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111.
Fertilizers and liming agents are generally used to achieve optimal economic yields. However, several negative effects of long‐term annual fertilization of nitrogen (N) in particular have been observed, such as reduced cation exchange capacity and decreased base saturation, which may stimulate accelerated leaching loss of other nutrients. Equilibrium‐tension lysimeters installed at a depth of 1.4 m were used to evaluate leaching of soil‐solution ionic constituents from a tallgrass prairie restoration and optimally and deficiently N‐fertilized, no‐tillage (NT) and chisel‐plowed (CP) maize (Zea mays L.) agroecosystems on Plano silt loam soil (fine‐silty, mixed, superactive, mesic Typic Argiudoll). This study was conducted in south‐central Wisconsin, USA during a 1‐year period of above‐normal precipitation between January 2000 and January 2001. The loss of soluble constituents added to agroecosystems to maintain adequate soil fertility and pH, such as N, phosphorus, potassium, calcium, and magnesium, was generally numerically smaller from the natural prairie 25 years after conversion from cultivated agriculture than from optimally and deficiently N‐fertilized, NT and CP maize agroecosystems, though the differences were not significant. Tillage and fertilizer N‐rate generally did not significantly affect drainage, ionic concentrations, or their leaching losses in the maize agroecosystems, though all parameters evaluated tended to be numerically smaller in the deficiently than optimally N‐fertilized maize agroecosystems. Nitrate‐N leaching losses were generally significantly positively correlated with leaching losses of K, Ca, Mg, and Na in the maize agroecosystems, but not for the prairie, indicating that nitrate‐N leaching plays a significant role in the concomitant loss of cations to maintain soil‐solution charge balance in N‐fertilized maize agroecosystems in a temperate environment. 相似文献
112.
The present paper reports recent improvements in sealed tube combustion technique used for the determination of N isotopic composition in various rocks characterized by low N contents (i.e. few ppm). Nitrogen is extracted from samples by combustion in quartz tubes sealed under vacuum. The nitrogen gas purified using Cu, CuO and CaO, is quantified as dinitrogen N2 by capacitance manometry in ultra-high vacuum line. Nitrogen isotopic analysis is performed on a triple-collector static vacuum mass spectrometer, allowing measurement of nanomole quantity of N2. Nitrogen amount and isotopic composition of the analytical blanks are low and describe Gaussian distribution with mean values of 0.65 ± 0.30 nmol N and − 3.7‰ ± 2.7‰, respectively (2σ). Systematic analyses of international and internal standards demonstrate that this technique provides accurate and precise results. The precision on N content and isotopic composition are better than ± 8% and ± 0.5‰ respectively, even for samples containing less than 2 ppm N. The sealed tube combustion technique is shown to apply successfully to rocks of various lithologies such as metagabbros, metaperidotites and altered basalts. It is thus suitable for studying oceanic crust in a perspective to better constrain N exchanges between Earth mantle and surface reservoirs. The investigation can also be extended to analysis of small size samples, particularly when little sample exists and when high spatial resolution is required. 相似文献
113.
The chemical reactivity of NO and NO2 is so rapid that their fluxes and concentrations can be considerably modified from that expected for conserved variables in the atmospheric surface layer, even as low as a meter above the surface. Fitzjarrald and Lenschow (1983) have calculated flux and mean concentration profiles for NO, NO2 and O3 in the surface layer using numerical techniques. However, their solutions do not approach the photostationary state at large heights. Here we solve a simpler set of equations analytically (i.e. we assume a constant O3 concentration and neutral hydrodynamic stability), and are able to show how the flux profiles behave at large heights assuming that the concentrations approach their photostationary values. We find, for example, that at large heights the ratio of the flux of NO to that of NO2 is equal to the ratio of their concentrations. These results are relevant to estimating surface fluxes of NO and NO2, and are most applicable to nonurban environments where NO and NO2 concentrations are usually much less than O3 concentration.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
114.
A.P Yelisseyev N.P. Pokhilenko J.W. Steeds D.A. Zedgenizov V.P. Afanasiev 《Lithos》2004,77(1-4):83-97
Confocal photoluminescence (PL) and local absorption spectroscopy were used to study the types and spatial distribution of point defects in coated diamonds, the input of which is about 30% in the Snap Lake deposit, Canada. Nitrogen concentration is on the level of several hundreds of ppm in the core, with a nitrogen-poor layer in its outer part, whereas in the coat it is usually several times higher as a result of fast growth. Nitrogen defects in the core are strongly aggregated with N3, B and B′-forms dominating, whereas A-defects are typical of the coat. The rounded shape of the coated diamonds is a result of the combined effect of partial dissolution of the octahedral core and the “abnormal” growth of the coat, which produces a fibrous structure. Analysis of PL and PL excitation spectra showed that structureless yellow-green PL of the coat is likely to be due to nickel-nitrogen complexes with their fine structure broadened in the strain fields. The presence of irradiation/annealing products such as vacancies V0 and nitrogen-vacancy complexes NV−, N2V2 shows that the diamonds studied have undergone post-growth ionizing irradiation with further low-temperature annealing in natural conditions. 相似文献
115.
An understanding of the dynamic relationship between nitrogen supply and the formation of phytoplankton biomass is important in predicting and avoiding marine eutrophication. This relationship can be expressed as the short-term yield q of chlorophyll from dissolved available inorganic nitrogen (DAIN), the sum of nitrate, nitrite and ammonium. This paper communicates the results of a continuous culture nitrate enrichment experiment undertaken to investigate the cumulative yield of chlorophyll from DAIN (q). The purposes of the study were: to acquire a better understanding of the relationship between chlorophyll formation and DAIN; to obtain values that could be used in models for predicting eutrophication. The results of a time series experiment carried out using microplankton (all organisms <200 μm in size) indicate that the parameter q does not have a single value but is affected by the ecophysiological response of phytoplankton to changing nutrient status after an enrichment event. It is also dependent on changes in the allocation of nitrogen between autotrophs and heterotrophs. The value of yield obtained at the height of the bloom can be represented by q (max) (2.35 μg chl (μmol N)−1). The post-bloom, steady state value of q can be represented by qeq (0.95 μg chl (μmol N)−1). The microcosm steady state yield was not significantly different from the median value obtained from synoptic studies of Scottish west coast waters. It is proposed that qeq is the most appropriate value for assessing the general potential for eutrophication resulting from continuous nutrient enrichment into coastal waters. It is further proposed that q (max) be used for cases of sporadic enrichment and where a short burst of unrestricted growth may be detrimental. 相似文献
116.
Major and trace elements and nitrogen were analysed in 59 Cambrian and Ordovician slates/phyllites of various lithostratigraphic levels within the Meguma Supergroup, 14 Ordovician slates/phyllites of The Ovens gold mineralisation, and 16 Ordovician slates/phyllites of the Eastville Pb-Zn-Cu mineralisation.The fixed nitrogen content and the normative Nfix/K2O ratio of muscovite separates members of the Goldenville (sandstone-greywacke-quartzite dominated) and Halifax Formation (slate-phyllite dominated). Low fixed nitrogen concentration is related to high manganese concentration. Black slates/phyllites of the saddle-reef-type Au-mineralisation in The Ovens area are characterised by high fixed nitrogen and a high normative Nfix/K2O ratio of muscovite. The nitrogen is of secondary hydrothermal origin. Therefore, it might be possible to use the fixed nitrogen as an exploration tool for black slates/phyllite hosted gold mineralisation in Nova Scotia. Mineralised slates/phyllites of the Eastville stratabound Pb-Zn mineralisation cannot be distinguished from nonmineralised time equivalent lithologies on the basis of the fixed nitrogen distribution or the Nfix/K2O ratio of muscovite. 相似文献
117.
118.
人为活动通常是地下水硝酸盐污染的主要原因。不同来源的NO3^-具有不同的氮、氧同位素组成,利用地下水NO3^-中的δ15N和δ18O值可有效识别地下水硝酸盐污染的来源。引起地下水中NO3^-含量显著减少的不同物理、化学和生物过程,所产生的氮、氧同位素分馏效应有明显差别。地下水系统中反硝化作用发生时,NO3^-中氮和氧同位素分馏系数呈一定比例。因此NO3^-中δ15N和δ18O值也是示踪地下水硝酸盐循环,尤其是反硝化作用的有效手段。利用NO3^-中氮和氧双同位素,并与其他环境同位素及化学分析技术相结合,示踪NO3^-来源及其循环是地下水硝酸盐污染研究的重要方向之一。综述了利用地下水硝酸盐中氮和氧同位素识别NO3^-污染源与循环的研究进展,简述了近年迅速发展的阴离子交换树脂取样法,概述了此方面研究存在的主要问题,并展望了今后的研究方向。 相似文献
119.
Arkadiusz Derkowski Wojciech Franus Halina Waniak-Nowicka Adriana Czímerová 《International Journal of Mineral Processing》2007
Zeolite Na–X (FAU type) was synthesized from F-class fly ash in simple and economical way. Several months of storage of fly ash in NaOH solution, at room temperature, without any prior treatment, results in the production of material with ca. 50% content of Na–X zeolite. The most efficient reaction takes place at (OH)− activity of 0.1–0.15 mol (OH)−/g of ash and at S/L ratio of 33 to 67 g/dm3. Higher S/L value causes an accelerating dissolution–crystallization equilibrium attainment. Cl− ion acts as the inhibitor of this reaction. 相似文献
120.
Z.-H. Shon G. Lee S.-K. Song M. Lee J. Han D. Lee 《Journal of Atmospheric Chemistry》2007,58(3):203-218
This study examines the general characteristics of reactive nitrogen oxides (NOy) at urban and rural sites in terms of measurement- and modeling-based analyses. In this field study, NOx at urban and rural sites were 92 and 89% of NOy on average, respectively. HONO levels (e.g., 1.8 ppbv) at the urban site were significantly higher than those at the rural
site by a factor of 4.5. HONO concentrations at the urban site during the night were clearly higher than those during the
day, which were likely to result from heterogeneous reactions on the surfaces of airborne aerosols and/or grounds. In contrast,
there were no significant differences of PAN concentrations in either the temporal or spatial distributions. The significantly
low ratios of NOz/NOy at both sampling sites indicated a more limited chemical aging process in air mass. O3 levels were weakly related to NOx oxidation at both sites, especially at the rural site. 相似文献