis requires measurements to be made at a range of distances from the CH4 source. For this study 20 samples were taken between 10 m and ~1 km from the site. Each sample was analysed for CH4 and δ13CH4. The image below shows where samples were taken downwind of the site throughout the day with wind direction marked. The wind speed on the day was low (~5 mph).

Sampling sites for CH4 and δ13CH4 at the Welbeck Landfill.

The key aim of the experiement is to determine the δ13CH4 isotopic signature from the landfill site. Knowledge of individual source signatures can be used to inform emission estimates used in models, which can improve understanding of atmospheric CH4 trends.

The plot (right) shows results from the measurements indicating an isotopic source signature from the landfill site of δ13CH4 = -58, this is in general agreement with previous studies performed at landfill sites. The success of the pilot study indicates the sampling campaign can begin in tropical wetlands in the Amazon.

Keeling plot analysis from the Welbeck Landfill.

Following on from the successful pilot study a field measurement campaign is currently in planning at 3 South American wetland sites, with the aim of determining possible spatial and temporal variations in tropical wetland δ13CH4 signatures.

Moya @ Leeds Website 2017