Simulating methane emission from a Chinese rice field as influenced by fertilizer and water level     

Z. Yu  X. Shangguan  D. Pollard  E. J. Barron 《水文研究》2003,17(17):3485-3501

Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH₄). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Hard X-ray spectrum of Mkn 421 during the active phase     

R. K. Manchanda 《Journal of Astrophysics and Astronomy》2001,22(2-3):145-154

Spectral measurement of Mkn 421 were made in the hard X-ray energy band of 20–200 keV using a high sensitivity, large area scintillation counter telescope on November 21, 2000 and these coincided with the onset of an active X-ray phase as seen in the ASM counting rates on board RXTE. The observed spectrum can not be fitted to a single power law similar to the PDS data of BeppoSAX. The data can be fitted both by a two component power-law function or a combination of an exponential function with a power law component at the high energies above 80 keV. We identify these components with those arising from the synchrotron self compton and the high energy power-law tail arising from the upgrading of the thermal photons due to multiple Compton scattering a la Cyg X-1. A comparison with the earlier data clearly suggests a spectral variability in the hard X-ray spectrum of the source. We propose a continuously flaring geometry for the source as the underlying mechanism for energy release.  相似文献   

Solar radio burst (type III)     

Hari Om Vats  M. R. Deshpande  K. N. Iyer  Tetsuro Kondo  Takeshi Isobe 《Astrophysics and Space Science》1996,243(1):251-254

This article describes the observations of a type III radio burst observed at 103 MHz simultaneously by the two radio telescopes situated at Rajkot (22.3°N, 70.7°E) and Thaltej (23°N, 72.4°E). This event occurred on September 30, 1993 at about 0430 UT and lasted for only half a minute. The event consisted of several sharp spikes in a group. The rise and fall time of these are comparable, however the peaks of individual spikes varied by a factor of four. The comparison of these observations with the data of solar radio spectrograph HiRAS indicates that this was a metric radio burst giving highest emission at about 103 MHz.  相似文献   

电感耦合等离子体发射光谱法同时测定玻璃中铝钙铁钾镁钠钛硫   总被引：2，自引：2，他引：0  

杜米芳 《岩矿测试》2008,27(2):146-148

通过选择分析谱线、处理样品方法和消除干扰因素等实验,建立了电感耦合等离子体发射光谱法同时测定玻璃中的Al2O3、CaO、Fe2O3、K2O、MgO、Na2O、TiO2和SO3的方法,克服了利用常规化学法测定玻璃中各氧化物步骤繁琐、耗时长、工作量大的不足。方法的回收率为95.0%~103.0%,精密度(RSD,n=10)为0.20%~1.72%。方法具有快速、简便、线性范围宽等优点,分析误差满足常规化学分析法的要求。用于钠钙硅玻璃及其制品的分析,结果令人满意。  相似文献   

Recovery of thermohaline circulation under CO₂ stabilization and overshoot scenarios   总被引：1，自引：0，他引：1  

Norikazu. Nakashiki  Dong-Hoon Kim  Frank O. Bryan  Yoshikatsu Yoshida  Daisuke Tsumune  Koki Maruyama  Hideyuki Kitabata 《Ocean Modelling》2006,15(3-4):200

In this study we examine the behavior of the thermohaline circulation, as simulated by the Community Climate System Model version 3 (CCSM3), for several centuries following CO₂ stabilization for the SRES B1 and A1B scenarios and for an “overshoot” scenario in which CO₂ levels temporarily reach the same level as in the A1B scenario before declining to an ultimate stabilization level that is identical to the B1 case. While we find no evidence for irreversible changes of the thermohaline circulation in the overshoot experiment, the interplay of the different timescales of the temperature response of the surface and interior ocean does lead to a number of differences in the long-term response of the ocean between it and the B1 stabilization scenario where the same GHG levels are approached by different paths. The stronger initial warming and its slow penetration into the deeper ocean, followed by a transient surface cooling in the overshoot scenario leads to lower static stability, deeper mixing, and a more rapid recovery of the thermohaline circulation than in the B1 stabilization scenario. While the overshoot scenario recovers surface conditions (e.g. SST, sea ice extent) very similar to the B1 scenario shortly after reaching the same GHG levels, the additional accumulation of heat in the interior ocean during the period of higher forcing causes the global mean ocean temperature and steric sea level to remain higher than in the B1 stabilization scenario for at least another several centuries.  相似文献   

Sustainable shellfish aquaculture in Saldanha Bay,South Africa     

A Santa Marta  JG Ferreira  GC Pitcher  J Lencart e Silva 《African Journal of Marine Science》2020,42(2):151-166

The carrying capacity for bivalve shellfish culture in Saldanha Bay, South Africa, was analysed through the application of the well-tested EcoWin ecological model, in order to simulate key ecosystem variables. The model was set up using: (i) oceanographic and water-quality data collected from Saldanha Bay, and (ii) culture-practice information provided by local shellfish farmers. EcoWin successfully reproduced key ecological processes, simulating an annual mean phytoplankton biomass of 7.5 µg Chl a l^–1 and an annual harvested shellfish biomass of about 3 000 tonnes (t) y^–1, in good agreement with reported yield. The maximum annual carrying capacity of Small Bay was estimated as 20 000 t live weight (LW) of oysters Crassostrea gigas, or alternatively 5 100 t LW of mussels Mytilus galloprovincialis, and for Big Bay as 100 000 t LW of oysters. Two production scenarios were investigated for Small Bay: a production of 4 000 t LW y^–1 of mussels, and the most profitable scenario for oysters of 19 700 t LW y^–1. The main conclusions of this work are: (i) in 2015–2016, both Small Bay and Big Bay were below their maximum production capacity; (ii) the current production of shellfish potentially removes 85% of the human nitrogen inputs; (iii) a maximum-production scenario in both Big Bay and Small Bay would result in phytoplankton depletion in the farmed area; (iv) increasing the production intensity in Big Bay would probably impact the existing cultures in Small Bay; and (v) the production in Small Bay could be increased, resulting in higher income for farmers.  相似文献   

环胶州湾公路海上段汽车尾气的环境影响     

杨三才  徐静琦  竺维丽  洪光  吴玉坤 《中国海洋大学学报(自然科学版)》1993,(1)

对类比路段进行连续模拟试验,进行现场调查,给出汽车尾气主要污染物的排污强度,预测了汽车尾气中CO、C_nH_m和NO_x的扩散范围。  相似文献   

中国海洋交通运输业碳排放效率测度及影响因素分析     

董梦如  韩增林  郭建科 《海洋通报》2020,39(2):169-177

海洋交通运输业碳排放研究对制定行之有效的低碳海洋交通政策具有重要意义。本文首先对2006—2015年中国沿海11个省(区、市)的海洋交通运输业碳排放量进行估算,然后运用超效率SBM模型对碳排放效率进行测度,最后运用Tobit模型探究碳排放效率的影响因素。结果表明:①中国海洋交通运输业碳排放效率整体上处于低效率状态,且各省(区、市)间差异明显,但差异正在逐渐缩小。②2006—2015年沿海各省(区、市)市海洋交通运输业碳排放效率变动呈现出“M”形波动上升趋势。③将各省(区、市)海洋交通运输业碳排放效率水平划分为不同类型,其中上海和天津属于高效率型,河北属于中效率型,其余省(区、市)市属于低效率型。④货运距离和能源结构对海洋交通运输业碳排放效率具有显著的正向作用,而能源强度对其具有显著的负向作用。  相似文献   

The effects of solar and ionospheric parameters on seasonal variation of 6300 Å line emission at Calcutta     

S. K. Midya  R. Chattopadhyay 《Earth, Moon, and Planets》1996,74(2):123-129

The purpose of this paper is to find correlation between OI 6300 Å line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained:

(i)	Solar flare index plays more important role for the emissions of 6300 Å line than other solar parameters.
(ii)	Intensity of 6300 Å line increases linearly with the increase of solar flare index.
(iii)	Virtual height plays more important role than critical frequency for the emission of 6300 Å line-intensity.
(iv)	Possible explanation of this type of variation is also presented.

  相似文献   

Particulate content of savanna fire emissions   总被引：9，自引：0，他引：9  

Hélène Cachier  Catherine Liousse  Patrick Buat-Menard  Annie Gaudichet 《Journal of Atmospheric Chemistry》1995,22(1-2):123-148

As part of the FOS-DECAFE experiment at Lamto (Ivory Coast) in January 1991, various aerosol samples were collected at ground level near prescribed fires or under local background conditions, to characterize the emissions of particulate matter from the burning of savanna vegetation. This paper deals with total aerosol (TPM) and carbon measurements. Detailed trace element and polycyclic hydrocarbon data are discussed in other papers presented in this issue.Near the fire plumes, the aerosols from biomass burning are primarily of a carbonaceous nature (C%70% of the aerosol mass) and consist predominantly of submicron particles (more than 90% in mass.) They are characterized by their organic nature (black to total carbon ratio Cb/Ct in the range 3–20%) and their high potassium content (K/Cb0.6). These aerosols undergo aging during their first minutes in the atmosphere causing slight alterations in their size distribution and chemical composition. However, they remain enriched in potassium (K/Cb=0.21) and pyrene, a polycyclic aromatic hydrocarbon, such that both of these species may be used as tracers of savanna burning aerosols. We show that during this period of the year, the background atmosphere experiences severe pollution from both terrigenous sources and regional biomass burning (44% of the aerosol). Daynight variations of the background carbon concentrations suggest that fire ignition and spreading occur primarily during the day. Simultaneous TPM and CO₂ real-time measurements point to a temporal and spatial heterogeneity of the burning so that the ratio of the above background concentrations (TPM/CO₂) varies from 2 to 400 g/kg C. Smoldering processes are intense sources of particles but particulate emissions may also be important during the rapidly spreading heading fires in connection with the generation of heavy brown smoke. We propose emission factor values (EF) for aerosols from the savanna biomass burning aerosols: EF (TPM)=11.4±4.6 and 69±25 g/kg C_{dry plant} and EF(Ct)=7.4±3.4 and 56±16 g C/kg C_{dry plant} for flaming and smoldering processes respectively. In these estimates, the range of uncertainty is mostly due to the intra-fire variability. These values are significantly lower than those reported in the literature for the combustion of other types of vegetation. But due to the large amounts of vegetation biomass being burnt in African savannas, the annual flux of particulate carbon into the atmosphere is estimated to be of the order of 8 Tg C, which rivals particulate carbon emissions from anthropogenic activities in temperate regions.  相似文献