共查询到20条相似文献,搜索用时 125 毫秒
1.
Daniel L. Warner Samuel Villarreal Kelsey McWilliams Shreeram Inamdar Rodrigo Vargas 《Ecosystems》2017,20(6):1205-1216
Forest soils and canopies are major components of ecosystem CO2 and CH4 fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO2 and CH4 fluxes. We measured CO2 and CH4 fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO2 sources (4.58 ± 2.46 µmol m?2 s?1, mean ± 1 SD) and net sinks of CH4 (?2.17 ± 1.60 nmol m?2 s?1). Coarse woody debris was a CO2 source (4.23 ± 3.42 µmol m?2 s?1) and net CH4 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 CO2 sources (1.93 ± 1.63 µmol m?2 s?1), but also net CH4 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 CH4, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO2 fluxes, whereas CH4 emissions from living stems offset net soil and CWD CH4 uptake by 3.5%. Our results demonstrate the importance of CH4 emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO2 and CH4 dynamics. 相似文献
2.
Crop residues like corn (Zea mays L.) stover perform important functions that promote soil health and provide ecosystem services that influence agricultural sustainability and global biogeochemical cycles. We evaluated the effect of corn stover removal from a no-till, corn-soybean (Glycine max (L.) Merr) rotation on soil greenhouse gas (GHG; CO2, N2O, CH4) fluxes, crop yields, and soil organic carbon (SOC) dynamics. We conducted a 4-year study using replicated field plots managed with two levels of corn stover removal (none; 55 % stover removal) for four complete crop cycles prior to initiation of ground surface gas flux measurements. Corn and soybean yields were not affected by stover removal with yields averaging 7.28 Mg ha?1 for corn and 2.64 Mg ha?1 for soybean. Corn stover removal treatment did not affect soil GHG fluxes from the corn phase; however, the treatment did significantly increase (107 %, P?=?0.037) N2O fluxes during the soybean phase. The plots were a net source of CH4 (~0.5 kg CH4-C ha?1 year?1 average of all treatments and crops) during the generally wet study duration. Soil organic carbon stocks increased in both treatments during the 4-year study (initiated following 8 years of stover removal), with significantly higher SOC accumulation in the control plots compared to plots with corn stover removal (0–15 cm, P?=?0.048). Non-CO2 greenhouse gas emissions (945 kg CO2-eq ha?1 year?1) were roughly half of SOC (0–30 cm) gains with corn stover removal (1.841 Mg CO2-eq ha?1 year?1) indicating that no-till practices greatly improve the viability of biennial corn stover harvesting under local soil-climatic conditions. Our results also show that repeated corn stover harvesting may increase N loss (as N2O) from fields and thereby contribute to GHG production and loss of potential plant nutrients. 相似文献
3.
Assessing the effects of chamber placement, manual sampling and headspace mixing on CH4 fluxes in a laboratory experiment 总被引:1,自引:0,他引:1
Jesper Riis Christiansen Janne F. J. Korhonen Radoslaw Juszczak Michael Giebels Mari Pihlatie 《Plant and Soil》2011,343(1-2):171-185
A laboratory experiment was conducted with two types of closed static chambers to estimate the effects of chamber placement, manual headspace sampling and headspace mixing on methane (CH4) fluxes. Chamber fluxes were compared to a known reference flux in a chamber calibration system. The measurements were conducted with three types of soils (coarse dry, fine dry and fine wet quarts sand) at five flux levels ranging from 60 to 2000 ??g CH4 m?2 h?1. We found that the placement of a non-vented chamber disturbed the initial CH4 concentration development within the chamber headspace for 10 to 30 s. Excluding this short period from the flux calculation resulted in a lower flux estimate (mean±SE) of 126?±?26 ??g CH4 m?2 h?1 compared to 134?±?26 ??g CH4 m?2 h?1 if data from time zero of the enclosure were included. We also found that in non-mixed chambers (no fan mixing) the gas sampling by syringes or gas bottles disturbed the development of CH4 concentration during the enclosure. Furthermore, flux estimates in non-mixed chambers were significantly underestimated (on average 36%) compared to the measured reference fluxes. However, the use of fans to constantly mix the chamber headspace during enclosure significantly improved the goodness-of-fit of the regression analysis used to calculate the flux and further eliminated the disturbance of the manual sampling on the concentration development. We recommend that chambers should be vented during the placement of the chamber, and that fans are used as an integrated part of static chambers while headspace mixing with syringes should be avoided. 相似文献
4.
We evaluated the nighttime CO2 flux (ecosystem respiration) on Rishiri Island, located at the northern tip of Hokkaido, Japan, from 2009 to 2011, by using the relationship between atmospheric 222Rn and CO2 concentrations. The annual mean CO2 flux was 1.8 μmol m?2 s?1, with a maximum monthly mean in July (4.6 ± 2.6 μmol m?2 s?1) and a broad minimum from December to March (0.33 ± 0.29 μmol m?2 s?1). The annual mean was comparable to fluxes at the JapanFlux sites in northern Japan. During the season of snow cover (mid-December to early April), the CO2 flux was low (0.45 ± 0.43 μmol m?2 s?1). Total annual respiration was estimated at 679 ± 174 g cm?2, about 8 % of which occurred during the season of snow cover. 相似文献
5.
Alberto V. Borges Gaëlle Speeckaert Willy Champenois Mary I. Scranton Nathalie Gypens 《Ecosystems》2018,21(4):583-599
Dissolved CH4 concentrations in the Belgian coastal zone (North Sea) ranged between 670 nmol l?1 nearshore and 4 nmol l?1 offshore. Spatial variations of CH4 were related to sediment organic matter (OM) content and gassy sediments. In nearshore stations with fine sand or muddy sediments, the CH4 seasonal cycle followed water temperature, suggesting methanogenesis control by temperature in these OM-rich sediments. In offshore stations with permeable sediments, the CH4 seasonal cycle showed a yearly peak following the chlorophyll-a spring peak, suggesting that in these OM-poor sediments, methanogenesis depended on freshly produced OM delivery. This does not exclude the possibility that some CH4 might originate from dimethylsulfide (DMS) or dimethylsulfoniopropionate (DMSP) or methylphosphonate transformations in the most offshore stations. Yet, the average seasonal CH4 cycle was unrelated to those of DMS(P), very abundant during the Phaeocystis bloom. The annual average CH4 emission was 126 mmol m?2 y?1 in the most nearshore stations (~4 km from the coast) and 28 mmol m?2 y?1 in the most offshore stations (~23 km from the coast), 1260–280 times higher than the open ocean average value (0.1 mmol m?2 y?1). The strong control of CH4 by sediment OM content and by temperature suggests that marine coastal CH4 emissions, in particular in shallow areas, should respond to future eutrophication and warming of climate. This is supported by the comparison of CH4 concentrations at five stations obtained in March 1990 and 2016, showing a decreasing trend consistent with alleviation of eutrophication in the area. 相似文献
6.
Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity 总被引:1,自引:0,他引:1
S. J. Livesley R. Kiese J. Graham C. J. Weston K. Butterbach-Bahl S. K. Arndt 《Plant and Soil》2008,309(1-2):89-103
Temperate pastures are often managed with P fertilizers and N2-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N2O) emissions and reduced methane (CH4) uptake. However, the diel and inter-daily variation in N2O and CH4 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 N2O and CH4 flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N2O and CH4 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 CH4 uptake was similar (?6.3?±?SE 0.3 to ?8.6?±?0.4 μg C m?2 hr?1) as were mean N2O emissions (6.5 to 7.9?±?0.8 μg N m?2 hr?1), although N2O flux in the No P pasture did not respond to changing soil water conditions. N2O emissions were greatest in the Low P sheep camp (12.4 μg?±?1.1 N m?2 hr?1) where there were also net CH4 emissions of 5.2?±?0.5 μg C m?2 hr?1. There were significant, but weak, relationships between soil water and N2O emissions, but not between soil water and CH4 flux. The diel temperature cycle strongly influenced CH4 and N2O 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 N2O emissions, or reduce CH4 uptake, during this 4 week measurement period, but the lack of an N2O 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 N2O and CH4 trace gas balance. 相似文献
7.
Seasonal and spatial variations of methane emissions from coastal marshes in the northern Yellow River estuary, China 总被引:1,自引:0,他引:1
Zhigao Sun Huanhuan Jiang Lingling Wang Xiaojie Mou Wanlong Sun 《Plant and Soil》2013,369(1-2):317-333
Aims and methods
To evaluate the seasonal and spatial variations of methane (CH4) emissions and understand the controlling factors, we measured CH4 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
CH4 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, CH4 fluxes averaged between ?0.392 mgCH4 m?2?h?1 and 0.495 mgCH4 m?2?h?1, and emissions occurred during spring (0.008 mgCH4 m?2?h?1) and autumn (0.068 mgCH4 m?2?h?1) while sinks were observed during summer (?0.110 mgCH4 m?2?h?1) and winter (?0.009 mgCH4 m?2?h?1). CH4 fluxes from the four marshes were not significantly different (p?>?0.05), and emissions occurred in LSM (0.026 mgCH4 m?2?h?1) and BF (0.055 mgCH4 m?2?h?1) while sinks were observed in HSM (?0.035 mgCH4 m?2?h?1) and MSM (?0.022 mgCH4 m?2?h?1). The annual average CH4 flux from the intertidal zone was 0.002 mgCH4 m?2?h?1, indicating that coastal marsh acted as a weak CH4 source. Temporal variations of CH4 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 CH4 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 CH4 budget was evaluated precisely. With increasing exogenous nitrogen loading to the Yellow River estuary, the magnitude of CH4 emission might be enhanced, which should also be paid more attentions as the annual CH4 inventory was assessed accurately. 相似文献8.
The positive net radiative greenhouse gas forcing of increasing methane emissions from a thawing boreal forest‐wetland landscape
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Manuel Helbig Laura E. Chasmer NatasCha Kljun William L. Quinton Claire C. Treat Oliver Sonnentag 《Global Change Biology》2017,23(6):2413-2427
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 (CH4) emissions. Here, we quantify the thaw‐induced increase in CH4 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 (CO2) exchange. Using nested wetland and landscape eddy covariance net CH4 flux measurements in combination with flux footprint modeling, we find that landscape CH4 emissions increase with increasing wetland‐to‐forest ratio. Landscape CH4 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 CH4 emission of ~13 g CH4 m?2 is the dominating contribution to the landscape CH4 emission of ~7 g CH4 m?2. In contrast, forest contributions to landscape CH4 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 CH4 m?2 yr?1 in landscape CH4 emissions. A long‐term net CO2 uptake of >200 g CO2 m?2 yr?1 is required to offset the positive radiative forcing of increasing CH4 emissions until the end of the 21st century as indicated by an atmospheric CH4 and CO2 concentration model. However, long‐term apparent carbon accumulation rates in similar boreal forest‐wetland landscapes and eddy covariance landscape net CO2 flux measurements suggest a long‐term net CO2 uptake between 49 and 157 g CO2 m?2 yr?1. Thus, thaw‐induced CH4 emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century. 相似文献
9.
Hilary A. Thompson Jeffrey R. White Lisa M. Pratt Peter E. Sauer 《Biogeochemistry》2016,131(1-2):17-33
Small lakes in northern latitudes represent a significant source of CH4 to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH4 budgets are lacking as are measurements of δ13C-CH4 and δ2H-CH4. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH4 and corresponding δ13C-CH4 and δ2H-CH4 in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH4 flux was highly variable, ranging from an average flux of 7 mg CH4 m?2 d?1 in the deep-water zone to 154 mg CH4 m?2 d?1 along the lake margin. Diffusive flux accounted for ~8.5 % of mean net CH4 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 CH4 emissions varied widely throughout the system, with δ13C-CH4 ranging from ?66.2 to ?55.5 ‰, and δ2H-CH4 ranging from ?345 to ?258 ‰. Carbon isotope composition of CH4 in ebullitive flux showed wider variation compared to net flux, ranging from ?69.2 to ?49.2 ‰. Dissolved CH4 concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH4 in the hypoxic deep water coincided with decreasing dissolved O2 concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ13C-CH4 and δ2H-CH4. The most depleted 13C- and 2H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ13C and δ2H observations of CH4, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH4 in deeper sediments were consistent with mixing/transition between CH4 production pathways, indicating a higher contribution of the CO2 reduction pathway. The large spatial variability in fluxes of CH4 and in isotopic composition of CH4 throughout a single lake system indicates that the underlying mechanisms controlling CH4 cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH4 emissions in these systems. Future studies of whole-lake CH4 budgets should consider this significant spatial heterogeneity. 相似文献
10.
Influence of weather variables on methane and carbon dioxide flux from a shallow pond 总被引:5,自引:0,他引:5
Sivakiruthika Natchimuthu Balathandayuthabani Panneer Selvam David Bastviken 《Biogeochemistry》2014,119(1-3):403-413
Freshwaters are important sources of the greenhouse gases methane (CH4) and carbon dioxide (CO2) 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 CH4 and CO2 flux from a small shallow pond during a period of 4 months. Mean CH4 flux and surface water CH4 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 CO2 flux was 1.1 [?9.8 to 16.0] ± 6.9 mmol m?2 day?1. Substantial diel changes in CO2 flux and surface water CH4 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 CH4 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). CO2 flux on the other hand was negatively correlated to temperature and solar radiation, presumably because CO2 consumption by plants was higher relative to CO2 production by respiration during warm sunny days. Interestingly, CH4 fluxes were comparable to ponds with similar morphometry and macrophyte abundance in the tropics. We therefore hypothesize that CH4 and CO2 summer emissions from ponds could be more related to the morphometry and dominating primary producers rather than latitude per se. Data indicate that CH4 emissions, given the system characteristic frameworks, is positively affected by increased temperatures or prolonged growth seasons. 相似文献
11.
Currently, there is a lack of knowledge about GHG emissions, specifically N2O and CH4, in subtropical coastal freshwater wetland and mangroves in the southern hemisphere. In this study, we quantified the gas fluxes and substrate availability in a subtropical coastal wetland off the coast of southeast Queensland, Australia over a complete wet-dry seasonal cycle. Sites were selected along a salinity gradient ranging from marine (34 psu) in a mangrove forest to freshwater (0.05 psu) wetland, encompassing the range of tidal influence. Fluxes were quantified for CH4 (range ?0.4–483 mg C–CH4 h?1 m?2) and N2O (?5.5–126.4 μg N–N2O h?1 m?2), with the system acting as an overall source for CH4 and N2O (mean N2O and CH4 fluxes: 52.8 μg N–N2O h?1 m?2 and 48.7 mg C–CH4 h?1 m?2, respectively). Significantly higher N2O fluxes were measured during the summer months (summer mean 64.2 ± 22.2 μg N–N2O h?1 m?2; winter mean 33.1 ± 24.4 µg N–N2O h–1 m?2) but not CH4 fluxes (summer mean 30.2 ± 81.1 mg C–CH4 h?1 m?2; winter mean 37.4 ± 79.6 mg C–CH4 h?1 m?2). The changes with season are primarily driven by temperature and precipitation controls on the dissolved inorganic nitrogen (DIN) concentration. A significant spatial pattern was observed based on location within the study site, with highest fluxes observed in the freshwater tidal wetland and decreasing through the mangrove forest. The dissolved organic carbon (DOC) varied throughout the landscape and was correlated with higher CH4 fluxes, but this was a nonlinear trend. DIN availability was dominated by N–NH4 and correlated to changes in N2O fluxes throughout the landscape. Overall, we did not observe linear relationships between CH4 and N2O fluxes and salinity, oxygen or substrate availability along the fresh-marine continuum, suggesting that this ecosystem is a mosaic of processes and responses to environmental changes. 相似文献
12.
The semiarid and arid zones cover a quarter of the global land area and support one‐fifth of the world's human population. A significant fraction of the global soil–atmosphere exchange for climatically active gases occurs in semiarid and arid zones yet little is known about these exchanges. A study was made of the soil–atmosphere exchange of CH4, CO, N2O and NOx in the semiarid Mallee system, in north‐western Victoria, Australia, at two sites: one pristine mallee and the other cleared for approximately 65 years for farming (currently wheat). The mean (± standard error) rates of CH4 exchange were uptakes of ?3.0 ± 0.5 ng(C) m?2 s?1 for the Mallee and ?6.0 ± 0.3 ng(C) m?2 s?1 for the Wheat. Converting mallee forest to wheat crop increases CH4 uptake significantly. CH4 emissions were observed in the Mallee in summer and were hypothesized to arise from termite activity. We find no evidence that in situ growing wheat plants emit CH4, contrary to a recent report. The average CO emissions of 10.1 ± 1.8 ng(C) m?2 s?1 in the Mallee and 12.6 ± 2.0 ng(C) m?2 s?1 in the Wheat. The average N2O emissions were 0.5 ± 0.1 ng(N) m?2 s?1 from the pristine Mallee and 1.4 ± 0.3 ng(N) m?2 s?1 from the Wheat. The experimental results show that the processes controlling these exchanges are different to those in temperate systems and are poorly understood. 相似文献
13.
Mohammad Babar Ali Serida Khatun Eun-Joo Hahn Kee-Yoeup Paek 《Plant Growth Regulation》2006,49(2-3):137-146
Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 μmol m−2s−1) were investigated in one-month-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 μmol m−2s−1, while net CO2 assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 μmol m−2s−1, indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and β-glucosidase (β-GS) activities increased to a maximum in acclimatised plants at 300 μmol m−2s−1. A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 μmol m−2s−1. The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 μmol m−2s−1was suitable for acclimatisation when plants were transferred from in vitro conditions. 相似文献
14.
Methane flux from rainforest soils in northeast Queensland, Australia, was investigated using a combination of laboratory, field and simulation modelling. In aerobic laboratory incubations, CH4 uptake in the top 0.1 m of the soil (?2.5 to ?7.3 μg CH4 kg?1 SDW day?1) is approximately one order of magnitude higher than CH4 production under anaerobic conditions. The highest CH4 uptake, as well as potential CH4 production is found in the uppermost C rich soil layers. Detailed measurements from three contrasting rainforest sites identified the soils to be functioning as sinks for atmospheric CH4. Fifteen months continuous measurement at one of the lowland rainforest sites showed that the seasonality of CH4 uptake was mainly driven by changes in soil moisture rather than by temperature changes. Maximum CH4 uptake (109 μg CH4 m?2 h?1) was observed during dry season conditions, whereas during the wet season, CH4 uptake decreased significantly to near zero. Based on our laboratory experiments and on published literature we developed a semi-empirical CH4 module for the biogeochemical model ForestDNDCtropica. Tests at several sites showed the robustness of our modelling approach with mean simulated values within 12% of observed values. To estimate regional CH4 uptake by rainforest soils in the region of the ‘Wet Tropics’, Queensland, Australia, we linked CH4 uptake and production algorithms to a regional GIS database. We estimated that the lowland and montane rainforest soils in northeast Queensland, Australia, were a net sink for CH4 with a mean uptake rate of ?2.89 kg CH4 ha?1 year?1 during July 1996 to June 1997 period. 相似文献
15.
Julia Schneider Boris Ťupek Maria Lukasheva Vasiliy Gudyrev Mikhail Miglovets Hermann F. Jungkunst 《Ecosystems》2018,21(5):827-838
Spatial or temporal forest–peatland transition zones were proposed as potential hot spots of methane (CH4) emissions. Consequently, paludified soils are an important component of boreal landscape biogeochemistry. However, their role in the regional carbon cycle remains unclear. This study presents CH4 fluxes from two forest–peatland transition zones, two wet forest sites and two clear-cut sites which were compared to fluxes of open peatlands and dry forest. The median fluxes measured using the closed-chamber technique varied from ? 0.04 to 12.6 mg m?2 h?1 during three climatically different years. The annual mean CH4 emissions of the forest–peatland transition zone were significantly lower than the fluxes of the open peatland sites, 7.9 ± 0.5 and 21.9 ± 1.6 g m?2a?1, respectively. The dry forest site was characterized by a small uptake of CH4 (? 2.3 ± 0.2 g m?2a?1). Although clear-cut forest area drastically increased in European Russia during the last two decades, if water level depths in these forests remains below 10 cm they do not act as CH4 sources. Fluxes of CH4 from the transition zone sites showed a higher response to soil temperature than to water table level. Fluxes of CH4 between the atmosphere and the two investigated peatlands were not significantly different, although a significant difference in water table level could be observed. The meteorological conditions of the investigated summers changed from being hot and dry in 2013 to cold and wet in 2014; the summer of 2015 was characterized as warmer and drier in the first half and colder and wetter in the second half. Significant differences in CH4 fluxes were measured only between 2014 and 2013. Significant differences in CH4 fluxes and in nonlinear regressions showed that the CH4 fluxes of the different site types such as dry forests, transition zones and open peatlands need to be modelled separately on a landscape level. Obviously, underlying processes vary with the ecosystem and (along with regional aspects) have to be understood first before large-scale modelling is possible. 相似文献
16.
Carbon dioxide and methane emissions from interfluvial wetlands in the upper Negro River basin, Brazil 总被引:1,自引:0,他引:1
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. CO2 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. CO2 and CH4 emissions increased when dissolved O2 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 km2) emitted 1147 Gg C year?1 as CO2 and 31 Gg C year?1 as CH4. If these rates are extrapolated to the area occupied by hydromorphic soils in the upper Negro basin, 63 Tg C year?1 of CO2 and 1.7 Tg C year?1 as CH4 are estimated as the regional evasion to the atmosphere. 相似文献
17.
Helen Karu Margus Pensa Eva-Ingrid Rõõm Angelika Portsmuth Triin Triisberg 《Wetlands Ecology and Management》2014,22(4):399-417
Bog ecosystems are sensitive to anthropogenic disturbance, including drainage and air pollution. Carbon (C) balance measurements to determine the effect of disturbance on bog functioning are laborious; therefore reliable proxies for C fluxes that could facilitate upscaling from single studies to a larger scale would be valuable. We measured peat CO2 emissions (R s), CH4 efflux and vegetation characteristics in four bog areas that formed a gradient from pristine to severely disturbed peatlands, affected by drainage, peat mining, alkaline air pollution and underground oil-shale mining. We expected that sites experiencing higher human impact (i.e., the vegetation was more distinct from that of a natural bog) would have higher R s and lower CH4 emissions, but differences in peat C emissions between the most disturbed and pristine sites were not significant. Growing period median R s ranged from 0.5 to 2.2 g C m?2 day?1 for our plots; methane emissions, measured from July to December were an order of magnitude lower, ranging from ?5.9 to 126.7 mg C m?2 day?1. R s and CH4 emissions were primarily determined by water table depth, as was tree stand productivity. Therefore, stand structural parameters could potentially be good indicators of soil C emissions from poorly drained forested bogs. 相似文献
18.
Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH4) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH4 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 CH4 emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH4 emission rates varied between 0.24 and 293 mg CH4 m?2 h?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH4 m?2 h?1 or 558 ± 53 mg CH4 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 CH4 m?2 h?1 than in floodplains (20.4 ± 2.5 mg CH4 m?2 h?1) and lagoons (16.9 ± 2.6 mg CH4 m?2 h?1). Diffusive CH4 emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH4 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 km2, the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH4 emission from global tropical wetlands. 相似文献
19.
Hong Li Shengqi Dai Zutao Ouyang Xiao Xie Haiqiang Guo Caihong Gu Xiangming Xiao Zhenming Ge Changhui Peng Bin Zhao 《Biogeochemistry》2018,137(1-2):163-179
CH4 emissions could vary with biotic and abiotic factors at different time scales. However, little is known about temporal dynamics of CH4 flux and its controls in coastal marshes. In this study, CH4 flux was continuously measured with the eddy covariance technique for 2 years in a subtropical salt marsh in eastern China. Wavelet analysis was applied to explore the multi-scale variations of CH4 flux and its controls. Additionally, partial wavelet coherence was used to disentangle confounding effects of measured variables. No consistent diurnal pattern was found in CH4 fluxes. However, the hot-moments of CH4 flux were observed after nighttime high tide on days near the spring tide. Periodic dynamics were also observed at multi-day, semilunar and seasonal scales. Tide height in summer had a negative effect on CH4 flux at the semilunar scale. Air temperature explained most variations in CH4 fluxes at the multi-day scale but CH4 flux was mainly controlled by PAR and GEP at the seasonal scale. Air temperature explained 48% and 56% of annual variations in CH4 fluxes in 2011 and 2012, respectively. In total, the salt marsh acted as a CH4 source (17.6 ± 3.0 g C–CH4 m?2 year?1), which was higher than most studies report for inland wetlands. Our results show that CH4 fluxes exhibit multiple periodicities and its controls vary with time scale; moreover, CH4 flux is strongly modified by tide. This study emphasizes the importance of ecosystem-specific measurements of CH4 fluxes, and more work is needed to estimate regional CH4 budgets. 相似文献
20.
The transfer of carbon (C) from Amazon forests to aquatic ecosystems as CO2 supersaturated in groundwater that outgases to the atmosphere after it reaches small streams has been postulated to be an important component of terrestrial ecosystem C budgets. We measured C losses as soil respiration and methane (CH4) flux, direct CO2 and CH4 fluxes from the stream surface and fluvial export of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate C over an annual hydrologic cycle from a 1,319-ha forested Amazon perennial first-order headwater watershed at Tanguro Ranch in the southern Amazon state of Mato Grosso. Stream pCO2 concentrations ranged from 6,491 to 14,976 ??atm and directly-measured stream CO2 outgassing flux was 5,994 ± 677 g C m?2 y?1 of stream surface. Stream pCH4 concentrations ranged from 291 to 438 ??atm and measured stream CH4 outgassing flux was 987 ± 221 g C m?2 y?1. Despite high flux rates from the stream surface, the small area of stream itself (970 m2, or 0.007% of watershed area) led to small directly-measured annual fluxes of CO2 (0.44 ± 0.05 g C m2 y?1) and CH4 (0.07 ± 0.02 g C m2 y?1) per unit watershed land area. Measured fluvial export of DIC (0.78 ± 0.04 g C m?2 y?1), DOC (0.16 ± 0.03 g C m?2 y?1) and coarse plus fine particulate C (0.001 ± 0.001 g C m?2 y?1) per unit watershed land area were also small. However, stream discharge accounted for only 12% of the modeled annual watershed water output because deep groundwater flows dominated total runoff from the watershed. When C in this bypassing groundwater was included, total watershed export was 10.83 g C m?2 y?1 as CO2 outgassing, 11.29 g C m?2 y?1 as fluvial DIC and 0.64 g C m?2 y?1 as fluvial DOC. Outgassing fluxes were somewhat lower than the 40?C50 g C m?2 y?1 reported from other Amazon watersheds and may result in part from lower annual rainfall at Tanguro. Total stream-associated gaseous C losses were two orders of magnitude less than soil respiration (696 ± 147 g C m?2 y?1), but total losses of C transported by water comprised up to about 20% of the ± 150 g C m?2 (±1.5 Mg C ha?1) that is exchanged annually across Amazon tropical forest canopies. 相似文献