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 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.

scholarly journals Wet-season spatial variability of N<sub>2</sub>O emissions from a tea field in subtropical central China

2015 ◽  
Vol 12 (2) ◽  
pp. 1475-1508
Author(s):  
X. Fu ◽  
X. Liu ◽  
Y. Li ◽  
J. Shen ◽  
Y. Wang ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Ordinary Kriging ◽  
Spatial Interpolation ◽  
Central China ◽  
N2o Emissions ◽  
Regression Kriging ◽  
Wet Season ◽  
Interpolation Methods ◽  
N2o Fluxes ◽  
Tea Field

Abstract. Tea fields emit large amounts of nitrous oxide (N2O) to the atmosphere. Obtaining accurate estimations of N2O emissions from tea-planted soils is challenging due to strong spatial variability. We examined the spatial variability of N2O emissions from a red-soil tea field in Hunan province, China, on 22 April 2012 (in a wet season) using 147 static mini chambers approximately regular gridded in a 4.0 ha tea field. The N2O fluxes for a 30 min snapshot (10–10.30 a.m.) ranged from −1.73 to 1659.11 g N ha−1 d−1 and were positively skewed with an average flux of 102.24 g N ha−1 d−1. The N2O flux data were transformed to a normal distribution by using a logit function. The geostatistical analyses of our data indicated that the logit-transformed N2O fluxes (FLUX30t) exhibited strong spatial autocorrelation, which was characterized by an exponential semivariogram model with an effective range of 25.2 m. As observed in the wet season, the logit-transformed soil ammonium-N (NH4Nt), soil nitrate-N (NO3Nt), soil organic carbon (SOCt), total soil nitrogen (TSNt) were all found to be significantly correlated with FLUX30t (r=0.57–0.71, p<0.001). Three spatial interpolation methods (ordinary kriging, regression kriging and cokriging) were applied to estimate the spatial distribution of N2O emissions over the study area. Cokriging with NH4Nt and NO3Nt as covariables (r= 0.74 and RMSE =1.18) outperformed ordinary kriging (r= 0.18 and RMSE =1.74), regression kriging with the sample position as a predictor (r= 0.49 and RMSE =1.55) and cokriging with SOCt as a covariable (r= 0.58 and RMSE =1.44). The predictions of the three kriging interpolation methods for the total N2O emissions of the 4.0 ha tea field ranged from 148.2 to 208.1 g N d−1, based on the 30 min snapshots obtained during the wet season. Our findings suggested that to accurately estimate the total N2O emissions over a region, the environmental variables (e.g., soil properties) and the current land use pattern (e.g., tea row transects in the present study) must be included in spatial interpolation. Additionally, compared with other kriging approaches, the cokriging prediction approach showed great advantages in being easily deployed, and more importantly providing accurate regional estimation of N2O emissions from tea-planted soils.

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 Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin

2017 ◽  
Vol 14 (15) ◽  
pp. 3669-3683 ◽  
Author(s):  
Yit Arn Teh ◽  
Wayne A. Murphy ◽  
Juan-Carlos Berrio ◽  
Arnoud Boom ◽  
Susan E. Page
Keyword(s):  
Nitrous Oxide ◽  
Amazon Basin ◽  
High Water ◽  
Trace Gas ◽  
Vegetation Types ◽  
Wet Season ◽  
N2o Flux ◽  
Ch4 Flux ◽  
Tropical Peatlands ◽  
Ch4 And N2o

Abstract. The Amazon plays a critical role in global atmospheric budgets of methane (CH4) and nitrous oxide (N2O). However, while we have a relatively good understanding of the continental-scale flux of these greenhouse gases (GHGs), one of the key gaps in knowledge is the specific contribution of peatland ecosystems to the regional budgets of these GHGs. Here we report CH4 and N2O fluxes from lowland tropical peatlands in the Pastaza–Marañón foreland basin (PMFB) in Peru, one of the largest peatland complexes in the Amazon basin. The goal of this research was to quantify the range and magnitude of CH4 and N2O fluxes from this region, assess seasonal trends in trace gas exchange, and determine the role of different environmental variables in driving GHG flux. Trace gas fluxes were determined from the most numerically dominant peatland vegetation types in the region: forested vegetation, forested (short pole) vegetation, Mauritia flexuosa-dominated palm swamp, and mixed palm swamp. Data were collected in both wet and dry seasons over the course of four field campaigns from 2012 to 2014. Diffusive CH4 emissions averaged 36.05 ± 3.09 mg CH4–C m−2 day−1 across the entire dataset, with diffusive CH4 flux varying significantly among vegetation types and between seasons. Net ebullition of CH4 averaged 973.3 ± 161.4 mg CH4–C m−2 day−1 and did not vary significantly among vegetation types or between seasons. Diffusive CH4 flux was greatest for mixed palm swamp (52.0 ± 16.0 mg CH4–C m−2 day−1), followed by M. flexuosa palm swamp (36.7 ± 3.9 mg CH4–C m−2 day−1), forested (short pole) vegetation (31.6 ± 6.6 mg CH4–C m−2 day−1), and forested vegetation (29.8 ± 10.0 mg CH4–C m−2 day−1). Diffusive CH4 flux also showed marked seasonality, with divergent seasonal patterns among ecosystems. Forested vegetation and mixed palm swamp showed significantly higher dry season (47.2 ± 5.4 mg CH4–C m−2 day−1 and 85.5 ± 26.4 mg CH4–C m−2 day−1, respectively) compared to wet season emissions (6.8 ± 1.0 mg CH4–C m−2 day−1 and 5.2 ± 2.7 mg CH4–C m−2 day−1, respectively). In contrast, forested (short pole) vegetation and M. flexuosa palm swamp showed the opposite trend, with dry season flux of 9.6 ± 2.6 and 25.5 ± 2.9 mg CH4–C m−2 day−1, respectively, versus wet season flux of 103.4 ± 13.6 and 53.4 ± 9.8 mg CH4–C m−2 day−1, respectively. These divergent seasonal trends may be linked to very high water tables (> 1 m) in forested vegetation and mixed palm swamp during the wet season, which may have constrained CH4 transport across the soil–atmosphere interface. Diffusive N2O flux was very low (0.70 ± 0.34 µg N2O–N m−2 day−1) and did not vary significantly among ecosystems or between seasons. We conclude that peatlands in the PMFB are large and regionally significant sources of atmospheric CH4 that need to be better accounted for in regional emissions inventories. In contrast, N2O flux was negligible, suggesting that this region does not make a significant contribution to regional atmospheric budgets of N2O. The divergent seasonal pattern in CH4 flux among vegetation types challenges our underlying assumptions of the controls on CH4 flux in tropical peatlands and emphasizes the need for more process-based measurements during periods of high water table.

scholarly journals Wet-season spatial variability in N<sub>2</sub>O emissions from a tea field in subtropical central China

2015 ◽  
Vol 12 (12) ◽  
pp. 3899-3911 ◽  
Author(s):  
X. Fu ◽  
X. Liu ◽  
Y. Li ◽  
J. Shen ◽  
Y. Wang ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Ordinary Kriging ◽  
Spatial Interpolation ◽  
Central China ◽  
N2o Emissions ◽  
Regression Kriging ◽  
Wet Season ◽  
Interpolation Methods ◽  
N2o Fluxes ◽  
Tea Field

Abstract. Tea fields emit large amounts of nitrous oxide (N2O) to the atmosphere. Obtaining accurate estimations of N2O emissions from tea-planted soils is challenging due to strong spatial variability. We examined the spatial variability in N2O emissions from a red-soil tea field in Hunan Province, China, on 22 April 2012 (in a wet season) using 147 static mini chambers approximately regular gridded in a 4.0 ha tea field. The N2O fluxes for a 30 min snapshot (10:00–10:30 a.m.) ranged from −1.73 to 1659.11 g N ha−1 d−1 and were positively skewed with an average flux of 102.24 g N ha−1 d−1. The N2O flux data were transformed to a normal distribution by using a logit function. The geostatistical analyses of our data indicated that the logit-transformed N2O fluxes (FLUX30t) exhibited strong spatial autocorrelation, which was characterized by an exponential semivariogram model with an effective range of 25.2 m. As observed in the wet season, the logit-transformed soil ammonium-N (NH4Nt), soil nitrate-N (NO3Nt), soil organic carbon (SOCt) and total soil nitrogen (TSNt) were all found to be significantly correlated with FLUX30t (r = 0.57–0.71, p < 0.001). Three spatial interpolation methods (ordinary kriging, regression kriging and cokriging) were applied to estimate the spatial distribution of N2O emissions over the study area. Cokriging with NH4Nt and NO3Nt as covariables (r = 0.74 and RMSE = 1.18) outperformed ordinary kriging (r = 0.18 and RMSE = 1.74), regression kriging with the sample position as a predictor (r = 0.49 and RMSE = 1.55) and cokriging with SOCt as a covariable (r = 0.58 and RMSE = 1.44). The predictions of the three kriging interpolation methods for the total N2O emissions of 4.0 ha tea field ranged from 148.2 to 208.1 g N d−1, based on the 30 min snapshots obtained during the wet season. Our findings suggested that to accurately estimate the total N2O emissions over a region, the environmental variables (e.g., soil properties) and the current land use pattern (e.g., tea row transects in the present study) must be included in spatial interpolation. Additionally, compared with other kriging approaches, the cokriging prediction approach showed great advantages in being easily deployed and, more importantly, providing accurate regional estimation of N2O emissions from tea-planted soils.

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.

scholarly journals The riverine source of tropospheric CH<sub>4</sub> and N<sub>2</sub>O from the Republic of Congo, Western Congo Basin

2016 ◽  
Author(s):  
Robert C. Upstill-Goddard ◽  
Matthew E. Salter ◽  
Paul J. Mann ◽  
Jonathan Barnes ◽  
John Poulsen ◽  
...  
Keyword(s):  
Tropical Forest ◽  
Dry Season ◽  
Congo Basin ◽  
N2o Emissions ◽  
Wet Season ◽  
Swamp Forest ◽  
N2o Production ◽  
Republic Of Congo ◽  
Sub Saharan ◽  
Ch4 And N2o

Abstract. Abstract. We report concentrations of dissolved CH4, N2O, O2, NO3− and NH4+, and corresponding CH4 and N2O emissions for river sites in savanna, swamp forest and tropical forest, along the Congo main stem and in several of its tributary systems of the Western Congo Basin, Republic of Congo, during November 2010 (41 samples; ''wet season'') and August 2011 (25 samples; ''dry season''; CH4 and N2O only). Dissolved inorganic nitrogen (DIN: wet season; NH4&amp;plus; &amp;plus;  NO3−) was dominated by NO3− (63 ± 19 % of DIN), total DIN concentrations (1.5–45.3 nmol L−1) being consistent with small agricultural, domestic and industrial sources. Dissolved O2 (wet season) was mostly under-saturated in swamp forest (36 ± 29 %) and tropical forest (77 ± 36 %) rivers but predominantly super-saturated in savannah rivers (100 ± 17 %). Dissolved CH4 and N2O were within previously reported ranges for sub-Saharan African rivers. While CH4 was always super-saturated (11.2–9553 nmol L−1; 440–354 400 %), N2O ranged from strong under-saturation to strong super-saturation (3.2–20.6 nmol L−1; 47–205 %). Evidently, rivers of the ROC are persistent local sources of tropospheric CH4 but can be small sources or sinks for N2O. Dry season concentration means and ranges of CH4 and N2O were indistinguishable for all three land types and seasonal differences in means and ranges were not significant for N2O for any land type or for CH4 in savannah rivers; the latter is consistent with seasonal buffering of river discharge by an underlying sandy-sandstone aquifer. By contrast, swamp and forest river CH4 was significantly higher in the wet season, possibly reflecting CH4 derived from floating macrophytes during flooding and/or enhanced methanogenesis in adjacent flooded soils. Swamp rivers exhibited both low (47 %) and high (205 %) N2O saturations but wet season values were overall significantly lower than in either tropical forest or savannah rivers, which were always super-saturated (103–266 %) and for which the overall means and ranges of N2O were not significantly different. In swamp and forest rivers % O2 co-varied negatively with log % CH4 and positively with % N2O. The strong positive N2O–O2 correlation in swamp rivers was coincident with strong N2O and O2 under-saturation, indicating N2O consumption by sediment denitrification. In savannah rivers persistent N2O super-saturation and a negative N2O–O2 correlation may indicate N2O production mainly by nitrification, consistent with a stronger correlation between N2O and NH4&amp;plus; than between N2O and NO3−. Our range in CH4 and N2O emissions fluxes (33–48 705  μmol CH4 m−2 d−1; 1–67 μmol N2O m−2 d−1), is wider than previously estimated for sub-Saharan African rivers but it includes uncertainties deriving from our use of ''basin-wide'' values for CH4 and N2O gas transfer velocities. Even so, because we did not account for any contribution from ebullition, which for CH4 is likely to be at least 20 %, our emissions estimates for CH4 are probably conservative.

scholarly journals Different responses of CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O fluxes to seasonally asymmetric warming in an alpine grassland of Tianshan Mountains

2020 ◽  
Author(s):  
Yanming Gong ◽  
Ping Yue ◽  
Kaihui Li ◽  
Anwar Mohammat ◽  
Yanyan Liu
Keyword(s):  
Temperature Increase ◽  
Response Rate ◽  
Co2 Flux ◽  
Growing Season ◽  
Tianshan Mountains ◽  
Alpine Grassland ◽  
Ch4 Flux ◽  
Greenhouse Gas Flux ◽  
N2o Fluxes ◽  
Ch4 And N2o

Abstract. An experiment was conducted to investigate the effect of seasonally asymmetric warming on CO2, CH4, and N2O fluxes in alpine grassland of Tianshan Mountains of Central Asia, from October 2016 to September 2019. Our results indicated that the CO2, CH4 and N2O fluxes varied in the range 0.56–98.03 mg C m−2 h−1, −94.30–0.23 μg C m−2 h−1, and −1.28–10.09 μg N m−2 h−1, respectively. The CO2 and N2O fluxes were negatively correlated with soil temperature, but the CH4 fluxes decreased with the increase in temperature. Furthermore, the variation in greenhouse gas flux under seasonally asymmetric warming was different between the growing season (June to September) and the non-growing season (October to May). In addition, the response rates of CO2 and N2O fluxes to temperature increases was significantly reduced due to warming throughout the year. Warming during the growing season led to a significant decrease in the response rate of CO2 flux to temperature increases. However, warming during the non-growing season caused a significant increase in the response rate of CO2 flux to temperature increases. The response rate of CH4 flux was insensitive to temperature increase under seasonally asymmetric warming. Thus, the main finding of our results was that seasonally asymmetric warming resulted in different responses in the fluxes of individual greenhouse gases to rising temperatures in the alpine grassland.

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.

Sign in / Sign up

Export Citation Format

Share Document