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1.
Emissions of CH 4 and N 2O related to private pig farming under a tropical climate in Uvéa Island were studied in this paper. Physicochemical soil parameters such as nitrate, nitrite, ammonium, Kjeldahl nitrogen, total organic carbon, pH and moisture were measured. Gaseous soil emissions as well as physicochemical parameters were compared in two private pig farming strategies encountered on this island on two different soils (calcareous and ferralitic) in order to determine the best pig farming management: in small concrete pens or in large land pens. Ammonium levels were higher in control areas while nitrate and nitrite levels were higher in soils with pig slurry inputs, indicating that nitrification was the predominant process related to N 2O emissions. Nitrate contents in soils near concrete pens were important (≥55 μg N/g) and can thus be a threat for the groundwater. For both pig farming strategies, N 2O and CH 4 fluxes can reach high levels up to 1 mg N/m 2/h and 1 mg C/m 2/h, respectively. CH 4 emissions near concrete pens were very high (≥10.4 mg C/m 2/h). Former land pens converted into agricultural land recover low N 2O emission rates (≤0.03 mg N/m 2/h), and methane uptake dominates. N 2O emissions were related to nitrate content whereas CH 4 emissions were found to be moisture dependent. As a result relating to the physicochemical parameters as well as to the gaseous emissions, we demonstrate that pig farming in large land pens is the best strategy for sustainable family pig breeding in Uvéa Islands and therefore in similar small tropical islands. 相似文献
2.
High-density polyethylene (HDPE) membranes are commonly used as a cover component in sanitary landfills, although only limited evaluations of its effect on greenhouse gas (GHG) emissions have been completed. In this study, field GHG emission were investigated at the Dongbu landfill, using three different cover systems: HDPE covering; no covering, on the working face; and a novel material-Oreezyme Waste Cover (OWC) material as a trial material. Results showed that the HDPE membrane achieved a high CH 4 retention, 99.8% (CH 4 mean flux of 12 mg C m -2 h -1) compared with the air-permeable OWC surface (CH4 mean flux of 5933 mg C m -2 h -1) of the same landfill age. Fresh waste at the working face emitted a large fraction of N 2O, with average fluxes of 10 mg N m -2 h -2, while N 2O emissions were small at both the HDPE and the OWC sections. At the OWC section, CH 4 emissions were elevated under high air temperatures but decreased as landfill age increased. N 2O emissions from the working face had a significant negative correlation with air temperature, with peak values in winter. A massive presence of CO 2 was observed at both the working face and the OWC sections. Most importantly, the annual GHG emissions were 4.9 Gg yr -1 in CO 2 equivalents for the landfill site, of which the OWC-covered section contributed the most CH 4 (41.9%), while the working face contributed the most N 2O (97.2%). HDPE membrane is therefore, a recommended cover material for GHG control. Implications: Monitoring of GHG emissions at three different cover types in a municipal solid waste landfill during a 1-year period showed that the working face was a hotspot of N2O, which should draw attention. High CH4 fluxes occurred on the permeable surface covering a 1- to 2-year-old landfill. In contrast, the high-density polyethylene (HDPE) membrane achieved high CH4 retention, and therefore is a recommended cover material for GHG control. 相似文献
3.
As a convenient method, the closed chamber method has been applied to determine gaseous emission fluxes from fully open animal feeding operations despite the measured fluxes being theoretically affected by deployment time, wind speed over the emitting surface and detected gas mass. This laboratory study evaluated the effects of deployment time (0 to 120 min) and external surface wind speed (ESWS) (0.00, 0.25, 0.50, 0.75, 1.00, 1.50 and 2.00 m sec -1) on the measurement accuracy of a 300 mm (diameter) × 400 mm (height) (D300×H400) closed chamber using methane (CH 4), nitrous oxide (N 2O) and sulfur hexafluoride (SF 6) as reference gases. The results showed that the overall deviation ratio between the measured and reference CH 4 fluxes ranged from 9.99 % to -37.32 % and the flux was overestimated in the first 20 min. The measured N 2O and SF 6 emissions were smaller than the reference fluxes using the chamber. N 2O measurement accuracy decreased from -14.47 to -35.09% with deployment time extended to 120 min, while SF 6 accuracy sharply increased in the first 40 min, with the deviation stabilizing at approximately -5.00%. CH 4, N 2O and SF 6 measurements were significantly affected by deployment time and ESWS (P<0.05), and the interaction of those two factors greatly influenced CH 4 and SF 6 measurements (P<0.05). With the D300×H400 closed chamber, deployment times of 20 to 30 min and 10 to 20 min are recommended to measure CH 4 and N 2O, respectively, from the open operations of dairy farms under wind speeds lower than 2 m sec -1. Implications: This study recommended the suitable deployment times and wind speeds for using a D300 × H400 closed chamber to measure CH4, N2O, and SF6 in an open system, such as a dairy open lot and manure stockpile, to help researchers and other related industry workers get accurate data for gas emission rate. Deployment times of 20 to 30 min and 10 to 20 min were recommended to measure CH4 and N2O emissions using the D300 × H400 closed chamber, respectively, from the open operations of dairy farms under wind speeds lower than 2 m sec?1. For the measurement of SF6, a typical tracer gas, a deployment of 70 to 90 min was suggested. 相似文献
4.
An environmental parameters study has examined the impact of indoor temperature ( T) and relative humidity ( RH) levels on formaldehyde (CH 2O) concentrations inside two unoccupied research houses where the primary CH 2O emitter is particleboard underlayment. The data were fit to a simple three-term, steady state model describing the T and RH dependence of CH 2O concentration in a single compartment with a single CH 2O emitter. The model incorporates an Arrhenius T dependence and a nonlinear RH dependence of the CH 2O vapor concentration within the solid CH 2O emitter. The RH dependence is based on Freundlich's theory of the adsorption of water vapor on solid surfaces. The model is used to estimate potential seasonal variation in CH 2O concentrations under specified experimental conditions inside the research houses. The modeled results indicate six- to ninefold variation between 18°C, 20% RH and 32°C, 80% RH, simulating potential winter/summer conditions with minimal indoor climate control. In comparison, Indoor conditions ranging from 20°C, 30% RH to 26°C, 60% RH yielded approximate two- to fourfold fluctuations in CH 2O concentration. The research house data were also used to evaluate the limitations and applicability of more complex five-term models developed from small-scale chamber studies of the environmental dependence of CH 2O emissions from particleboard underlayment. These models also incorporate a linear T and RH dependence of the CH 2O transport rate through the CH 2O emitter in addition to the T and RH dependence of the CH 2O concentration within the emitter. Good correlation is observed between the results of the research house studies and 1) a selected (i.e., single) underlayment model over a broad range of environmental conditions and 2) a combined underlayment model over a restricted range of environmental conditions. 相似文献
5.
Measurements of ammonia (NH 3), nitrous oxide (N 2O) and methane (CH 4) were made from 11 outdoor concrete yards used by livestock. Measurements of NH 3 emission were made using the equilibrium concentration technique while closed chambers were used to measure N 2O and CH 4 emissions. Outdoor yards used by livestock proved to be an important source of NH 3 emission. Greatest emission rates were measured from dairy cow feeding yards, with a mean of 690 mg NH 3-N m −2 h −1. Smaller emission rates were measured from sheep handling areas, dairy cow collecting yards, beef feeding yards and a pig loading area, with respective mean emission rates of 440, 280, 220 and 140 mg NH 3-N m −2 h −1. Emission rates of N 2O and CH 4 were much smaller and for CH 4, in particular, emission rates were influenced greatly by the presence or absence of dung on the measurement area. 相似文献
6.
The open lots and manure stockpiles of dairy farm are major sources of greenhouse gas (GHG) emissions in typical dairy cow housing and manure management system in China. GHG (CO 2, CH 4 and N 2O) emissions from the ground level of brick-paved open lots and uncovered manure stockpiles were estimated according to the field measurements of a typical dairy farm in Beijing by closed chambers in four consecutive seasons. Location variation and manure removal strategy impacts were assessed on GHG emissions from the open lots. Estimated CO 2, CH 4 and N 2O emissions from the ground level of the open lots were 137.5±64.7 kg hd -1 yr -1, 0.45±0.21 kg hd -1 yr -1 and 0.13±0.08 kg hd -1 yr -1, respectively. There were remarkable location variations of GHG emissions from different zones (cubicle zone vs. aisle zone) of the open lot. However, the emissions from the whole open lot were less affected by the locations. After manure removal, lower CH 4 but higher N 2O emitted from the open lot. Estimated CO 2, CH 4 and N 2O emissions from stockpile with a stacking height of 55±12 cm were 858.9±375.8 kg hd -1 yr -1, 8.5±5.4 kg hd -1 yr -1 and 2.3±1.1 kg hd -1 yr -1, respectively. In situ storage duration, which estimated by manure volatile solid contents (VS), would affect GHG emissions from stockpiles. Much higher N 2O was emitted from stockpiles in summer due to longer manure storage. Implications: This study deals with greenhouse gas (GHG) emissions from open lots and stockpiles. It’s an increasing area of concern in some livestock producing countries. The Intergovernmental Panel on Climate Change (IPCC) methodology is commonly used for estimation of national GHG emission inventories. There is a shortage of on-farm information to evaluate the accuracy of these equations and default emission factors. This work provides valuable information for improving accounting practices within China or for similar manure management practice in other countries. 相似文献
7.
The wetlands play an important role in global carbon and nitrogen storage, and they are also natural sources of greenhouse gases such as methane (CH 4) and nitrous oxide (N 2O). Land-use change is an important factor affecting the exchange of greenhouse gases between wetlands and the atmosphere. However, few studies have investigated the effect of land-use change on CH 4 and N 2O emissions from freshwater marsh in China. Therefore, a field study was carried out over a year to investigate the seasonal changes of the emissions of CH 4 and N 2O at three sites ( Deyeuxia angustifolia marsh, dryland and rice field) in the Sanjiang Plain of Northeast China. Marsh was the source of CH 4 showing a distinct temporal variation. Maximum fluxes occurred in June and the highest value was 20.69 ± 2.57 mg CH 4 m ?2 h ?1. The seasonal change of N 2O fluxes from marsh was not obvious, consisted of a series of emission pulses. The marsh acted as a N 2O sink during winter, while became a N 2O source in the growing season. The results showed that gas exchange between soil/snow and the atmosphere in the winter season contributed greatly to the annual budgets. The winter season CH 4 flux was about 3.24% of the annual flux and the winter uptake of N 2O accounted for 13.70% of the growing-season emission. Conversion marsh to dryland resulted in a shift from a strong CH 4 source to a weak sink (from 199.12 ± 39.04 to ?1.37 ± 0.68 kg CH 4 ha ?1 yr ?1), while increased N 2O emissions somewhat (from 4.07 ± 1.72 to 4.90 ± 1.52 kg N 2O ha ?1 yr ?1). Conversion marsh to rice field significantly decreased CH 4 emission from 199.12 ± 39.04 to 94.82 ± 9.86 kg CH 4 ha ?1 yr ?1 and N 2O emission from 4.07 ± 1.72 to 2.09 ± 0.79 kg N 2O ha ?1 yr ?1. 相似文献
8.
Environmental test chambers are an important tool in the characterization of organic emissions from solid consumer and construction products and in the evaluation of their potential impact on indoor air quality. The results of extensive research concerning formaldehyde (CH 2O) emissions from such products strongly support this application of environmental chambers to measure product emissions and provide useful input for the design of environmental chamber studies. The physical design and test methodology for environmental chambers are strongly influenced by several elements in a comprehensive project plan for source characterization, including the selection process for test samples and the mathematical models used to interpret the organic emissions data. The protocol for environmental chamber testing extends broadly from the acquisition, preparation and conditioning of test specimens, to the selection and control of environmental test conditions, and to the calibration and measurement of system parameters and organic emissions. The requirements for environmental control inside the test chamber can be estimated from the sensitivity of the organic emission rates of the test products (e.g. CH 2O emissions from pressed-wood products) to variation in environmental parameters. The cost of the numerous, multiple-organic analyses required for environmental chamber testing of solid emitters is seen as a strong limitation to product selection strategies and modeling efforts. The modeling of organic emissions from solid emitters can be both a planning tool for development of chamber test methodology and a means to interpret test chamber results. 相似文献
9.
The soil in a drained fjord area, reclaimed for arable farming, produced N 2O mainly at 75–105 cm depth, just above the ground water level. Surface emissions of N 2O were measured from discrete small areas by closed and open-flow chamber methods, using gas chromatographic analysis and over larger areas by integrative methods: flux gradient (analysis by FTIR), conditional sampling (analysis by TDLAS), and eddy covariance (analysis by TDLAS). The mean emission of N 2O as determined by chamber procedures during a 9-day campaign was 162–202 μg N 2ONm −2h −1 from a wheat stubble and 328–467 μg N 2ONm −2 h −1 from a carrot field. The integrative approaches gave N 2O emissions of 149–495 μg N 2ONm −2 h −1, i.e. a range similar to those determined with the chamber methods. Wind direction affected the comparison of chamber and integrative methods because of patchiness of the N 2O emission over the area. When a uniform area with a single type of vegetation had a dominant effect on the N 2O gradient at the sampling mast, the temporal variation in N 2O emission determined by the flux gradient/FTIR method and chamber methods was very similar, with differences of only 18% or less in mean N 2O emission, well below the variation encountered with the chamber methods themselves. A detailed comparison of FTIR gradient and chamber data taking into account the precise emission footprint showed good agreement. It is concluded that there was no bias between the different approaches used to measure the N 2O emission and that the precision of the measurements was determined by the spatial variability of the N 2O emission at the site and the variability inherent in the individual techniques. These results confirm that measurements of N 2O emissions from different ecosystems obtained by the different methods can be meaningfully compared. 相似文献
10.
Chamber techniques can easily be applied to field trials with multiple small plots measuring carbon- and nitrogen-trace gas fluxes. Nevertheless, such chamber measurements are usually made weekly and rarely more frequently than once daily. However, automatic chambers do allow flux measurements on sub-daily time scales. It has been hypothesized that sub-daily measurements provide more reliable results, as diurnal variations are captured better compared to manual measurements. To test this hypothesis we compared automatic and manual measurements of N 2O, CO 2 and CH 4 fluxes from tilled and non-tilled plots of a rice–wheat rotation ecosystem over a non-waterlogged period. Our results suggest that both techniques, i.e., either manual or automatic chambers of N 2O and CO 2 emissions resulted in biased fluxes. The manual measurements were adequate to capture either day-to-day or seasonal dynamics of N 2O, CO 2 and CH 4 exchanges, but overestimated the cumulative N 2O and CO 2 emissions by 18% and 31%, respectively. This was due to neglecting temperature-dependent diurnal variations of C and N trace gas fluxes. However, the automatic measurements underestimated the cumulative emissions of N 2O and CO 2 by 22% and 17%, respectively. This underestimation resulted from chamber effects upon soil moisture during rainfall processes. No significant difference was detected between the two methods in CH 4 exchanges over the non-waterlogged soils. The bias of manual chambers may be significant when pronounced diurnal variations occur. The bias of automatic measurements can only be avoided/minimized if chamber positions are frequently changed and/or if chambers are automatically opened during rainfall events. We therefore recommend using automatic chambers together with continuous measurements of soil chamber moisture to allow for soil moisture correction of fluxes or to correct flux estimates as derived by manual chambers for possible diurnal variations. 相似文献
11.
To investigate the spatial and seasonal variations of nitrous oxide (N 2O) fluxes and understand the key controlling factors, we explored N 2O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N 2O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N 2O fluxes ranged from ?0.0051 to 0.0805 mg N 2O m ?2 h ?1, and high N 2O emissions occurred during spring (0.0278 mg N 2O m ?2 h ?1) and winter (0.0139 mg N 2O m ?2 h ?1) while low fluxes were observed during summer (0.0065 mg N 2O m ?2 h ?1) and autumn (0.0060 mg N 2O m ?2 h ?1). The annual average N 2O flux from the intertidal zone was 0.0117 mg N 2O m ?2 h ?1, and the cumulative N 2O emission throughout a year was 113.03 mg N 2O m ?2, indicating that coastal marsh acted as N 2O source. Over all seasons, N 2O fluxes from the four marshes were significantly different ( p?<?0.05), in the order of HM (0.0256?±?0.0040 mg N 2O m ?2 h ?1)?>?MF (0.0107?±?0.0027 mg N 2O m ?2 h ?1)?>?LM (0.0073?±?0.0020 mg N 2O m ?2 h ?1)?>?MM (0.0026?±?0.0011 mg N 2O m ?2 h ?1). Temporal variations of N 2O emissions were related to the vegetations ( Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N 2O contributions (particularly during non-growing season) to the estimation of local N 2O inventory, and highlighted both the large spatial variation of N 2O fluxes across the coastal marsh (CV?=?158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N 2O emission should be considered before the annual or local N 2O inventory was evaluated accurately. 相似文献
12.
Greenhouse gas emissions from hydroelectric dams have recently given rise to controversies about whether hydropower still provides clean energy. China has a large number of dams used for energy supply and irrigation, but few studies have been carried out on aquatic nitrous oxide (N 2O) variation and its emissions in Chinese river-reservoir systems. In this study, N 2O spatiotemporal variations were investigated monthly in two reservoirs along the Wujiang River, Southwest China, and the emission fluxes of N 2O were estimated. N 2O production in the reservoirs tended to be dominated by nitrification, according to the correlation between N 2O and other parameters. N 2O saturation in the surface water of the Wujiangdu reservoir ranged from 214% to 662%, with an average fluctuation of 388%, while in the Hongjiadu reservoir, it ranged from 201% to 484%, with an average fluctuation of 312%. The dissolved N 2O in both reservoirs was over-saturated with respect to atmospheric equilibrium levels, suggesting that the reservoirs were net sources of N 2O emissions to the atmosphere. The averaged N 2O emission flux in the Wujiangdu reservoir was 0.64 μmol m ?2 h ?1, while it was 0.45 μmol m ?2 h ?1 in the Hongjiadu reservoir, indicating that these two reservoirs had moderate N 2O emission fluxes as compared to other lakes in the world. Downstream water of the dams had quite high levels of N 2O saturation, and the estimated annual N 2O emissions from hydropower generation were 3.60 × 10 5 and 2.15 × 10 5 mol N 2O for the Wujiangdu and the Hongjiadu reservoir, respectively. These fluxes were similar to the total N 2O emissions from the reservoir surfaces, suggesting that water released from reservoirs would be another important way for N 2O to diffuse into the atmosphere. It can be concluded that dam construction significantly changes the water environment, especially in terms of nutrient status and physicochemical conditions, which have obvious influences on the N 2O spatiotemporal variations and emissions. 相似文献
13.
Nitrous oxide (N 2O) is a trace gas contributing to stratospheric ozone depletion and global warming. Although a large quantity of information exists about N 2O emissions from various ecosystems, this study was initiated to demonstrate the features of N 2O emissions from sea-based waste disposal sites in Osaka City in relation to CH 4 emissions. Average N 2O emissions at an active landfill (S-Site) were several times higher than those at a closed landfill (N Site). Average CH 4 emissions were also much greater at the S-Site. Regarding the nature of N 2O emissions, remarkable emissions often were observed with aerobic waste layers at the N-Site, suggesting almost inversely related N 2O emissions with CH 4 production at the N-Site. However, at the S-Site a few exceptionally high N 2O emissions were noted in cases of high CH 4 emissions. 相似文献
14.
Abstract The CO 2 and N 2O soil emissions at a rice paddy in Mase, Japan, were measured by enclosures during a fallow winter season. The Mase site, one of the AsiaFlux Network sites in Japan, has been monitored for moisture, heat, and CO 2 fluxes since August 1999. The paddy soil was found to be a source of both CO 2 and N 2O flux from this experiment. The CO 2 and N 2O fluxes ranged from -27.6 to 160.4μg CO 2/m 2/sec (average of 49.1 ± 42.7 μg CO 2/m 2/sec) and from -4.4 to 129.5 ng N 2O/m 2/sec (average of 40.3 ± 35.6 ng N 2O/m 2/sec), respectively. A bimodal trend, which has a sub-peak in the morning around 10:00 a.m. and a primary peak between 2:00 and 3:00 p.m., was observed. Gas fluxes increased with soil temperature, but this temperature dependency seemed to occur only on the calm days. Average CO 2 and N 2O fluxes were 27.7 μg CO 2/m 2/sec and 13.4 ng N 2O/m 2/sec, with relatively small fluctuation during windy days, while averages of 69.3 μg CO 2/m 2/sec and 65.8 ng N 2O/m 2/sec were measured during calm days. This relationship was thought to be a result of strong surface winds, which enhance gas exchange between the soil surface and the atmosphere, thus reducing the gas emissions from soil surfaces. 相似文献
15.
Micrometeorological flux-gradient and nocturnal boundary layer methods were combined with Fourier transform infrared (FTIR) spectroscopy for high-precision trace gas analysis to measure fluxes of the trace gases CO 2, CH 4 and N 2O between agricultural fields and the atmosphere. The FTIR measurements were fully automated and routinely obtained a precision of 0.1–0.2% for several weeks during a measurement campaign in October 1995. In flux-gradient measurements, vertical profiles of the trace gases were measured every 30 min from the ground to 22 m. When combined with independent micrometeorological measurements of water vapour fluxes, trace gas fluxes from the underlying surface could be determined. In the nocturnal boundary layer method the rate of change in mass storage in the 0–22 m layer was combined with fluxes measured at 22 m to estimate surface fluxes. Daytime fluxes for CO 2 were −0.78±0.40 (1 σ) mg CO 2 m −2 s −1. Daytime fluxes of N 2O and CH 4 were very small and difficult to measure reliably using the flux-gradient technique, despite the high precision of the concentration measurements. Mean daytime flux for N 2O was 17±48 ng N m −2 s −1, while the corresponding flux for CH 4 was 47±410 ng CH 4 m −2 s −1. The mean nighttime flux of CO 2 estimated using the nocturnal boundary layer method was +0.15±0.05 mg CO 2 m −2 s −1, in good agreement with chamber measurements of respiration rates. Nighttime fluxes of CH 4 and N 2O from the nocturnal boundary layer method were 109±69 ng CH 4 m −2 s −1 and 2±3.2 ng N m −2 s −1, respectively, in good agreement with chamber measurements and inventory estimates based on the sheep and cattle stocking rates in the region. The suitability of FTIR-based methods for long term monitoring of spatially and temporally averaged flux measurements is discussed. 相似文献
16.
Water management is one of the most important practices that affect methane (CH 4) and nitrous oxide (N 2O) emissions from paddy fields. A field experiment was designed to study the effects of controlled irrigation (CI) on CH 4 and N 2O emissions from paddy fields, with traditional irrigation (TI) as the control. The effects of CI on CH 4 and N 2O emissions from paddy fields were very clear. The peaks of CH 4 emissions from the CI paddies were observed 1-2 d after the water layer disappeared. Afterward, the emissions reduced rapidly and remained low until the soil was re-flooded. A slight increase of CH 4 emission was observed in a short period after re-flooding. N 2O emissions peaks from CI paddies were all observed 8-10 d after the fertilization at the WFPS ranging from 78.1% to 85.3%. Soil drying caused substantial N 2O emissions, whereas no substantial N 2O emissions were observed when the soil was re-wetted after the dry phase. Compared with TI, the cumulative CH 4 emissions from the CI fields were reduced by 81.8% on the average, whereas the cumulative N 2O emissions were increased by 135.4% on the average. The integrative global warming potential of CH 4 and N 2O on a 100-year horizon decreased by 27.3% in the CI paddy fields, whereas no significant difference in the rice yield was observed between the CI and TI fields. These results suggest that CI can effectively mitigate the integrative greenhouse effect caused by CH 4 and N 2O emissions from paddy fields while ensuring the rice yield. 相似文献
17.
Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH 4) and nitrous oxide (N 2O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH 4 fluxes at the expense of increasing the N 2O fluxes. Furthermore, fertilization significantly decreased the CH 4 fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH 4 fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N 2O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH 4 emissions from the OF were 100 % lower, and N 2O emissions were 421 % higher than those from the PF. Although cumulative N 2O emissions were stimulated in the newly converted orchard, the strong reduction of CH 4 led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH 4 +-N) and nitrate (NO 3 ?-N) contents indicated a significant variation in soil properties and contributed to variations in soil CH 4 and N 2O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH 4 and N 2O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH 4 and N 2O emissions. 相似文献
18.
Municipal solid waste landfills are the significant anthropogenic sources of N 2O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH 4 fumigation, as evidenced by both laboratory incubation and field measurement. During a 10-day incubation with leachate addition, the average N 2O fluxes in the soil samples, collected from the three selected landfill covers, were multiplied by 1.75 ( p < 0.01), 3.56 ( p < 0.01), and 2.12 ( p < 0.01) from the soil samples preincubated with 5% CH 4 for three months when compared with the control, respectively. Among the three selected landfill sites, N 2O fluxes in two landfill sites were significantly correlated with the variations of the CH 4 emissions without landfill gas recovery ( p < 0.001). N 2O fluxes were also elevated by the increase of the CH 4 emissions with landfill gas recovery in another landfill site ( p > 0.05). The annual average N 2O flux was 176 ± 566 μg N 2O–N m ?2 h ?1 ( p < 0.01) from sandy soil–covered landfill site, which was 72% ( p < 0.05) and 173% ( p < 0.01) lower than the other two clay soil covered landfill sites, respectively. The magnitude order of N 2O emissions in three landfill sites was also coincident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landfill N 2O emissions. 相似文献
19.
Great efforts have been devoted to assessing the effects of straw managements on greenhouse gas (GHG) emissions, global warming potential (GWP), and net economic budget in rice monoculture (RM). However, few studies have evaluated the effects of straw managements on GHG emissions and net ecosystem economic budget (NEEB) in integrated rice-crayfish farming (RC). Here, a randomized block field experiment was performed to comprehensively evaluate the effects of aquatic breeding practices (feeding or no feeding of forage) and straw managements (rice straw returning or removal) on soil NH4+–N and NO?3–N contents, redox potential (Eh), CH4 and N2O emissions, GWP, and NEEB of fluvo-aquic paddy soil in a rice-crayfish co-culture system in Jianghan Plain of China. We also compared the differences in CH4 and N2O emissions, GWP, and NEEB between RM and RC. Straw returning significantly increased CH4 and N2O emissions by 34.9–46.1% and 6.2–23.1% respectively compared with straw removal. Feeding of forage decreased CH4 emissions by 13.9–18.7% but enhanced N2O emissions by 24.4–33.2% relative to no feeding. Compared with RM treatment, RC treatment decreased CH4 emissions by 18.1–19.6% but increased N2O emissions by 16.8–21.0%. Moreover, RC treatment decreased GWP by 16.8–22.0% while increased NEEB by 26.9–75.6% relative to RM treatment, suggesting that the RC model may be a promising option for mitigating GWP and increasing economic benefits of paddy fields. However, the RC model resulted in a lower grain yield compared with the RM model, indicating that more efforts are needed to simultaneously increase grain yield and NEEB and decrease GWP under RC model. 相似文献
20.
Denitrification is an important N removal process in aquatic systems but is also implicated as a potential source of global N 2O emissions. However, the key factors controlling this process as well as N 2O emissions remain unclear. In this study, we identified the main factors that regulate the production of net N 2 and N 2O in sediments collected from rivers with a large amount of sewage input in the Taihu Lake region. Net N 2 and N 2O production were strongly associated with the addition of NO 3 ?-N and NH 4 +-N. Specifically, NO 3 ?-N controlled net N 2 production following Michaelis–Menten kinetics. The maximum rate of net N 2 production ( V max) was 116.3 μmol N 2-N m ?2 h ?1, and the apparent half-saturation concentration ( k m) was 0.65 mg N L ?1. N 2O to N 2 ratios increased from 0.18?±?0.03 to 0.68?±?0.16 with the addition of NO 3 ?-N, suggesting that increasing NO 3 ?-N concentrations favored the production of N 2O more than N 2. The addition of acetate enhanced net N 2 production and N 2O to N 2 ratios, but the ratios decreased by about 59.5 % when acetate concentrations increased from 50 to 100 mg C L ?1, suggesting that the increase of N 2O to N 2 ratios had more to do with the net N 2 production rate rather than acetate addition in this experiment. The addition of Cl ? did not affect the net N 2 production rates, but significantly enhanced N 2O to N 2 ratios (the ratios increased from 0.02?±?0.00 to 0.10?±?0.00), demonstrating that the high salinity effect might have a significant regional effect on N 2O production. Our results suggest that the presence of N-enriching sewage discharges appear to stimulate N removal but also increase N 2O to N 2 ratios. 相似文献
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