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1.
全球气候变化引起的中高纬度地区积雪覆盖和降雪格局变化,造成该区域土壤冻融交替强度和频次变化,是土壤氮循环的重要影响因素。冻融温差和冻融循环次数影响微生物数量和群落的变化,进而影响土壤氮素生物地球化学循环。以大伙房水库实验林场小流域的河岸缓冲带生态系统为研究对象,通过分析冻融交替对河岸缓冲带土壤无机氮和土壤微生物量氮的影响,阐明冻融交替对土壤无机氮含量变化的影响机制,为评估小流域氮素流失风险提供依据。结果表明：随着冻融循环次数的增加,土壤无机氮含量呈增加趋势;不同温差的冻融循环处理对土壤无机氮影响不同,冻融条件为-5/+5℃和-20/+5℃时土壤无机氮含量在冻融循环10次之后分别为34.9±0.9 mg/kg和37.2±0.8 mg/kg,是处理前的1.21和1.41倍;冻融温差和冻融循环次数对土壤NH4+–N含量有极显著影响(P<0.01),土壤冻融10次后土壤NH4+–N含量是对照处理的4-10倍;冻融循环次数对土壤NO3－–N含量有显著影响(P<0.05),冻融温差对NO3－–N含量无显著影响(P>0.05);土壤微生物量氮含量对冻融循环的响应显著(P<0.01)。可见,冻融交替显著增加了土壤无机氮含量,由于早春季节植被对无机氮吸收较少,可能增大土壤氮素随冰雪融化的淋溶流失风险。  相似文献   

2.
Dry deposition of reduced nitrogen   总被引：2，自引：0，他引：2  
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3.
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4.
To quantitatively address the role of tissue N in crop respiration under various agricultural practices, and to consequently evaluate the impact of synthetic fertilizer N application on biomass production and respiration, and hence net carbon fixation efficiency （Encf）, pot and field experiments were carried out for an annual rotation of a rice-wheat cropping system from 2001 to 2003. The treatments of the pot experiments included fertilizer N application, sowing date and planting density. Different rates of N application were tested in the field experiments. Static opaque chambers were used for sampling the gas. The respiration as CO2 emission was detected by a gas chromatograph. A successive biomass clipping method was employed to determine the crop autotrophic respiration coefficient （Ra）. Results from the pot experiments revealed a linear relationship between Ra and tissue N content as Ra = 4.74N-1.45 （R^2= 0.85, P 〈 0.001）. Measurements and calculations from the field experiments indicated that fertilizer N application promoted not only biomass production but also increased the respiration of crops. A further investigation showed that the increase of carbon loss in terms of respiration owing to fertilizer N application exceeded that of net carbon gain in terms of aboveground biomass when fertilizer N was applied over a certain rate. Consequently, the Encf declined as the N application rate increased.  相似文献   

5.
人工湿地污水处理系统对氮磷的净化效果研究   总被引：2，自引：1，他引：1       下载免费PDF全文
人工湿地是一种新型的污水处理工艺。以沈阳市浑南新区人工湿地示范工程为研究对象,分析了人工湿地污水处理系统对氮磷的净化效果,探讨了垂直流湿地系统以及自由表面流湿地系统对氮磷的净化机理。结果表明:垂直流湿地对总氮有一定的净化效果,但稳定性较差。氨氮和总磷的去除率在运行期间始终保持较高水平,平均去除率分别为97.75%和81.03%;表面流湿地对总氮的净化受温度影响,湿地植物对氮磷的净化受生长环境和季节的影响。  相似文献   

6.
Direct measurements of nitrogen oxides and ozone fluxes over grassland   总被引：1，自引：0，他引：1  
Using the eddy correlation method, fluxes of nitric oxide, nitrogen dioxide, ozone, water, and sensible heat were measured at a site 20 km north of Denver, Colorado over mature crested wheat grass, 0.75 m high in late June and early July. During this period the weather was fair with no synoptic disturbances. In the early morning a well-mixed diluted urban pollution plume traversed the site, by late morning aged pollution had mixed downward into the local boundary layer, and by afternoon the air came from a relatively unpolluted area of the high plains. The mean trace gas concentrations reflect this repeated pattern of local air flow. The fluxes of the trace gases were influenced both by the variation of the means and by other factors including temperature and biological activity. Ozone fluxes were found to be always negative and proportional to the mean, with an average deposition velocity for this case of about 0.006 m s-1. For the oxides of nitrogen this simple treatment was not appropriate. Both deposition and emission were observed, generally deposition predominated in the morning and emission in the afternoon with observed variations in the fluxes of NOx=NO+NO2 from –0.3 to +0.2 ppbv m s-1.The National Center for Atmospheric Research is sponsored by the National Science Foundation  相似文献   

7.
Soluble organic nitrogen in Venezuelan rains   总被引：2，自引：0，他引：2  
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8.
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9.
Nitrogen compounds are produced by biological reactions and by industrial processes from the abundant nitrogen gas (N2) in the atmosphere. The formation of compounds from atmospheric nitrogen is called fixation. In nature, nitrogen compounds undergo many conversions, but under aerobic conditions, characterized by the presence of oxygen, they tend to be converted to the nitrate (NO 3 - ) form. Under anaerobic conditions, characterized by the absence of oxygen, the nitrate is denitrified, and the nitrogen contained therein is converted into nitrogen gas (N2) and nitrous oxide (N2O), which escape into the atmosphere. The nitrous oxide diffuses into the stratosphere, where it decomposes to yield nitrogen gas and small amounts of nitric oxide (NO) and nitrogen dioxide (NO2), which react with ozone (O3) to convert it to oxygen (O2). The ozone in the stratosphere is produced by the reaction of light with oxygen and is destroyed primarily by reactions with the nitrogen oxides.As long as the production and destruction are equal, the ozone in the stratosphere is maintained at a constant concentration. Increased nitrogen fixation will lead to increased denitrification, increased amount of nitrous oxide moving into the stratosphere, and a reduction in ozone concentration.Ozone in the stratosphere attenuates the ultraviolet light received from the sun. As the ozone concentration decreases, more ultraviolet light will reach the surface of the earth. The fear is that this additional radiation will have detrimental effects on living organisms and possibly on the climate.Because the global use of fixed nitrogen in fertilizers has increased greatly in recent years and in 1974 amounted to almost 40 million metric tons, the eventual generation of nitrous oxide from the fertilizer nitrogen after application to the soil has been cited as a potential environmental hazard. In response to this concern, this document estimates nitrogen fixation, nitrous oxide production, and ozone reduction based on two methods of calculation and on various increases in nitrogen fixation. Uncertainties and information gaps in the nitrogen cycle are pointed out.This document does not review either the projected biological effects of ozone depletion or the stratospheric chemistry of ozone. These topics are dealt with at length in other studies.World fixation of nitrogen in 1974, expressed in millions of metric tons per year (MT/yr), was estimated to be as follows.Most of the estimates given are based on inadequate data; consequently, actual amounts may be significantly different from those shown. The study of nitrogen fixed in the oceans has not progressed far enough to permit reliable estimates. However, estimates of the amount of nitrogen fixed for fertilizer and other industrial uses in 1974 are considered reliable. The trend of industrial fixation of nitrogen offers some indication of the trend in total amount of nitrogen fixed. It is estimated that 174 MT of nitrogen were fixed by all processes in 1950. Total fixation in 1850 could have been 150 MT of nitrogen.Nitrous oxide-nitrogen production on land is estimated as 5 to 10 MT/yr; published estimates of production in the ocean, however, range from less than 1 to 100 MT/yr. The higher value was based on reported supersaturation of ocean waters with nitrous oxide.Two methods of estimating the decrease in ozone concentration in the stratosphere were used. Method I is based on nitrogen fixation. It involves the assumptions that the relative increase in production of nitrous oxide is proportional to the relative increase in total nitrogen fixation and that sufficient time has elapsed for the rate of denitrification to come to equilibrium with fixation; i.e., the lag time between increased fixation and increased denitrification has passed. This method, using fixation estimated for 1950 as a base, suggests that the reduction in ozone would be 5.8 and 11.5% as a consequence of increased fixation of 50 and 100 MT of nitrogen per year, respectively.Method II is based on nitrous oxide evolution. It involves the assumption that the global rate of production of nitrous oxide is 100 MT/yr (based on supersaturation of this gas in the ocean and on changes in measured concentrations of nitrous oxide in the atmosphere). Method II leads to estimates of ozone reduction much lower than those from Method I. For example, on the assumption that global production of nitrous oxide-nitrogen is 100 MT/yr and that 5% of the nitrogen denitrified is released as nitrous oxide, the estimated ozone reduction is 1% with an increase of 100 MT/yr in nitrogen fixation. This method is forced to assume an unknown source of nitrous oxide in the ocean and an unknown sink for nitrous oxide in the troposphere.There are great uncertainties in many of the estimates that have been made for nitrogen fixation and for nitrous oxide production, and there are many information gaps that need to be filled before the question of the effects of increased nitrogen fixation on the ozone layer can be answered. Perhaps the biggest information needs are in the areas of nitrogen transformations and the quantities of nitrous oxide produced in the ocean. Other needs deal with the complexities of the nitrogen cycle on land. The lag time between fixation by various processes and denitrification must be known as a basis for estimating how soon predicted effects based on equilibrium conditions can be expected. Concentrations of nitrous oxide and their fluctuations in the troposphere (lower atmosphere) need to be monitored to provide an index to variations and increases in production. Improved models are needed to relate the ozone concentration in the stratosphere to nitrogen fixation and nitrous oxide production on earth.In spite of the uncertainties in the predictions of the effects of increased fixation of nitrogen on stratospheric ozone, the potential hazard is sufficiently serious that, in addition to research on the various phases of the global nitrogen cycle that impinge upon the nitrous oxide-ozone question, research on the efficiency of use of all fixed forms of nitrogen should be worthwhile. Editor's Note: Although the data for sources, sinks, reservoirs, and rate processes in this article are undergoing rapid revision presently, it, nonetheless, is one of the clearest statements of the physics, chemistry, and biology of the fertilizer/ozone problem available to date.This report was developed by eleven scientists (see Appendix 1 for names and affiliations) representing the subject matter areas of atmospheric chemistry, chemical engineering, environmental science and chemistry, microbiology, oceanography, plant genetics, soil biochemistry, soil physics, and soil chemistry. This task force of scientists chaired by Parker F. Pratt, met under the auspices of the Council for Agricultural Science and Technology (CAST), whose headquarters office is at the Department of Agronomy, Iowa State University, Ames, Iowa 50011, U.S.A. The task force met in Denver, Colorado from October 23 to 25, 1975, to prepare a first draft of the report. The chairman then prepared a revised version and returned it to members of the task force for review and comment. A second revision was then prepared and returned for further comment. Finally, the report was edited and reproduced for transmittal through the U.S. Congressional Committees concerned with the matter of ozone depletion. It was originally issued as a CAST Report Number 53, January, 1976, but had not been formally published heretofore.  相似文献   

10.
In the present study, the wet and dry depositions of particulate NO3−, SO42−, Cl− and NH4+ were measured using a wet/dry sampler as a surrogate surface. Gas phase compounds of nitrogen, sulfur and chloride (HNO3, NH3, SO2 and HCl) were measured by an annular denuder system (ADS) equipped with a back up filter for the collection of particles with diameter ≤ 5 μm. Ambient concentrations of NO, NO2 and SO2 were also taken into consideration. Sampling was conducted at an urban site in the center of the city of Thessaloniki, northern Greece. The presence of the aerosol species was examined by cold/warm period and the possible compounds in dry deposits were also considered. Dry deposition fluxes were found to be well correlated with ambient particle concentrations in order to be used for the calculation of particle deposition velocity. Average particulate deposition velocities calculated were 0.36, 0.20, 0.20 and 0.10 cm s− 1 for Cl−, NO3−, SO42− and NH4+, respectively. Total dry deposition fluxes (gas and particles) were estimated at 3.24 kg ha− 1 year− 1 for chloride (HCl + p-Cl), 9.97 kg ha− 1 year− 1 for nitrogen oxidized (NO + NO2 + HNO3 + p-NO3), 5.32 kg ha− 1 year− 1 for nitrogen reduced (NH3 + p-NH4) and 15.77 kg ha− 1 year− 1 for sulfur (SO2 + p-SO4). 70–90% total dry deposition was due to gaseous species deposition. The contribution of dry deposition to the total (wet + dry) was at the level of 60–70% for sulfur and nitrogen (oxidized and reduced), whereas dry chloride deposition contributed 35% to the total. The dry-to-wet deposition ratio of all the studied species was found to be significantly associated with the precipitation amount, with nitrogen species being better and higher correlated. Wet, dry and total depositions measured in Thessaloniki, were compared with other countries of Europe, US and Asia.  相似文献   

11.
南京郊区大气氮化物浓度和氮沉降通量的研究   总被引：12，自引：0，他引：12  
为研究南京郊区的大气氮化物污染状况,进而估算其大气氮沉降通量,2005年6月-2006年5月在南京大学浦口校区气象园进行了大气、气溶胶和雨水样本的收集,同步进行近地面气象观测.在实验室分析大气氮化物NOx、NH3和有机氮浓度、总悬浮颗粒物(TSP)中硝酸盐、亚硝酸盐、铵盐和有机氮的质量浓度、雨水中NO-3、NO-2、NH+4离子和有机氮的质量浓度,利用气象资料和大叶阻力相似模型计算大气氮化物的干沉降速度,进而定量估算大气氮沉降通量.研究结果表明:南京郊区大气中有机氮浓度水平较高,无机氮(氨态氮和硝态氮)浓度水平较低.大气氮沉降量较大,且湿沉降和有机沉降贡献率占主导地位,这取决于本地区的下垫面和污染状况,同时也与气象条件有密切关系.  相似文献   

12.
In summer, atmospheric ozone was measured from an aircraft platform simultaneously with nitric oxide (NO), oxides of nitrogen (NO y ), and water vapor over the Pacific Ocean in east Asia from 34° N to 19° N along the longitude of 138±3°E. NO y was measured with the aid of a ferrous sulfate converter. The altitude covered was from 0.5 to 5 km. A good correlation in the smoothed meridional distributions between ozone and NO y was seen. In particular, north of 25° N, ozone and NO y mixing ratios were considerably higher than those observed in tropical marine air south of 25° N. NO y and O3 reached a minimum of 50 pptv and 4 ppbv respectively in the boundary layer at a latitude of 20° N. The NO concentration between 2 and 5 km at the same latitude was 30 pptv. The profiles of ozone and water vapor mixing ratios were highly anti-correlated between 25° N and 20° N. In contrast, it was much poorer at the latitude of 33° N, suggesting a net photochemical production of ozone there.  相似文献   

13.
为了探讨膜下滴灌棉花水肥耦合效应,于2003-2004年在新疆北疆雨水较少地区开展不同水氮条件对棉花产量效应的大田试验研究。结果表明,在该试验条件下,土壤水分对产量的作用最大,氮肥次之;水氮耦合的产量效应表现为适宜土壤水分中施肥量效果最高,高土壤水分中施肥量次之,低土壤水分低施氮量最低;水氮交互大小的顺序是水氮耦合＞土壤水分＞施氮量;获得最高籽棉产量5253kg/hm2的灌水量为4190m3/hm2,施氮量为276kg/hm2。  相似文献   

14.
The kinetics of the reaction of NO2 with O3 have been investigated at 296 K, using UV absorption spectroscopy to monitor decay of NO2 or O3 and infrared laser absorption spectroscopy to monitor formation of the reaction product N2O5. The results both for the rate coefficient at 296 K (k 1=3.5×10-17 cm3 molecule-1 s-1) and the reaction stoichiometry (NO2/O3=1.85±0.09) are in good agreement with previous studies, confirming that the two step mechanism involving formation of symmetrical NO3 as an intermediate is predominant.% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOtaiaab+% eadaWgaaWcbaGaaeOmaaqabaGccqGHRaWkcaqGpbWaaSbaaSqaaiaa% bodaaeqaaOWaa4ajaSqaaaqabOGaayPKHaGaaeOtaiaab+eadaWgaa% WcbaGaae4maaqabaGccqGHRaWkcaqGpbWaaSbaaSqaaiaabkdaaeqa% aaaa!41D7!\[{\text{NO}}_{\text{2}} + {\text{O}}_{\text{3}} \xrightarrow{{}}{\text{NO}}_{\text{3}} + {\text{O}}_{\text{2}} \]% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOtaiaab+% eadaWgaaWcbaGaae4maaqabaGccqGHRaWkcaqGobGaae4tamaaBaaa% leaacaqGYaaabeaakiabgUcaRiaab2eadaGdKaWcbaaabeGccaGLsg% cacaqGobWaaSbaaSqaaiaabkdaaeqaaOGaae4tamaaBaaaleaacaqG% 1aaabeaakiabgUcaRiaab2eaaaa!4464!\[{\text{NO}}_{\text{3}} + {\text{NO}}_{\text{2}} + {\text{M}}\xrightarrow{{}}{\text{N}}_{\text{2}} {\text{O}}_{\text{5}} + {\text{M}}\]A possible minor role for the unsymmetrical ONOO species is suggested to account for the lower-than-expected stoichiometry factor. The importance of this reaction in the oxidation of atmospheric NO2 is discussed.  相似文献   

15.
干旱和复水对羊草碳氮分配的影响   总被引：1，自引：0，他引：1  
植物的碳氮营养及其相互关系是最重要的基本生物过程之一,阶段性干旱对植物碳氮分配的影响研究甚少。实验以中国北方草原的典型植物羊草为材料,研究不同干旱持续期复水对羊草碳氮含量、分配及其相互关系的影响。结果表明:短期和中期干旱使植株生物量、氮素水平和单株总氮量增加,但长期干旱使之降低。水分处理对碳含量的影响不显著。干旱后复水降低了各器官特别是绿叶的碳氮比。中度持续干旱的氮素利用率(NUE)最高、短期干旱最低。羊草各器官氮素绝对量占整株的百分比从大到小依次为:绿叶、根茎、根、枯叶和茎鞘,其中叶片的氮素总量占植株的一半以上;随着干旱持续期的增加,氮素对根部的投资亦加大。羊草受到适当干旱驯化后复水引发的超补偿作用可促进羊草植株生长、提高氮素水平,并在一定程度上通过碳氮分配的调节作用来适应于阶段性的干旱胁迫。  相似文献   

16.
有机碳氮是影响陆地生态系统的重要因子,保持并提高土壤碳氮储量,是稳定生态系统生产力的关键.以南京紫金山土壤为研究对象,依照海拔高度进行采样,对比分析了土壤有机碳氮的变化规律.研究结果表明:紫金山土壤有机碳氮受地表植被的影响比较大,混交林>林地>草地,土壤有机碳氮总量随海拔的升高呈现上升趋势,土壤碳氮比高达34~45,且随海拔升高呈下降趋势.相关分析表明,紫金山土壤有机碳与全氮质量分数呈显著正相关关系,由此说明氮素主要以有机氮的形式存在于有机质中.  相似文献   

17.
The release of excessive anthropogenic nitrogen contributes to global climate change, biodiversity loss, and the degradation of ecosystem services. Despite being an urgent global problem, the excess nitrogen is not governed globally. This paper considers possible governance options for dealing with excessive nitrogen through target setting, which is an approach commonly adopted to address global environmental problems. The articulation of the nitrogen problem and the numerous international institutions dealing with it, provide evidence of a nitrogen regime characterised by limited coordination and targets covering sources and impacts only partially. This calls for improving the nitrogen governance in the direction of more integrated approaches at the global scale. In this vein, the paper investigates two opposite governance options – here labelled as ‘holistic’ and ‘origin-based’ – and evaluates them for their capability to define solutions and targets for human-induced nitrogen. From the analysis, it emerges that origin-based solutions can be preferable to holistic solutions as they can be more specific and potentially have greater immediate results. Independent from which governance arrangement is chosen, what matters most is the speed at which an arrangement can deploy solutions to combat (fast-growing) nitrogen pollution.  相似文献   

18.
Surface ozone, NO, NO2, and NO x were measured at a coastal site (Shihua) and a nearby inland site (Zhujing) in suburban Shanghai for the whole year of 2009. More days with ozone pollution in a longer time range were observed at the coastal site than the inland site. The diurnal variations of NO x concentrations were obviously higher at Zhujing station, while those of ozone concentrations were higher at Shihua station, indicating their different air pollution conditions. Coastal wind has significant influence on the levels and characteristics of the air pollutants. The ozone concentrations during maritime winds (MW) were much higher than those during continental winds (CW) at each of the site, while the NO and NO2 concentrations were both opposite. The ozone concentrations at Shihua station were much higher than those at Zhujing station, while the NO and NO2 concentrations were both opposite. The ozone concentrations at both of the two sites showed a distinct “weekend effects” and “weekdays effects” patterns during CW and MW, respectively. Correlation analysis of the pollutants showed that, the compounds during MW were more age than those during CW, and the compounds at Shihua were more age than those at Zhujing. The air pollutions at both of the two sites are mainly associated with the pollutants emitted in this region instead of long range transport.  相似文献   

19.
Abstract

Changes to the Beaufort Sea shoreline occur due to the impact of storms and rising relative sea level. During the open‐water season (June to October), storm winds predominantly from the north‐west generate waves and storm surges which are effective in eroding thawing ice‐rich cliffs and causing overwash of gravel beaches. Climate change is expected to be enhanced in Arctic regions relative to the global mean and include accelerated sea‐level rise, more frequent extreme storm winds, more frequent and extreme storm surge flooding, decreased sea‐ice extent, more frequent and higher waves, and increased temperatures. We investigate historical records of wind speeds and directions, water levels, sea‐ice extent and temperature to identify variability in past forcing and use the Canadian Global Coupled Model ensembles 1 and 2 (CGCM1 and CGCM2) climate modelling results to develop a scenario forcing future change of Beaufort Sea shorelines. This scenario and future return periods of peak storm wind speeds and water levels likely indicate increased forcing of coastal change during the next century resulting in increased rates of cliff erosion and beach migration, and more extreme flooding.  相似文献   

20.
研究了在高氮/低氧混合气氛下热处理(500~700 ℃)对AlN(氮化铝)粉体表面特性及粉体抗水解性能的影响.实验结果表明：在高氮/低氧混合气氛保护下的AlN粉末表面覆盖了氧化铝薄膜层结构,有效地抑制了AlN与水的反应,阻碍了水分子向AlN粉末表面侵蚀的作用,提高了AlN粉末在潮湿环境中的抗水化能力,且热处理后粉末在水溶液中高剪切应力球磨过程中具有非常好的稳定性.  相似文献   

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