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1.
Most fluvial networks worldwide include watercourses that recurrently cease to flow and run dry. The spatial and temporal extent of the dry phase of these temporary watercourses is increasing as a result of global change. Yet, current estimates of carbon emissions from fluvial networks do not consider temporary watercourses when they are dry. We characterized the magnitude and variability of carbon emissions from dry watercourses by measuring the carbon dioxide (CO 2) flux from 10 dry streambeds of a fluvial network during the dry period and comparing it to the CO 2 flux from the same streambeds during the flowing period and to the CO 2 flux from their adjacent upland soils. We also looked for potential drivers regulating the CO 2 emissions by examining the main physical and chemical properties of dry streambed sediments and adjacent upland soils. The CO 2 efflux from dry streambeds (mean ± SD = 781.4 ± 390.2 mmol m ?2 day ?1) doubled the CO 2 efflux from flowing streambeds (305.6 ± 206.1 mmol m ?2 day ?1) and was comparable to the CO 2 efflux from upland soils (896.1 ± 263.2 mmol m ?2 day ?1). However, dry streambed sediments and upland soils were physicochemically distinct and differed in the variables regulating their CO 2 efflux. Overall, our results indicate that dry streambeds constitute a unique and biogeochemically active habitat that can emit significant amounts of CO 2 to the atmosphere. Thus, omitting CO 2 emissions from temporary streams when they are dry may overlook the role of a key component of the carbon balance of fluvial networks. 相似文献
2.
Ephemeral streams and wetlands are characterized by complex cycles of submersion and emersion, which influence the greenhouse gas flux rates. In this study we quantify the spatiotemporal variability in CO 2 and CH 4 concentrations and fluxes of an intermittent first-order stream over three consecutive wet and dry cycles spanning 56 days, to assess how hydrologic phase transitions influence greenhouse gas evasion. Water column excess CO 2 ranged from ?11 to 1600 μM, and excess CH 4 from 1 to 15 μM. After accounting for temporal changes in the ratio of wet versus dry streambed hydraulic radius, total CO 2–C fluxes ranged from 12 to 156 mmol m ?2 day ?1, with an integrated daily mean of 61 ± 25 mmol m ?2 day ?1. Soil–air evasion rates were approximately equal to those of water–air evasion. Rainfall increased background water–air CO 2–C fluxes by up to 780% due to an increase in gas transfer velocity in the otherwise still waters. CH 4–C fluxes increased 19-fold over the duration of the initial, longer wet-cycle from 0.1 to 1.9 mmol m ?2 day ?1. Temporal shifts in water depth and site-specific ephemerality were key drivers of carbon dynamics in the upper Jamison Creek watercourse. Based on these findings, we hypothesise that the cyclic periodicity of fluxes of biogenic gases from frequently intermittent streams (wet and dry cycles ranging from days to weeks) and seasonally ephemeral watercourses (dry for months at a time) are likely to differ, and therefore these differences should be considered when integrating transient systems into regional carbon budgets and models of global change. 相似文献
3.
Temperate pastures are often managed with P fertilizers and N 2-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N 2O) emissions and reduced methane (CH 4) uptake. However, the diel and inter-daily variation in N 2O and CH 4 flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N 2O and CH 4 flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N 2O and CH 4 flux was measured continuously in a High P (23 kg P ha ?1 yr ?1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha ?1 yr ?1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH 4 uptake was similar (?6.3?±?SE 0.3 to ?8.6?±?0.4 μg C m ?2 hr ?1) as were mean N 2O emissions (6.5 to 7.9?±?0.8 μg N m ?2 hr ?1), although N 2O flux in the No P pasture did not respond to changing soil water conditions. N 2O emissions were greatest in the Low P sheep camp (12.4 μg?±?1.1 N m ?2 hr ?1) where there were also net CH 4 emissions of 5.2?±?0.5 μg C m ?2 hr ?1. There were significant, but weak, relationships between soil water and N 2O emissions, but not between soil water and CH 4 flux. The diel temperature cycle strongly influenced CH 4 and N 2O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N 2O emissions, or reduce CH 4 uptake, during this 4 week measurement period, but the lack of an N 2O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N 2O and CH 4 trace gas balance. 相似文献
4.
Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH 4 and CO 2 fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH 4 and CO 2 from these lakes and ditches. The lakes and ditches acted as CO 2 and CH 4 sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m ?2 h ?1 for CO 2 and 33.7 ± 9.3 and 3.9 ± 1.6 mg m ?2 h ?1 for CH 4, respectively. In most water bodies CH 4 was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH 4 could be explained by PO 4 3? concentration in the sediment and Fe 2+ concentration in the water, and 89% of the CO 2 flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO 2 and CH 4 from these water bodies. 相似文献
5.
We report a data-set of dissolved methane (CH 4) in three rivers (Comoé, Bia and Tanoé) and five lagoons (Grand-Lahou, Ebrié, Potou, Aby and Tendo) of Ivory Coast (West Africa), during the four main climatic seasons (high dry season, high rainy season, low dry season and low rainy season). The surface waters of the three rivers were over-saturated in CH 4 with respect to atmospheric equilibrium (2221–38719%), and the seasonal variability of CH 4 seemed to be largely controlled by dilution during the flooding period. The strong correlation of CH 4 concentrations with the partial pressure of CO 2 (pCO 2) and dissolved silicate (DSi) confirm the dominance of a continental sources (from soils) for both CO 2 and CH 4 in these rivers. Diffusive air–water CH 4 fluxes ranged between 25 and 1187 μmol m ?2 day ?1, and annual integrated values were 288 ± 107, 155 ± 38, and 241 ± 91 μmol m ?2 day ?1 in the Comoé, Bia and Tanoé rivers, respectively. In the five lagoons, surface waters were also over-saturated in CH 4 (ranging from 1496 to 51843%). Diffusive air–water CH 4 fluxes ranged between 20 and 2403 μmol m ?2 day ?1, and annual integrated values were 78 ± 34, 338 ± 217, 227 ± 79, 330 ± 153 and 326 ± 181 μmol m ?2 day ?1 in the Grand-Lahou, Ebrié, Potou, Aby and Tendo lagoons, respectively. The largest CH 4 over-saturations were observed in the Tendo and Aby lagoons that are permanently stratified systems (unlike the other three lagoons), leading to anoxic bottom waters favorable for a large CH 4 production. In addition, these two stratified lagoons showed low pCO 2 values due to high primary production, which suggests an efficient transfer of organic matter across the pycnocline. As a result, the stratified Tendo and Aby lagoons were respectively, a low source of CO 2 to the atmosphere and a sink of atmospheric CO 2 while the other three well-mixed lagoons were strong sources of CO 2 to the atmosphere but less over-saturated in CH 4. 相似文献
6.
Atmospheric CO 2 and CH 4 exchange in peatlands is controlled by water table levels and soil moisture, but impacts of short periods of dryness and rainfall are poorly known. We conducted drying-rewetting experiments with mesocosms from an ombrotrophic northern bog and an alpine, minerotrophic fen. Efflux of CO 2 and CH 4 was measured using static chambers and turnover and diffusion rates were calculated from depth profiles of gas concentrations. Due to a much lower macroporosity in the fen compared to the bog peat, water table fluctuated more strongly when irrigation was stopped and resumed, about 11 cm in the fen and 5 cm in the bog peat. Small changes in air filled porosity caused CO 2 and CH 4 concentrations in the fen peat to be insensitive to changes in water table position. CO 2 emission was by a factor of 5 higher in the fen than in the bog mesocosms and changed little with water table position in both peats. This was probably caused by the importance of the uppermost, permanently unsaturated zone for auto- and heterotrophic CO 2 production, and a decoupling of air filled porosity from water table position. CH 4 emission was <0.4 mmol m ?2 day ?1 in the bog peat, and up to >12.6 mmol m ?2 day ?1 in the fen peat, where it was lowered by water table fluctuations. CH 4 production was limited to the saturated zone in the bog peat but proceeded in the capillary fringe of the fen peat. Water table drawdown partly led to inhibition of methanogenesis in the newly unsaturated zone, but CH 4 production appeared to continue after irrigation without time-lag. The identified effects of irrigation on soil moisture and respiration highlight the importance of peat physical properties for respiratory dynamics; but the atmospheric carbon exchange was fairly insensitive to the small-scale fluctuations induced. 相似文献
7.
Sheepfolds represent significant hot spot sources of greenhouse gases (GHG) in semi-arid grassland regions, such as Inner Mongolia in China. However, the annual contribution of sheepfolds to regional GHG emissions is still unknown. In order to quantify its annual contribution, we conducted measurements of carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2O) fluxes at two sheepfold sites in the Baiyinxile administrative region of Inner Mongolia for 1 year, using static opaque chamber and gas chromatography methods. Our data show that, at an annual scale, both sheepfolds functioned as net sources of CO 2, CH 4 and N 2O. Temperatures primarily determined the seasonal pattern of CO 2 emission; 60–84% of the CO 2 flux variation could be explained by temperature changes. High rates of net CH 4 emissions from sheepfold soils were only observed when animals (sheep and goats) were present. While nitrous oxide emissions were also stimulated by the presence of animals, pulses of N 2O emissions were also be related to rainfall and spring-thaw events. The total annual cumulative GHG emissions in CO 2 equivalents (CO 2: 1; CH 4: 25; and N 2O: 298) were quantified as 87.4?±?18.4 t ha ?1 for the sheepfold that was used during the non-grazing period (i.e., winter sheepfold) and 136.7?±?15.9 t ha ?1 used during the grazing period (i.e., summer sheepfold). Of the annual total GHG emissions, CH 4 release accounted for approximately 1% of emissions, while CO 2 and N 2O emissions contributed to approximately 59% and 40%, respectively. The total GHG emission factor (CO 2?+?CH 4?+?N 2O) per animal for the sheepfolds investigated in this study was 30.3 kg CO 2 eq yr ?1 head ?1, which translates to 0.3, 18.8 and 11.2 kg CO 2 eq yr ?1 head ?1 for CH 4, CO 2 and N 2O, respectively. Sheepfolds accounted for approximately 34% of overall N 2O emissions in the Baiyinxile administrative region, a typical steppe region within Inner Mongolia. The contribution of sheepfolds to the regional CO 2 or CH 4 exchange is marginal. 相似文献
8.
Wetland ecosystems are a major natural source of the important greenhouse gas methane (CH 4). Among these ecosystems, fens have been shown to release high quantities of CH 4. Data on CH 4 emissions from alpine fens are scarce and mainly limited to the United States and China. Therefore, static chambers were used to quantify CH 4 emissions from 14 fens located in the Swiss Alps. The aims of this study were to determine the spatial variability of the emissions and to identify potential key factors which influence CH 4 turnover. The fens were located at altitudes between 1,800 and 2,600 m a.s.l., the pore water varied from acidic to slightly acidic (pH 4.5–6.4) and the vegetation was dominated by plants of the genus Carex. In addition, the underlying bedrock was either siliceous or calcareous. Methane emissions ranged from 74 ± 43 to 711 ± 212 mg CH 4 m ?2 day ?1. The type of bedrock, the plant biomass above the water table and the CH 4 pore water concentrations at depths from 0 to 20 cm were the main factors influencing CH 4 emissions. Detailed measurements in three selected fens suggested that more than 98 % of the total CH 4 emissions are due to plant-mediated transport. 相似文献
9.
Forest soils and canopies are major components of ecosystem CO 2 and CH 4 fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO 2 and CH 4 fluxes. We measured CO 2 and CH 4 fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO 2 sources (4.58 ± 2.46 µmol m ?2 s ?1, mean ± 1 SD) and net sinks of CH 4 (?2.17 ± 1.60 nmol m ?2 s ?1). Coarse woody debris was a CO 2 source (4.23 ± 3.42 µmol m ?2 s ?1) and net CH 4 sink, but with large uncertainty (?0.27 ± 1.04 nmol m ?2 s ?1) and with substantial differences depending on wood decay status. Stems were CO 2 sources (1.93 ± 1.63 µmol m ?2 s ?1), but also net CH 4 sources (up to 0.98 nmol m ?2 s ?1), with a mean of 0.11 ± 0.21 nmol m ?2 s ?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH 4, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO 2 fluxes, whereas CH 4 emissions from living stems offset net soil and CWD CH 4 uptake by 3.5%. Our results demonstrate the importance of CH 4 emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO 2 and CH 4 dynamics. 相似文献
10.
Extensive interfluvial wetlands occur in the upper Negro River basin (Brazil) and contain a mosaic of vegetation dominated by emergent grasses and sedges with patches of shrubs and palms. To characterize the release of carbon dioxide and methane from these habitats, diffusive and ebullitive emissions and transport through plant aerenchyma were measured monthly during 2005 in permanently and seasonally flooded areas. CO 2 emissions averaged 2193 mg C m ?2 day ?1. Methane was consumed in unflooded environments and emitted in flooded environments with average values of ?4.8 and 60 mg C m ?2 day ?1, respectively. Bubbles were emitted primarily during falling water periods when hydrostatic pressure at the sediment?Cwater interface declined. CO 2 and CH 4 emissions increased when dissolved O 2 decreased and vegetation was more abundant. Total area and seasonally varying flooded areas for two wetlands, located north and south of the Negro River, were determined through analysis of synthetic aperture radar and optical remotely sensed data. The combined areas of these two wetlands (3000 km 2) emitted 1147 Gg C year ?1 as CO 2 and 31 Gg C year ?1 as CH 4. If these rates are extrapolated to the area occupied by hydromorphic soils in the upper Negro basin, 63 Tg C year ?1 of CO 2 and 1.7 Tg C year ?1 as CH 4 are estimated as the regional evasion to the atmosphere. 相似文献
11.
The aim of this study is to estimate emissions of greenhouse gases CO 2, CH 4 and N 2O, and the effects of drainage and peat extraction on these processes, in Estonian transitional fens and ombrotrophic bogs. Closed-chamber-based sampling lasted from January to December 2009 in nine peatlands in Estonia, covering areas with different land-use practices: natural (four study sites), drained (six sites), abandoned peat mining (five sites) and active peat mining areas (five sites). Median values of soil CO 2 efflux were 1,509, 1,921, 2,845 and 1,741 kg CO 2-C ha ?1 year ?1 from natural, drained, abandoned and active mining areas, respectively. Emission of CH 4-C (median values) was 85.2, 23.7, 0.07 and 0.12 kg ha ?1 year ?1, and N 2O-N ?0.05, ?0.01, 0.18 and 0.19 kg ha ?1 year ?1, respectively. There were significantly higher emissions of CO 2 and N 2O from abandoned and active peat mining areas, whereas CH 4 emissions were significantly higher in natural and drained areas. Significant Spearman rank correlation was found between soil temperature and CO 2 flux at all sites, and CH 4 flux with high water level at natural and drained areas. Significant increase in CH 4 flux was detected for groundwater levels above 30 cm. 相似文献
12.
We measured CO 2 concentration and determined evasion rate and piston velocity across the water–air interface in flow-through chambers at eight stations along two 20 km long streams in agricultural landscapes in Zealand, Denmark. Both streams were 9–18-fold supersaturated in CO 2 with daily means of 240 and 340 μM in January–March and 130 and 180 μM in June–August. Annual CO 2 medians were 212 μM in six other streams and 460 μM in four groundwater wells, while seven lakes were weakly supersaturated (29 μM). Air concentrations immediately above stream surfaces were close to mean atmospheric conditions except during calm summer nights. Piston velocity from 0.4 to 21.6 cm h ?1 was closely related to current velocity permitting calculation of evasion rates for entire streams. CO 2 evasion rates were highest in midstream reaches (170–1,200 mmol m ?2 day ?1) where CO 2-rich soil water entered fast stream flow, while rates were tenfold lower (25–100 mmol m ?2 day ?1) in slow-flowing lower reaches. CO 2 evasion mainly derived from the input of CO 2 in soil water. The variability of CO 2 evasion along the two lowland streams covered much of the range in sub-Arctic and temperate streams reported previously. In budgets for the two stream catchments, loss of carbon from soils via the hydrological cycle was substantial (3.2–5.7 mmol m ?2 day ?1) and dominated by CO 2 consumed to form HCO 3 ? by mineral dissolution (69–76%) and export of organic carbon (15–23%) relative to dissolved CO 2 export (7–9%). 相似文献
13.
Northern lakes are a source of greenhouse gases to the atmosphere and contribute substantially to the global carbon budget. However, the sources of methane (CH4) to northern lakes are poorly constrained limiting our ability to the assess impacts of future Arctic change. Here we present measurements of the natural groundwater tracer, radon, and CH4 in a shallow lake on the Yukon-Kuskokwim Delta, AK and quantify groundwater discharge rates and fluxes of groundwater-derived CH4. We found that groundwater was significantly enriched (2000%) in radon and CH4 relative to lake water. Using a mass balance approach, we calculated average groundwater fluxes of 1.2 ± 0.6 and 4.3 ± 2.0 cm day−1, respectively as conservative and upper limit estimates. Groundwater CH4 fluxes were 7—24 mmol m−2 day−1 and significantly exceeded diffusive air–water CH4 fluxes (1.3–2.3 mmol m−2 day−1) from the lake to the atmosphere, suggesting that groundwater is an important source of CH4 to Arctic lakes and may drive observed CH4 emissions. Isotopic signatures of CH4 were depleted in groundwaters, consistent with microbial production. Higher methane concentrations in groundwater compared to other high latitude lakes were likely the source of the comparatively higher CH4 diffusive fluxes, as compared to those reported previously in high latitude lakes. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for CH4 release across Arctic landscapes. 相似文献
14.
Small lakes in northern latitudes represent a significant source of CH 4 to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH 4 budgets are lacking as are measurements of δ 13C-CH 4 and δ 2H-CH 4. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH 4 and corresponding δ 13C-CH 4 and δ 2H-CH 4 in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH 4 flux was highly variable, ranging from an average flux of 7 mg CH 4 m ?2 d ?1 in the deep-water zone to 154 mg CH 4 m ?2 d ?1 along the lake margin. Diffusive flux accounted for ~8.5 % of mean net CH 4 flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean ± SD 10 ± 17 %) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH 4 emissions varied widely throughout the system, with δ 13C-CH 4 ranging from ?66.2 to ?55.5 ‰, and δ 2H-CH 4 ranging from ?345 to ?258 ‰. Carbon isotope composition of CH 4 in ebullitive flux showed wider variation compared to net flux, ranging from ?69.2 to ?49.2 ‰. Dissolved CH 4 concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH 4 in the hypoxic deep water coincided with decreasing dissolved O 2 concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ 13C-CH 4 and δ 2H-CH 4. The most depleted 13C- and 2H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ 13C and δ 2H observations of CH 4, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH 4 in deeper sediments were consistent with mixing/transition between CH 4 production pathways, indicating a higher contribution of the CO 2 reduction pathway. The large spatial variability in fluxes of CH 4 and in isotopic composition of CH 4 throughout a single lake system indicates that the underlying mechanisms controlling CH 4 cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH 4 emissions in these systems. Future studies of whole-lake CH 4 budgets should consider this significant spatial heterogeneity. 相似文献
15.
Wetlands can influence global climate via greenhouse gas (GHG) exchange of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O). Few studies have quantified the full GHG budget of wetlands due to the high spatial and temporal variability of fluxes. We report annual open‐water diffusion and ebullition fluxes of CO 2, CH 4, and N 2O from a restored emergent marsh ecosystem. We combined these data with concurrent eddy‐covariance measurements of whole‐ecosystem CO 2 and CH 4 exchange to estimate GHG fluxes and associated radiative forcing effects for the whole wetland, and separately for open‐water and vegetated cover types. Annual open‐water CO 2, CH 4, and N 2O emissions were 915 ± 95 g C‐CO 2 m ?2 yr ?1, 2.9 ± 0.5 g C‐CH 4 m ?2 yr ?1, and 62 ± 17 mg N‐N 2O m ?2 yr ?1, respectively. Diffusion dominated open‐water GHG transport, accounting for >99% of CO 2 and N 2O emissions, and ~71% of CH 4 emissions. Seasonality was minor for CO 2 emissions, whereas CH 4 and N 2O fluxes displayed strong and asynchronous seasonal dynamics. Notably, the overall radiative forcing of open‐water fluxes (3.5 ± 0.3 kg CO 2‐eq m ?2 yr ?1) exceeded that of vegetated zones (1.4 ± 0.4 kg CO 2‐eq m ?2 yr ?1) due to high ecosystem respiration. After scaling results to the entire wetland using object‐based cover classification of remote sensing imagery, net uptake of CO 2 (?1.4 ± 0.6 kt CO 2‐eq yr ?1) did not offset CH 4 emission (3.7 ± 0.03 kt CO 2‐eq yr ?1), producing an overall positive radiative forcing effect of 2.4 ± 0.3 kt CO 2‐eq yr ?1. These results demonstrate clear effects of seasonality, spatial structure, and transport pathway on the magnitude and composition of wetland GHG emissions, and the efficacy of multiscale flux measurement to overcome challenges of wetland heterogeneity. 相似文献
16.
Inland waters were recently recognized to be important sources of methane (CH 4) and carbon dioxide (CO 2) to the atmosphere, and including inland water emissions in large scale greenhouse gas (GHG) budgets may potentially offset the estimated carbon sink in many areas. However, the lack of GHG flux measurements and well‐defined inland water areas for extrapolation, make the magnitude of the potential offset unclear. This study presents coordinated flux measurements of CH 4 and CO 2 in multiple lakes, ponds, rivers, open wells, reservoirs, springs, and canals in India. All these inland water types, representative of common aquatic ecosystems in India, emitted substantial amounts of CH 4 and a major fraction also emitted CO 2. The total CH 4 flux (including ebullition and diffusion) from all the 45 systems ranged from 0.01 to 52.1 mmol m ?2 d ?1, with a mean of 7.8 ± 12.7 (mean ± 1 SD) mmol m ?2 d ?1. The mean surface water CH 4 concentration was 3.8 ± 14.5 μm (range 0.03–92.1 μm ). The CO 2 fluxes ranged from ?28.2 to 262.4 mmol m ?2 d ?1 and the mean flux was 51.9 ± 71.1 mmol m ?2 d ?1. The mean partial pressure of CO 2 was 2927 ± 3269 μatm (range: 400–11 467 μatm). Conservative extrapolation to whole India, considering the specific area of the different water types studied, yielded average emissions of 2.1 Tg CH 4 yr ?1 and 22.0 Tg CO 2 yr ?1 from India's inland waters. When expressed as CO 2 equivalents, this amounts to 75 Tg CO 2 equivalents yr ?1 (53–98 Tg CO 2 equivalents yr ?1; ± 1 SD) , with CH 4 contributing 71%. Hence, average inland water GHG emissions, which were not previously considered, correspond to 42% (30–55%) of the estimated land carbon sink of India. Thereby this study illustrates the importance of considering inland water GHG exchange in large scale assessments. 相似文献
17.
At the southern margin of permafrost in North America, climate change causes widespread permafrost thaw. In boreal lowlands, thawing forested permafrost peat plateaus (‘forest’) lead to expansion of permafrost‐free wetlands (‘wetland’). Expanding wetland area with saturated and warmer organic soils is expected to increase landscape methane (CH 4) emissions. Here, we quantify the thaw‐induced increase in CH 4 emissions for a boreal forest‐wetland landscape in the southern Taiga Plains, Canada, and evaluate its impact on net radiative forcing relative to potential long‐term net carbon dioxide (CO 2) exchange. Using nested wetland and landscape eddy covariance net CH 4 flux measurements in combination with flux footprint modeling, we find that landscape CH 4 emissions increase with increasing wetland‐to‐forest ratio. Landscape CH 4 emissions are most sensitive to this ratio during peak emission periods, when wetland soils are up to 10 °C warmer than forest soils. The cumulative growing season (May–October) wetland CH 4 emission of ~13 g CH 4 m ?2 is the dominating contribution to the landscape CH 4 emission of ~7 g CH 4 m ?2. In contrast, forest contributions to landscape CH 4 emissions appear to be negligible. The rapid wetland expansion of 0.26 ± 0.05% yr ?1 in this region causes an estimated growing season increase of 0.034 ± 0.007 g CH 4 m ?2 yr ?1 in landscape CH 4 emissions. A long‐term net CO 2 uptake of >200 g CO 2 m ?2 yr ?1 is required to offset the positive radiative forcing of increasing CH 4 emissions until the end of the 21st century as indicated by an atmospheric CH 4 and CO 2 concentration model. However, long‐term apparent carbon accumulation rates in similar boreal forest‐wetland landscapes and eddy covariance landscape net CO 2 flux measurements suggest a long‐term net CO 2 uptake between 49 and 157 g CO 2 m ?2 yr ?1. Thus, thaw‐induced CH 4 emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century. 相似文献
18.
Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH 4) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH 4 in the world contributing between 100 and 231 Tg year ?1 to the total budget of 503–610 Tg year ?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH 4 emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH 4 emission rates varied between 0.24 and 293 mg CH 4 m ?2 h ?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH 4 m ?2 h ?1 or 558 ± 53 mg CH 4 m ?2 day ?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher ( P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH 4 m ?2 h ?1 than in floodplains (20.4 ± 2.5 mg CH 4 m ?2 h ?1) and lagoons (16.9 ± 2.6 mg CH 4 m ?2 h ?1). Diffusive CH 4 emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH 4 m ?2 h ?1) and lowest (0.2–3.0 mg m ?2 h ?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km 2, the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH 4 emission from global tropical wetlands. 相似文献
19.
Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO 2) and methane (CH 4) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We monitored GHG flux dynamics via high‐resolution flow‐through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10–15 cm of permafrost under dry conditions increased CO 2 emissions to the atmosphere (without vegetation: 0.74 ± 0.49 vs. 0.84 ± 0.60 g CO 2–C m ?2 day ?1; with vegetation: 1.20 ± 0.50 vs. 1.32 ± 0.60 g CO 2–C m ?2 day ?1, mean ± SD, pre‐ and post‐thaw, respectively). Radiocarbon dating ( 14C) of respired CO 2, supported by an independent curve‐fitting approach, showed a clear contribution (9%–27%) of old carbon to this enhanced post‐thaw CO 2 flux. Elevated concentrations of CO 2, CH 4, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH 4 in the peat column, however, prevented CH 4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost–carbon feedback by adding to the atmospheric CO 2 burden post‐thaw. However, as long as the water table remains low, our results reveal a strong CH 4 sink capacity in these types of Arctic ecosystems pre‐ and post‐thaw, with the potential to compensate part of the permafrost CO 2 losses over longer timescales. 相似文献
20.
The biosphere–atmosphere exchange of methane (CH 4) was estimated for a temperate/boreal lowland and wetland forest ecosystem in northern Wisconsin for 1997–1999 using the modified Bowen ratio (MBR) method. Gradients of CH 4 and CO 2 and CO 2 flux were measured on the 447‐m WLEF‐TV tower as part of the Chequamegon Ecosystem–Atmosphere Study (ChEAS). No systematic diurnal variability was observed in regional CH 4 fluxes measured using the MBR method. In all 3 years, regional CH 4 emissions reached maximum values during June–August (24±14.4 mg m ?2 day ?1), coinciding with periods of maximum soil temperatures. In 1997 and 1998, the onset in CH 4 emission was coincident with increases in ground temperatures following the melting of the snow cover. The onset of emission in 1999 lagged 100 days behind the 1997 and 1998 onsets, and was likely related to postdrought recovery of the regional water table to typical levels. The net regional emissions were 3.0, 3.1, and 2.1 g CH 4 m ?2 for 1997, 1998, and 1999, respectively. Annual emissions for wetland regions within the source area (28% of the land area) were 13.2, 13.8, and 10.3 g CH 4 m ?2 assuming moderate rates of oxidation of CH 4 in upland regions in 1997, 1998, and 1999, respectively. Scaling these measurements to the Chequamegon Ecosystem (CNNF) and comparing with average wetland emissions between 40°N and 50°N suggests that wetlands in the CNNF emit approximately 40% less than average wetlands at this latitude. Differences in mean monthly air temperatures did not affect the magnitude of CH 4 emissions; however, reduced precipitation and water table levels suppressed CH 4 emission during 1999, suggesting that long‐term climatic changes that reduce the water table will likely transform this landscape to a reduced source or possibly a sink for atmospheric CH 4. 相似文献
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