Greenhouse gas fluxes in rural landscapes of Estonia
Kuupäev
2010-11-23
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Kasvuhoonegaase on maailmas väga põhjalikult uuritud. Käesolev doktoritöö sisaldab 165 ISI Web of Science andmebaasis publitseeritud artiklite kirjanduslikku ülevaadet ja laiamahulist uurimustööd, mille raames mõõdeti Eestis CH4, N2O ja CO2 emissioone 14 erinevalt maakasutusega alalt . Kirjanduse analüüsi tulemused näitavad, et suurimad metaani emissioonid leiti looduslikelt märgaladelt (106 kg CH4-C ha–1 yr–1). Suurimad lämmastikoksiidi mediaanväärtused leiti kuivendatud (osaliselt taastatud) turbaaladelt ja lammialadelt (vastavalt 7,2 ja 6,5 kg N2O-N ha-1 a-1), millele järgnesid hüdromorfsed põllumaad (4,5 kg N2O-N ha-1 a-1), väetatud heinamaad (4,2-4,7 kg N2O-N ha-1 a-1) ja hüdromorfsed lehtpuumetsad (3,8 kg N2O-N ha–1 a–1). Kõigi kolme mõõdetud kasvuhoonegaaside emissioonid näitasid nii ruumilist kui ka ajalist varieeruvust ning erinevusi vastavalt keskkonnatingimustele. Suurimad CH4 mediaanväärtused määrati hüdromorfsetes kaldaäärsetes metsamuldades ning kuivendatud siirdesoo heinamaa muldades. Kõrgeimad N2O emissioonid tekkisid väetatud autotroofsetel põllumuldadel, automorfsetel kaldaäärsetel metsamuldadel ning kuivendatud siirdesoo metsamuldadel. Suurimad CO2 aastased mediaanväärtused olid automorfsetel söötis maa ja heinamaa muldadel. Kui CO2 ja CH4 emissioonid näitasid uurimisaladel erinevusi vastavalt aastaaegadele, siis dilämmastikoksiidi emiteerimisel ei leitud selgelt ajalist trendi. CO2 emissioonide puhul leiti tugev korrelatsioon (kõikidel uurimisaladel¸ R2=0,72) mulla temperatuuriga, seega emissioonid olid suuremad suveperioodil. CH4 puhul ilmnes erinevus auto- ja hüdromorfsete muldade vahel, mil esimesed olid eelkõige metaani sidujad ning hüdromorfsed mullad emiteerijad. Viiratsi ja Porijõe kaldaäärsete kaitsevööndite puhul leiti tugevad seosed mõõdetud gaaside ja keskmise kuu temperatuuri ning CH4 emissiooni ja kuu sademete hulga vahel. Samuti, kui veetase on väiksem kui 20 cm maapinnast, siis CH4 emissioon suurenes ja N2O ja CO2 vähenes. Reovee järelpuhastina kasutavast pilliroostikust saadud tulemused näitasid, et keskmised N2O emissioonid olid suhteliselt madalad, varieerudes –5,0 to 3,7 μg N2O m–2 h–1. CH4 emissioonide puhul ilmnesid suured ajalis-ruumilised erinevused, kus suurimad väärtused olid sissevoolus. Keskmised CO2 emissioonid roostikust varieerusid 14,3 to 334 mg CO2-C m–2 h–1.
The discharge of the greenhouse gases (GHG) is a thoroughly studied environmental pheno¬menon. In this PhD dissertation, a literature review (based on 165 scienti¬fic papers indexed by the ISI Web of Science) and analysis of measured GHG emissions from 14 different agricultural study sites in Estonia (according to their land-use types) were completed. Literature analysis showed that the most intensive methane emitters were natural peatlands and marshes (106 kg CH4-C ha–1 yr–1), whereas nitrous oxide was mainly emitted from drained (partly restored) peatlands and marshes (7.2 and 6.5 kg N2O-N ha–1 yr–1 respectively), followed by conventional arable lands on hydromorphic soils (4.5 kg N2O-N ha–1 yr–1), fertilized grasslands (4.2–4.7 kg N2O-N ha–1 yr–1) and coniferous forests on hydromorphic soils (3.8 kg N2O-N ha–1 yr–1). The fluxes of all measured gases varied remarkably at both temporal and spatial scales, and were strongly influenced by changes in en¬viron¬mental conditions. The highest CH4 emissions were detected from deci¬duous (riparian alder) forests on hydromorphic soil and drained fen grass¬land, especially before drainage. The hot spots of N2O were drained fen forests, fertilized arable land and riparian forests on automorphic soils. In case of CO2, the highest emissions came from grassland on automorphic soil. While the fluxes of CO2 and CH4 showed different seasonal variations throughout all of the studied groups, no clear differences in the case of N2O, were found between colder and warmer periods. Emissions of CO2 were strongly correlated with soil temperature (through all of the study sites; R2=0.72), and hence the emissions were higher in the summer season. In the case of CH4, a different pattern was seen for automorphic soils, which frequently acted as a sink for CH4, whereas hydromorphic soils were shown to behave as emitters of methane. In cases of the riparian grey alder forest in Porijõgi and riparian ecosystem in Viiratsi, a significant correlation was found between mean monthly air temperature and measured fluxes and between monthly precipitation and CH4 fluxes. Groundwater levels higher than 20 cm from the surface significantly increased CH4 emissions and decreased CO2 and N2O emis¬sions. The average N2O fluxes from the wastewater treatment reedbed were relatively low, varying from –5.0 to 3.7 μg N2O m–2 h–1. The spatial-temporal variation of CH4 emission was great (10.5–16397 μg CH4 m–2 h–1), showing higher values in the inflow. The average CO2 emission from the reedbed varied from 14.3 to 334 mg CO2-C m–2 h–1.
The discharge of the greenhouse gases (GHG) is a thoroughly studied environmental pheno¬menon. In this PhD dissertation, a literature review (based on 165 scienti¬fic papers indexed by the ISI Web of Science) and analysis of measured GHG emissions from 14 different agricultural study sites in Estonia (according to their land-use types) were completed. Literature analysis showed that the most intensive methane emitters were natural peatlands and marshes (106 kg CH4-C ha–1 yr–1), whereas nitrous oxide was mainly emitted from drained (partly restored) peatlands and marshes (7.2 and 6.5 kg N2O-N ha–1 yr–1 respectively), followed by conventional arable lands on hydromorphic soils (4.5 kg N2O-N ha–1 yr–1), fertilized grasslands (4.2–4.7 kg N2O-N ha–1 yr–1) and coniferous forests on hydromorphic soils (3.8 kg N2O-N ha–1 yr–1). The fluxes of all measured gases varied remarkably at both temporal and spatial scales, and were strongly influenced by changes in en¬viron¬mental conditions. The highest CH4 emissions were detected from deci¬duous (riparian alder) forests on hydromorphic soil and drained fen grass¬land, especially before drainage. The hot spots of N2O were drained fen forests, fertilized arable land and riparian forests on automorphic soils. In case of CO2, the highest emissions came from grassland on automorphic soil. While the fluxes of CO2 and CH4 showed different seasonal variations throughout all of the studied groups, no clear differences in the case of N2O, were found between colder and warmer periods. Emissions of CO2 were strongly correlated with soil temperature (through all of the study sites; R2=0.72), and hence the emissions were higher in the summer season. In the case of CH4, a different pattern was seen for automorphic soils, which frequently acted as a sink for CH4, whereas hydromorphic soils were shown to behave as emitters of methane. In cases of the riparian grey alder forest in Porijõgi and riparian ecosystem in Viiratsi, a significant correlation was found between mean monthly air temperature and measured fluxes and between monthly precipitation and CH4 fluxes. Groundwater levels higher than 20 cm from the surface significantly increased CH4 emissions and decreased CO2 and N2O emis¬sions. The average N2O fluxes from the wastewater treatment reedbed were relatively low, varying from –5.0 to 3.7 μg N2O m–2 h–1. The spatial-temporal variation of CH4 emission was great (10.5–16397 μg CH4 m–2 h–1), showing higher values in the inflow. The average CO2 emission from the reedbed varied from 14.3 to 334 mg CO2-C m–2 h–1.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Märksõnad
dissertatsioonid, geograafia, kasvuhoonegaasid, maastikud