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1.
Drainage of peatlands for forestry starts a succession of ground vegetation in which mire species are gradually replaced by forest species. Some mire plant communities vanish quickly following the water-level drawdown; some may prevail longer in the moister patches of peatland. Drainage ditches, as a new kind of surface, introduce another component of spatial variation in drained peatlands. These variations were hypothesized to affect methane (CH 4) fluxes from drained peatlands. Methane fluxes from different plant communities and unvegetated surfaces, including ditches, were measured at the drained part of Lakkasuo mire, Central Finland. The fluxes were found to be related to peatland site type, plant community, water-table position and soil temperature. At nutrient-rich fen sites fluxes between plant communities differed only a little: almost all plots acted as CH 4 sinks (−0.9 to −0.4 mg CH 4 m −2 d −1), with the exception of Eriophorum angustifolium Honck. communities, which emitted 0.9 g CH 4 m −2 d −1. At nutrient-poor bog site the differences between plant communities were clearer. The highest emissions were measured from Eriophorum vaginatum L. communities (29.7 mg CH 4 m −2 d −1), with a decreasing trend to Sphagna (10.0 mg CH 4 m −2 d −1) and forest moss communities (2.6 mg CH 4 m −2 d −1). CH 4 emissions from different kinds of ditches were highly variable, and extremely high emissions (summertime averages 182–600 mg CH 4 m −2 d −1) were measured from continuously water-covered ditches at the drained fen. Variability in the emissions was caused by differences in the origin and movement of water in the ditches, as well as differences in vegetation communities in the ditches. While drainage on average greatly decreases CH 4 emissions from peatlands, a great spatial variability in fluxes is emerged. Emissions from ditches constantly covered with water, may in some cases have a great impact on the overall CH 4 emissions from drained peatlands. 相似文献
2.
Pristine peatlands are a significant source of atmospheric methane (CH 4). Large spatio–temporal variation has been observed in flux rates within and between peatlands. Variation is commonly associated
with water level, vegetation structure, soil chemistry and climatic variability. We measured spatial and temporal variation
in CH 4 fluxes in a blanket bog during the period 2003–2005. The surface of the bog was composed of different vegetation communities
(hummocks, lawns and hollows) along a water level gradient. CH 4 fluxes were measured in each community using a chamber method. Regression modelling was used to relate the fluxes with environmental
variables and to integrate fluxes over the study period. Water level was the strongest controller of spatial variation; the
average flux rate was lowest in hummocks and highest in hollows, ranging from 3 to 53 mg CH 4 m −2 day −1. In vegetation communities with a permanently high water level, the amount and species composition of vegetation was also
a good indicator of flux rate. We observed a clear seasonal variation in flux that was chiefly controlled by temperature.
The annual average flux (6.2 g CH 4 m −2 year −1) was similar to previous estimates from blanket bogs and continental raised bogs. No interannual variation was observed. 相似文献
3.
As surface temperatures are expected to rise in the future, ice‐rich permafrost may thaw, altering soil topography and hydrology and creating a mosaic of wet and dry soil surfaces in the Arctic. Arctic wetlands are large sources of CH 4, and investigating effects of soil hydrology on CH 4 fluxes is of great importance for predicting ecosystem feedback in response to climate change. In this study, we investigate how a decade‐long drying manipulation on an Arctic floodplain influences CH 4‐associated microorganisms, soil thermal regimes, and plant communities. Moreover, we examine how these drainage‐induced changes may then modify CH 4 fluxes in the growing and nongrowing seasons. This study shows that drainage substantially lowered the abundance of methanogens along with methanotrophic bacteria, which may have reduced CH 4 cycling. Soil temperatures of the drained areas were lower in deep, anoxic soil layers (below 30 cm), but higher in oxic topsoil layers (0–15 cm) compared to the control wet areas. This pattern of soil temperatures may have reduced the rates of methanogenesis while elevating those of CH 4 oxidation, thereby decreasing net CH 4 fluxes. The abundance of Eriophorum angustifolium, an aerenchymatous plant species, diminished significantly in the drained areas. Due to this decrease, a higher fraction of CH 4 was alternatively emitted to the atmosphere by diffusion, possibly increasing the potential for CH 4 oxidation and leading to a decrease in net CH 4 fluxes compared to a control site. Drainage lowered CH 4 fluxes by a factor of 20 during the growing season, with postdrainage changes in microbial communities, soil temperatures, and plant communities also contributing to this reduction. In contrast, we observed CH 4 emissions increased by 10% in the drained areas during the nongrowing season, although this difference was insignificant given the small magnitudes of fluxes. This study showed that long‐term drainage considerably reduced CH 4 fluxes through modified ecosystem properties. 相似文献
4.
Tropical peatlands play an important role in the global storage and cycling of carbon (C) but information on carbon dioxide (CO 2) and methane (CH 4) fluxes from these systems is sparse, particularly in the Neotropics. We quantified short and long‐term temporal and small scale spatial variation in CO 2 and CH 4 fluxes from three contrasting vegetation communities in a domed ombrotrophic peatland in Panama. There was significant variation in CO 2 fluxes among vegetation communities in the order Campnosperma panamensis > Raphia taedigera > Cyperus. There was no consistent variation among sites and no discernible seasonal pattern of CH 4 flux despite the considerable range of values recorded (e.g. ?1.0 to 12.6 mg m ?2 h ?1 in 2007). CO 2 fluxes varied seasonally in 2007, being greatest in drier periods (300–400 mg m ?2 h ?1) and lowest during the wet period (60–132 mg m ?2 h ?1) while very high emissions were found during the 2009 wet period, suggesting that peak CO 2 fluxes may occur following both low and high rainfall. In contrast, only weak relationships between CH 4 flux and rainfall (positive at the C. panamensis site) and solar radiation (negative at the C. panamensis and Cyperus sites) was found. CO 2 fluxes showed a diurnal pattern across sites and at the Cyperus sp. site CO 2 and CH 4 fluxes were positively correlated. The amount of dissolved carbon and nutrients were strong predictors of small scale within‐site variability in gas release but the effect was site‐specific. We conclude that (i) temporal variability in CO 2 was greater than variation among vegetation communities; (ii) rainfall may be a good predictor of CO 2 emissions from tropical peatlands but temporal variation in CH 4 does not follow seasonal rainfall patterns; and (iii) diurnal variation in CO 2 fluxes across different vegetation communities can be described by a Fourier model. 相似文献
5.
BackgroundRice paddies have been identified as major methane (CH 4) source induced by human activities. As a major rice production region in Northern China, the rice paddies in the Three-Rivers Plain (TRP) have experienced large changes in spatial distribution over the recent 20 years (from 1990 to 2010). Consequently, accurate estimation and characterization of spatiotemporal patterns of CH 4 emissions from rice paddies has become an pressing issue for assessing the environmental impacts of agroecosystems, and further making GHG mitigation strategies at regional or global levels. Methodology/Principal FindingsIntegrating remote sensing mapping with a process-based biogeochemistry model, Denitrification and Decomposition (DNDC), was utilized to quantify the regional CH 4 emissions from the entire rice paddies in study region. Based on site validation and sensitivity tests, geographic information system (GIS) databases with the spatially differentiated input information were constructed to drive DNDC upscaling for its regional simulations. Results showed that (1) The large change in total methane emission that occurred in 2000 and 2010 compared to 1990 is distributed to the explosive growth in amounts of rice planted; (2) the spatial variations in CH 4 fluxes in this study are mainly attributed to the most sensitive factor soil properties, i.e., soil clay fraction and soil organic carbon (SOC) content, and (3) the warming climate could enhance CH 4 emission in the cool paddies. Conclusions/SignificanceThe study concluded that the introduction of remote sensing analysis into the DNDC upscaling has a great capability in timely quantifying the methane emissions from cool paddies with fast land use and cover changes. And also, it confirmed that the northern wetland agroecosystems made great contributions to global greenhouse gas inventory. 相似文献
6.
Thawing permafrost in the sub‐Arctic has implications for the physical stability and biological dynamics of peatland ecosystems. This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub‐Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO 2) and CH 4 over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet‐growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO 2 sink function with about 16% and the CH 4 emissions with 22%. Calculating the flux as CO 2 equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100‐year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH 4 emissions. 相似文献
7.
The carbon budgets of the atmosphere and terrestrial ecosystems are closely coupled by vertical gas exchange fluxes. Uncertainties remain with respect to high latitude ecosystems and the processes driving their temporally and spatially highly variable methane (CH 4) exchange. Problems associated with scaling plot measurements to larger areas in heterogeneous environments are addressed based on intensive field studies on two nested spatial scales in Northern Siberia. CH 4 fluxes on the microsite scale (0.1–100 m 2) were measured in the Lena River Delta from July through September 2006 by closed chambers and were compared with simultaneous ecosystem scale (10 4–10 6 m 2) flux measurements by the eddy covariance (EC) method. Closed chamber measurements were conducted almost daily on 15 plots in four differently developed polygon centers and on a polygon rim. Controls on CH 4 emission were identified by stepwise multiple regression. In contrast to relatively low ecosystem‐scale fluxes controlled mainly by near‐surface turbulence, fluxes on the microsite scale were almost an order of magnitude higher at the wet polygon centers and near zero at the drier polygon rim and high‐center polygon. Microsite scale CH 4 fluxes varied strongly even within the same microsites. The only statistically significant control on chamber‐based fluxes was surface temperature calculated using the Stefan–Boltzmann equation in the wet polygon centers, whereas no significant control was found for the low emissions from the dry sites. The comparison with the EC measurements reveals differences in controls and the seasonal dynamics between the two measurement scales, which may have consequences for scaling and process‐based models. Despite those differences, closed chamber measurements from within the EC footprint could be scaled by an area‐weighting approach of landcover classes based on high‐resolution imagery to match the total ecosystem‐scale emission. Our nested sampling design allowed for checking scaling results against measurements and to identify potentially missed sources or sinks. 相似文献
8.
Boreal peatlands in Canada have harbored relict permafrost since the Little Ice Age due to the strong insulating properties of peat. Ongoing climate change has triggered widespread degradation of localized permafrost in peatlands across continental Canada. Here, we explore the influence of differing permafrost regimes (bogs with no surface permafrost, localized permafrost features with surface permafrost, and internal lawns representing areas of permafrost degradation) on rates of peat accumulation at the southernmost limit of permafrost in continental Canada. Net organic matter accumulation generally was greater in unfrozen bogs and internal lawns than in the permafrost landforms, suggesting that surface permafrost inhibits peat accumulation and that degradation of surface permafrost stimulates net carbon storage in peatlands. To determine whether differences in substrate quality across permafrost regimes control trace gas emissions to the atmosphere, we used a reciprocal transplant study to experimentally evaluate environmental versus substrate controls on carbon emissions from bog, internal lawn, and permafrost peat. Emissions of CO 2 were highest from peat incubated in the localized permafrost feature, suggesting that slow organic matter accumulation rates are due, at least in part, to rapid decomposition in surface permafrost peat. Emissions of CH 4 were greatest from peat incubated in the internal lawn, regardless of peat type. Localized permafrost features in peatlands represent relict surface permafrost in disequilibrium with the current climate of boreal North America, and therefore are extremely sensitive to ongoing and future climate change. Our results suggest that the loss of surface permafrost in peatlands increases net carbon storage as peat, though in terms of radiative forcing, increased CH 4 emissions to the atmosphere will partially or even completely offset this enhanced peatland carbon sink for at least 70 years following permafrost degradation. 相似文献
9.
A comprehensive biogeochemistry model, DNDC, was revised to simulate crop growth and soil processes more explicitly and improve its ability to estimate methane (CH 4) emission from rice paddy fields under a wide range of climatic and agronomic conditions. The revised model simulates rice growth by tracking photosynthesis, respiration, C allocation, tillering, and release of organic C and O 2 from roots. For anaerobic soil processes, it quantifies the production of electron donors [H 2 and dissolved organic carbon (DOC)] by decomposition and rice root exudation, and simulates CH 4 production and other reductive reactions based on the availability of electron donors and acceptors (NO 3?, Mn 4+, Fe 3+, and SO 42?). Methane emission through rice is simulated by a diffusion routine based on the conductance of tillers and the CH 4 concentration in soil water. The revised DNDC was tested against observations at three rice paddy sites in Japan and China with varying rice residue management and fertilization, and produced estimates consistent with observations for the variation in CH 4 emission as a function of residue management. It also successfully predicted the negative effect of (NH 4) 2SO 4 on CH 4 emission, which the current model missed. Predicted CH 4 emission was highly sensitive to the content of reducible soil Fe 3+, which is the dominant electron acceptor in anaerobic soils. The revised DNDC generally gave acceptable predictions of seasonal CH 4 emission, but not of daily CH 4 fluxes, suggesting the model's immaturity in describing soil heterogeneity or rice cultivar‐specific characteristics of CH 4 transport. It also overestimated CH 4 emission at one site in a year with low temperatures, suggesting uncertainty in root biomass estimates due to the model's failure to consider the temperature dependence of leaf area development. Nevertheless, the revised DNDC explicitly reflects the effects of soil electron donors and acceptors, and can be used to quantitatively estimate CH 4 emissions from rice fields under a range of conditions. 相似文献
10.
Waterbodies in the arctic permafrost zone are considered a major source of the greenhouse gas methane (CH 4) in addition to CH 4 emissions from arctic wetlands. However, the spatio‐temporal variability of CH 4 fluxes from waterbodies complicates spatial extrapolation of CH 4 measurements from single waterbodies. Therefore, their contribution to the CH 4 budget of the arctic permafrost zone is not yet well understood. Using the example of two study areas of 1,000 km² each in the Mackenzie Delta, Canada, we approach this issue (i) by analyzing correlations on the landscape scale between numerous waterbodies and CH 4 fluxes and (ii) by analyzing the influence of the spatial resolution of CH 4 flux data on the detected relationships. A CH 4 flux map with a resolution of 100 m was derived from two aircraft eddy‐covariance campaigns in the summers of 2012 and 2013. We combined the CH 4 flux map with high spatial resolution (2.5 m) waterbody maps from the Permafrost Region Pond and Lake Database and classified the waterbody depth based on Sentinel‐1 SAR backscatter data. Subsequently, we reduced the resolution of the CH 4 flux map to analyze if different spatial resolutions of CH 4 flux data affected the detectability of relationships between waterbody coverage, number, depth, or size and the CH 4 flux. We did not find consistent correlations between waterbody characteristics and the CH 4 flux in the two study areas across the different resolutions. Our results indicate that waterbodies in permafrost landscapes, even if they seem to be emission hot spots on an individual basis or contain zones of above average emissions, do currently not necessarily translate into significant CH 4 emission hot spots on a regional scale, but their role might change in a warmer climate. 相似文献
11.
Arctic wetlands are currently net sources of atmospheric CH 4. Due to their complex biogeochemical controls and high spatial and temporal variability, current net CH 4 emissions and gross CH 4 processes have been difficult to quantify, and their predicted responses to climate change remain uncertain. We investigated CH 4 production, oxidation, and surface emissions in Arctic polygon tundra, across a wet‐to‐dry permafrost degradation gradient from low‐centered (intact) to flat‐ and high‐centered (degraded) polygons. From 3 microtopographic positions (polygon centers, rims, and troughs) along the permafrost degradation gradient, we measured surface CH 4 and CO 2 fluxes, concentrations and stable isotope compositions of CH 4 and DIC at three depths in the soil, and soil moisture and temperature. More degraded sites had lower CH 4 emissions, a different primary methanogenic pathway, and greater CH 4 oxidation than did intact permafrost sites, to a greater degree than soil moisture or temperature could explain. Surface CH 4 flux decreased from 64 nmol m ?2 s ?1 in intact polygons to 7 nmol m ?2 s ?1 in degraded polygons, and stable isotope signatures of CH 4 and DIC showed that acetate cleavage dominated CH 4 production in low‐centered polygons, while CO 2 reduction was the primary pathway in degraded polygons. We see evidence that differences in water flow and vegetation between intact and degraded polygons contributed to these observations. In contrast to many previous studies, these findings document a mechanism whereby permafrost degradation can lead to local decreases in tundra CH 4 emissions. 相似文献
12.
Terrestrial ecosystems in northern high latitudes exchange large amounts of methane (CH 4) with the atmosphere. Climate warming could have a great impact on CH 4 exchange, in particular in regions where degradation of permafrost is induced. In order to improve the understanding of the present and future methane dynamics in permafrost regions, we studied CH 4 fluxes of typical landscape structures in a small catchment in the forest tundra ecotone in northern Siberia. Gas fluxes were measured using a closed‐chamber technique from August to November 2003 and from August 2006 to July 2007 on tree‐covered mineral soils with and without permafrost, on a frozen bog plateau, and on a thermokarst pond. For areal integration of the CH 4 fluxes, we combined field observations and classification of functional landscape structures based on a high‐resolution Quickbird satellite image. All mineral soils were net sinks of atmospheric CH 4. The magnitude of annual CH 4 uptake was higher for soils without permafrost (1.19 kg CH 4 ha −1 yr −1) than for soils with permafrost (0.37 kg CH 4 ha −1 yr −1). In well‐drained soils, significant CH 4 uptake occurred even after the onset of ground frost. Bog plateaux, which stored large amounts of frozen organic carbon, were also a net sink of atmospheric CH 4 (0.38 kg CH 4 ha −1 yr −1). Thermokarst ponds, which developed from permafrost collapse in bog plateaux, were hot spots of CH 4 emission (approximately 200 kg CH 4 ha −1 yr −1). Despite the low area coverage of thermokarst ponds (only 2.1% of the total catchment area), emissions from these sites resulted in a mean catchment CH 4 emission of 3.8 kg CH 4 ha −1 yr −1. Export of dissolved CH 4 with stream water was insignificant. The results suggest that mineral soils and bog plateaux in this region will respond differently to increasing temperatures and associated permafrost degradation. Net uptake of atmospheric CH 4 in mineral soils is expected to gradually increase with increasing active layer depth and soil drainage. Changes in bog plateaux will probably be much more rapid and drastic. Permafrost collapse in frozen bog plateaux would result in high CH 4 emissions that act as positive feedback to climate warming. 相似文献
13.
Northern peatlands constitute a significant source of atmospheric methane (CH 4). However, management of undisturbed peatlands, as well as the restoration of disturbed peatlands, will alter the exchange of CH 4 with the atmosphere. The aim of this systematic review and meta‐analysis was to collate and analyze published studies to improve our understanding of the factors that control CH 4 emissions and the impacts of management on the gas flux from northern (latitude 40° to 70°N) peatlands. The analysis includes a total of 87 studies reporting measurements of CH 4 emissions taken at 186 sites covering different countries, peatland types, and management systems. Results show that CH 4 emissions from natural northern peatlands are highly variable with a 95% CI of 7.6–15.7 g C m ?2 year ?1 for the mean and 3.3–6.3 g C m ?2 year ?1 for the median. The overall annual average (mean ± SD) is 12 ± 21 g C m ?2 year ?1 with the highest emissions from fen ecosystems. Methane emissions from natural peatlands are mainly controlled by water table (WT) depth, plant community composition, and soil pH. Although mean annual air temperature is not a good predictor of CH 4 emissions by itself, the interaction between temperature, plant community cover, WT depth, and soil pH is important. According to short‐term forecasts of climate change, these complex interactions will be the main determinant of CH 4 emissions from northern peatlands. Drainage significantly ( p < .05) reduces CH 4 emissions to the atmosphere, on average by 84%. Restoration of drained peatlands by rewetting or vegetation/rewetting increases CH 4 emissions on average by 46% compared to the original premanagement CH 4 fluxes. However, to fully evaluate the net effect of management practice on the greenhouse gas balance from high latitude peatlands, both net ecosystem exchange (NEE) and carbon exports need to be considered. 相似文献
14.
With rapid climate warming, ecosystems will probably exhibit complex dynamics because local factors and life history attributes of species mediate the effects of regional climate change. To assess the relative importance of local vs. regional processes on permafrost formation in boreal peatlands, I sampled for permafrost and factors affecting its formation in 38 collapse scars across a 4 °C mean annual temperature (MAT) gradient in the discontinuous permafrost zone of northern Manitoba, Canada. Three complimentary approaches were used to model factors important to permafrost formation at both local and regional scales. In the first analysis, a mechanistic, spatial model of permafrost formation was developed as a function of Picea mariana size and proximity. In the second approach, permafrost formation was modelled as a function of two local factors, diameter of Picea mariana trees and emergent organic matter depth, and the regional factor, mean annual temperature (MAT). Finally, published aerial photography data were used to determine whether the proportion of bogs with permafrost changes across a MAT gradient. Results show that permafrost formation in boreal permafrost peatlands is best described as a locally driven process within regional climatic constraints. At local scales of 1–2 meters, the spatial and size distributions of trees controlled the spatial distribution of permafrost. At regional scales, tree size was a significantly better predictor than emergent organic matter or MAT. These results suggest that transient models of discontinuous permafrost based only on climate may poorly predict changes in vegetation and permafrost. 相似文献
15.
Drainage of waterlogged sites has been part of the normal forestry practice in Fennoscandia, the Baltic countries, the British Isles and in some parts of Russia since the early 20 th century, and currently, about 15 million hectares of peatlands and other wetlands have been drained for forestry purposes. The rate of forest clear-felling on drained peatlands will undergo a rapid increase in the near future, when a large number of these forests approach their regeneration age. A small-scale pilot survey was performed at two nutrient-rich and old peatland drainage areas in southern Finland to study if forest clear-felling has significant impacts on the exchange of nitrous oxide (N 2O) and methane (CH 4) between soil and atmosphere. The average N 2O emissions from the two drainage areas during three growing seasons following clear-felling were 945 and 246 g m –2 d –1. The corresponding CH 4 fluxes were –0.07 and –0.52 mg m –2 d –1. Clear-felling had impacts on the environmental factors known to affect the N 2O and CH 4 fluxes of peatlands, i.e. clear-felling raised the water table level and increased the peat temperature. However, no substantial changes in the fluxes of CH 4 following clear-felling were observed. The results concerning N 2O indicated a potential for increased emissions following clear-felling of drained peatland forests, but further studies are needed for a critical evaluation of the impacts of clear-felling on the fluxes of CH 4 and N 2O. 相似文献
16.
Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH 4 emissions reduced in favor of greater CO 2 losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on
N 2O or global warming potential. We report greenhouse gas fluxes (CH 4, CO 2, N 2O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that
is, pasture). This ecosystem was a net source of CH 4 (25.8 ± 1.4 mg CH 4-C m −2 d −1) and N 2O (6.4 ± 0.4 mg N 2O-N m −2 d −1). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N 2O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale
CH 4 fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of
emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous
oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables,
especially soil moisture. Elevated CH 4 and N 2O fluxes contributed to a high overall ecosystem global warming potential (531 g CO 2-C equivalents m −2 y −1), with non-CO 2 trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta
peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating
the relative importance of each gas for ecosystem global warming potential. 相似文献
17.
Northern peatlands accumulate atmospheric CO 2 thus counteracting climate warming. However, CH 4 which is more efficient as a greenhouse gas than CO 2, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO 2, CH 4 and N 2O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO 2 emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO 2, drainage had decreased the emissions of CH 4, the drained fen even consumed atmospheric CH 4. CO 2 and CH 4 emissions were higher in the virgin fen than in the virgin bog. There were no N 2O emissions from neither type of virgin sites. Drainage had, however, highly increased the N 2O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires. 相似文献
18.
Spatial or temporal forest–peatland transition zones were proposed as potential hot spots of methane (CH 4) 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 CH 4 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 CH 4 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 CH 4 (? 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 CH 4 sources. Fluxes of CH 4 from the transition zone sites showed a higher response to soil temperature than to water table level. Fluxes of CH 4 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 CH 4 fluxes were measured only between 2014 and 2013. Significant differences in CH 4 fluxes and in nonlinear regressions showed that the CH 4 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
19.
中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。 相似文献
20.
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
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