scholarly journals CH<sub>4</sub> and N<sub>2</sub>O dynamics in the boreal forest–mire ecotone

2014 ◽  
Vol 11 (6) ◽  
pp. 8049-8084 ◽  
Author(s):  
B. Tupek ◽  
K. Minkkinen ◽  
J. Pumpanen ◽  
T. Vesala ◽  
E. Nikinmaa
Keyword(s):  
Ground Water ◽  
N2o Emission ◽  
N2o Emissions ◽  
Summer Drought ◽  
Drought Period ◽  
Local Climate ◽  
N2o Fluxes ◽  
Spatio Temporal ◽  
Ch4 And N2o ◽  
Water Saturated

Abstract. In spite of advances in greenhouse gas research, the spatio-temporal CH4 and N2O dynamics of boreal landscape remain challenging, e.g. we need clarification of whether the forest–mire transitions are occasional hotspots of landscape CH4 and N2O emissions during exceptionally high and low ground water level events. In our study, we tested the differences and drivers of CH4 and N2O dynamics of forest/mire types in field conditions along the soil moisture gradient of the forest–mire ecotone. Soils changed from podzols to histosols and ground water rose downslope from the depth of 10 m in upland sites to 0.1 m in mires. Yearly meteorological conditions changed from being exceptionally wet to typical and exceptionally dry for the local climate. The median fluxes measured with a static chamber technique varied from −51 to 586 μg m−2 h−1 for CH4 and from 0 to 6 μg m−2 h−1 for N2O between forest/mire types throughout the entire wet-dry period. In spite of the highly dynamic soil water fluctuations in carbon rich soils in forest–mire transitions, there were no large peak emissions in CH4 and N2O fluxes and the flux rates changed minimally between years. Methane oxidations were significantly lower in poorly drained transitions than in the well-drained uplands. Water saturated mires showed large CH4 emissions, which were reduced entirely during the exceptional summer drought period. Near zero N2O fluxes did not differ significantly between the forest/mire types probably due to their low nitrification potential. When up scaling boreal landscapes, pristine forest–mire transitions should be categorized as CH4 oxidation types and background N2O emission types instead of CH4 and N2O emission hotspots.

scholarly journals CH<sub>4</sub> and N<sub>2</sub>O dynamics in the boreal forest–mire ecotone

2015 ◽  
Vol 12 (2) ◽  
pp. 281-297 ◽  
Author(s):  
B. Tupek ◽  
K. Minkkinen ◽  
J. Pumpanen ◽  
T. Vesala ◽  
E. Nikinmaa
Keyword(s):  
Ground Water ◽  
N2o Emission ◽  
N2o Emissions ◽  
Summer Drought ◽  
Drought Period ◽  
Local Climate ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Water Saturated ◽  
Boreal Landscapes

Abstract. In spite of advances in greenhouse gas research, the spatiotemporal CH4 and N2O dynamics of boreal landscapes remain challenging, e.g., we need clarification of whether forest–mire transitions are occasional hotspots of landscape CH4 and N2O emissions during exceptionally high and low ground water level events. In our study, we tested the differences and drivers of CH4 and N2O dynamics of forest/mire types in field conditions along the soil moisture gradient of the forest–mire ecotone. Soils changed from Podzols to Histosols and ground water rose downslope from a depth of 10 m in upland sites to 0.1 m in mires. Yearly meteorological conditions changed from being exceptionally wet to typical and exceptionally dry for the local climate. The median fluxes measured with a static chamber technique varied from −51 to 586 μg m−2 h−1 for CH4 and from 0 to 6 μg m−2 h−1 for N2O between forest and mire types throughout the entire wet–dry period. In spite of the highly dynamic soil water fluctuations in carbon rich soils in forest–mire transitions, there were no large peak emissions in CH4 and N2O fluxes and the flux rates changed minimally between years. Methane uptake was significantly lower in poorly drained transitions than in the well-drained uplands. Water-saturated mires showed large CH4 emissions, which were reduced entirely during the exceptional summer drought period. Near-zero N2O fluxes did not differ significantly between the forest and mire types probably due to their low nitrification potential. When upscaling boreal landscapes, pristine forest–mire transitions should be regarded as CH4 sinks and minor N2O sources instead of CH4 and N2O emission hotspots.

scholarly journals Water Salinity Should Be Reduced for Irrigation to Minimize Its Risk of Increased Soil N2O Emissions

2018 ◽  
Vol 15 (10) ◽  
pp. 2114 ◽  
Author(s):  
Qi Wei ◽  
Junzeng Xu ◽  
Linxian Liao ◽  
Yawei Li ◽  
Haiyu Wang ◽  
...  
Keyword(s):  
Saline Water ◽  
N2o Emission ◽  
Salinity Level ◽  
N2o Emissions ◽  
Low Salinity ◽  
Nitrogen Inputs ◽  
Salinity Levels ◽  
N2o Fluxes ◽  
Moisture Dynamics ◽  
Irrigated Soils

To reveal the effect of irrigation salinity on soil nitrous oxide (N2O) emission, pot experiments were designed with three irrigation salinity levels (NaCl and CaCl2 of 1, 2.5 and 4 g/L equivalence, Ec = 3.6, 8.1 and 12.7 ds/m), either for 0 kg N/ha (N0) or 120 kg N/ha (N120) nitrogen inputs. N2O emissions from soils irrigated at different salinity levels varied in a similar pattern which was triggered by soil moisture dynamics. Yet, the magnitudes of pulse N2O fluxes were significantly varied, with the peak flux at 5 g/L irrigation salinity level being much higher than at 2 and 8 g/L. Compared to fresh water irrigated soils, cumulative N2O fluxes were reduced by 22.7% and 39.6% (N0), 29.1% and 39.2% (N120) for soils irrigated with 2 and 8 g/L saline water, while they were increased by 87.7% (N0) and 58.3% (N120) for soils irrigated with 5 g/L saline water. These results suggested that the effect degree of salinity on consumption and production of N2O might vary among irrigation salinity ranges. As such, desalinating brackish water to a low salinity level (such as 2 g/L) before it is used for irrigation might be helpful for solving water resources crises and mitigating soil N2O emissions.

scholarly journals Water regime affects soil N2O emission and tomato yield grown under different types of fertilisers

2017 ◽  
pp. 74-79 ◽  
Author(s):  
Luca Vitale ◽  
Anna Tedeschi ◽  
Franca Polimeno ◽  
Lucia Ottaiano ◽  
Giuseppe Maglione ◽  
...  
Keyword(s):  
Water Supply ◽  
Plant Biomass ◽  
N Uptake ◽  
Photochemical Efficiency ◽  
N2o Emission ◽  
Fruit Production ◽  
N2o Emissions ◽  
Mineral Fertiliser ◽  
N2o Fluxes ◽  
Reduced Water

Tomato plants were subjected to three fertilisation treatments (M: mineral fertiliser; DMPP: mineral fertiliser + 3,4- dimethylpyrazole phosphate; OM: NKP + organic animal manure) in combination with two water regimes (100% and 50% evapotranspiration). Plant biomass, fruit production, nitrogen use efficiency (NUE) and N uptake, maximal PSII photochemical efficiency, Fv/Fm and cumulative soil N2O emission were determined. Well-watered OM plants showed higher values of biomass, fruit production, NUE and N uptake than M and DMPP plants; cumulative N2O fluxes were lower in DMPP plots than in M and OM plots. The reduced water supply determined a drop in crop biomass, fruit production, NUE and N uptake, and cumulative N2O fluxes in M and OM treatments that were higher in OM plots, whereas it determined a significant rise in cumulative N2O fluxes in DMPP plots that was lower in absolute term compared to M and OM plots recorded under well-water irrigation. It can be concluded that DMPP added-fertiliser has a good performance in semiarid environment resulting a better nitrogen source compared to conventional and organo-mineral fertilisers under reduced water supply, able to preserve crop yield and to determine soil N2O emissions (as expressed in CO2 eq) not dangerous for global environment.

scholarly journals Methane and nitrous oxide fluxes across an elevation gradient in the tropical Peruvian Andes

2014 ◽  
Vol 11 (8) ◽  
pp. 2325-2339 ◽  
Author(s):  
Y. A. Teh ◽  
T. Diem ◽  
S. Jones ◽  
L. P. Huaraca Quispe ◽  
E. Baggs ◽  
...  
Keyword(s):  
Elevation Gradient ◽  
Laboratory Data ◽  
Montane Forest ◽  
N2o Emissions ◽  
Ch4 Flux ◽  
Peruvian Andes ◽  
Modelling Studies ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Montane Grasslands

Abstract. Remote sensing and inverse modelling studies indicate that the tropics emit more CH4 and N2O than predicted by bottom-up emissions inventories, suggesting that terrestrial sources are stronger or more numerous than previously thought. Tropical uplands are a potentially large and important source of CH4 and N2O often overlooked by past empirical and modelling studies. To address this knowledge gap, we investigated spatial, temporal and environmental trends in soil CH4 and N2O fluxes across a long elevation gradient (600–3700 m a.s.l.) in the Kosñipata Valley, in the southern Peruvian Andes, that experiences seasonal fluctuations in rainfall. The aim of this work was to produce preliminary estimates of soil CH4 and N2O fluxes from representative habitats within this region, and to identify the proximate controls on soil CH4 and N2O dynamics. Area-weighted flux calculations indicated that ecosystems across this altitudinal gradient were both atmospheric sources and sinks of CH4 on an annual basis. Montane grasslands (3200–3700 m a.s.l.) were strong atmospheric sources, emitting 56.94 ± 7.81 kg CH4-C ha−1 yr−1. Upper montane forest (2200–3200 m a.s.l.) and lower montane forest (1200–2200 m a.s.l.) were net atmospheric sinks (−2.99 ± 0.29 and −2.34 ± 0.29 kg CH4-C ha−1 yr−1, respectively); while premontane forests (600–1200 m a.s.l.) fluctuated between source or sink depending on the season (wet season: 1.86 ± 1.50 kg CH4-C ha−1 yr−1; dry season: −1.17 ± 0.40 kg CH4-C ha−1 yr−1). Analysis of spatial, temporal and environmental trends in soil CH4 flux across the study site suggest that soil redox was a dominant control on net soil CH4 flux. Soil CH4 emissions were greatest from habitats, landforms and during times of year when soils were suboxic, and soil CH4 efflux was inversely correlated with soil O2 concentration (Spearman's ρ = −0.45, P < 0.0001) and positively correlated with water-filled pore space (Spearman's ρ = 0.63, P <0.0001). Ecosystems across the region were net atmospheric N2O sources. Soil N2O fluxes declined with increasing elevation; area-weighted flux calculations indicated that N2O emissions from premontane forest, lower montane forest, upper montane forest and montane grasslands averaged 2.23 ± 1.31, 1.68 ± 0.44, 0.44 ± 0.47 and 0.15 ± 1.10 kg N2O-N ha−1 yr−1, respectively. Soil N2O fluxes from premontane and lower montane forests exceeded prior model predictions for the region. Comprehensive investigation of field and laboratory data collected in this study suggest that soil N2O fluxes from this region were primarily driven by denitrification; that nitrate (NO3−) availability was the principal constraint on soil N2O fluxes; and that soil moisture and water-filled porosity played a secondary role in modulating N2O emissions. Any current and future changes in N management or anthropogenic N deposition may cause shifts in net soil N2O fluxes from these tropical montane ecosystems, further enhancing this emission source.

Effects of nitrogen fertiliser and wheat straw application on CH4 and N2O emissions from a paddy rice field

Soil Research ◽  
2007 ◽  
Vol 45 (5) ◽  
pp. 359 ◽  
Author(s):  
J. Ma ◽  
X. L. Li ◽  
H. Xu ◽  
Y. Han ◽  
Z. C. Cai ◽  
...  
Keyword(s):  
Wheat Straw ◽  
N2o Emission ◽  
Application Rate ◽  
N2o Emissions ◽  
Ch4 Emission ◽  
Nitrogen Fertiliser ◽  
Paddy Rice Field ◽  
Straw Incorporation ◽  
Ch4 And N2o ◽  
Fertiliser Application

A 3-year field experiment was conducted to study the effects of nitrogen fertiliser and straw application on CH4 and N2O emissions from a paddy rice field in China from 2003 to 2005. Three rates of nitrogen fertiliser (0, 200, and 270 kg N/ha) and 2 levels of wheat straw (0 and 3.75 × 103 kg/ha) were adopted in this experiment. The effect of nitrogen fertiliser application on CH4 emission seemed to be affected by application rate. Nitrogen fertiliser decreased CH4 emission relative to the control when applied at a rate of 200 kg N/ha, but the effect lessened if the application rate was further increased to a rate of 270 kg N/ha. The depressive effect of nitrogen fertiliser application on CH4 emissions from rice fields became more pronounced when wheat straw was also incorporated with fertiliser, compared with nitrogen fertiliser application alone. Straw incorporation significantly enhanced CH4 emission by 3–11 times (P < 0.05). Nitrogen fertiliser application increased N2O emission by 5–6 times when applied at a rate of 200 kg N/ha and by 10–14 times when applied at a rate of 270 kg N/ha. On average, straw incorporation tended to decrease N2O emission by about 30% significant (P > 0.05). More than 50% of seasonal total amount of N2O was emitted within 11 days after fertiliser application at panicle initiation. The global warming potential caused by both CH4 and N2O emissions was affected by nitrogen fertiliser application rate and significantly stimulated by wheat straw incorporation. The global warming potential was lowest when nitrogen fertiliser was applied at a rate of 200 kg N/ha.

scholarly journals Methane and nitrous oxide fluxes from the tropical Andes

2013 ◽  
Vol 10 (11) ◽  
pp. 17397-17438 ◽  
Author(s):  
Y. A. Teh ◽  
T. Diem ◽  
S. Jones ◽  
L. P. Huaraca Quispe ◽  
E. Baggs ◽  
...  
Keyword(s):  
Elevation Gradient ◽  
Laboratory Data ◽  
Montane Forest ◽  
N2o Emissions ◽  
Wet Season ◽  
Ch4 Flux ◽  
Modelling Studies ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Montane Grasslands

Abstract. Remote sensing and inverse modelling studies indicate that the tropics emit more CH4 and N2O than predicted by bottom-up emissions inventories, suggesting that terrestrial sources are stronger or more numerous than previously thought. Tropical uplands are a potentially large and important source of CH4 and N2O often overlooked by past empirical and modelling studies. To address this knowledge gap, we investigated spatial, temporal and environmental trends in CH4 and N2O fluxes across a~long elevation gradient (600–3700 m a.s.l.) in the Kosñipata Valley, in the southern Peruvian Andes that experiences seasonal fluctuations in rainfall. The aim of this work was to produce preliminary estimates of CH4 and N2O fluxes from representative habitats within this region, and to identify the proximate controls on soil CH4 and N2O dynamics. Ecosystems across this altitudinal gradient were both atmospheric sources and sinks of CH4 on an annual basis. Montane grasslands (or, puna; 3200–3700 m a.s.l.) were strong atmospheric sources, emitting 56.94 ± 7.81kg CH4-C ha−1 yr−1. Upper montane forest (2200–3200 m a.s.l.) and lower montane forest (1200–2200 m a.s.l.) were net atmospheric sinks (−2.99 ± 0.29 kg CH4-C ha−1 yr−1 and −2.34 ± 0.29 kg CH4-C ha−1 yr−1, respectively); while premontane forests (600–1200 m a.s.l.) fluctuated between source or sink depending on the season (wet season: 1.86 ± 1.50 CH4-C ha−1 yr−1; dry season: −1.17 ± 0.40 CH4-C ha−1 yr−1). Analysis of spatial, temporal and environmental trends in CH4 flux across the study site suggest that soil redox was a dominant control on net CH4 flux. CH4 emissions were greatest from elevations, landforms and during times of year when soils were sub-oxic, and CH4 efflux was inversely correlated with soil O2 concentration (r2 = 0.82, F1, 125 = 588.41, P < 0.0001). Ecosystems across the region were net atmospheric N2O sources. N2O fluxes declined with increasing elevation; N2O emissions from premontane forest, lower montane forest, upper montane forest and montane grasslands averaged 2.23 ± 1.31 kg N2O-N ha−1 yr−1, 1.68 ± 0.44 kg N2O-N ha−1 yr−1, 0.44 ± 0.47 kg N2O-N ha−1 yr−1 and 0.15 ± 1.10 kg N2O-N ha−1 yr−1, respectively. N2O fluxes from premontane and lower montane forests exceeded prior model predictions for the region. Comprehensive investigation of field and laboratory data collected in this study suggest that N2O fluxes from this region were primarily driven by denitrification; that nitrate (NO3−) availability was the principal constraint on N2O fluxes; and that soil moisture and water-filled porosity played a secondary role in modulating N2O emissions. Any current and future changes in N management or anthropogenic N deposition may cause shifts in net N2O fluxes from these tropical montane ecosystems, further enhancing this emission source.

scholarly journals Combining two complementary micrometeorological methods to measure CH<sub>4</sub> and N<sub>2</sub>O fluxes over pasture

2015 ◽  
Vol 12 (18) ◽  
pp. 15245-15299 ◽  
Author(s):  
J. Laubach ◽  
M. Barthel ◽  
A. Fraser ◽  
J. E. Hunt ◽  
D. W. T. Griffith
Keyword(s):  
Large Fraction ◽  
Industrial Sector ◽  
N2o Emissions ◽  
Emission Rates ◽  
Co2 Fluxes ◽  
Nitrogen Inputs ◽  
Animal Excreta ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Carbon Dioxide Co2

Abstract. New Zealand's largest industrial sector is pastoral agriculture, giving rise to a large fraction of the country's emissions of methane (CH4) and nitrous oxide (N2O). We designed a system to continuously measure CH4 and N2O fluxes at the field scale on two adjacent pastures that differed with respect to management. At the core of this system was a closed-cell Fourier-transform infrared spectrometer (FTIR), measuring the mole fractions of CH4, N2O and carbon dioxide (CO2) at two heights at each site. In parallel, CO2 fluxes were measured using eddy-covariance instrumentation. We applied two different micrometeorological ratio methods to infer the CH4 and N2O fluxes from their respective mole fractions and the CO2 fluxes. The first is a variant of the flux-gradient method, where it is assumed that the turbulent diffusivities of CH4 and N2O equal that of CO2. This method was reliable when the CO2 mole-fraction difference between heights was at least 4 times greater than the FTIR's resolution of differences. For the second method, the temporal increases of mole fractions in the stable nocturnal boundary layer, which are correlated for concurrently-emitted gases, are used to infer the unknown fluxes of CH4 and N2O from the known flux of CO2. This method was sensitive to "contamination" from trace gas sources other than the pasture of interest and therefore required careful filtering. With both methods combined, estimates of mean daily CH4 and N2O fluxes were obtained for 60 % of days at one site and 77 % at the other. Both methods indicated both sites as net sources of CH4 and N2O. Mean emission rates for one year at the unfertilised, winter-grazed site were 8.2 (± 0.91) nmol CH4 m−2 s−1 and 0.40 (± 0.018) nmol N2O m−2 s−1. During the same year, mean emission rates at the irrigated, fertilised and rotationally-grazed site were 7.0 (± 0.89) nmol CH4 m−2 s−1 and 0.57 (± 0.019) nmol N2O m−2 s−1. At this site, the N2O emissions amounted to 1.19 (± 0.15) % of the nitrogen inputs from animal excreta and fertiliser application.

Nitrous oxide emission factor from cattle urine and dung in native grassland of the Pampa biome, South Brazil

Soil Research ◽  
2020 ◽  
Vol 58 (2) ◽  
pp. 198 ◽  
Author(s):  
Janquieli Schirmann ◽  
Diego Fernandes de Bastos ◽  
Douglas Adams Weiler ◽  
Murilo G. Veloso ◽  
Jeferson Dieckow ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Emission Factor ◽  
Live Weight ◽  
N2o Emission ◽  
N2o Emissions ◽  
Native Grassland ◽  
Tier 1 ◽  
N2o Fluxes ◽  
The Impact ◽  
South Brazil

Native grassland supports extensive livestock production in the Pampas of South America, but the impact of cattle excreta on nitrous oxide (N2O) emissions remains unknown in this biome. The objective of this study was to determine the N2O emission factor (EF-N2O, % of N applied that is emitted as N2O) for urine and dung from beef cattle grazing on native grasslands. A field trial was conducted under low and moderate forage allowances (FA4 and FA12; i.e. 4 and 12 kg dry matter/100 kg live weight respectively) during the 30th year of a long-term grassland experiment on a Typic Paleudult in South Brazil. Urine and dung were applied onto separate patches, at rates equivalent to one average urination or defecation; and N2O fluxes were monitored with closed static chambers over 338 days. In adjacent microplots receiving the same excreta treatment, water-filled pore space, nitrate, ammonium and extractable dissolved organic carbon were monitored in the top 0.1 m of soil. Averaged across the forage allowances, daily soil N2O fluxes were low in the control without excreta (1.3 g N ha–1), but increased upon application of dung (3.8 g N ha–1) and urine (66 g N ha–1). The annual N2O emission and the EF-N2O for urine were greater under FA12 than FA4, but no difference was observed for dung. The positive relationships between N2O-N emissions and ammonium intensity and nitrate intensity suggest that N2O may have been produced concurrently by nitrification, nitrifier/denitrification and denitrification. On average, the EF-N2O was almost 10 times higher for urine than for dung (0.74% vs 0.08%), both much lower than the IPCC’s Tier 1 default value of 2%. Our findings reinforce the need for disaggregating the EF-N2O for urine and dung and of revising the IPCC’s Tier 1 EF-N2O.

scholarly journals Carbon Sequestration and Contribution of CO2, CH4 and N2O Fluxes to Global Warming Potential from Paddy-Fallow Fields on Mineral Soil Beneath Peat in Central Hokkaido, Japan

Agriculture ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 6 ◽  
Author(s):  
Habib Mohammad Naser ◽  
Osamu Nagata ◽  
Sarmin Sultana ◽  
Ryusuke Hatano
Keyword(s):  
Global Warming ◽  
Carbon Sequestration ◽  
Growing Season ◽  
Rice Paddy ◽  
Paddy Fields ◽  
N2o Emissions ◽  
Growing Period ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Winter Fallow

Since each greenhouse gas (GHG) has its own radiative capacity, all three gasses (CO2, CH4 and N2O) must be accounted for by calculating the net global warming potential (GWP) in a crop production system. To compare the impact of GHG fluxes from the rice growing and the fallow season on the annual gas fluxes, and their contribution to the GWP and carbon sequestration (CS) were evaluated. From May to April in Bibai (43°18′ N, 141°44′ E), in central Hokkaido, Japan, three rice paddy fields under actual management conditions were investigated to determine CS and the contribution of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes to GWP. Methane and N2O fluxes were measured by placing the chamber over the rice plants covering four hills and CO2 fluxes from rice plants root free space in paddy fields were taken as an indicator of soil microbial respiration (Rm) using the closed chamber method. Soil CS was calculated as the difference between net primary production (NPP) and loss of carbon (C) through Rm, emission of CH4 and harvest of crop C. Annual cumulative Rm ranged from 422 to 519 g C m−2 yr−1; which accounted for 54.7 to 55.5% of the rice growing season in particular. Annual cumulative CH4 emissions ranged from 75.5 to 116 g C m−2 yr−1 and this contribution occurred entirely during the rice growing period. Total cumulative N2O emissions ranged from 0.091 to 0.154 g N m−2 yr−1 and from 73.5 to 81.3% of the total N2O emissions recorded during the winter-fallow season. The CS ranged from −305 to −365 g C m−2 yr−1, suggesting that C input by NPP may not be compensate for the loss of soil C. The loss of C in the winter-fallow season was much higher (62 to 66%) than in the growing season. The annual net GWP from the investigated paddy fields ranged from 3823 to 5016 g CO2 equivalent m−2 yr−1. Annual GWPCH4 accounted for 71.9 to 86.1% of the annual net GWP predominantly from the rice growing period. These results indicate that CH4 dominated the net GWP of the rice paddy.

scholarly journals Methane and nitrous oxide exchange over a managed hay meadow

2014 ◽  
Vol 11 (24) ◽  
pp. 7219-7236 ◽  
Author(s):  
L. Hörtnagl ◽  
G. Wohlfahrt
Keyword(s):  
Nitrous Oxide ◽  
Sink Strength ◽  
N2o Emissions ◽  
Eddy Covariance Method ◽  
Sources And Sinks ◽  
Mountain Grassland ◽  
Time Period ◽  
Soil Temperatures ◽  
N2o Fluxes ◽  
Ch4 And N2o

Abstract. The methane (CH4) and nitrous oxide (N2O) exchange of a temperate mountain grassland near Neustift, Austria, was measured during 2010–2012 over a time period of 22 months using the eddy covariance method. Exchange rates of both compounds at the site were low, with 97% of all half-hourly CH4 and N2O fluxes ranging between ±200 and ±50 ng m−2 s−1, respectively. The meadow acted as a sink for both compounds during certain time periods, but was a clear source of CH4 and N2O on an annual timescale. Therefore, both gases contributed to an increase of the global warming potential (GWP), effectively reducing the sink strength in terms of CO2 equivalents of the investigated grassland site. In 2011, our best guess estimate showed a net greenhouse gas (GHG) sink of −32 g CO2 equ. m−2 yr−1 for the meadow, whereby 55% of the CO2 sink strength of −71 g CO2 m−2 yr−1 was offset by CH4 (N2O) emissions of 7 (32) g CO2 equ. m−2 yr−1. When all data were pooled, the ancillary parameters explained 27 (42)% of observed CH4 (N2O) flux variability, and up to 62 (76)% on shorter timescales in-between management dates. In the case of N2O fluxes, we found the highest emissions at intermediate soil water contents and at soil temperatures close to 0 or above 14 °C. In comparison to CO2, H2O and energy fluxes, the interpretation of CH4 and N2O exchange was challenging due to footprint heterogeneity regarding their sources and sinks, uncertainties regarding post-processing and quality control. Our results emphasize that CH4 and N2O fluxes over supposedly well-aerated and moderately fertilized soils cannot be neglected when evaluating the GHG impact of temperate managed grasslands.

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