共查询到20条相似文献,搜索用时 35 毫秒
1.
Greenhouse gas (GHG) emissions from concentrated animal feeding operations vary by stage of production and management practices. The objective of this research was to study the effect of two dietary crude protein levels (12 and 16%) fed to beef steers in pens with or without corn stover bedding. Manure characteristics and GHG emissions were measured from feedlot pen surfaces. Sixteen equal-sized feedlot pens (19?×?23 m) were used. Eight were bedded approximately twice a week with corn stover and the remaining eight feedlot pens were not bedded. Angus steers (n = 138) were blocked by live weights (lighter and heavier) with 7 to 10 animals per pen. The trial was a 2?×?2 factorial design with factors of two protein levels and two bedding types (bedding vs. non bedding), with four replicates. The study was conducted from June through September and consisted of four ?28-day periods. Manure from each pen was scrapped once every 28 days and composite manure samples from each pen were collected. Air samples from pen surfaces were sampled in Tedlar bags using a Vac-U-Chamber coupled with a portable wind tunnel and analyzed with a greenhouse gas gas chromatograph within 24 hr of sampling. The manure samples were analyzed for crude protein (CP), total nitrogen (TN), ammonia (NH 3), total volatile fatty acid (TVFA), total carbon (TC), total phosphorus (TP), and potassium (K). The air samples were analyzed for methane (CH 4), carbon dioxide (CO 2), and nitrous oxide (N 2O) concentrations. The concentration of TN was significantly higher (p < 0.05) in manure from pens with cattle fed the high protein diets. The volatile fatty acids (VFAs) such as acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids concentrations were similar across both treatments. There were no significant differences in pen surface GHG emissions across manure management and dietary crude protein levels. Implications: Livestock manure produces odor and emits GHGs (CO2, CH4, and N2O) at different stages of production and management practices that have significant environmental concerns. Thus, it is important to measure GHG contributions from different sources and develop appropriate mitigation strategies for minimizing GHG contribution from livestock production facilities. Two dietary protein levels (12 and 16%) fed to beef steers in pens with or without corn stover bedding were studied. The results indicated that dietary protein levels and bedding vs. no bedding had very little effect on GHG emissions and manure composition under open feedlot conditions in North Dakota climatic conditions and management practices. 相似文献
2.
Intensive beef production has increased during recent decades in Brazil and may substantially increase both methane (CH 4) and nitrous oxide (N 2O) emissions from manure management. However, the quantification of these gases and methods for extrapolating them are scarce in Brazil. A case study examines CH 4 and N 2O emissions from one typical beef cattle feedlot manure management continuum in Brazil and the applicability of Manure-DNDC model in predicting these emissions for better understand fluxes and mitigation options. Measurements track CH 4 and N 2O emissions from manure excreted in one housing floor holding 21 animals for 78 days, stockpiled for 73 days and field spread (360 kg N ha ?1). We found total emissions (CH 4 + N 2O) of 0.19 ± 0.10 kg CO 2eq per kg of animal live weight gain; mostly coming from field application (73%), followed housing (25%) and storage (2%). The Manure-DNDC simulations were generally within the statistical deviation ranges of the field data, differing in ?28% in total emission. Large uncertainties in measurements showed the model was more accurate estimating the magnitude of gases emissions than replicate results at daily basis. Modeled results suggested increasing the frequency of manure removal from housing, splitting the field application and adopting no-tillage system is the most efficient management for reducing emissions from manure (up to about 75%). Since this work consists in the first assessment under Brazilian conditions, more and continuous field measurements are required for decreasing uncertainties and improving model validations. However, this paper reports promising results and scientific perceptions for the design of further integrated work on farm-scale measurements and Manure-DNDC model development for Brazilian conditions. 相似文献
3.
Energy supply utilities release significant amounts of greenhouse gases (GHGs) into the atmosphere. It is essential to accurately estimate GHG emissions with their uncertainties, for reducing GHG emissions and mitigating climate change. GHG emissions can be calculated by an activity-based method (i.e., fuel consumption) and continuous emission measurement (CEM). In this study, GHG emissions such as CO 2, CH 4, and N 2O are estimated for a heat generation utility, which uses bituminous coal as fuel, by applying both the activity-based method and CEM. CO 2 emissions by the activity-based method are 12–19% less than that by the CEM, while N 2O and CH 4 emissions by the activity-based method are two orders of magnitude and 60% less than those by the CEM, respectively. Comparing GHG emissions (as CO 2 equivalent) from both methods, total GHG emissions by the activity-based methods are 12–27% lower than that by the CEM, as CO 2 and N 2O emissions are lower than those by the CEM. Results from uncertainty estimation show that uncertainties in the GHG emissions by the activity-based methods range from 3.4% to about 20%, from 67% to 900%, and from about 70% to about 200% for CO 2, N 2O, and CH 4, respectively, while uncertainties in the GHG emissions by the CEM range from 4% to 4.5%. For the activity-based methods, an uncertainty in the Intergovernmental Panel on Climate Change (IPCC) default net calorific value (NCV) is the major uncertainty contributor to CO 2 emissions, while an uncertainty in the IPCC default emission factor is the major uncertainty contributor to CH 4 and N 2O emissions. For the CEM, an uncertainty in volumetric flow measurement, especially for the distribution of the volumetric flow rate in a stack, is the major uncertainty contributor to all GHG emissions, while uncertainties in concentration measurements contribute a little to uncertainties in the GHG emissions. Implications:Energy supply utilities contribute a significant portion of the global greenhouse gas (GHG) emissions. It is important to accurately estimate GHG emissions with their uncertainties for reducing GHG emissions and mitigating climate change. GHG emissions can be estimated by an activity-based method and by continuous emission measurement (CEM), yet little study has been done to calculate GHG emissions with uncertainty analysis. This study estimates GHG emissions and their uncertainties, and also identifies major uncertainty contributors for each method. 相似文献
4.
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
5.
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.
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
8.
In Canada approximately 45% of ammonia (NH 3) emissions are attributed to dairy and beef cattle industries. The present study focused on NH 3 emissions from a beef feedlot with a one-time capacity of 17,220 head. The aim was to improve the Canadian NH 3 emission inventories and air quality forecasting capabilities. A Cessna 207, equipped with a fast-response NH 3/NO y detector and a quadrupole aerosol mass spectrometer, was flown in a grid pattern covering an area of 8 × 8 km centered on a feedlot (800 × 800 m) at altitudes ranging from 30 to 300 m above ground. Stationary ground measurements of NH 3 concentration and turbulence parameters were made downwind of the feedlot. Three flights were conducted under varying meteorological conditions, ranging from very calm to windy with near-neutral stratification. NH 3 mixing ratios up to 100 ppbv were recorded on the calm day, up to 300 m above ground. An average feedlot NH 3 emission rate of 76 ± 4 μg m ?2 s ?1 (equivalent to 10.2 g head ?1 h ?1) was estimated. Characteristics of the measured NH 3 plume were compared to those predicted by a Lagrangian dispersion model. The spatially integrated pattern of NH 3 concentrations predicted and measured agreed but the measured was often more complex than the predicted spatial distribution. The study suggests that the export of NH 3 through advection accounted for about 90% of the emissions from the feedlot, chemical transformation was insignificant, and dry deposition accounted for the remaining 10%. 相似文献
9.
Soilless culture systems offer an environmentally friendly and resource-efficient alternative to traditional cultivation systems fitting within the scheme of a circular economy. The objective of this research was to examine the sustainable integration of recycling fertilizers in hydroponic cultivation—creating a nutrient cycling concept for horticultural cultivation. Using the nutrient film technique (NFT), three recycling-based fertilizer variants were tested against standard synthetic mineral fertilization as the control, with 11 tomato plants (Solanum lycopersicum L. cv. Pannovy) per replicate (n = 4) and treatment: two nitrified urine-based fertilizers differing in ammonium/nitrate ratio (NH4+:NO3?), namely (1) “Aurin” (AUR) and (2) “Crop” (CRO); as well as (3) an organo-mineral mixture of struvite and vinasse (S+V); and (4) a control (NPK). The closed chamber method was adapted for gas fluxes (N2O, CH4, and CO2) from the root zone. There was no indication in differences of the total shoot biomass fresh matter and uptake of N, P and K between recycling fertilizers and the control. Marketable fruit yield was comparable between NPK, CRO and S+V, whereas lower yields occurred in AUR. The higher NH4+:NO3? of AUR was associated with an increased susceptibility of blossom-end-rot, likely due to reduced uptake and translocation of Ca. Highest sugar concentration was found in S+V, which may have been influenced by the presence of organic acids in vinasse. N2O emissions were highest in S+V, which corresponded to our hypothesis that N2O emissions positively correlate with organic-C input by the fertilizer amendments. Remaining treatments showed barely detectable GHG emissions. A nitrified urine with a low NH4+:NO3– (e.g., CRO) has a high potential as recycling fertilizer in NFT systems for tomato cultivation, and S+V proved to supply sufficient P and K for adequate growth and yield. Alternative cultivation strategies may complement the composition of AUR. 相似文献
10.
In this paper the authors have estimated for 1990 and 1995 the inventory of greenhouse gases CO 2, CH 4 and N 2O for India at a national and sub-regional district level. The district level estimates are important for improving the national inventories as well as for developing sound mitigation strategies at manageable smaller scales. Our estimates indicate that the total CO 2, CH 4 and N 2O emissions from India were 592.5, 17, 0.2 and 778, 18, 0.3 Tg in 1990 and 1995, respectively. The compounded annual growth rate (CAGR) of these gases over this period were 6.3, 1.2 and 3.3%, respectively. The districts have been ranked according to their order of emissions and the relatively large emitters are termed as hotspots. A direct correlation between coal consumption and districts with high CO 2 emission was observed. CO 2 emission from the largest 10% emitters increased by 8.1% in 1995 with respect to 1990 and emissions from rest of the districts decreased over the same period, thereby indicating a skewed primary energy consumption pattern for the country. Livestock followed by rice cultivation were the dominant CH 4 emitting sources. The waste sector though a large CH 4 emitter in the developed countries, only contributed about 10% the total CH 4 emission from all sources as most of the waste generated in India is allowed to decompose aerobically. N 2O emissions from the use of nitrogen fertilizer were maximum in both the years (more than 60% of the total N 2O). High emission intensities, in terms of CO 2 equivalent, are in districts of Gangetic plains, delta areas, and the southern part of the country. These overlap with districts with large coal mines, mega power plants, intensive paddy cultivation and high fertilizer use. The study indicates that the 25 highest emitting districts account for more than 37% of all India CO 2 equivalent GHG emissions. Electric power generation has emerged as the dominant source of GHG emissions, followed by emissions from steel and cement plants. It is therefore suggested, to target for GHG mitigation, the 40 largest coal-based thermal plants, five largest steel plants and 15 largest cement plants in India as the first step. 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.
Abstract The objective of this study was to obtain diurnal variation profiles of odor and gas (ammonia [NH 3], hydrogen sulfide [H 2S], carbon dioxide [CO 2]) concentrations and emission rate (OGCER) from confined swine grower/finisher rooms under three typical weather conditions (warm, mild, and cold weather) in a year. Two grower/finisher rooms, one with a fully slatted floor and the other with partially slatted floors, were measured for 2 consecutive days under each weather condition. The results revealed that the diurnal OGCER in the room with a fully slatted floor was 9.2–39.4% higher than that with a partially slatted floor; however, no significant differences in the diurnal OGCER were found between these two rooms, except for the NH 3 concentrations in August, the NH 3 and H 2S concentrations and emissions in October, and odor concentrations and emissions in February ( p > 0.05). The OGCER variations presented different diurnal patterns as affected by time of day, season, type of floor, ventilation rate, animal growth cycles, in-house manure storage, and weather conditions. Significant diurnal fluctuations in the OGCER (except for the odor concentrations and H 2S emissions) were observed in August ( p < 0.05); all of the gas emissions in October and the CO 2 concentrations and emissions in February also showed significant diurnal variations ( p < 0.05). These significant diurnal variations indicated that the OGCER during different periods of a day should be monitored when quantifying OGCER concentrations and emissions; for example, source emission data used in air dispersion modeling to decrease the great incertitude of setback determination using randomly measured data. 相似文献
13.
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
14.
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
15.
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
16.
To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH 4, CO 2 and N 2O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH 4 uptake, CO 2 and N 2O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO 2 and N 2O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO 2 and N 2O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO 2 and N 2O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers. 相似文献
17.
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
18.
In this research, in order to develop technology/country-specific emission factors of methane (CH 4) and nitrous oxide (N 2O), a total of 585 samples from eight gas-fired turbine combined cycle (GTCC) power plants were measured and analyzed. The research found that the emission factor for CH 4 stood at “0.82 kg/TJ”, which was an 18 % lower than the emission factor for liquefied natural gas (LNG) GTCC “1 kg/TJ” presented by Intergovernmental Panel on Climate Change (IPCC). The result was 8 % up when compared with the emission factor of Japan which stands at “0.75 kg/TJ”. The emission factor for N 2O was “0.65 kg/TJ”, which is significantly lower than “3 kg/TJ” of the emission factor for LNG GTCC presented by IPCC, but over six times higher than the default N 2O emission factor of LNG. The evaluation of uncertainty was conducted based on the estimated non-CO 2 emission factors, and the ranges of uncertainty for CH 4 and N 2O were between ?12.96 and +13.89 %, and ?11.43 and +12.86 %, respectively, which is significantly lower than uncertainties presented by IPCC. These differences proved that non-CO 2 emissions can change depending on combustion technologies; therefore, it is vital to establish country/technology-specific emission factors. 相似文献
19.
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
20.
ABSTRACT This study presents a novel method for integrating the output of a microscopic emission modeling approach with a regional traffic assignment model in order to achieve an accurate greenhouse gas (GHG, in CO 2-eq) emission estimate for transportation in large metropolitan regions. The CLustEr-based Validated Emission Recalculation (CLEVER) method makes use of instantaneous speed data and link-based traffic characteristics in order to refine on-road GHG inventories. The CLEVER approach first clusters road links based on aggregate traffic characteristics, then assigns representative emission factors (EFs), calibrated using the output of microscopic emission modeling. In this paper, cluster parameters including number and feature vector were calibrated with different sets of roads within the Greater Toronto Area (GTA), while assessing the spatial transferability of the algorithm. Using calibrated cluster sets, morning peak GHG emissions in the GTA were estimated to be 2,692 tons, which is lower than the estimate generated by a traditional, average speed approach (3,254 tons). Link-level comparison between CLEVER and the average speed approach demonstrates that GHG emissions for uncongested links were overestimated by the average speed model. In contrast, at intersections and ramps with more congested links and interrupted traffic flow, the average speed model underestimated GHG emissions. This proposed approach is able to capture variations in traffic conditions compared to the traditional average speed approach, without the need to conduct traffic simulation. Implications: A reliable traffic emissions estimate is necessary to evaluate transportation policies. Currently, accuracy and transferability are major limitations in modeling regional emissions. This paper develops a hybrid modeling approach (CLEVER) to bridge between computational efficiency and estimation accuracy. Using a k-means clustering algorithm with street-level traffic data, CLEVER generates representative emission factors for each cluster. The approach was validated against the baseline (output of a microscopic emission model), demonstrating transferability across different cities . 相似文献
|