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2.
Lakes are a major component of boreal landscapes, and whereas lake CO 2 emissions are recognized as a major component of regional C budgets, there is still much uncertainty associated to lake CH 4 fluxes. Here, we present a large‐scale study of the magnitude and regulation of boreal lake summer diffusive CH 4 fluxes, and their contribution to total lake carbon (C) emissions, based on in situ measurements of concentration and fluxes of CH 4 and CO 2 in 224 lakes across a wide range of lake type and environmental gradients in Québec. The diffusive CH 4 flux was highly variable (mean 11.6 ± 26.4 SD mg m ?2 d ?1), and it was positively correlated with temperature and lake nutrient status, and negatively correlated with lake area and colored dissolved organic matter (CDOM). The relationship between CH 4 and CO 2 concentrations fluxes was weak, suggesting major differences in their respective sources and/or regulation. For example, increasing water temperature leads to higher CH 4 flux but does not significantly affect CO 2 flux, whereas increasing CDOM concentration leads to higher CO 2 flux but lower CH 4 flux. CH 4 contributed to 8 ± 23% to the total lake C emissions (CH 4 + CO 2), but 18 ± 25% to the total flux in terms of atmospheric warming potential, expressed as CO 2‐equivalents. The incorporation of ebullition and plant‐mediated CH 4 fluxes would further increase the importance of lake CH 4. The average Q 10 of CH 4 flux was 3.7, once other covarying factors were accounted for, but this apparent Q 10 varied with lake morphometry and was higher for shallow lakes. We conclude that global climate change and the resulting shifts in temperature will strongly influence lake CH 4 fluxes across the boreal biome, but these climate effects may be altered by regional patterns in lake morphometry, nutrient status, and browning. 相似文献
3.
Thermokarst lakes are potentially important sources of methane (CH 4) and carbon dioxide (CO 2). However, considerable uncertainty exists regarding carbon emissions from thermokarst lakes owing to a limited understanding of their patterns and motivators. In this study, we measured CH 4 and CO 2 diffusive fluxes in 163 thermokarst lakes in the Qinghai–Tibet Plateau (QTP) over 3 years from May to October. The median carbon emissions from the QTP thermokarst lakes were 1440 mg CO 2 m −2 day −1 and 60 mg CH 4 m −2 day −1, respectively. The diffusive rates of CO 2 and CH 4 are related to the catchment land cover type. Sediment microbial abundance and hydrochemistry explain 51.9% and 38.3% of the total variance in CH 4 diffusive emissions, respectively, while CO 2 emissions show no significant relationship with environmental factors. When upscaling carbon emissions from the QTP thermokarst lakes, the annual average CH 4 release per lake area is equal to that of the pan-Arctic region. Our findings highlight the importance of incorporating in situ observation data with different emission pathways for different land cover types in predicting carbon emissions from thermokarst lakes in the future. 相似文献
4.
Agricultural drainage of organic soils has resulted in vast soil subsidence and contributed to increased atmospheric carbon dioxide (CO 2) concentrations. The Sacramento‐San Joaquin Delta in California was drained over a century ago for agriculture and human settlement and has since experienced subsidence rates that are among the highest in the world. It is recognized that drained agriculture in the Delta is unsustainable in the long‐term, and to help reverse subsidence and capture carbon (C) there is an interest in restoring drained agricultural land‐use types to flooded conditions. However, flooding may increase methane (CH 4) emissions. We conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land‐use types (a rice paddy and two restored wetlands) to assess the impact of drained to flooded land‐use change on CO 2 and CH 4 fluxes in the Delta. We found that the drained sites were net C and greenhouse gas (GHG) sources, releasing up to 341 g C m ?2 yr ?1 as CO 2 and 11.4 g C m ?2 yr ?1 as CH 4. Conversely, the restored wetlands were net sinks of atmospheric CO 2, sequestering up to 397 g C m ?2 yr ?1. However, they were large sources of CH 4, with emissions ranging from 39 to 53 g C m ?2 yr ?1. In terms of the full GHG budget, the restored wetlands could be either GHG sources or sinks. Although the rice paddy was a small atmospheric CO 2 sink, when considering harvest and CH 4 emissions, it acted as both a C and GHG source. Annual photosynthesis was similar between sites, but flooding at the restored sites inhibited ecosystem respiration, making them net CO 2 sinks. This study suggests that converting drained agricultural peat soils to flooded land‐use types can help reduce or reverse soil subsidence and reduce GHG emissions. 相似文献
6.
Freshwater ecosystems play a major role in global carbon cycling through the breakdown of organic material and release of greenhouse gases (GHGs). Carbon dioxide (CO 2) and methane (CH 4) emissions from lakes, wetlands, reservoirs and small natural ponds have been well studied, however, the GHG emissions of highly abundant, small‐scale (<0.01 km 2) agricultural dams (small stream and run‐off impoundments) are still unknown. Here, we measured the diffusive CO 2 and CH 4 flux of 77 small agricultural dams within south‐east Australia. The GHG emissions from these waterbodies, which are currently unaccounted for in GHG inventories, amounted to 11.12 ± 2.59 g CO 2‐equivalent m 2/day, a value 3.43 times higher than temperate reservoir emissions. Upscaling these results to the entire state of Victoria, Australia, resulted in a farm dam CO 2‐equivalent/day emission rate of 4,853 tons, 3.1 times higher than state‐wide reservoir emissions in spite of farm dams covering only 0.94 times the comparative area. We also show that CO 2 and CH 4 emission rates were both significantly positively correlated with dissolved nitrate concentrations, and significantly higher in livestock rearing farm dams when compared to cropping farm dams. The results from this study demonstrate that small agricultural farm dams can be a major source of greenhouse gas emissions, thereby justifying their inclusion in global carbon budgets. 相似文献
7.
The effects of elevated concentrations of atmospheric CO 2 on CH 4 and N 2O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated
CO 2 significantly increased CH 4 emission by 58% compared with ambient CO 2. The CH 4 emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding
period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated
CO 2 level, respectively. No CH 4 was emitted from plant-free pots, suggesting that the main source of emitted CH 4 was root exudates or autolysis products. Most N 2O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO 3− contained in the experimental soil, and was not affected by the CO 2 concentration. Pre-harvest drainage suppressed CH 4 emission but did not cause much N 2O emission (< 10 μg N m −2 h −1) from the rice-plant pots at both CO 2 concentrations. 相似文献
9.
Large uncertainties in estimates of methane (CH4) emissions from tropical inland waters reflect the paucity of information at appropriate temporal and spatial scales. CH4 concentrations, diffusive and ebullitive fluxes, and environmental parameters in contrasting aquatic habitats of Lake Janauacá, an Amazon floodplain lake, measured for two years revealed patterns in temporal and spatial variability related to different aquatic habitats and environmental conditions. CH4 concentrations ranged from below detection to 96 µM, CH4 diffusive fluxes from below detection to 2342 µmol m−2 h−1, and CH4 ebullitive fluxes from 0 to 190 mmol m−2 d−1. Vegetated aquatic habitats had higher surface CH4 concentrations than open water habitats, and no significant differences in diffusive CH4 fluxes, likely due to higher k values measured in open water habitats. CH4 emissions were enhanced after a prolonged low water period, when the exposed sediments were colonized by herbaceous plants that decomposed after water levels rose, possibly fueling CH4 production. Statistical models indicated the importance of variables related to CH4 production (temperature, dissolved organic carbon) and consumption (dissolved nitrogen, oxygenated water column), as well as maximum depth, in controlling surface water CH4 concentrations. 相似文献
10.
It is now widely accepted that boreal rivers and streams are regionally significant sources of carbon dioxide (CO 2), yet their role as methane (CH 4) emitters, as well as the sensitivity of these greenhouse gas (GHG) emissions to climate change, are still largely undefined. In this study, we explore the large‐scale patterns of fluvial CO 2 and CH 4 partial pressure ( pCO 2, pCH 4) and gas exchange (k) relative to a set of key, climate‐sensitive river variables across 46 streams and rivers in two distinct boreal landscapes of Northern Québec. We use the resulting models to determine the direction and magnitude of C‐gas emissions from these boreal fluvial networks under scenarios of climate change. River pCO 2 and pCH 4 were positively correlated, although the latter was two orders of magnitude more variable. We provide evidence that in‐stream metabolism strongly influences the dynamics of surface water pCO 2 and pCH 4, but whereas pCO 2 is not influenced by temperature in the surveyed streams and rivers, pCH 4 appears to be strongly temperature‐dependent. The major predictors of ambient gas concentrations and exchange were water temperature, velocity, and DOC, and the resulting models indicate that total GHG emissions (C‐CO 2 equivalent) from the entire network may increase between by 13 to 68% under plausible scenarios of climate change over the next 50 years. These predicted increases in fluvial GHG emissions are mostly driven by a steep increase in the contribution of CH 4 (from 36 to over 50% of total CO 2‐equivalents). The current role of boreal fluvial networks as major landscape sources of C is thus likely to expand, mainly driven by large increases in fluvial CH 4 emissions. 相似文献
11.
Atmospheric nitrogen deposition is anticipated to increase over the next decades with possible implications for future forest-atmosphere
interactions. Increased soil N 2O emissions, depressed CH 4 uptake and depressed soil respiration CO 2 loss is considered a likely response to increased N deposition. This study examined fluxes of N 2O, CH 4 and CO 2 over two growing seasons from soils in unmanaged forest and grassland communities on abandoned agricultural areas in Michigan.
All sites were subject to simulated increased N-deposition in the range of 1–3 g N m −2 annually. Nitrous oxide fluxes and soil N concentrations in coniferous and grassland sites were on the whole unaffected by
the increased N-inputs. It is noteworthy though that N 2O emissions increased three-fold in the coniferous sites in the first growing season in response to the low N treatment, although
the response was barely significant ( p<0.06). In deciduous forests, we observed increased levels of soil mineral N during the second year of N fertilization, however
N 2O fluxes did not increase. Rates of methane oxidation were similar in all sites with no affect of field N application. Likewise,
we did not observe any changes in soil CO 2 efflux in response to N additions. The combination of tillage history and vegetation type was important for the trace gas
fluxes, i.e. soil CO 2 efflux was greater in successional grassland sites compared with the forested sites and CH 4 uptake was reduced in post-tillage coniferous- and successional sites compared with the old-growth deciduous site. Our results
indicate that short-term increased N availability influenced individual processes linked to trace gas turnover in the soil
independently from the ecosystem N status. However, changes in whole system fluxes were not evident and were very likely mediated
by competitive N uptake processes. 相似文献
12.
The first full greenhouse gas (GHG) flux budget of an intensively managed grassland in Switzerland (Chamau) is presented. The three major trace gases, carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) were measured with the eddy covariance (EC) technique. For CO 2 concentrations, an open‐path infrared gas analyzer was used, while N 2O and CH 4 concentrations were measured with a recently developed continuous‐wave quantum cascade laser absorption spectrometer (QCLAS). We investigated the magnitude of these trace gas emissions after grassland restoration, including ploughing, harrowing, sowing, and fertilization with inorganic and organic fertilizers in 2012. Large peaks of N 2O fluxes (20–50 nmol m ?2 s ?1 compared with a <5 nmol m ?2 s ?1 background) were observed during thawing of the soil after the winter period and after mineral fertilizer application followed by re‐sowing in the beginning of the summer season. Nitrous oxide (N 2O) fluxes were controlled by nitrogen input, plant productivity, soil water content and temperature. Management activities led to increased variations of N 2O fluxes up to 14 days after the management event as compared with background fluxes measured during periods without management (<5 nmol m ?2 s ?1). Fluxes of CO 2 remained small until full plant development in early summer 2012. In contrast, methane emissions showed only minor variations over time. The annual GHG flux budget was dominated by N 2O (48% contribution) and CO 2 emissions (44%). CH 4 flux contribution to the annual budget was only minor (8%). We conclude that recently developed multi‐species QCLAS in an EC system open new opportunities to determine the temporal variation of N 2O and CH 4 fluxes, which further allow to quantify annual emissions. With respect to grassland restoration, our study emphasizes the key role of N 2O and CO 2 losses after ploughing, changing a permanent grassland from a carbon sink to a significant carbon source. 相似文献
13.
Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH 4 and CO 2 fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH 4 and CO 2 from these lakes and ditches. The lakes and ditches acted as CO 2 and CH 4 sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m ?2 h ?1 for CO 2 and 33.7 ± 9.3 and 3.9 ± 1.6 mg m ?2 h ?1 for CH 4, respectively. In most water bodies CH 4 was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH 4 could be explained by PO 4 3? concentration in the sediment and Fe 2+ concentration in the water, and 89% of the CO 2 flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO 2 and CH 4 from these water bodies. 相似文献
14.
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
15.
基于排放因子法构建了包含种植业和牲畜养殖业的农业系统温室气体排放核算体系,系统核算了1980-2020年我国全国尺度上的农业系统温室气体排放总量和变化趋势,并在区县级尺度下对1980、2000、2011年的中国农业系统的温室气体排放量进行核算,对比不同阶段农业系统温室气体排放变化的时空异质性规律。研究发现:1980-2020年我国农业系统温室气体排放量呈波动增长趋势,增长了近46%。CH 4是农业系统排放贡献最大的温室气体,占总排放量的47.33%。我国农业系统温室气体排放与不同地区农业生产方式有关,CH 4排放量高的地区主要位于我国主要水稻产区以及旱地作物产区。CO 2排放量高的地区主要位于东北、西北等地区以及华东地区。N 2O排放量较高地区主要位于西北的主要畜牧养殖地区,以及我国农业经济发展水平高的中南部地区。研究有助于揭示我国农业温室气体排放的动态特征,现状规律,以及空间差异性特征,从农业减排角度为实现双碳目标提供科学参考。 相似文献
16.
Canopy soils can significantly contribute to aboveground labile biomass, especially in tropical montane forests. Whether they also contribute to the exchange of greenhouse gases is unknown. To examine the importance of canopy soils to tropical forest‐soil greenhouse gas exchange, we quantified gas fluxes from canopy soil cores along an elevation gradient with 4 yr of nutrient addition to the forest floor. Canopy soil contributed 5–12 percent of combined (canopy + forest floor) soil CO 2 emissions but CH 4 and N 2O fluxes were low. At 2000 m, phosphorus decreased CO 2 emissions (>40%) and nitrogen slightly increased CH 4 uptake and N 2O emissions. Our results show that canopy soils may contribute significantly to combined soil greenhouse gas fluxes in montane regions with high accumulations of canopy soil. We also show that changes in fluxes could occur with chronic nutrient deposition. 相似文献
17.
The critical role streamside riparian zones play in mitigating the movement of nitrogen (N) and other elements from terrestrial to aquatic ecosystems could be threatened by residential development in the southern Appalachian Mountains. Many studies have investigated the influence of agriculture on N loading to streams but less is known about the impacts of residential development. Here we consider the dynamics of changing riparian land use in the southern Appalachians that includes increased residential development at the expense of both forests and agriculture. We hypothesized that increased inputs of inorganic N from residential development will increase nitrogen cycling rates relative to forests, thereby preventing terrestrial N retention and increasing soil nitrate losses through leaching. In addition, we hypothesized that such development will increase emissions of N 2O, CO 2, and CH 4, all potent greenhouse gases. We found riparian soil potential N cycling rates as well as N 2O and CO 2 efflux to be much greater with agricultural land use compared to either forested or residential land use. Our data suggest that residential development of forested riparian ecosystems does not increase N cycling or removal and, thus, might allow for greater potential N leaching into streams. Both agricultural and residential land use exhibited CH 4 efflux while forested ecosystems were responsible for CH 4 uptake. Overall, regional greenhouse gas emissions are projected to decline as high N 2O and CO 2 emitting agricultural land is converted to residential use. 相似文献
18.
Rapid, precise, and globally comparable methods for monitoring greenhouse gas (GHG) fluxes are required for accurate GHG inventories from different cropping systems and management practices. Manual gas sampling followed by gas chromatography (GC) is widely used for measuring GHG fluxes in agricultural fields, but is laborious and time‐consuming. The photo‐acoustic infrared gas monitoring system (PAS) with on‐line gas sampling is an attractive option, although it has not been evaluated for measuring GHG fluxes in cereals in general and rice in particular. We compared N 2O, CO 2, and CH 4 fluxes measured by GC and PAS from agricultural fields under the rice–wheat and maize–wheat systems during the wheat (winter), and maize/rice (monsoon) seasons in Haryana, India. All the PAS readings were corrected for baseline drifts over time and PAS‐CH 4 (PCH 4) readings in flooded rice were corrected for water vapor interferences. The PCH 4 readings in ambient air increased by 2.3 ppm for every 1000 mg cm ?3 increase in water vapor. The daily CO 2, N 2O, and CH 4 fluxes measured by GC and PAS from the same chamber were not different in 93–98% of all the measurements made but the PAS exhibited greater precision for estimates of CO 2 and N 2O fluxes in wheat and maize, and lower precision for CH 4 flux in rice, than GC. The seasonal GC‐ and PAS‐N 2O (PN 2O) fluxes in wheat and maize were not different but the PAS‐CO 2 (PCO 2) flux in wheat was 14–39% higher than that of GC. In flooded rice, the seasonal PCH 4 and PN 2O fluxes across N levels were higher than those of GC‐CH 4 and GC‐N 2O fluxes by about 2‐ and 4fold, respectively. The PAS (i) proved to be a suitable alternative to GC for N 2O and CO 2 flux measurements in wheat, and (ii) showed potential for obtaining accurate measurements of CH 4 fluxes in flooded rice after making correction for changes in humidity. 相似文献
19.
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
20.
Greenhouse gases (GHG) can be affected by grazing intensity, soil, and climate variables. This study aimed at assessing GHG emissions from a tropical pasture of Brazil to evaluate (i) how the grazing intensity affects the magnitude of GHG emissions; (ii) how season influences GHG production and consumption; and (iii) what are the key driving variables associated with GHG emissions. We measured under field conditions, during two years in a palisade-grass pasture managed with 3 grazing intensities: heavy (15 cm height), moderate (25 cm height), and light (35 cm height) N 2O, CH 4 and CO 2 fluxes using static closed chambers and chromatographic quantification. The greater emissions occurred in the summer and the lower in the winter. N 2O, CH 4, and CO 2 fluxes varied according to the season and were correlated with pasture grazing intensity, temperature, precipitation, % WFPS (water-filled pores space), and soil inorganic N. The explanatory variables differ according to the gas and season. Grazing intensity had a negative linear effect on annual cumulative N 2O emissions and a positive linear effect on annual cumulative CO 2 emissions. Grazing intensity, season, and year affected N 2O, CH 4, and CO 2 emissions. Tropical grassland can be a large sink of N 2O and CH 4. GHG emissions were explained for different key driving variables according to the season. 相似文献
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