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1.
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
2.
Riparian zones are an important strategy to mitigate N and P export to streams. However, their efficiency with respect to nitrate (NO 3 ?), ammonium (NH 4 +), or soluble reactive phosphorus (SRP) in groundwater remains uncertain in the US Midwest. This study investigates water table fluctuations and NO 3 ?, NH 4 +, and SRP concentration dynamics in two riparian zone types (outwash vs. glacial till) common in the upper US Midwest. During low water table periods, NO 3 ? removal was 93 % at WR (outwash site), and 75 % at LWD (glacial till site); but during high water table periods, NO 3 ? removal efficiencies dropped to 50 % at WR, and 14 % at LWD. Median seasonal mass fluxes of NO 3 ? removed at WR (9.4–21.7 mg N day ?1 m ?1 of stream length) and LWD (0.4–1.9 mg N day ?1 m ?1) were small compared to other riparian zones in glaciated landscapes. The WR site was a small SRP sink (0.114 and 0.118 mg day ?1 m ?1 during the dry period and wet period, respectively), while LWD acted as a small SRP source to the stream (0.004 mg day ?1 m ?1 during the dry period; 0.075 mg day ?1 m ?1 during the wet period). Both LWD and WR acted as sources of NH 4 + to the stream with mass fluxes ranging from 0.17 to 7.75 mg N day ?1 m ?1. Although riparian zones in the US Midwest provide many ecosystem services, results suggest they are unlikely to efficiently mitigate N and P pollution in subsurface flow. 相似文献
3.
Ephemeral streams and wetlands are characterized by complex cycles of submersion and emersion, which influence the greenhouse gas flux rates. In this study we quantify the spatiotemporal variability in CO 2 and CH 4 concentrations and fluxes of an intermittent first-order stream over three consecutive wet and dry cycles spanning 56 days, to assess how hydrologic phase transitions influence greenhouse gas evasion. Water column excess CO 2 ranged from ?11 to 1600 μM, and excess CH 4 from 1 to 15 μM. After accounting for temporal changes in the ratio of wet versus dry streambed hydraulic radius, total CO 2–C fluxes ranged from 12 to 156 mmol m ?2 day ?1, with an integrated daily mean of 61 ± 25 mmol m ?2 day ?1. Soil–air evasion rates were approximately equal to those of water–air evasion. Rainfall increased background water–air CO 2–C fluxes by up to 780% due to an increase in gas transfer velocity in the otherwise still waters. CH 4–C fluxes increased 19-fold over the duration of the initial, longer wet-cycle from 0.1 to 1.9 mmol m ?2 day ?1. Temporal shifts in water depth and site-specific ephemerality were key drivers of carbon dynamics in the upper Jamison Creek watercourse. Based on these findings, we hypothesise that the cyclic periodicity of fluxes of biogenic gases from frequently intermittent streams (wet and dry cycles ranging from days to weeks) and seasonally ephemeral watercourses (dry for months at a time) are likely to differ, and therefore these differences should be considered when integrating transient systems into regional carbon budgets and models of global change. 相似文献
4.
Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH 4) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH 4 in the world contributing between 100 and 231 Tg year ?1 to the total budget of 503–610 Tg year ?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH 4 emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH 4 emission rates varied between 0.24 and 293 mg CH 4 m ?2 h ?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH 4 m ?2 h ?1 or 558 ± 53 mg CH 4 m ?2 day ?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher ( P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH 4 m ?2 h ?1 than in floodplains (20.4 ± 2.5 mg CH 4 m ?2 h ?1) and lagoons (16.9 ± 2.6 mg CH 4 m ?2 h ?1). Diffusive CH 4 emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH 4 m ?2 h ?1) and lowest (0.2–3.0 mg m ?2 h ?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km 2, the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH 4 emission from global tropical wetlands. 相似文献
5.
We report a data-set of dissolved methane (CH 4) in three rivers (Comoé, Bia and Tanoé) and five lagoons (Grand-Lahou, Ebrié, Potou, Aby and Tendo) of Ivory Coast (West Africa), during the four main climatic seasons (high dry season, high rainy season, low dry season and low rainy season). The surface waters of the three rivers were over-saturated in CH 4 with respect to atmospheric equilibrium (2221–38719%), and the seasonal variability of CH 4 seemed to be largely controlled by dilution during the flooding period. The strong correlation of CH 4 concentrations with the partial pressure of CO 2 (pCO 2) and dissolved silicate (DSi) confirm the dominance of a continental sources (from soils) for both CO 2 and CH 4 in these rivers. Diffusive air–water CH 4 fluxes ranged between 25 and 1187 μmol m ?2 day ?1, and annual integrated values were 288 ± 107, 155 ± 38, and 241 ± 91 μmol m ?2 day ?1 in the Comoé, Bia and Tanoé rivers, respectively. In the five lagoons, surface waters were also over-saturated in CH 4 (ranging from 1496 to 51843%). Diffusive air–water CH 4 fluxes ranged between 20 and 2403 μmol m ?2 day ?1, and annual integrated values were 78 ± 34, 338 ± 217, 227 ± 79, 330 ± 153 and 326 ± 181 μmol m ?2 day ?1 in the Grand-Lahou, Ebrié, Potou, Aby and Tendo lagoons, respectively. The largest CH 4 over-saturations were observed in the Tendo and Aby lagoons that are permanently stratified systems (unlike the other three lagoons), leading to anoxic bottom waters favorable for a large CH 4 production. In addition, these two stratified lagoons showed low pCO 2 values due to high primary production, which suggests an efficient transfer of organic matter across the pycnocline. As a result, the stratified Tendo and Aby lagoons were respectively, a low source of CO 2 to the atmosphere and a sink of atmospheric CO 2 while the other three well-mixed lagoons were strong sources of CO 2 to the atmosphere but less over-saturated in CH 4. 相似文献
6.
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
7.
Atmospheric CO 2 and CH 4 exchange in peatlands is controlled by water table levels and soil moisture, but impacts of short periods of dryness and rainfall are poorly known. We conducted drying-rewetting experiments with mesocosms from an ombrotrophic northern bog and an alpine, minerotrophic fen. Efflux of CO 2 and CH 4 was measured using static chambers and turnover and diffusion rates were calculated from depth profiles of gas concentrations. Due to a much lower macroporosity in the fen compared to the bog peat, water table fluctuated more strongly when irrigation was stopped and resumed, about 11 cm in the fen and 5 cm in the bog peat. Small changes in air filled porosity caused CO 2 and CH 4 concentrations in the fen peat to be insensitive to changes in water table position. CO 2 emission was by a factor of 5 higher in the fen than in the bog mesocosms and changed little with water table position in both peats. This was probably caused by the importance of the uppermost, permanently unsaturated zone for auto- and heterotrophic CO 2 production, and a decoupling of air filled porosity from water table position. CH 4 emission was <0.4 mmol m ?2 day ?1 in the bog peat, and up to >12.6 mmol m ?2 day ?1 in the fen peat, where it was lowered by water table fluctuations. CH 4 production was limited to the saturated zone in the bog peat but proceeded in the capillary fringe of the fen peat. Water table drawdown partly led to inhibition of methanogenesis in the newly unsaturated zone, but CH 4 production appeared to continue after irrigation without time-lag. The identified effects of irrigation on soil moisture and respiration highlight the importance of peat physical properties for respiratory dynamics; but the atmospheric carbon exchange was fairly insensitive to the small-scale fluctuations induced. 相似文献
8.
Peatland landscapes typically exhibit large variations in greenhouse gas (GHG) emissions due to microtopographic and vegetation heterogeneity. As many peatland budgets are extrapolated from small-scale chamber measurements it is important to both quantify and understand the processes underlying this spatial variability. Here we carried out a mesocosm study which allowed a comparison to be made between different microtopographic features and vegetation communities, in response to conditions of both static and changing water table. Three mesocosm types (hummocks?+? Juncus effusus, hummocks?+? Eriophorum vaginatum, and hollows dominated by moss) were subjected to two water table treatments (0–5 cm and 30–35 cm depth). Measurements were made of soil-atmosphere GHG exchange, GHG concentration within the peat profile and soil water solute concentrations. After 14 weeks the high water table group was drained and the low water table group flooded. Measurement intensity was then increased to examine the immediate response to change in water table position. Mean CO 2, CH 4 and N 2O exchange across all chambers was 39.8 μg m ?2 s ?1, 54.7 μg m ?2 h ?1 and ?2.9 μg m ?2 h ?1, respectively. Hence the GHG budget was dominated in this case by CO 2 exchange. CO 2 and N 2O emissions were highest in the low water table treatment group; CH 4 emissions were highest in the saturated mesocosms. We observed a strong interaction between mesocosm type and water table for CH 4 emissions. In contrast to many previous studies, we found that the presence of aerenchyma-containing vegetation reduced CH 4 emissions. A significant pulse in both CH 4 and N 2O emissions occurred within 1–2 days of switching the water table treatments. This pulsing could potentially lead to significant underestimation of landscape annual GHG budgets when widely spaced chamber measurements are upscaled. 相似文献
9.
Hot spots of CH 4 emissions are a typical feature of pristine peatlands at the microsite and landscape scale. To determine whether rewetting and lake construction in a cutaway peatland would result in the re‐creation of hot spots, we first measured CH 4 fluxes over a 2‐year period with static chambers and estimated annual emissions. Second, to assess whether rewetting and lake creation would produce hot spots at the landscape level, we hypothesized a number of alternative land use scenarios for the peatland following the cessation of peat extraction. Using the results from this study and other studies from literature, we calculated the global warming potential (GWP) of each scenario and the respective contribution of CH 4. The results showed that hot spots of CH 4 fluxes were observed as a consequence of microsite‐specific differences in water table (WT) position and plant productivity. CH 4 fluxes were closely related to peat temperature at 10 cm depth and WT position. Annual emissions ranged from 4.3 to 38.8 g CH 4 m ?2 yr ?1 in 2002 and 3.2 to 28.8 g CH 4 m ?2 yr ?1 in 2003. The scenario results suggest that lake creation is likely to result in the re‐creation of a hot spot at the landscape level. However, the transition from cutaway to wetland ecosystem may lead to a reduction in the GWP of the peatland. 相似文献
10.
It is anticipated that a lowering of the water table and reduced soil moisture levels in peatlands may increase peat decomposition rates and consequently affect nutrient availability. However, it is not clear if patterns will be consistent across different peatland types or within peatlands given the natural range of ecohydrological conditions within these systems. We examined the effect of persistent drought on peatland nutrient dynamics by quantifying the effects of an experimentally lowered water table position (drained for a 10-year period) on peat KCl-extractable total inorganic nitrogen (ext-TIN), peat KCl-extractable nitrate (ext-NO 3 ?), and water-extractable ortho-phosphorus (ext-PO 4 3?) concentrations and net phosphorus (P) and nitrogen (N) mineralization and nitrification rates at natural (control) and drained microforms (hummocks, lawns) of a bog and poor fen near Québec City, Canada. Drainage (water table drawdown) decreased net nitrification rates across the landscape and increased ext-NO 3 ? concentrations, but did not affect net N and P mineralization rates or ext-TIN and ext-PO 4 3? concentrations. We suggest that the thick capillary fringe at the drained peatland likely maintained sufficient moisture above the water table to limit the effects of drainage on microbial activity, and a 20 cm lowering of the water table does not appear to have been sufficient to create a clear difference in nutrient dynamics in this peatland landscape. We found some evidence of differences in nutrient concentrations with microforms, where concentrations were greater in lawn than hummock microforms at control sites indicating some translocation of nutrients. In general, the same microtopographic differences were not observed at drained sites. The general spatial patterns in nutrient concentrations did not reflect net mineralization/immobilization rates measured at our control or drained peatlands. Rather, the spatial patterns in nutrient availability may be regulated by differences in vegetation (mainly Sphagnum moss) cover between control and drained sites and possibly differences in hydrologic connection between microforms. Our results suggest that microform distribution and composition within a peatland may be important for determining how peatland nutrient dynamics will respond to water table drawdown in northern peatlands, as some evidence of microtopographic differences in nutrient dynamics was found. 相似文献
11.
Across Canada's boreal forest, linear disturbances, including cutlines such as seismic lines and roads, crisscross the landscape to facilitate resource exploration and extraction; many of these linear disturbances cross peatland ecosystems. Changes in tree canopy cover and the compression of the peat by heavy equipment alter local thermal, hydrological, and ecological conditions, likely changing carbon exchange on the disturbance, and possibly in the adjacent peatland. We measured bulk density, water table, soil temperature, plant cover, and CO 2 and CH 4 flux along triplicate transects crossing a winter road through a wooded fen near Peace River, Alberta, Canada. Sample plots were located 1, 5, and 10 m from the road on both sides with an additional three plots on the road. Productivity of the overstory trees, when present, was also determined. The winter road had higher bulk density, shallower water table, higher graminoid cover, and thawed earlier than the adjacent peatland. Tree productivity and CO 2 flux varied between the plots, and there was no clear pattern in relation to distance from the road. The plots on the winter road acted as a greater CO 2 sink and greater CH 4 source compared to the adjacent peatland with plots on the winter road emitting on average (standard error) 479 (138) compared to 41 (10) mg CH 4 m ?2 day ?1 in the adjacent peatland. Considering both gases, global warming potential increased from 70 to 250 g CO 2e m ?2 year ?1 in the undisturbed area to 2100 g CO 2e m ?2 year ?1 on the winter road. Although carbon fluxes on any given cutline through peatland will vary depending on level of compaction, line width and vegetation community shifts, the large number of linear disturbances in Canada's boreal forest and slow recovery on peatland ecosites suggest they could represent an important anthropogenic greenhouse gas source. 相似文献
12.
The study investigates the effect of land‐use change on nitrous oxide (N 2O) and methane (CH 4) fluxes from soil, in savanna ecosystems of the Orinoco region (Venezuela). Gas fluxes were measured by closed static chambers, in the wet and dry season, in representative systems of land management of the region: a cultivated pasture, an herbaceous savanna, a tree savanna and a woodland (control site). Higher N 2O emissions were observed in the cultivated pasture and in the herbaceous savanna compared with the tree savanna and the woodland, and differences were mainly related to fine soil particle content and soil volumetric water content measured in the studied sites. Overall N 2O emissions were quite low in all sites (0–1.58 mg N 2O‐N m ?2 day ?1). The cultivated pasture and the woodland savanna were on average weak CH 4 sinks (?0.05±0.07 and ?0.08±0.05 mg CH 4 m ?2 day ?1, respectively), whereas the herbaceous savanna and the tree savanna showed net CH 4 production (0.23±0.05 and 0.19±0.05 mg CH 4 m ?2 day ?1, respectively). Variations of CH 4 fluxes were mainly driven by variation of soil water‐filled pore space (WFPS), and a shift from net CH 4 consumption to net CH 4 production was observed at around 30% WFPS. Overall, the data suggest that conversion of woodland savanna to managed landscape could alter both CH 4 and N 2O fluxes; however, the magnitude of such variation depends on the soil characteristics and on the type of land management before conversion. 相似文献
13.
Vernal pools are small, seasonal wetlands that are a common landscape feature contributing to biodiversity in northeastern North American forests. Basic information about their biogeochemical functions, such as carbon cycling, is limited. Concentrations of dissolved methane (CH 4) and carbon dioxide (CO 2) and other water chemistry parameters were monitored weekly at the bottom and surface of four vernal pools in central and eastern Maine, USA, from April to August 2016. The vernal pools were supersaturated with respect to CH 4 and CO 2 at all sampling dates and locations. Concentrations of dissolved CH 4 and CO 2 ranged from 0.4 to 210 μmol L ?1 and 72–2300 μmol L ?1, respectively. Diffusive fluxes of CH 4 and CO 2 into the atmosphere ranged from 0.2 to 73 mmol m ?2 d ?1, and 30–590 mmol m ?2 d ?1, respectively. During the study period, the four vernal pools emitted 0.1–5.8 kg C m ?2 and 9.6–120 kg C m ?2 as CH 4 and CO 2, respectively. The production fluxes (production rates normalized to surface area) of CH 4 and CO 2 ranged from ? 0.02 to 0.66 and 0.40–4.6 g C m ?2 d ?1, respectively, and increased significantly over the season. Methane concentrations were best predicted by alkalinity, ortho-phosphate and depth, while CO 2 concentrations were best predicted with only alkalinity. Alkalinity as a predictor variable highlights the importance of anaerobic respiration in production of both gases. Our study pools had large concentrations and effluxes of CH 4 and CO 2 compared to permanently inundated wetlands, indicating vernal pools are metabolically active sites and may be important contributors to the global carbon budget. 相似文献
14.
The Mer Bleue peatland is a large ombrotrophic bog with hummock-lawn microtopography, poor fen sections and beaver ponds at
the margin. Average growing-season (May–October) fluxes of methane (CH 4) measured in 2002–2003 across the bog ranged from less than 5 mg m −2 d −1 in hummocks, to greater than 100 mg m −2 d −1 in lawns and ponds. The average position of the water table explained about half of the variation in the season average CH 4 fluxes, similar to that observed in many other peatlands in Canada and elsewhere. The flux varied most when the water table
position ranged between −15 and −40 cm. To better establish the factors that influence this variability, we measured CH 4 flux at approximately weekly intervals from May to November for 5 years (2004–2008) at 12 collars representing the water
table and vegetation variations typical of the peatland. Over the snow-free season, peat temperature is the dominant correlate
and the difference among the collars’ seasonal average CH 4 flux is partially dependent on water table position. A third important correlate on CH 4 flux is vegetation, particularly the presence of Eriophorum vaginatum, which increases CH 4 flux, as well as differences in the potential of the peat profile to produce and consume CH 4 under anaerobic and aerobic conditions. The combination of peat temperature and water table position with vegetation cover
was able to explain approximately 44% of the variation in daily CH 4 flux, based on 1097 individual measurements. There was considerable inter-annual variation in fluxes, associated with varying
peat thermal and water table regimes in response to variations in weather, but also by variations in the water level in peripheral
ponds, associated with beaver dam activity. Raised water level in the beaver ponds led to higher water tables and increased
CH 4 emission in the peatland. 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.
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
17.
Northern peatland water table position is tightly coupled to carbon (C) cycling dynamics and is predicted to change from shifts in temperature and precipitation patterns associated with global climate change. However, it is uncertain how long-term water table alterations will alter C dynamics in northern peatlands because most studies have focused on short-term water table manipulations. The goal of our study was to quantify the effect of long-term water table changes (~80 years) on gaseous C fluxes in a peatland in the Upper Peninsula of Michigan. Chamber methods were utilized to measure ecosystem respiration (ER), gross primary production (GPP), net ecosystem exchange (NEE), and methane (CH 4) fluxes in a peatland experiencing levee induced long-term water table drawdown and impoundment in relation to an unaltered site. Inundation raised water table levels by approximately ~10 cm and resulted in a decrease in ER and GPP, but an increase of CH 4 emissions. Conversely, the drained sites, with water table levels ~15 cm lower, resulted in a significant increase in ER and GPP, but a decrease in CH 4 emissions. However, NEE was not significantly different between the water table treatments. In summary, our data indicates that long-term water table drawdown and inundation was still altering peatland gaseous C fluxes, even after 80 years. In addition, many of the patterns we found were of similar magnitude to those measured in short-term studies, which indicates that short-term studies might be useful for predicting the direction and magnitude of future C changes in peatlands. 相似文献
18.
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 CO 2 emissions ( R s), CH 4 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 CH 4 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 CH 4 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
19.
Forest soils and canopies are major components of ecosystem CO 2 and CH 4 fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO 2 and CH 4 fluxes. We measured CO 2 and CH 4 fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO 2 sources (4.58 ± 2.46 µmol m ?2 s ?1, mean ± 1 SD) and net sinks of CH 4 (?2.17 ± 1.60 nmol m ?2 s ?1). Coarse woody debris was a CO 2 source (4.23 ± 3.42 µmol m ?2 s ?1) and net CH 4 sink, but with large uncertainty (?0.27 ± 1.04 nmol m ?2 s ?1) and with substantial differences depending on wood decay status. Stems were CO 2 sources (1.93 ± 1.63 µmol m ?2 s ?1), but also net CH 4 sources (up to 0.98 nmol m ?2 s ?1), with a mean of 0.11 ± 0.21 nmol m ?2 s ?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH 4, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO 2 fluxes, whereas CH 4 emissions from living stems offset net soil and CWD CH 4 uptake by 3.5%. Our results demonstrate the importance of CH 4 emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO 2 and CH 4 dynamics. 相似文献
20.
A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO 2) and methane (CH 4) were studied at various peat water table depths in a mixed‐type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO 2 emission rate regardless of the water table position in peat. In nearly vegetation‐free hollows, CO 2 emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water‐saturated peat. By applying long‐term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO 2 m ?2 and less than 1.36±0.57 g CH 4 m ?2. On the basis of the carbon emitted, CO 2 is clearly a more important greenhouse gas than CH 4. CO 2 emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering. 相似文献
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