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1.
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
2.
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
3.
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
4.
In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing–thawing cycles (FTCs) under ambient air and under N 2. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N 2O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N 2. The highest N 2O cumulative emission of 138.24 μg N 2O–N kg ?1 was observed from seal colony soils. Cumulative CO 2 and CH 4 emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO 2 (433.0 mgCO 2–C kg ?1) and CH 4 (2.9 mgCH 4–C kg ?1) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH 4 and CO 2 while ornithogenic soil was a stronger emitter for N 2O during FTCs. CO 2 and CH 4 fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M c) in penguin guanos and ornithogenic soils. The specific CO 2–C production rate (CO 2–C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica. 相似文献
5.
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
6.
Manure-based soil amendments (herein “amendments”) are important fertility sources, but differences among amendment types and management can significantly affect their nutrient value and environmental impacts. A 6-month in situ decomposition experiment was conducted to determine how protection from wintertime rainfall affected nutrient losses and greenhouse gas (GHG) emissions in poultry (broiler chicken and turkey) and horse amendments. Changes in total nutrient concentration were measured every 3 months, changes in ammonium (NH 4+) and nitrate (NO 3?) concentrations every month, and GHG emissions of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) every 7–14 days. Poultry amendments maintained higher nutrient concentrations (except for K), higher emissions of CO 2 and N 2O, and lower CH 4 emissions than horse amendments. Exposing amendments to rainfall increased total N and NH 4+ losses in poultry amendments, P losses in turkey and horse amendments, and K losses and cumulative N 2O emissions for all amendments. However, it did not affect CO 2 or CH 4 emissions. Overall, rainfall exposure would decrease total N inputs by 37% (horse), 59% (broiler chicken), or 74% (turkey) for a given application rate (wet weight basis) after 6 months of decomposition, with similar losses for NH 4+ (69–96%), P (41–73%), and K (91–97%). This study confirms the benefits of facilities protected from rainfall to reduce nutrient losses and GHG emissions during amendment decomposition. Implications: The impact of rainfall protection on nutrient losses and GHG emissions was monitored during the decomposition of broiler chicken, turkey, and horse manure-based soil amendments. Amendments exposed to rainfall had large ammonium and potassium losses, resulting in a 37–74% decrease in N inputs when compared with amendments protected from rainfall. Nitrous oxide emissions were also higher with rainfall exposure, although it had no effect on carbon dioxide and methane emissions. Overall, this work highlights the benefits of rainfall protection during amendment decomposition to reduce nutrient losses and GHG emissions. 相似文献
7.
Landfills are among the major sources of anthropogenic methane (CH 4) estimated to reach 40?×?10 9kg per year worldwide by 2015 ( IPCC, 2007 IPCC. 2007. Intergovernmental Panel on Climate Change, Synthesis Report on Contributions of Work Groups 1, 2, and 3 to the Fourth Assessment Report Core Writing Team, Edited by: Pauchar, R.K. and Reisinger, A. Geneva, Switzerland: IPCC. [Google Scholar]). A 2½-year field experiment was conducted at a closed landfill in western Michigan where methanotrophs, methane-consuming bacteria, were stimulated by nutrient addition to the soil without significantly increasing biogenic nitrous oxide (N 2O) production. The effects of the nitrogen amendments (KNO 3 and NH 4Cl), phenylacetylene (a selective inhibitor of nitrifying bacteria that contribute to N 2O production), and a canopy (to reduce direct water infiltration) on the vertical soil gas profiles of CH 4, CO 2, and O 2 were measured in the top meter of the soil. Methane and nitrous oxide fluxes were calculated from the corresponding soil gas concentration gradients with respect to depth and a Millington–Quirk diffusivity coefficient in soil derived empirically from soil porosity, water content, and diffusivity coefficients in air from the literature. Methane flux estimates were as high as 218.4 g m ?2 day ?1 in the fall and 12.8 g/m ?2 day ?1 in the summer. During the spring and summer, CH 4 fluxes were reduced by more than half by adding KNO 3 and NH 4Cl into the soil as compared to control plots, while N 2O fluxes increased substantially. The concurrent addition of phenylacetylene to the amendment decreased peak N 2O production by half and the rate of peak methane oxidation by about one-third. The seasonal average methane and N 2O flux data were extrapolated to estimate the reduction of CH 4 and N 2O fluxes into the atmosphere by nitrogen and inhibitor addition to the cover soils. The results suggest that such additions coupled with soil moisture management may provide a potential strategy to significantly reduce greenhouse gas emissions from landfills. Implications The results of a 2½-year study of effects of nutrient stimulation on methane oxidation in landfill cover soils demonstrates that nutrient addition does decrease methane emissions. The work further underscores the control which soil moisture exerts on methane oxidation. Water management is critical to the success of methane oxidation strategies. 相似文献
8.
利用SBR,控制曝气量为60 L/h,利用在线pH曲线控制曝气时间,成功实现了短程生物脱氮过程,并考察了不同进水方式下SBR运行性能及N2O产量。结果表明,分段进水能够有效降低短程生物脱氮过程中外加碳源投加量。在原水进水碳氮比较低时,采用递增进水量的进水方式,能够有效降低生物脱氮过程中NO-2积累量,从而降低系统N2O产量。1次进水、2次等量进水和2次递增进水方式下,生物脱氮过程中N2O产量分别为11.1、8.86和5.04 mg/L。硝化过程中NO-2-N的积累是导致系统N2O产生的主要原因。部分氨氧化菌(AOB)在限氧条件下以NH+4-N作为电子供体,NO-2-N作为电子受体进行反硝化,最终产物是N2O。 相似文献
9.
Greenhouse gas (GHG) emissions by constructed wetlands (CWs) could mitigate the environmental benefits of nutrient removal in these man-made ecosystems. We studied the effect of 3 different macrophyte species and artificial aeration on the rates of nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4) production in CW mesocosms over three seasons. CW emitted 2-10 times more GHG than natural wetlands. Overall, CH 4 was the most important GHG emitted in unplanted treatments. Oxygen availability through artificial aeration reduced CH 4 fluxes. Plant presence also decreased CH 4 fluxes but favoured CO 2 production. Nitrous oxide had a minor contribution to global warming potential (GWP < 15%). The introduction of oxygen through artificial aeration combined with plant presence, particularly Typha angustifolia, had the overall best performance among the treatments tested in this study, including lowest GWP, greatest nutrient removal, and best hydraulic properties. 相似文献
10.
Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298?±?2 K) and atmospheric pressure (708?±?8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm 3 molecule ?1 s ?1): (3.27?±?0.33)?×?10 ?11 and (4.43?±?0.42)?×?10 ?11, for CH 3CH═CHC(O)OCH 3 and (CH 3) 2CH═CHC(O)OCH 3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N 2 and air were used as the bath gases. The following rate coefficients were obtained (in cm 3 molecule ?1 s ?1): k 3 (CH 2═CHC(O)O(CH 2) 5CH 3?+?Cl)?=?(3.31?±?0.31)?×?10 ?10, k 4(CH 2═CHC(O)OCH 2CH(CH 2CH 3)(CH 2) 3CH 3?+?Cl)?=?(3.46?±?0.31)?×?10 ?10, k 5(CH 2═CHC(O)O(CH 2) 5CH 3?+?OH)?=?(2.28?±?0.23)?×?10 ?11, and k 6(CH 2═CHC(O)OCH 2CH(CH 2CH 3)(CH 2) 3CH 3?+?OH)?=?(2.74?±?0.26)?×?10 ?11. The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in –C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming. 相似文献
11.
An automated system for continuous measurement of N 2O fluxes on an hourly basis was employed to study N 2O emissions in an intensively managed low carbon calcareous soil under sub-humid temperate monsoon conditions. N 2O emissions occurred mainly within two weeks of application of NH 4+-based fertilizer and total N 2O emissions in wheat (average 0.35 or 0.21 kg N ha −1 season −1) and maize (average 1.47 or 0.49 kg N ha −1 season −1) under conventional and optimum N fertilization (300 and 50-122 kg N ha −1, respectively) were lower than previously reported from low frequency measurements. Results from closed static chamber showed that N 2O was produced mainly from nitrification of NH 4+-based fertilizer, with little denitrification occurring due to limited readily oxidizable carbon and low soil moisture despite consistently high soil nitrate-N concentrations. Significant reductions in N 2O emissions can be achieved by optimizing fertilizer N rates, using nitrification inhibitors, or changing from NH 4+- to NO 3ˉ-based fertilizers. 相似文献
12.
Abstract The long-term stability of a biofilter loaded with waste gases containing NH 3 concentrations larger than 100 ppmv was studied in a laboratory-scale compost reactor. At an empty bed residence time (τ) of 21 sec, elimination capacities of more than 300 g NH 3/m 3/day were obtained at elimination efficiencies up to 87%. Because of absorption and nitrification, almost 80% of the NH 3-N eliminated from the waste gas could be recovered in the compost as NH 4+-N or NO 2 ?/NO 3 ?-N. The high elimination capacities could be maintained as long as the NH 4+/NO x concentration in the carrier material was less than 4 g NH 4+/NO x ?-N/kg wet compost. Above this critical value, osmotic effects inhibited the nitrifying activity, and the elimination capacity for NH 3 decreased. To restore the biofilter performance, a carbon source (methanol) was added to reduce NH 4+/NO x ? accumulated in the compost. Results indicate that methylotrophic microorganisms did convert NH 4+/NO x ? into biomass, as long as the NO 3 ? content in the compost was larger than 0.1 g NO 3 ?-N/kg compost. Removal efficiencies of CH 3OH of more than 90% were obtained at volumetric loads up to 11,000 g CH 3OH/m 3/day. It is shown that addition of CH 3OH is a suitable technique for regenerating the compost material from osmotic inhibition as a result of high NH 3 loading. The biofilter was operated for 4 months with alternating loading of NH 3 and CH 3OH. 相似文献
13.
Spartina alterniflora exhibits great invading potential in the coastal marsh ecosystems. Also, nitrogen (N) deposition shows an apparent increase in the east of China. To evaluate CH 4 emissions in the coastal marsh as affected by the invasion of S. alterniflora and N deposition, we measured CH 4 emission from brackish marsh mesocosms vegetated with S. alterniflora and a native plant, Suaeda salsa, and fertilized with exogenous N at the rates of 0 and 2.7 g N m ?2, respectively. Dissolved porewater CH 4 concentration and redox potentials in soils as well as aboveground biomass and stem density of plants were also monitored. The averaged rate of CH 4 emission during the growing season in the S. alterniflora and S. salsa mesocosms without N application was 0.88 and 0.54 mg CH 4 m ?2 h ?1, respectively, suggesting that S. alterniflora plants significantly increased CH 4 emission mainly because of higher plant biomass rather than stem density compared to S. salsa, which delivered more substrates to the soil for methanogenesis. Exogenous N input dramatically stimulated CH 4 emission by 71.7% in the S. alterniflora mesocosm. This increase was attributable to enhancement in biomass and particularly stem density of S. alterniflora driven by N application, which transported greater photosynthesis products than oxygen into soils for CH 4 production and provided more pathways for CH 4 emission. In contrast, there was no significant effect of N fertilization on CH 4 emission in the S. salsa mesocosm. Although N fertilization significantly stimulated CH 4 production by increasing S. salsa biomass, no significant increase in stem density was observed. This fact, along with the low gas transport capacity of S. salsa, failed to efficiently transport CH 4 from wetlands into the atmosphere. Thus we argue that the stimulatory or inhibitory effect of N fertilization on CH 4 emission from wetlands might depend on the gas transport capacity of plants and their relative contribution to substrates for CH 4 production and oxygen for CH 4 oxidation in soil. 相似文献
14.
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
15.
A budget for the methane (CH 4) cycle in the Xilin River basin of Inner Mongolia is presented. The annual CH 4 budget in this region depends primarily on the sum of atmospheric CH 4 uptake by upland soils, emission from small wetlands, and emission from grazing ruminants (sheep, goats, and cattle). Flux rates for these processes were averaged over multiple years with differing summer rainfall. Although uplands constitute the vast majority of land area, they consume much less CH 4 per unit area than is emitted by wetlands and ruminants. Atmospheric CH 4 uptake by upland soils was ?3.3 and ?4.8 kg CH 4 ha ?1 y ?1 in grazed and ungrazed areas, respectively. Average CH 4 emission was 791.0 kg CH 4 ha ?1 y ?1 from wetlands and 8.6 kg CH 4 ha ?1 y ?1 from ruminants. The basin area-weighted average of all three processes was 6.8 kg CH 4 ha ?1 y ?1, indicating that ruminant production has converted this basin to a net source of atmospheric CH 4. The total CH 4 emission from the Xilin River basin was 7.29 Gg CH 4 y ?1. The current grazing intensity is about eightfold higher than that which would result in a net zero CH 4 flux. Since grazing intensity has increased throughout western China, it is likely that ruminant production has converted China's grazed temperate grasslands to a net source of atmospheric CH 4 overall. 相似文献
16.
To understand the effect of water level on CH 4 emissions from an invasive Spartina alterniflora coastal brackish marsh, we measured CH 4 emissions from intermittently and permanently (5 cm water depth) inundated mesocosms with or without N fertilizer added at a rate of 2.7 g N m ?2. Dissolved CH 4 concentrations in porewater and vertically-profiled sediment redox potential were measured, as were aboveground biomass and stem density of S. alterniflora. Mean CH 4 fluxes during the growing season in permanently inundated mesocosms without and with N fertilizer were 1.03 and 1.73 mg CH 4 m ?2 h ?1, respectively, which were significantly higher than in the intermittently inundated mesocosms. This response indicates that prolonged submergence of sediment, up to a water depth of 5 cm, stimulated CH 4 release. Inundation did not greatly affect aboveground biomass and stem density, but did significantly reduce redox potential in sediment, which in turn stimulated CH 4 production and increased the CH 4 concentration of porewater, resulting in higher CH 4 emission in the mesocosm. Our data showed that the stimulatory effect of shallow, permanent inundation on CH 4 emission in S. alterniflora marsh sediment was due primarily to an improved methanogenic environment rather than an increase in plant-derived substrates and/or the number of gas emission pathways through the plant’s aerenchymal system. 相似文献
17.
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
18.
Combination of divergent active principles to achieve broad-spectrum control is gaining popularity to manage the weed menace in intensive agriculture. However, such application could have non-target impacts on the soil processes affecting soil ecology and environmental interactions. A field experiment was conducted to investigate the impact of separate and combined applications of herbicides bensulfuron methyl and pretilachlor on the emission of N 2O and CH 4, and related soil and microbial parameters in a flooded alluvial field planted to rice cv Lalat. Single application of the herbicide bensulfuron methyl or pretilachlor resulted in a significant reduction of N 2O and CH 4 emissions while the combination of these two herbicides distinctly increased N 2O and CH 4 emissions. Cumulative N 2O emissions (kg N 2O-N) followed the order of bensulfuron methyl (0.35 kg ha −1) < pretilachlor (0.36 kg ha −1) < control (0.45 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (0.49 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (0.54 kg ha −1). Cumulative CH 4 emissions (kg CH 4), on the other hand, followed the order of bensulfuron methyl (47.89 kg ha −1) < pretilachlor (73.17 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (93.50 kg ha −1) < control (106.54 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (124.67 kg ha −1). The inhibitory effect of separate application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% on N 2O emission was linked to lower mineral N, lower denitrifying and nitrifying activity and low denitrifier and nitrifier populations. Inhibitory effect on CH 4 emission, on the contrary, was linked to prevention in the drop of redox potential, lower readily mineralizable carbon (RMC) and microbial biomass carbon (MBC) contents as well as lower methanogenic and higher methanotrophic bacterial population. Admittedly, stimulatory effect of combined application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% at double dose on N 2O and CH 4 emission was related to reversal of the identified indicators of inhibition. Results indicate that while individual application of herbicides bensulfuron methyl 0.6% or pretilachlor 6.0% can reduce N 2O and CH 4 emission from flooded soil planted to rice, their combined application at normal dose can keep the emission at a comparatively lower level with significantly higher grain yield as compared to the herbicides applied alone. 相似文献
19.
An increasing nitrogen deposition experiment (2 g N m ?2 year ?1) was initiated in an alpine meadow on the Qinghai-Tibetan Plateau in May 2007. The greenhouse gases (GHGs), including CO 2, CH 4 and N 2O, was observed in the growing season (from May to September) of 2008 using static chamber and gas chromatography techniques. The CO 2 emission and CH 4 uptake rate showed a seasonal fluctuation, reaching the maximum in the middle of July. We found soil temperature and water-filled pore space (WFPS) were the dominant factors that controlled seasonal variation of CO 2 and CH 4 respectively and lacks of correlation between N 2O fluxes and environmental variables. The temperature sensitivity ( Q10) of CO 2 emission and CH 4 uptake were relatively higher (3.79 for CO 2, 3.29 for CH 4) than that of warmer region ecosystems, indicating the increase of temperature in the future will exert great impacts on CO 2 emission and CH 4 uptake in the alpine meadow. In the entire growing season, nitrogen deposition tended to increase N 2O emission, to reduce CH 4 uptake and to decrease CO 2 emission, and the differences caused by nitrogen deposition were all not significant ( p < 0.05). However, we still found significant difference ( p < 0.05) between the control and nitrogen deposition treatment at some observation dates for CH 4 rather than for CO 2 and N 2O, implying CH 4 is most susceptible in response to increased nitrogen availability among the three greenhouse gases. In addition, we found short-term nitrogen deposition treatment had very limited impacts on net global warming potential (GWP) of the three GHGs together in term of CO 2-equivalents. Overall, the research suggests that longer study periods are needed to verify the cumulative effects of increasing nitrogen deposition on GHG fluxes in the alpine meadow. 相似文献
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