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81.
The bioavailability of field‐aged Cd and Cu was calculated, and compared to the total concentrations determined by acid digestion. Only 0.60–4.15% for Cd and 0.59–9.43% for Cu were found to be bioavailable when determined by stomach‐phase extraction. The incorporation of bioavailability reduced more than 90% of the calculated risk of the metals at the site of study. It should be noted that such a reduction may not be generalized and the site‐specific bioavailability needs to be determined case by case. 相似文献
82.
C. J. Walcek H. R. Pruppacher J. H. Topalian S. K. Mitra 《Journal of Atmospheric Chemistry》1983,1(3):291-306
For the purpose of testing our previously described theory of SO2 scavenging a laboratory investigation was carried out in the UCLA 33 m long rainshaft. Drops with radii between 250 and 2500 m were allowed to come to terminal velocity, after which they passed through a chamber of variable length filled with various SO2 concentrations in air. After falling through a gas separating chamber consisting of a fluorocarbon gas the drops were collected and analyzed for their total S content in order to determine the rate of SO
2
absorption.The SO2 concentration in air studied ranged between 1 and 60% (v). Such relatively large concentrations were necessary due to the short times the drops were exposed to SO2 in the present setup. The present experimental results were therefore not used to simulate atmospheric conditions but rather to test our previously derived theory which is applicable to any laboratory or atmospheric condition. Comparison of our studies with the results from our theory applied to our laboratory conditions led to predicted values for the S concentration in the drops which agreed well with those observed if the drops had radii smaller than 500 m. In order to obtain agreement between predicted and observed S concentrations in larger drops, an empirically derived eddy diffusivity for SO2 in water had to be included in the theory to take into account the effect of turbulent mixing inside such large drops.In a subsequent set of experiments, drops initially saturated with S (IV) were allowed to fall through S-free air to determine the rate of SO
2
desorption. The results of these studies also agreed well with the results of our theoretical model, thus justifying the reversibility assumption made in our theoretical models.In a final set of experiments, the effects of oxidation on SO2 absorption was studied by means of drops containing various amounts of H2O2. For comparable exposure times to SO2, the S concentration in drops with H2O2 was found to be up to 10 times higher than the concentration in drops in which no oxidation occurred. 相似文献
83.
Desertification in the Sahel: Towards better accounting for ecosystem dynamics in the interpretation of remote sensing images 总被引:3,自引:0,他引:3
L. Hein N. de RidderP. Hiernaux R. LeemansA. de Wit M. Schaepman 《Journal of Arid Environments》2011,75(11):1164-1172
To date, the interpretation of remote sensing images has not revealed wide-spread degradation of the vegetation in the Sahel. However, the interpretation of spectral information depends on a range of assumptions regarding the dynamics of the Sahelian vegetation as a function of rainfall variability and human management. Recent papers have presented diverging views on the vegetation dynamics of the Sahel and how these can be analysed with remote sensing images. We present a further analysis of the vegetation dynamics of semi-arid rangelands, in particular the Sahel, and the subsequent implications for the interpretation of remote sensing images. Specifically, the ecological processes driving the response of the Sahelian vegetation to rainfall variation are re-examined, and a regression analysis of NPP versus rainfall data is carried out. It is shown that the relation between the interannual variation in NPP and rainfall in the Sahel is non-linear and that this relation differs between sites with different average annual rainfall. It has been common practise in remote sensing studies for the Sahel to aggregate data from various Sahelian sites in order to obtain an average relation between rainfall, NPP and Rain Use Efficiency, and to assume these relations to be linear. This paper shows that this approach may lead to a bias in the interpretation of remote sensing images and that further work is required to clarify if wide-spread ecosystem degradation has occurred in the Sahel. 相似文献
84.
85.
N. Thinakaran P. Baskaralingam K. V. Thiruvengada Ravi P. Panneerselvam Subramanian Sivanesan 《洁净——土壤、空气、水》2008,36(9):798-804
Activated carbons prepared from sunflower seed hull have been used as adsorbents for the removal of acid blue 15 (AB‐15) from aqueous solution. Batch adsorption techniques were performed to evaluate the influences of various experimental parameters, e. g., temperature, adsorbent dosage, pH, initial dye concentration and contact time on the adsorption process. The optimum conditions for AB‐15 removal were found to be pH = 3, adsorbent dosage = 3 g/L and equilibrium time = 4 h at 30°C. The adsorption of AB‐15 onto the adsorbent was found to increase with increasing dosage. It was found from experimental results that the Langmuir isotherm fits the data better than the Freundlich and Temkin isotherms. The maximum adsorption capacity, Qm (at 30°C) was calculated for SF1, SF2, and SF3 as 75, 125 and 110 mg g–1 of adsorbent, respectively. It was found that the adsorption follows pseudo‐second order kinetics. The thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were also evaluated. The activated carbons prepared were characterized by FT‐IR, SEM and BET analysis. 相似文献
86.
A non-parametric automatic blending methodology to estimate rainfall fields from rain gauge and radar data 总被引:1,自引:0,他引:1
Carlos A. Velasco-Forero Daniel Sempere-Torres Eduardo F. Cassiraga J. Jaime Gómez-Hernández 《Advances in water resources》2009
Quantitative estimation of rainfall fields has been a crucial objective from early studies of the hydrological applications of weather radar. Previous studies have suggested that flow estimations are improved when radar and rain gauge data are combined to estimate input rainfall fields. This paper reports new research carried out in this field. Classical approaches for the selection and fitting of a theoretical correlogram (or semivariogram) model (needed to apply geostatistical estimators) are avoided in this study. Instead, a non-parametric technique based on FFT is used to obtain two-dimensional positive-definite correlograms directly from radar observations, dealing with both the natural anisotropy and the temporal variation of the spatial structure of the rainfall in the estimated fields. Because these correlation maps can be automatically obtained at each time step of a given rainfall event, this technique might easily be used in operational (real-time) applications. This paper describes the development of the non-parametric estimator exploiting the advantages of FFT for the automatic computation of correlograms and provides examples of its application on a case study using six rainfall events. This methodology is applied to three different alternatives to incorporate the radar information (as a secondary variable), and a comparison of performances is provided. In particular, their ability to reproduce in estimated rainfall fields (i) the rain gauge observations (in a cross-validation analysis) and (ii) the spatial patterns of radar fields are analyzed. Results seem to indicate that the methodology of kriging with external drift [KED], in combination with the technique of automatically computing 2-D spatial correlograms, provides merged rainfall fields with good agreement with rain gauges and with the most accurate approach to the spatial tendencies observed in the radar rainfall fields, when compared with other alternatives analyzed. 相似文献
87.
Wind tunnel experiments for ‘Raindrop Detachment and Wind-Driven Transport’ (RD–WDT) process were conducted under improved lateral jetting induced by wind velocities of 6.4, 10, and 12 m s− 1 at nozzle operating pressures of 75, 100, and 150 kPa. Wind-driven rainfalls were also incident on the windward and leeward slopes of 4° and 9° to have a broad variation in the angle of incidence. The objective of this experimental set-up was to distinguish the roles of both impact components of obliquely striking wind-driven raindrops on RD and wind on WDT. Raindrop impact components and reference horizontal wind were quantified by normal (Etz) and horizontal (Etx) kinetic energy fluxes and wind shear velocity (u), respectively, to physically model the process of RD–WDT. The results showed, at each level of u, differential sand transport rates by RD–WDT (qm(RD–WDT)) occurred depending on the magnitude of raindrop impact components, and qm(RD–WDT) increased as the relative contribution of Etz increased. Although Etx was more correlated with qm(RD–WDT) than Etz, the extreme increases in Etx at the expense of Etz brought about no increases but decreases in qm(RD–WDT). An RD–WDT model was built under the process of examining the discrete effects of Etz and Etx on RD together with u and resulted in a better coefficient of determination (R2 = 0.89) than only total kinetic energy (Et) did alone with u (R2 = 0.84). In this study, Etx was strongly related to u and not to Etz, which was the principal difference from the previous rainsplash studies, which relied on the compensatory lateral jet development by the compressive pressure build-up at the raindrop–soil interface. Including Etx in the RD–WDT model both separated the distinct role of each raindrop impact component in RD and improved the performance of u in WDT by better distinguishing its interaction with Etx, which was not explicitly separated in previous models of RD–WDT. 相似文献
88.
Hydrochemical characterization of acute acid mine drainage at Iron Duke mine, Mazowe, Zimbabwe 总被引:8,自引:0,他引:8
Acid mine drainage (AMD) with a minimum pH of 0.52 was recorded at Iron Duke mine near Mazowe, Zimbabwe during an investigation
of the environmental geochemistry of mine waters in the Greenstone Belts of Zimbabwe. Hydrochemical data for waters emanating
from the Iron Duke waste-rock pile indicate their super-saturation with respect to Fe and SO4
2–. Extremely high dissolved concentrations of Al, Zn, Cu, Co, Ni, V, Cr, Cd and As also prevail. Substantial losses of metals
from solution occur within 400 m of the AMD source through the precipitation of crystalline sulphates, principally melanterite.
Further downstream, hydrous oxide precipitation forms the dominant mechanism of metal attenuation in waters characteristically
under-saturated with respect to Fe sulphates. Speciation and saturation index data generated using the equilibrium model WATEQ4F,
suggest that such codes have broad utility for generic prediction of the mineralogical contraints on metal mobility in acute
AMD systems. Major discrepancies between modelled and empirical hydrochemistries are, however, evident for super-saturated
waters in which the kinetics of Fe precipitation are slow, and in which total ionic strengths markedly exceed their theoretical
maximum.
Received: 28 August 1998 · Accepted: 7 December 1998 相似文献
89.
对9711号台风天气形势和物理量场的诊断分析结果表明:东南低空急流和高层的西风急流与台风的相互作用,高层辐散区与低层辐合区同时北抬和重叠,是造成山东地区附近大范围暴雨的主要原因。暴雨区主要位于台风移动前方的右侧。台风的移向与副高的位置及强弱变化有关。 相似文献
90.