Greenhouse gas fluxes in natural and drained peatlands: spatial and temporal dynamics
Date
2021-10-18
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Soodel on oluline roll kliima reguleerimisel, tulvade leevendamisel ning bioloogilise- ja maastikulise mitmekesisuse säilitamisel. Looduslikud sood seovad õhust süsinikku ja talletavad selle turbana, sest keskkond on veega küllastunud. Soode kuivendamine – peamiselt põllumajanduse ja metsanduse tõttu – on muutnud sood olulisteks kasvuhoonegaaside (CO2 ja dilämmastikoksiidi (N2O) ehk naerugaas) allikaks. Turbaalad katavad maailma maismaast vaid 3%, kuid Eestis lausa 22,3% (~1 009 000 ha), ent jätkuvalt looduslikus seisundis soid leidub Eestis vaid 5,5% territooriumist. Doktoritöö eesmärk oli täpsustada kasvuhoonegaaside ‒ CO2, CH4, N2O ‒ vooge looduslikes ja kuivendatud soodes, analüüsida voogusid mõjutavaid keskkonnaparameetreid ning luua statistilised mudelid, mis võimaldaks kaudsete tunnuste abil gaasivooge hinnata. Turbaaladel mõõdeti kasvuhoonegaaside vooge, mulla- vee- taimkatte ning kaasnevate keskkonnaparameetrite andmeid nii Eestis (26 ala) kui ka mujalt (58 ala). Selgus, et intensiivne turbaalade majandamine muudab mulla süsiniku-lämmastiku tasakaalu, suurendab CO2 ja N2O voogusid ja nende varieeruvust. Kui toitainevaestes rabades olid naerugaasivood hoolimata kuivendusest väikesed, siis siirdesoodes, kus mulla lämmastikusisaldus on suurem, olid need ligi kümme korda kõrgemad. Kuivenduse väga tugev mõju ulatub kuni 50 m kaugusele kuivenduskraavist ning mõju on tugevam toitainerikkamates soodes. Looduslikel aladel on üksikute keskkonnatunnuste mõju kasvuhoonegaaside voogudele väiksem kui majandatavatel aladel, kus ökosüsteemi tasakaal on rikutud ning võtmetegurid (sügavam veetase, kõrgem pinnase temperatuur, hapnikusisaldus, parem lämmastiku kättesaadavus mikroorganismidele) tingivad kõrgemad vood nii lokaalselt kui ka globaalselt. Kuna soode taimkatet mõjutab otseselt veerežiim ja mullaprotsessid, on kaugseire vahenditega tuvastatavate taimkattemuutuste kasutamine KHG voogude uurimisel perspektiivne lahendus. Taimestiku indikaatoreid on maastikutasandil aga seni vähe kasutatud. Tulemuste põhjal võib väita, et turbasammalde katvus, aerolaserskanneerimise teel mõõdetud puude kõrgus ja võrakatvus on olulised indikaatorid, mis aitavad hinnata turbaalade kasvuhoonegaaside vooge. Näiteks kirjeldab turbasammalde katvus, sarnaselt puude võrakatvusega, 42% siirdesoode metaani ja 43% N2O voost. Satelliidilt mõõdetavat maapinna temperatuuri saab kasutada CO2 voo indikaatorina – see kirjeldab täpsemini kuivendatud alade CO2 voogu, näiteks mahajäetud turbatootmisaladel 69%, kuivenduskraavidega alal 65%, kui looduslikus rabas (26%). Töö näitab, et inimtekkelise kuivenduse mõju on CO2, CH4 ja N2O voogudele ulatuslik ning neid mõjutavad peamiselt veetase, mullaniiskus, mulla temperatuur, mulla süsiniku ja lämmastiku sisaldus, seda sõltumata turbaala tüübist, klimaatilisest vööndist või kontinendist.
Peatlands are important natural ecosystems with high value for climate regulation, biodiversity conservation and flood control. Intact peatlands bound atmospheric carbon dioxide (CO2) as carbon (C) and accumulate it as peat in water saturated environment. Land use change and associated drainage of mires have turned carbon accumulating peatlands to significant sources of greenhouse gases (GHG) CO2 and N2O. While peatlands cover merely 3% of the world’s land area, they form 22.3% (~1 009 000 ha) of Estonian territory, yet only 5.5% of the territory is covered with mires. The main aim of the study was to quantify GHG ‒ CO2, CH4, N2O ‒ fluxes from natural and drained peatlands, analyse the role of environmental factors on the fluxes and to create statistical models to assess the fluxes using indirect indicators. To conduct the study, 26 peatlands in Estonia and 58 all over the world were sampled for GHG fluxes, soil, water, vegetation, and other accompanying environmental parameters. The results demonstrate that intensive peatland management alters the soil carbon/nitrogen balance, increases emissions of CO2, N2O, and leads to higher variability of GHG emissions. Despite the drainage, emission of N2O was minor in nutrient poor bogs. On the other hand, in transitional bogs with higher soil nitrogen stocks, the emission of N2O was 10 times greater. The effect of drainage is very strong up to 50 m from the ditch and stronger in nutrient rich peatlands. In natural areas, the effect of any single environmental variable on GHG fluxes is smaller and emissions are lower than in managed areas where the ecosystem balance is affected and several key factors e.g. decreased water level, increased soil temperature, oxygen content, nitrogen availability contribute to higher emissions, both in local and global scale. Peatlands’ vegetation composition and structure, relatively easily detectable using remote sensing techniques, is partly controlled by the water level and soil processes. Therefore, vegetation changes are a convenient monitoring tool for the environmental changes related to GHG fluxes. Using vegetation based indicators for estimations of GHG fluxes in landscape level is almost absent in previous studies. The results show that the coverage of Sphagnum mosses, and airborne LIDAR-data based tree layer canopy height and cover are important indicators for assessing the emissions of GHG-s in peatlands. For example, the coverage of Sphagnum mosses alone explains 42% of the CH4 (as does the tree canopy coverage independently) and 43% of N2O flux in transitional bogs. Remotely sensed land surface temperature can be used as indicator for CO2 fluxes. Satellite based land surface temperature is better indicator of CO2 fluxes in drainage affected areas (abandoned peat extraction areas 69%, drained peatland 65%) rather than mires (26%). The results of this dissertation demonstrate the extensive impact of artificial drainage on the fluxes of CO2, CH4 and N2O, and that the leading driving factors of GHG-s such as water table depth or soil water content, soil temperature, soil carbon and nitrogen content are universal despite the type of peatland, climate zone or continent.
Peatlands are important natural ecosystems with high value for climate regulation, biodiversity conservation and flood control. Intact peatlands bound atmospheric carbon dioxide (CO2) as carbon (C) and accumulate it as peat in water saturated environment. Land use change and associated drainage of mires have turned carbon accumulating peatlands to significant sources of greenhouse gases (GHG) CO2 and N2O. While peatlands cover merely 3% of the world’s land area, they form 22.3% (~1 009 000 ha) of Estonian territory, yet only 5.5% of the territory is covered with mires. The main aim of the study was to quantify GHG ‒ CO2, CH4, N2O ‒ fluxes from natural and drained peatlands, analyse the role of environmental factors on the fluxes and to create statistical models to assess the fluxes using indirect indicators. To conduct the study, 26 peatlands in Estonia and 58 all over the world were sampled for GHG fluxes, soil, water, vegetation, and other accompanying environmental parameters. The results demonstrate that intensive peatland management alters the soil carbon/nitrogen balance, increases emissions of CO2, N2O, and leads to higher variability of GHG emissions. Despite the drainage, emission of N2O was minor in nutrient poor bogs. On the other hand, in transitional bogs with higher soil nitrogen stocks, the emission of N2O was 10 times greater. The effect of drainage is very strong up to 50 m from the ditch and stronger in nutrient rich peatlands. In natural areas, the effect of any single environmental variable on GHG fluxes is smaller and emissions are lower than in managed areas where the ecosystem balance is affected and several key factors e.g. decreased water level, increased soil temperature, oxygen content, nitrogen availability contribute to higher emissions, both in local and global scale. Peatlands’ vegetation composition and structure, relatively easily detectable using remote sensing techniques, is partly controlled by the water level and soil processes. Therefore, vegetation changes are a convenient monitoring tool for the environmental changes related to GHG fluxes. Using vegetation based indicators for estimations of GHG fluxes in landscape level is almost absent in previous studies. The results show that the coverage of Sphagnum mosses, and airborne LIDAR-data based tree layer canopy height and cover are important indicators for assessing the emissions of GHG-s in peatlands. For example, the coverage of Sphagnum mosses alone explains 42% of the CH4 (as does the tree canopy coverage independently) and 43% of N2O flux in transitional bogs. Remotely sensed land surface temperature can be used as indicator for CO2 fluxes. Satellite based land surface temperature is better indicator of CO2 fluxes in drainage affected areas (abandoned peat extraction areas 69%, drained peatland 65%) rather than mires (26%). The results of this dissertation demonstrate the extensive impact of artificial drainage on the fluxes of CO2, CH4 and N2O, and that the leading driving factors of GHG-s such as water table depth or soil water content, soil temperature, soil carbon and nitrogen content are universal despite the type of peatland, climate zone or continent.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
greenhouse gases, swamps, environmental indicators, statistical models, beat mineral deposit