Characterising methane emissions from dairy farm sources using mobile and dual-isotope measurements in Jersey, Channel Islands

This is the authors' abstract. We don't add key points for this paper.

Field campaigns in Jersey, Channel Islands (Crown Dependency of British Isles), were carried out to understand the distribution and scale of agricultural methane (CH 4 ) emissions. We used vehicle-mounted spectrometers and isotope analysis to fingerprint and map methane sources on Jersey dairy farms to test whether mobile dual-isotope surveys can quantitatively separate enteric and manure CH 4 sources on a regional-farm scale. Peak barn CH 4 mixing ratios ( ≤ 500 ppm), observed from continuous overnight monitoring in a confined cattle barn, fall within concentration windows targeted by catalytic-oxidation prototypes, suggesting potential for the successful implementation of removal techniques, subject to ventilation-rate and cost studies. CH 4 , CO 2 (carbon dioxide) and δ 13 C CH 4 were mapped across the 120 km 2 island of Jersey, visiting 11 dairy farms and one wastewater treatment works. Methane emissions from different sources at each farm were isolated in order to determine δ 13 C CH 4 and δ 2 H CH 4 source signatures and also typical CO 2 :CH 4 ratios proximal to cattle in barns, expressed as relative excess over background. Excess CO 2 :CH 4 ratios around 8–12 can be considered a cow barn signature. 138 grab samples were collected during two island-wide campaigns (November 2021, June 2023) and analysed for δ 13 C CH 4 and δ 2 H CH 4 . Isotopic source signatures were determined using Keeling plot analysis for 61 of these samples with δ 13 C CH 4 results showing clear distinction between manure management and eructation, although there was farm to farm variation in some cases. δ 13 C CH 4 source signatures also varied with the age of the manure, likely related to the progressive oxidation of the manure over time. In differentiating between methane from breath and manure, δ 13 C CH 4 was a more consistent indicator than δ 2 H CH 4 . • The atmospheric CH 4 distribution of Jersey, Channel Islands, was mapped. • Distinctive variability in δ 13 C-CH 4 signatures observed between eructation and manure • δ 2 H-CH 4 measurements less diagnostic than δ 13 C-CH 4 for eructation and manure. • CO 2 /CH 4 ratios can be used as a reliable tracer for cattle emissions. • Up to 500 ppm methane was observed overnight in barns, so CH 4 removal strategies may be viable.