Isotopic signatures of major methane sources in the coal seam gas fields and adjacent agricultural districts, Queensland, Australia

Lu, Xinyi; Harris, Stephen J.; Fisher, Rebecca E.; France, James L.; Nisbet, Euan G.; Lowry, David; Röckmann, Thomas; van der Veen, Carina; Menoud, Malika; Schwietzke, Stefan; Kelly, Bryce F. J.

In regions where there are multiple sources of methane (inline-formulaCH4) in close proximity, it can be difficult to apportion the inline-formulaCH4 measured in the atmosphere to the appropriate sources. In the Surat Basin, Queensland, Australia, coal seam gas (CSG) developments are surrounded by cattle feedlots, grazing cattle, piggeries, coal mines, urban centres and natural sources of inline-formulaCH4. The characterization of carbon (inline-formulaδ13C) and hydrogen (inline-formulaδD) stable isotopic composition of inline-formulaCH4 can help distinguish between specific emitters of inline-formulaCH4. However, in Australia there is a paucity of data on the various isotopic signatures of the different source types. This research examines whether dual isotopic signatures of inline-formulaCH4 can be used to distinguish between sources of inline-formulaCH4 in the Surat Basin. We also highlight the benefits of sampling at nighttime. During two campaigns in 2018 and 2019, a mobile inline-formulaCH4 monitoring system was used to detect inline-formulaCH4 plumes. Sixteen plumes immediately downwind from known inline-formulaCH4 sources (or individual facilities) were sampled and analysed for their inline-formulaCH4 mole fraction and inline-formula M14inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg1d1eae5b775e61a583e928af9d6abadd acp-21-10527-2021-ie00001.svg41pt18ptacp-21-10527-2021-ie00001.png and inline-formula M15inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg3f034aab678b35cdd6a950ab10b896d9 acp-21-10527-2021-ie00002.svg32pt14ptacp-21-10527-2021-ie00002.png signatures. The isotopic signatures of the inline-formulaCH4 sources were determined using the Keeling plot method. These new source signatures were then compared to values documented in reports and peer-reviewed journal articles. In the Surat Basin, CSG sources have inline-formula M17inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg42da5be3ee1259aed48175631a9ebeef acp-21-10527-2021-ie00003.svg41pt18ptacp-21-10527-2021-ie00003.png signatures between inline-formula−55.6 ‰ and inline-formula−50.9 ‰ and inline-formula M20inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg727a1f5b52f1ef3dd605c58191d5f5b2 acp-21-10527-2021-ie00004.svg32pt14ptacp-21-10527-2021-ie00004.png signatures between inline-formula−207.1 ‰ and inline-formula−193.8 ‰. Emissions from an open-cut coal mine have inline-formula M23inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg76c16cb94847cb6c106716d5ea60319e acp-21-10527-2021-ie00005.svg41pt18ptacp-21-10527-2021-ie00005.png and inline-formula M24inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg73c2e30734959e3febedf5865ec40a0d acp-21-10527-2021-ie00006.svg32pt14ptacp-21-10527-2021-ie00006.png signatures of inline-formula M25inlinescrollmathml - normal 60.0 ± normal 0.6 58pt10ptsvg-formulamathimg5256e0fdf5606884a02e4ba6415ac2a0 acp-21-10527-2021-ie00007.svg58pt10ptacp-21-10527-2021-ie00007.png  ‰ and inline-formula M26inlinescrollmathml - normal 209.7 ± normal 1.8 64pt10ptsvg-formulamathimgb8ada67f867afdba822f276417963a70 acp-21-10527-2021-ie00008.svg64pt10ptacp-21-10527-2021-ie00008.png  ‰ respectively. Emissions from two ground seeps (abandoned coal exploration wells) have inline-formula M27inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg68469465d4d1ae44db978e76d22c0822 acp-21-10527-2021-ie00009.svg41pt18ptacp-21-10527-2021-ie00009.png signatures of inline-formula M28inlinescrollmathml - normal 59.9 ± normal 0.3 58pt10ptsvg-formulamathimgd6637d9aa9c8a55f966608820bc8a060 acp-21-10527-2021-ie00010.svg58pt10ptacp-21-10527-2021-ie00010.png  ‰ and inline-formula M29inlinescrollmathml - normal 60.5 ± normal 0.2 58pt10ptsvg-formulamathimg7842699a583d50e46b4ea222a2cbc1a4 acp-21-10527-2021-ie00011.svg58pt10ptacp-21-10527-2021-ie00011.png  ‰ and inline-formula M30inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg6ff0d405767cebd4635d9d7ba9a0e6ee acp-21-10527-2021-ie00012.svg32pt14ptacp-21-10527-2021-ie00012.png signatures of inline-formula M31inlinescrollmathml - normal 185.0 ± normal 3.1 64pt10ptsvg-formulamathimgbb5674ef8f504c1e657dba6af0645f03 acp-21-10527-2021-ie00013.svg64pt10ptacp-21-10527-2021-ie00013.png  ‰ and inline-formula M32inlinescrollmathml - normal 190.2 ± normal 1.4 64pt10ptsvg-formulamathimg441cbe40347d9992825c8b00b5badb40 acp-21-10527-2021-ie00014.svg64pt10ptacp-21-10527-2021-ie00014.png  ‰. A river seep had a inline-formula M33inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg8e0218e2f726350c6d2760d57e52ea6d acp-21-10527-2021-ie00015.svg41pt18ptacp-21-10527-2021-ie00015.png signature of inline-formula M34inlinescrollmathml - normal 61.2 ± normal 1.4 58pt10ptsvg-formulamathimgb035e63aea2afab60c9a73b140034682 acp-21-10527-2021-ie00016.svg58pt10ptacp-21-10527-2021-ie00016.png  ‰ and a inline-formula M35inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg9013802da64b0ff1449b50e4c7ffff9b acp-21-10527-2021-ie00017.svg32pt14ptacp-21-10527-2021-ie00017.png signature of inline-formula M36inlinescrollmathml - normal 225.1 ± normal 2.9 64pt10ptsvg-formulamathimg06cb91ca4c80a28bf8d6308263b73c07 acp-21-10527-2021-ie00018.svg64pt10ptacp-21-10527-2021-ie00018.png  ‰. Three dominant agricultural sources were analysed. The inline-formula M37inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg485a1125f4a1ab40c73d663bc3dee66c acp-21-10527-2021-ie00019.svg41pt18ptacp-21-10527-2021-ie00019.png and inline-formula M38inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimgc098a2282e13ef9f62373f77e0b06802 acp-21-10527-2021-ie00020.svg32pt14ptacp-21-10527-2021-ie00020.png signatures of a cattle feedlot are inline-formula M39inlinescrollmathml - normal 62.9 ± normal 1.3 58pt10ptsvg-formulamathimg4b2916965dea04c6c9d667fcacb78ec2 acp-21-10527-2021-ie00021.svg58pt10ptacp-21-10527-2021-ie00021.png  ‰ and inline-formula M40inlinescrollmathml - normal 310.5 ± normal 4.6 64pt10ptsvg-formulamathimg12ac13028a289d1fc2825b39758cbc24 acp-21-10527-2021-ie00022.svg64pt10ptacp-21-10527-2021-ie00022.png  ‰ respectively, grazing (pasture) cattle have inline-formula M41inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimgcd0a208e4b4d2899640a4887a537e0d7 acp-21-10527-2021-ie00023.svg41pt18ptacp-21-10527-2021-ie00023.png and inline-formula M42inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg5d840c3785e377fcb2be2fdaf9ef06cc acp-21-10527-2021-ie00024.svg32pt14ptacp-21-10527-2021-ie00024.png signatures of inline-formula M43inlinescrollmathml - normal 59.7 ± normal 1.0 58pt10ptsvg-formulamathimgd2d514e4c1f7ecfd9c4dff51bcf582ca acp-21-10527-2021-ie00025.svg58pt10ptacp-21-10527-2021-ie00025.png  ‰ and inline-formula M44inlinescrollmathml - normal 290.5 ± normal 3.1 64pt10ptsvg-formulamathimg02ba9a450e2c4d7fad98baf33678dd9a acp-21-10527-2021-ie00026.svg64pt10ptacp-21-10527-2021-ie00026.png  ‰ respectively, and a piggery sampled had inline-formula M45inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg28878e980776554e9874acbbd3e88629 acp-21-10527-2021-ie00027.svg41pt18ptacp-21-10527-2021-ie00027.png and inline-formula M46inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg92a38a38ea8f2546e4f385db3b2d7fec acp-21-10527-2021-ie00028.svg32pt14ptacp-21-10527-2021-ie00028.png signatures of inline-formula M47inlinescrollmathml - normal 47.6 ± normal 0.2 58pt10ptsvg-formulamathimg9b1fb17755b66540a81e53684cec696d acp-21-10527-2021-ie00029.svg58pt10ptacp-21-10527-2021-ie00029.png  ‰ and inline-formula M48inlinescrollmathml - normal 300.1 ± normal 2.6 64pt10ptsvg-formulamathimg826504dfa3f99fad6751c15f1b3b54b3 acp-21-10527-2021-ie00030.svg64pt10ptacp-21-10527-2021-ie00030.png  ‰ respectively, which reflects emissions from animal waste. An export abattoir (meat works and processing) had inline-formula M49inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimgb36361797659dd2fd97c29a78371eb5f acp-21-10527-2021-ie00031.svg41pt18ptacp-21-10527-2021-ie00031.png and inline-formula M50inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg5e453361ca84b8850a253d762c935201 acp-21-10527-2021-ie00032.svg32pt14ptacp-21-10527-2021-ie00032.png signatures of inline-formula M51inlinescrollmathml - normal 44.5 ± normal 0.2 58pt10ptsvg-formulamathimg0727759c171cc0aa84a294bbcd5e22a4 acp-21-10527-2021-ie00033.svg58pt10ptacp-21-10527-2021-ie00033.png  ‰ and inline-formula M52inlinescrollmathml - normal 314.6 ± normal 1.8 64pt10ptsvg-formulamathimg1da53e6bd0d2affba58abd2a7bf12b80 acp-21-10527-2021-ie00034.svg64pt10ptacp-21-10527-2021-ie00034.png  ‰ respectively. A plume from a wastewater treatment plant had inline-formula M53inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg1a93b7e1851f6b4850ed595a6fc58e85 acp-21-10527-2021-ie00035.svg41pt18ptacp-21-10527-2021-ie00035.png and inline-formula M54inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimgfba2c118711602e40ee558e2b390904f acp-21-10527-2021-ie00036.svg32pt14ptacp-21-10527-2021-ie00036.png signatures of inline-formula M55inlinescrollmathml - normal 47.6 ± normal 0.2 58pt10ptsvg-formulamathimg9091337436331f59bd1399ee4bfb79f4 acp-21-10527-2021-ie00037.svg58pt10ptacp-21-10527-2021-ie00037.png  ‰ and inline-formula M56inlinescrollmathml - normal 177.3 ± normal 2.3 64pt10ptsvg-formulamathimg15c780d2354b97e2dbba7bf1c30c8bdf acp-21-10527-2021-ie00038.svg64pt10ptacp-21-10527-2021-ie00038.png  ‰ respectively. In the Surat Basin, source attribution is possible when both inline-formula M57inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg0b801a4e022e2f63902ed093fb5e7108 acp-21-10527-2021-ie00039.svg41pt18ptacp-21-10527-2021-ie00039.png and inline-formula M58inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimg1d59873d57ae30abbf08185a7776b95d acp-21-10527-2021-ie00040.svg32pt14ptacp-21-10527-2021-ie00040.png are measured for the key categories of CSG, cattle, waste from feedlots and piggeries, and water treatment plants. Under most field situations using inline-formula M59inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg16e70d572b6d6d02c9524107e9a51120 acp-21-10527-2021-ie00041.svg41pt18ptacp-21-10527-2021-ie00041.png alone will not enable clear source attribution. It is common in the Surat Basin for CSG and feedlot facilities to be co-located. Measurement of both inline-formula M60inlinescrollmathml chem italic δ normal 13 normal C chem normal CH normal 4 41pt18ptsvg-formulamathimg652b3aca945950480191fbb5cf261d69 acp-21-10527-2021-ie00042.svg41pt18ptacp-21-10527-2021-ie00042.png and inline-formula M61inlinescrollmathml chem italic δ normal D chem normal CH normal 4 32pt14ptsvg-formulamathimgb7918119e8a00d96169bddb28e2dc23e acp-21-10527-2021-ie00043.svg32pt14ptacp-21-10527-2021-ie00043.png will assist in source apportionment where the plumes from two such sources are mixed.

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Lu, Xinyi / Harris, Stephen J. / Fisher, Rebecca E. / et al: Isotopic signatures of major methane sources in the coal seam gas fields and adjacent agricultural districts, Queensland, Australia. 2021. Copernicus Publications.

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