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1.
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
2.
Variation of CH 4 emissions over a three-year period was studied in a reed-dominated ( Phragmites australis) littoral transect of a boreal lake undergoing shoreline displacement due to postglacial rebound. The seasonal variation in plant-mediated CH 4 emissions during open-water periods was significantly correlated with sediment temperature. The highest plant-mediated emission rates (up to 2050 mg CH 4 m –2 d –1) were found in the outermost reed zone, where culms of the previous growing seasons had accumulated and free-floating plants grew on the decomposing culms. In reed zones closer to the shoreline as well as in mixed stands of reed and cattail, the maximum daily rates were usually > 500 mg CH 4 m –2 d –1. The total plant-mediated CH 4 emission during the open-water period was significantly correlated with the seasonal maximum of green shoot biomass. This relationship was strongest in the continuously flooded (water depth > 25 cm) outermost zones. In this area, emissions through ebullition were of greatest importance and could exceed plant-mediated emissions. In general, total emissions of the open-water periods varied from ca. 20 to 50 g CH 4 m –2 a –1, but in the outermost reed zone, the plant-mediated emissions could be as high as 123 g CH 4 m –2 a –1; ebullition emissions from this zone reached > 100 g CH 4 m –2 a –1. The proportion of CH 4 released in winter was usually < 10% of annual emissions. Emissions of CH 4 were higher in this flooded transgression shore the than those measured in boreal peatlands, but the role of ancient carbon stores as a substrate supply compared with recent anthropogenic eutrophication is unknown. 相似文献
3.
Wetlands are estimated to contribute nearly 40 % of global annual methane (CH 4) emissions to the atmosphere. However, because CH 4 fluxes from these systems vary spatially, seasonally, and by wetland type, there is a large uncertainty associated with scaling up the CH 4 flux from these environments. We monitored seasonal patterns of CH 4 cycling from tidal mudflat wetland sediments adjacent to a vegetated freshwater wetland in coastal Georgia between 2008 and 2009. CH 4 emissions were significantly correlated with CH 4 production and sediment saturation state with respect to CH 4 but not with temperature. CH 4 cycling displayed distinct seasonal patterns. Winter months were characterized by low CH 4 production and emissions. During the spring, summer and fall, CH 4 fluxes exceeded CH 4 production in the top 40 cm. Comparison of CH 4 sources and sinks in conjunction with the interpretation of CH 4 concentration profiles using a 1D reactive transport model indicated that CH 4 delivered via lateral tidal pumping likely provided additional CH 4 to the upper sediment column. Seasonally high CH 4 ebullition rates reflected increased CH 4 production and decreased CH 4 solubility. The annual CH 4 flux was estimated to be on the order of 10 mol CH 4 m ?2 y ?1 which is 2–4 times the global average for wetland CH 4 emissions. Thus, even though tidal freshwater mudflats are of limited spatial extent, these environments may serve as globally significant sources of CH 4 to the atmosphere. This study highlights the importance of these dynamic environments to the global CH 4 cycle and their relevance to climate change. 相似文献
4.
Greenhouse gas emissions of Lake Neusiedl, the westernmost European shallow steppe lake, were analysed to identify differences between the seasons of the years and between different locations in the pelagic zone and reed belt. Emissions of CO 2, CH 4 and N 2O were measured in gas samples that had been recovered from the gas space of floating chambers operated as closed systems. Sampling periods covered all seasons except winter. Scaled up to the whole lake area (320 km 2), the diffusive emissions of spring, summer and autumn totalled to about 79,500 t CO 2e, disregarding bubble emissions, winter emissions and plant-mediated emissions. The emission sum consisted of about 57,000 t CO 2, 760 t CH 4, and 12 t N 2O. Approximately one-third of the methane and carbon dioxide emissions originated in the pelagic zone and two-thirds in the reed belt (without plant emissions) whereas nitrous oxide emissions were similar in these two zones. An estimate of ebullitive emissions resulted in additional 1,765 t CH 4 that predominantly originated in or near the reed belt from spring to autumn. 相似文献
5.
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
6.
Dynamics of greenhouse gases, CH 4, CO 2 and N 2O, and nutrients, NO
2
–
+ NO
3
–
, NH
4
+
and P, were studied in the sediments of the eutrophic, boreal Lake Kevätön in Finland. Undisturbed sediment cores taken in the summer, autumn and winter from the deep and shallow profundal and from the littoral were incubated in laboratory microcosms under aerobic and anaerobic water flow conditions. An increase in the availability of oxygen in water overlying the sediments reduced the release of CH 4, NH
4
+
and P, increased the flux of N 2O and NO
2
–
+ NO
3
–
, but did not affect CO 2 production. The littoral sediments produced CO 2 and CH 4 at high rates, but released only negligible amounts of nutrients. The deep profundal sediments, with highest carbon content, possessed the greatest release rates of CO 2, CH 4, NH
4
+
and P. The higher fluxes of these gases in summer and autumn than in winter were probably due to the supply of fresh organic matter from primary production. From the shallow profundal sediments fluxes of CH 4, NH 4
+ and P were low, but, in contrast, production of N 2O was the highest among the different sampling sites. Due to the large areal extension, the littoral and shallow profundal zones had the greatest importance in the overall gas and nutrient budgets in the lake. Methane emissions, especially the ebullition of CH 4 (up to 84% of the total flux), were closely related to the sediment P and NH
4
+
release. The high production and ebullition of CH 4, enhances the internal loading of nutrients, lake eutrophication status and the impact of boreal lakes to trophospheric gas budgets. 相似文献
7.
The fluxes of CH 4 and CO 2 to the atmosphere, and the relative contributions of ebullition and molecular diffusion, were determined for a small hypertrophic freshwater lake (Priest Pot, UK) over the period May to October 1997. The average total flux of CH 4 and CO 2 (estimated from 7 sites on the lake) was approximately 52 mmol m –2 d –1 and was apportioned 12 and 40 mmol m –2 d –1 toCH 4 and CO 2 respectively. Diffusion across the air-water interface accounted for the loss of 0.4and 40 mmol m –2 d –1 of CH 4 and CO 2 respectively whilst the corresponding figures for ebullition losses were 12.0 (CH 4) and 0.23 (CO 2) mmol m –2 d –1. Most CH 4 (96%) was lost by ebullition, and most CO 2 (99%) by diffusive processes. The ebullition of gas, measured at weekly intervals along a transect of the lake, showed high spatial and temporal variation. The CH 4 content of the trapped gas varied between 44 and 88% (by volume) and was highest at the deepest points. Pulses of gas ebullition were detected during periods of rapidly falling barometric pressure. Therelevance of the measurements to global estimates ofcarbon emission from freshwaters are discussed. 相似文献
8.
Anaerobic respiration and methanogenesis have been found to slow-down in water saturated peat soils with accumulation of metabolic end-products, i.e. dissolved inorganic carbon (DIC) and methane (CH 4), due to a lack of solute and gas transport. So far it is not well understood how solute and gas transport may control this effect. We conducted a column experiment with homogenized ombrotrophic peat over a period of 300 days at 20 °C. We specifically evaluated the effects of diffusive flux as control, downward advective water flux, intensified ebullition by conduit gas transport and diffusive oxygen supply on controlling anaerobic decomposition rates and carbon (C) turnover. To simulate advective flux, water and solutes were recirculated downward through the column after stripping of dissolved gases. We analyzed DIC and CH 4 concentrations, production rates and fluxes, gas filled porosity, oxygen profiles (O 2) and microbial C biomass over time. DIC residence time thereby served as proxy to characterize transport. A slowdown of anaerobic respiration and methanogenesis evolved with the accumulation of the end-products DIC and CH 4 and set in after 150 days. This slow-down was accompanied by a decrease in the distribution of microbial biomass C with depths. Anaerobic DIC and CH 4 production rates were fastest close to the water table and sharply slowed with depth. Accumulation of DIC and CH 4 in the homogeneous peat material throughout the column decreased decomposition constants from about 10 ?5 near the surface to 10 ?9 year ?1 deeper in the profile. Advective water transport extended the zone of active methanogenesis compared to a diffusive system; experimental enhancement of ebullition had little or no effect as well as strictly anoxic conditions. DIC residence time was negatively correlated to anaerobic respiration suggesting this parameter to be a predictor of anaerobic peat decomposition in peatlands. Overall, this study suggests that burial of peat and accumulation of metabolic end-products effectively slows decomposition and that this effect needs to be considered to explain peat accumulation and the response of peat mineralization rates to changes in environmental conditions. 相似文献
9.
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
10.
Large uncertainties in estimates of methane (CH4) emissions from tropical inland waters reflect the paucity of information at appropriate temporal and spatial scales. CH4 concentrations, diffusive and ebullitive fluxes, and environmental parameters in contrasting aquatic habitats of Lake Janauacá, an Amazon floodplain lake, measured for two years revealed patterns in temporal and spatial variability related to different aquatic habitats and environmental conditions. CH4 concentrations ranged from below detection to 96 µM, CH4 diffusive fluxes from below detection to 2342 µmol m−2 h−1, and CH4 ebullitive fluxes from 0 to 190 mmol m−2 d−1. Vegetated aquatic habitats had higher surface CH4 concentrations than open water habitats, and no significant differences in diffusive CH4 fluxes, likely due to higher k values measured in open water habitats. CH4 emissions were enhanced after a prolonged low water period, when the exposed sediments were colonized by herbaceous plants that decomposed after water levels rose, possibly fueling CH4 production. Statistical models indicated the importance of variables related to CH4 production (temperature, dissolved organic carbon) and consumption (dissolved nitrogen, oxygenated water column), as well as maximum depth, in controlling surface water CH4 concentrations. 相似文献
11.
Freshwaters are important sources of the greenhouse gases methane (CH 4) and carbon dioxide (CO 2) to the atmosphere. Knowledge about temporal variability in these fluxes is very limited, yet critical for proper study design and evaluating flux data. Further, to understand the reasons for the variability and allow predictive modeling, the temporal variability has to be related to relevant environmental variables. Here we analyzed the effect of weather variables on CH 4 and CO 2 flux from a small shallow pond during a period of 4 months. Mean CH 4 flux and surface water CH 4 concentration were 8.0 [3.3–15.1] ± 3.1 mmol m ?2 day ?1 (mean [range] ± 1 SD) and 1.3 [0.3–3.5] ± 0.9 µM respectively. Mean CO 2 flux was 1.1 [?9.8 to 16.0] ± 6.9 mmol m ?2 day ?1. Substantial diel changes in CO 2 flux and surface water CH 4 concentration were observed during detailed measurements over a 24 h cycle. Thus diel patterns need to be accounted for in future measurements. Significant positive correlations of CH 4 emissions with temperature were found and could include both direct temperature effects as well as indirect effects (e.g. related to the growth season and macrophyte primary productivity providing organic substrates). CO 2 flux on the other hand was negatively correlated to temperature and solar radiation, presumably because CO 2 consumption by plants was higher relative to CO 2 production by respiration during warm sunny days. Interestingly, CH 4 fluxes were comparable to ponds with similar morphometry and macrophyte abundance in the tropics. We therefore hypothesize that CH 4 and CO 2 summer emissions from ponds could be more related to the morphometry and dominating primary producers rather than latitude per se. Data indicate that CH 4 emissions, given the system characteristic frameworks, is positively affected by increased temperatures or prolonged growth seasons. 相似文献
12.
We performed field measurements on the spatial and temporal variability in CH 4 emissions from stem surfaces of mature Fraxinus mandshurica Rupr. trees in a floodplain forest of northern Japan. Stem CH 4 fluxes were measured by a static closed-chamber method at ca. 15 cm above ground on ten selected trees to test among-individual variability, and the diurnal and seasonal changes in three representative trees. Daytime stem CH 4 emission rates varied between 81 and 1,305 µg CH 4 m ?2 h ?1 among individual trees, and showed a spatial gradient apparently corresponding to the difference in water table depth at the experimental site. Stem CH 4 fluxes were quite stable throughout a 24 h period for foliated trees in August and were similar for defoliated trees in November. Large differences were observed in the magnitude of seasonal changes in stem CH 4 flux among individual trees; one sampled tree showed no clear seasonal changes in stem CH 4 flux, while another tree exhibited drastic seasonal changes ranging larger than one order of magnitude. Results demonstrated the high variability in stem CH 4 emissions in space and time, and suggested the importance of soil temperature, water table depth and porewater CH 4 concentration as possible environmental factors controlling stem CH 4 emissions from temperate forested wetlands. 相似文献
13.
To quantify the effects of water table drawdown and soil warming on CH 4 fluxes, we used a static chamber technique during the growing seasons (May–October) of 2011–2013 at hollow and hummock microforms at three sites of a continental bog near the town of Wandering River, Alberta, Canada: (1) Control, (2) Experimental drained, and (3) old Drained. To simulate climatic warming, we used open top chambers to passively warm half of the hollows and half of the hummocks at each of the water level treatment sites. Water table drawdown significantly reduced CH 4 flux by 50% in 3 years and 76% in 13 years of drainage. The hollows showed greater reduction of efflux as compared to hummocks. A persistent functional relationship of CH 4 flux with water level was found across all sites in all years. The relationship revealed that the contribution of change in vegetation type at hollows and hummocks to CH 4 production and emission was relatively less important than that of the water level. Hummocks and hollows responded to warming differently. At the control, experimental and drained sites, warming increased flux at hollows by 16, 21 and 26%, and reduced flux at hummocks by 4, 37, and 56%, respectively. The combined effect of lowered water table and warming on CH 4 emission was overall negative, although the interaction between the two contributing factors was not significant. Therefore, whereas climatic warming and subsequent lowering of water table are expected to reduce CH 4 efflux from dry ombrotrophic bogs of Alberta, different microforms at these bogs may respond differently with accelerated emissions at warmed, wetter (hollows) and reduced emissions at warmed, drier (hummocks) microforms. Overall, CH 4 efflux from Alberta’s dry continental bogs that are not underlain by permafrost might be affected only slightly by the direct effect of predicted climate warming, although initial water table position will be an important control on the overall response. 相似文献
14.
The magnitude of greenhouse gas (GHG) flux rates may be important in wet and intermediate wet forest soils, but published estimates are scarce. We studied the surface exchange of methane (CH 4) and nitrous oxide (N 2O) from soil along toposequences in two temperate deciduous forest catchments: Strødam and Vestskoven. The soil water regime ranged from fully saturated to aerated within the catchments. At Strødam the largest mean flux rates of N 2O (15 μg N 2O-N m ?2 h ?1) were measured at volumetric soil water contents (SWC) between 40 and 60% and associated with low soil pH compared to smaller mean flux rates of 0-5 μg N 2O-N m ?2 h ?1 for drier (SWC < 40%) and wet conditions (SWC > 80%). At Vestskoven the same response of N 2O to soil water content was observed. Average CH 4 flux rates were highly variable along the toposequences (?17 to 536 μg CH 4-C m ?2 h ?1) but emissions were only observed above soil water content of 45%. Scaled flux rates of both GHGs to catchment level resulted in emission of 322 and 211 kg CO 2-equivalents ha ?1 year ?1 for Strødam and Vestskoven, respectively, with N 2O contributing the most at both sites. Although the wet and intermediate wet forest soils occupied less than half the catchment area at both sites, the global warming potential (GWP) derived from N 2O and CH 4 was more than doubled when accounting for these wet areas in the catchments. The results stress the importance of wet soils in assessments of forest soil global warming potentials, as even small proportions of wet soils contributes substantially to the emissions of N 2O and CH 4. 相似文献
15.
Aims and methods To evaluate the seasonal and spatial variations of methane (CH 4) emissions and understand the controlling factors, we measured CH 4 fluxes and their environmental variables for the first time by a static chamber technique in high Suaeda salsa marsh (HSM), middle S. salsa marsh (MSM), low S. salsa marsh (LSM) and bare flat (BF) in the northern Yellow River estuary throughout a year. Results CH 4 emissions from coastal marsh varied throughout different times of the day and significant differences were observed in some sampling periods ( p?<?0.05). Over all sampling periods, CH 4 fluxes averaged between ?0.392 mgCH 4 m ?2?h ?1 and 0.495 mgCH 4 m ?2?h ?1, and emissions occurred during spring (0.008 mgCH 4 m ?2?h ?1) and autumn (0.068 mgCH 4 m ?2?h ?1) while sinks were observed during summer (?0.110 mgCH 4 m ?2?h ?1) and winter (?0.009 mgCH 4 m ?2?h ?1). CH 4 fluxes from the four marshes were not significantly different ( p?>?0.05), and emissions occurred in LSM (0.026 mgCH 4 m ?2?h ?1) and BF (0.055 mgCH 4 m ?2?h ?1) while sinks were observed in HSM (?0.035 mgCH 4 m ?2?h ?1) and MSM (?0.022 mgCH 4 m ?2?h ?1). The annual average CH 4 flux from the intertidal zone was 0.002 mgCH 4 m ?2?h ?1, indicating that coastal marsh acted as a weak CH 4 source. Temporal variations of CH 4 emission were related to the interactions of abiotic factors (temperatures, soil moisture and salinity) and the variations of limited C and mineral N in sediments, while spatial variations were mainly affected by the vegetation composition at spatial scale. Conclusions This study observed a large spatial variation of CH 4 fluxes across the coastal marsh of the Yellow River estuary (CV?=?7856.25 %), suggesting that the need to increase the spatial replicates at fine scales before the regional CH 4 budget was evaluated precisely. With increasing exogenous nitrogen loading to the Yellow River estuary, the magnitude of CH 4 emission might be enhanced, which should also be paid more attentions as the annual CH 4 inventory was assessed accurately. 相似文献
16.
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
17.
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
18.
Lakes are a major component of boreal landscapes, and whereas lake CO 2 emissions are recognized as a major component of regional C budgets, there is still much uncertainty associated to lake CH 4 fluxes. Here, we present a large‐scale study of the magnitude and regulation of boreal lake summer diffusive CH 4 fluxes, and their contribution to total lake carbon (C) emissions, based on in situ measurements of concentration and fluxes of CH 4 and CO 2 in 224 lakes across a wide range of lake type and environmental gradients in Québec. The diffusive CH 4 flux was highly variable (mean 11.6 ± 26.4 SD mg m ?2 d ?1), and it was positively correlated with temperature and lake nutrient status, and negatively correlated with lake area and colored dissolved organic matter (CDOM). The relationship between CH 4 and CO 2 concentrations fluxes was weak, suggesting major differences in their respective sources and/or regulation. For example, increasing water temperature leads to higher CH 4 flux but does not significantly affect CO 2 flux, whereas increasing CDOM concentration leads to higher CO 2 flux but lower CH 4 flux. CH 4 contributed to 8 ± 23% to the total lake C emissions (CH 4 + CO 2), but 18 ± 25% to the total flux in terms of atmospheric warming potential, expressed as CO 2‐equivalents. The incorporation of ebullition and plant‐mediated CH 4 fluxes would further increase the importance of lake CH 4. The average Q 10 of CH 4 flux was 3.7, once other covarying factors were accounted for, but this apparent Q 10 varied with lake morphometry and was higher for shallow lakes. We conclude that global climate change and the resulting shifts in temperature will strongly influence lake CH 4 fluxes across the boreal biome, but these climate effects may be altered by regional patterns in lake morphometry, nutrient status, and browning. 相似文献
19.
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
20.
Invasive plants can influence ecosystem processes such as greenhouse gas (GHG) emissions from wetland systems directly through plant-mediated transfer of GHGs to the atmosphere or through indirect modification of the environment. However, patterns of plant invasion often co-vary with other environmental gradients, so attributing ecosystem effects to invasion can be difficult in observational studies. Here, we assessed the impact of Phragmites australis invasion into native shortgrass communities on methane (CH 4) emissions by conducting field measurements of CH 4 emissions along transects of invasion by Phragmites in two neighboring brackish marsh sites and compared these findings to those from a field-based mesocosm experiment. We found remarkable differences in CH 4 emissions and the influence of Phragmites on CH 4 emissions between the two neighboring marsh sites. While Phragmites consistently increased CH 4 emissions dramatically by 10.4 ± 3.7 µmol m ?2 min ?1 (mean ± SE) in our high-porewater CH 4 site, increases in CH 4 emissions were much smaller (1.4 ± 0.5 µmol m ?2 min ?1) and rarely significant in our low-porewater CH 4 site. While CH 4 emissions in Phragmites-invaded zones of both marsh sites increased significantly, the presence of Phragmites did not alter emissions in a complementary mesocosm experiment. Seasonality and changes in temperature and light availability caused contrasting responses of CH 4 emissions from Phragmites- versus native zones. Our data suggest that Phragmites-mediated CH 4 emissions are particularly profound in soils with innately high rates of CH 4 production. We demonstrate that the effects of invasive species on ecosystem processes such as GHG emissions may be predictable qualitatively but highly variable quantitatively. Therefore, generalizations cannot be made with respect to invader-ecosystem processes, as interactions between the invader and local abiotic conditions that vary both spatially and temporally on the order of meters and hours, respectively, can have a stronger impact on GHG emissions than the invader itself. 相似文献
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