Fluxes of the greenhouse gases CO2, CH4 and N2O from abandoned peat extraction areas: Impact of bioenergy crop cultivation and peatland restoration
Kuupäev
2015-10-09
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Looduslikud sood on vaatamata nende küllaltki väikesele katvusele olulised süsiniku (C) sidujad. Soid on kasutatud väga mitmesugustel eesmärkidel, sealhulgas kütte- ja aiandusturba kaevandamiseks. Turbakaevandamise lõppedes jäävad soodest järele õhema või tüsedama jääkturbakihiga alad ehk jääkturbasood, mis on kuivendamise tulemusel kiirenenud turba lagunemise ja taimkatte ning seeläbi ka CO2 sidumise puudumise tõttu olulised kasvuhoonegaaside (KHGde) allikad. Seega on oluline jääkturbasood taastada viisil, mis nende KHGde emissiooni vähendaks. Erinevate korrastamisviiside aastaseid C ja KHGde bilansse kajastavaid uuringuid on seni aga kirjanduses jätkuvalt vähe. Käesoleva doktoritöö peamiseks eesmärgiks oli uurida päiderooga rekultiveerimise (väetatud ja väetamata uurimisalad) ja turbasamblaga taastamise (kõrge ja madala veetasemega uurimisalad) mõju jääkturbasoode KHGde (CO2, CH4 ja N2O) voogudele. Töö tulemused näitasid, et päiderooga taimestatud uurimisalade KHGde emissioonid olid mahajäetud turbatootmisalaga võrreldes madalamad. Lisaks oli näha, et väetamine vähendas päideroo kasvualade summaarset kasvuhooneefekti tekitavat mõju, kuna selle positiivne efekt biomassi produktsioonile ja seeläbi ka CO2 sidumise intensiivsusele ületas samaaegse N2O emissiooni suurenemise mitmekordselt. Aastased kogubilansid näitasid aga, et olenevalt sademete hulgast võivad päiderooga taimestatud turbatootmisalad olla kokkuvõttes nii C ja KHGde allikad kui ka sidujad ning seega on päiderooga taimestamise tulemuslikkus tugevalt mõjutatud klimaatilistest tingimustest. Veetaseme tõstmine ning turbasambla fragmentide külvamine vähendas KHGde emissiooni mahajäetud turbatootmisalaga võrreldes ligikaudu kaks korda. Selle peamiseks põhjuseks oli oluliselt kahanenud heterotroofne hingamine, mis näitab, et veetaseme tõstmine on väga efektiivne meetod kuivendatud soodes toimuva aeroobse turba lagunemise vähendamiseks. Aastased kogubilansid näitasid aga, et taimestikupoolne CO2 sidumine ei suutnud kolm aastat peale taastamist veel KHGde emissiooni tasakaalustada ning seetõttu olid alad jätkuvalt C ja KHGde allikad. Lisaks, veetaseme erinevuse mõju C ja KHGde bilansile oli taastatud alade omavahelisel võrdlemisel väike. Kokkuvõtvalt näitasid doktoritöö tulemused, et nii päiderooga rekultiveerimine kui ka turbasamblaga taastamine võivad olla efektiivsed meetodid jääkturbasoode kasvuhooneefekti tekitava mõju vähendamiseks.
Natural peatlands are an important global carbon (C) sink. Within the past century, however, many peatlands have been drained and exploited for various purposes, including peat extraction for fuel and horticultural use. After cessation of peat extraction activities, vast areas of degraded peat soils remain acting as persistent net sources of C and greenhouse gases (GHGs) due to enhanced peat decomposition and absence of plant CO2 uptake. Thus, there is a need for after-use strategies that mitigate the GHG emission from these areas; currently, however, knowledge about the impact of different after-use options and associated management practices on annual C and GHG balances of abandoned peat extraction areas is limited. The goal of this dissertation was to investigate the impact of i) fertilized and nonfertilized reed canary grass (RCG; Phalaris arundinacea) cultivation and ii) peatland restoration with high and low water table levels (WTLs) on the GHG exchanges (incl. CO2, CH4 and N2O) in abandoned peat extraction areas. The results showed that RCG cultivation reduced the net GHG emissions compared to bare peat soil. Moreover, fertilization increased the climate benefit potential of RCG cultivation since the additional nitrogen supply resulted in enhanced biomass production and associated CO2 uptake which largely exceeded the concurrent increase in N2O emissions. However, the annual C and GHG sink-source strength of the RCG cultivations varied between a sink in a wet and a source in a dry year highlighting its sensitivity to climatic conditions. Restoration of the peat extraction area reduced the net GHG emissions by half relative to bare peat soil. This was mainly due to a large reduction in heterotrophic respiration which advocates raising the WTL as an effective method to reduce the aerobic peat decomposition. On an annual scale, however, both restored treatments acted as net C and GHG sources indicating that CO2 uptake by the re-established vegetation was not yet able to compensate for the GHG emissions. Furthermore, the effect of contrasting WTLs on the C and GHG balances of the restored treatments was limited. Overall, this dissertation concludes that both RCG cultivation as well as peatland restoration may serve as effective methods to mitigate the negative climate impact of abandoned peat extractions areas.
Natural peatlands are an important global carbon (C) sink. Within the past century, however, many peatlands have been drained and exploited for various purposes, including peat extraction for fuel and horticultural use. After cessation of peat extraction activities, vast areas of degraded peat soils remain acting as persistent net sources of C and greenhouse gases (GHGs) due to enhanced peat decomposition and absence of plant CO2 uptake. Thus, there is a need for after-use strategies that mitigate the GHG emission from these areas; currently, however, knowledge about the impact of different after-use options and associated management practices on annual C and GHG balances of abandoned peat extraction areas is limited. The goal of this dissertation was to investigate the impact of i) fertilized and nonfertilized reed canary grass (RCG; Phalaris arundinacea) cultivation and ii) peatland restoration with high and low water table levels (WTLs) on the GHG exchanges (incl. CO2, CH4 and N2O) in abandoned peat extraction areas. The results showed that RCG cultivation reduced the net GHG emissions compared to bare peat soil. Moreover, fertilization increased the climate benefit potential of RCG cultivation since the additional nitrogen supply resulted in enhanced biomass production and associated CO2 uptake which largely exceeded the concurrent increase in N2O emissions. However, the annual C and GHG sink-source strength of the RCG cultivations varied between a sink in a wet and a source in a dry year highlighting its sensitivity to climatic conditions. Restoration of the peat extraction area reduced the net GHG emissions by half relative to bare peat soil. This was mainly due to a large reduction in heterotrophic respiration which advocates raising the WTL as an effective method to reduce the aerobic peat decomposition. On an annual scale, however, both restored treatments acted as net C and GHG sources indicating that CO2 uptake by the re-established vegetation was not yet able to compensate for the GHG emissions. Furthermore, the effect of contrasting WTLs on the C and GHG balances of the restored treatments was limited. Overall, this dissertation concludes that both RCG cultivation as well as peatland restoration may serve as effective methods to mitigate the negative climate impact of abandoned peat extractions areas.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Märksõnad
kasvuhoonegaasid, jääksood, ökoloogiline taastamine, päideroog, turbasammal, greenhouse gases, cut-over peatlands, ecological restoration, reed canary grass, peat moss