Arctic peatlands may become a substantial source of a greenhouse gas 300 times more potent than carbon dioxide when they thaw, a new study suggests.
- Researchers estimate regions with high probability of emitting N2O cover almost one-fourth of the entire Arctic
- Study suggests highest nitrous oxide emissions come from melting permafrost that has no plant cover
- Melting vegetated permafrost may also have a "small but significant effect"
The study by a team of Scandinavian scientists indicated that thawing permafrost could release nitrous oxide (N2O) — also known as 'laughing gas' — under increasing temperatures.
Based on an analysis of frozen peat cores exposed to warming conditions in the laboratory, they estimated nitrous oxide emissions could occur from surfaces covering almost one-fourth of the entire Arctic.
The highest emissions, from bare peat samples, were on a par with tropical forest soils — the largest known natural source of nitrous oxide — they reported in Proceedings of the National Academy of Sciences.
Lead author PhD candidate Carolina Voigt said the findings could alter the greenhouse gas budget for the Arctic circle.
She said while research had been done on how much methane and carbon dioxide might be released from thawing Arctic permafrost, few studies had looked at nitrous oxide.
"Usually nitrous oxide emissions from Arctic soils were believed to be negligible, basically because the nitrogen content — the substrate for production of N2O — is probably rather low, or the production rate is rather low due to the cold climate," said Ms Voigt, from the Department of Environmental and Biological Sciences at the University of Eastern Finland.
The study was prompted by the discovery of some nitrous oxide 'hot spots' in the sub-Arctic; regions of bare peatland that seemed to be emitting the gas at a much higher level than the surrounding terrain.
Peat samples from Finnish Lapland
To investigate what impact a warming climate might have on permanently frozen peat deposits, Ms Voight and her colleagues extracted 16 cores of frozen peat — along with whatever plant or lichens grew on their surface — from a site in Finnish Lapland.
The samples were kept frozen for around five months as an incubation period, then warmed in a specially-designed chamber, which allowed researchers to control light levels, humidity, and the water level of the peat.
The study revealed that the thawing of the bare peat permafrost — where there was no vegetation on the peat's surface — led to a five-fold increase in the amount of nitrous oxide release, compared to the amount released when only the uppermost part of the peat thaws, as it does seasonally.
The researchers also showed that a lack of surface vegetation significantly increase the release of nitrous oxide from the thawing peat.
"Plants take up nitrogen from the surface soil so they reduce the nitrogen pool that's available for N2O production in the soil profile, so plants are very effective at reducing N20 emissions," Ms Voigt said.
While the growth of surface plants lowers nitrous oxide emissions by 90 per cent, the researchers said plant-covered peatlands could still make a "small but significant" contribution to total emissions for the region
The study also showed that the wetter the peat, the less nitrous oxide is released.
"So future N2O emissions in the Arctic probably will depend largely on how vegetation and moisture conditions will develop in future," she said.
Commenting on the paper, Professor Peter Grace — Professor of global change at the Queensland University of Technology — said that the study could only add limited information to the understanding of nitrous oxide emissions in the Arctic because it was laboratory-based.
"They also do not present a full budget because of the uncertainties with the actual field based information, [such as] the extent of different peatlands," said Professor Grace, who has written previously about the issue of nitrous oxide release from nitrogen fertilised agricultural soils.
Mashamba ya peat ya Aktiki yanaweza kuwa chanzo kikubwa cha gesi ya chafu yenye nguvu mara 300 kuliko kaboni dioksidi wakati wa kuyeyuka, utafiti mpya unaonyesha. "Kama ilivyoelezwa hapo juu, ""Utafiti unaonyesha kwamba maeneo yenye uwezekano mkubwa wa kutokeza N2O yanafunika karibu robo ya eneo lote la Arctic, na kwamba uzalishaji mkubwa zaidi wa oksidi ya nitrous hutokana na kuyeyuka kwa barafu ya kudumu ambayo haina kifuniko cha mimea, na kuyeyuka kwa barafu ya kudumu ya mimea kunaweza pia kuwa na athari ndogo lakini muhimu.""" Kwa kuzingatia uchambuzi wa nyuklia za mchanga zilizogandishwa zilizofunikwa na hali ya joto katika maabara, walipima uzalishaji wa oksidi ya nitrous inaweza kutokea kutoka kwa nyuso zinazofunika karibu robo ya Arctic nzima. Uchunguzi huo ulionyesha kwamba kiwango cha juu cha uzalishaji wa gesi kutoka kwa sampuli za mchanga haikuwa sawa na ardhi ya misitu ya kitropiki, chanzo kikubwa zaidi cha oksidi nitriki kinachojulikana, kulingana na jarida la Proceedings of the National Academy of Sciences. Mwandishi mkuu wa utafiti huo, Carolina Voigt, alisema matokeo hayo yanaweza kubadilisha kiwango cha gesi zinazosababisha madhara ya joto katika eneo la Arctic. "Wakati huo huo, alisema, ""wakati utafiti umefanywa juu ya kiasi cha methane na kaboni dioksidi inayoweza kutolewa kutoka kwa kuyeyuka kwa barafu ya Arctic, masomo machache yameangalia oksidi ya nitrous.""" "Kila mtu anajua kwamba uzalishaji wa nitrous oxide kutoka udongo wa Arctic ni mdogo, hasa kwa sababu ya kiasi cha nitrojeni, substratum ya uzalishaji wa N2O, ni ya chini sana, au kiwango cha uzalishaji ni cha chini sana kutokana na hali ya hewa ya baridi, ""alisema Bi. Utafiti huo ulisababishwa na ugunduzi wa baadhi ya'mahali pa moto' vya oksidi ya nitrous katika eneo la chini ya Aktiki, maeneo ya peatlands tupu ambayo yalionekana kutokeza gesi kwa kiwango cha juu zaidi kuliko eneo linalozunguka. Kwa mfano, katika utafiti wa hali ya hewa ya joto, Voight na wenzake walichunguza 16 ya peat iliyopunguzwa na mimea iliyokuwa ikikua kwenye uso wake. Sampuli hizo zilihifadhiwa kwa miezi mitano, kisha zikapashwa joto katika chumba kilichotengenezwa kwa ajili ya utafiti huo, ambacho kiliwawezesha watafiti kudhibiti kiwango cha mwanga, unyevu na maji. Utafiti huo ulifunua kuwa kuyeyuka kwa peat permafrost - ambapo hakukuwa na mimea juu ya peat - ilisababisha ongezeko la mara tano katika kiasi cha kutolewa kwa oksidi ya nitrous, ikilinganishwa na kiasi kilichotolewa wakati sehemu ya juu ya peat huyeyuka, kama inavyofanya msimu. Watafiti pia walionyesha kwamba ukosefu wa mimea ya juu huongeza kwa kiasi kikubwa kutolewa kwa nitrous oxide kutoka kwa mchanga unayeyeyuka. "Mimea huchukua nitrojeni kutoka kwenye udongo wa uso, hivyo hupunguza dimbwi la nitrojeni linalopatikana kwa uzalishaji wa N2O katika wasifu wa udongo, kwa hivyo mimea ni bora sana katika kupunguza uzalishaji wa N2O. """ "Wanasayansi wanasema kuwa ""wakati ukuaji wa mimea ya juu hupunguza uzalishaji wa oksidi ya nitrous kwa asilimia 90,"" lakini watafiti wanasema ""miti iliyofunikwa na peat bado inaweza kutoa mchango mdogo lakini muhimu"" kwa uzalishaji wa jumla wa eneo hilo, na utafiti pia ulionyesha kuwa ""mchanga zaidi, oksidi ya nitrous ni kidogo.""" "Kwa hivyo uzalishaji wa N2O katika Arctic ya baadaye labda itategemea sana jinsi mimea na hali ya unyevu itakavyoendelea katika siku zijazo. """ "Profesa Peter Grace, profesa wa mabadiliko ya dunia katika Chuo Kikuu cha Teknolojia cha Queensland, alisema: ""Utafiti huo unaweza tu kuongeza habari ndogo kwa uelewa wa uzalishaji wa nitrous oxide katika Arctic kwa sababu ilikuwa ya maabara." "Hata hivyo, hakuna taarifa kamili kuhusu idadi ya viumbe vilivyopo katika eneo hilo, kama vile idadi ya maeneo ya peat, ""alisema Profesa Grace, ambaye aliandika hapo awali kuhusu suala la kutolewa kwa oksidi nitrous kutoka kwa udongo wa kilimo uliotengenezwa kwa nitrojeni."