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331.
In order to study the effect of thevegetation structure on atmospheric ammonia(NH3) dispersion and deposition, anexperiment was set up near Paris, in July 1997.Between 12 and 162 m downwind of a 200 m line-source releasing 600 to 1200 g NH3hr-1placed at the top of a maize canopy, NH3concentration was measured, within and above thecanopy, with a set of 30 active, acid-coateddenuders over periods of 2 to 3 hr. Eight datasets were collected over a one-month period.NH3 concentration decreased sharply withdistance to the source, from up to800 g NH3 m-3 at 12 m, to lessthan 10 g NH3 m-3 at 162 m andshowed strong vertical gradients. Within thecanopy, the concentration scaled using thefriction velocity, the canopy height, and thesource strength, exhibited a universal power lawrelationship as a function of the normaliseddownwind distance from the source. A mass balancemethod and a resistance model approach were usedas independent estimates of the cumulateddeposition at 162 m downwind from the source,which range between 1 and 29% of the emittedNH3. Both methods agreed approximately inmagnitude. A sensitivity analysis showed that thecuticular uptake and the compensation point aremajor parameters that needs to be bettercharacterised under high NH3 concentrationif one wants to improve NH3 short-rangedeposition modelling. 相似文献
332.
Benjamin F. Hobbs Peter M. Meier 《Journal of the American Water Resources Association》1979,15(6):1666-1676
ABSTRACT: Expansion of the electrical generation system in the Pennsylvania-Jersey-Maryland power pool will impact, and be constrained by, inland water availability. Future interpretations of the Federal Water Pollution Control Act Amendments of 1972 regarding evaporative cooling towers for coastal power plants, offshore siting and energy centers, and the policies and public acceptability of low flow augmentation reservoirs are some of the issues examined in this paper using scenarios generated by the Brookhaven National Laboratory Regional Energy Facility Siting Model (REFS). REFS is a multicommodity, transshipment-location linear programming model used here to allocate power plants among counties in a power pool under a minimization of cost objectives. The solutions are sensitive to the water resources assumptions in the model. For the year 2000, the amount of low flow augmentation allowed in the region's river basins and whether off-shore siting becomes a reality are the two water resources related issues which most affect the scenarios. The results show that decisions regarding specific water problems can have region wide implications for water and nonwater related issues. 相似文献
333.
334.
The biodiversity of many Brazilian rivers is seriously threatened by industrial and municipal pollution, and Rio Paraiba do Sul, located between two major industrial centers is one example of this situation. A survey of the fish assemblage was conducted from October 1998 to September 1999 and the data were used to develop an index of biotic integrity (IBI). We sampled three zones in bracketing a large urban–industrial complex to evaluate water quality changes and the usefulness of the IBI as a monitoring tool. Water quality was classified as poor upstream of the effluent discharges, very poor near the discharges, and poor–fair downstream of the discharges, with this latter situation revealing the current biological capacity of the river. Physical and chemical habitat characteristics were also measured at each site to construct an independent environmental index to validate the IBI. The habitat and IBI indices were highly correlated, suggesting this IBI would be applicable to other large rivers in southeast Brazil. 相似文献
335.
Katherine R. Weeks Scott C. Veenstra David L. Hill Benjamin P. Gregson 《补救:环境净化治理成本、技术与工艺杂志》2003,13(2):131-143
The Army National Guard initiated an Innovative Technology Evaluation (ITE) Program in March 2000 to study potential remedial technologies for the cleanup of explosives‐contaminated soil and groundwater at the Camp Edwards site on the Massachusetts Military Reservation. The soil technologies chosen for the ITE program were: soil washing, chemical oxidation, chemical reduction, thermal desorption/destruction (LTTD), bioslurry, composting, and solid phase bioremediation. The technologies were evaluated based on their ability to treat both washed and untreated soil. A major factor considered was the ability to degrade explosives, such as RDX, found in particulate form in the soils. The heterogeneous nature of explosives in soils dictates that the preferred technology must be able to treat explosives in all forms, including the particulate form. Groundwater remediation technologies considered include: in situ cometabolic reduction, two forms of in situ chemical oxidation, Fenton‐like oxidation and potassium permanganate. This article presents the results of each of the remedial technologies evaluated and discusses which technologies met the established ITE performance goals. © 2003 Wiley Periodicals, Inc. 相似文献
336.
Guang Hao Chen Wun Jern Ng Hiroaki Ozaki Yutaka Terashima 《Resources, Conservation and Recycling》1994,11(1-4)
The concentration of dissolved oxygen (DO) strongly influences the performance of aerobic biofilm reactors because organic oxidation is limited by the availability of oxygen. However, it is not necessary to maintain a high DO level in the reactors in order to overcome this limitation. Excessive aeration wastes energy. Therefore, the determination of the onset of DO limitation against organic substrate removal in aerobic biofilm reactors is important for their effective operation. This study is aimed at developing an expression to determine the onset of DO limitation and hence to control the aeration system. The expression developed is as follows:
, where Sb and Cb are the bulk concentrations of organic substrate and DO, respectively; Dws and Dwc are the diffusion coefficients of organic substrate and oxygen in the reactors respectively; and Rb is an overall ratio of oxygen consumption to organic substrate removal in the reactors. The latter is the key parameter in the equation, and is determined by the characteristics of the substrate, biofilm, and reactor. In order to measure the value of Rb, the authors have developed a micro-biofilm reactor. The value of Rb was determined to be 0.13 (mg O2 mg−1 CODcr) for glucose removal with this reactor. The equation has, subsequently, been verified with data from batch and continuous experiments. 相似文献
337.
338.
Hans Pohl Benjamin Wipfler David Grimaldi Felix Beckmann Rolf G. Beutel 《Die Naturwissenschaften》2010,97(9):855-859
Fossilization in amber is unique in preserving specimens with microscopic fidelity; however, arthropod inclusions are rarely
examined beyond the exoskeleton as this requires destructive sampling when traditional techniques are used. We report the
first complete, digital 3D, non-destructive reconstruction of the anatomy of an insect fossil, a specimen of †Mengea tertiaria embedded in a 42-Ma Baltic amber. This was made possible using Synchrotron μ-CT. The species belongs to the stem group of
the phylogenetically enigmatic and extremely specialized Strepsiptera. Most internal structures of the fossil are preserved,
but small parts of the lumen had decayed due to incomplete infiltration of the resin. Data on internal organs provided additional
information for resolving phylogenetic relationships. A sister group relationship between †Mengea and all extant lineages of the group was confirmed with characters previously not accessible. The newly gained information
also yielded some insights in the biology of †Mengea and the early evolutionary history of Strepsiptera. The technique has a tremendous potential for a more accurate interpretation
of diverse fossil arthropods preserved in ambers from 130 Ma to the present. 相似文献
339.
D.Y.C. Leung Daniel Yung Amanda Ng M.K.H. Leung Alan Chan 《Environmental Science & Policy》2009,12(1):92-101
With the approval of the Chinese central government, the Government of the Hong Kong Special Administrative Region (HKSAR) decided to participate in a regional emissions trading (ET) pilot scheme in the Pearl River Delta (PRD) region. This scheme, instead of aiming to curb global warming, is geared mostly toward reducing air pollutant (that is, SO2, NOx, RSP, and VOCs) emissions by 20–55% by 2010, thus improving air quality in the region. Both the HKSAR and the Guangdong Provincial Governments will impose emission caps on their respective power plants in the region and allocate emissions credits to them. This study explores the background of this regional ET scheme and correlates it with the emissions reduction scenario to provide more details for assessing its applicability to Hong Kong and Guangdong Province. Although practicing ET in the PRD region presents many challenges, establishing an appropriate ET scheme is of paramount importance for Hong Kong, as well as other cities in the PRD region, to achieve a sustainable air quality. 相似文献
340.
Raia-Silvia Massad Benjamin Loubet Andre Tuzet Herv Autret Pierre Cellier 《Agriculture, ecosystems & environment》2009,133(3-4):170
The plant can be a source or a sink of ammonia (NH3) depending on its nitrogen (N) supply, metabolism and on the background atmospheric concentrations. Thus plants play a major role in regulating atmospheric NH3 concentrations. For a better understanding of the factors influencing the NH3 stomatal compensation point, it is important to analyse the dynamics of leaf NH3 fluxes. The relationship between the leaf NH3 fluxes and the leaf apoplast ammonium and nitrate concentrations, N nutrition and the light and dark periods was studied here.We designed an experiment to quantitatively assess leaf-atmosphere NH3 exchange and the stomatal compensation point and to identify the main factors affecting the variation of NH3 fluxes in oilseed rape. We tested day and night dynamics as well as the effect of five different N treatments. Two experimental methods were used: a dynamic open flux chamber and extraction of the apoplastic solution.Chamber measurements showed that there was a good correlation between plant NH3 fluxes and water fluxes. Compensation points were calculated by two different methods and ranged between 0.8 and 12.2 μg m−3 NH3 (at 20 °C) for the different N treatments. Apoplastic solution measurements showed that there was no significant differences in the apoplastic NH4+ concentrations ([NH4+]apo) extracted in dark and light periods for the same N treatment. Statistical analysis also showed that [NH4+]apo was correlated with [NH4+] in the nutrient solution and weakly correlated with [NO3−]. Apoplast NH4+ concentrations ranged between 0.1 and 2.1 mM, bulk tissue NH4+ concentrations between 3.9 and 6.6 mM and xylem concentrations between 2.4 and 6.1 mM depending on the N supply.Calculated NH3 emission potential from the extraction measurements were over-estimated when compared with the value calculated from chamber measurements. Errors related to chamber measurements included separation of the cuticular and stomatal fluxes and the calculation of total resistance to NH3 exchange. Errors related to the extraction measurements included assessing the amount of cytoplasmic contamination. We do not have another method to assess the NH3 stomatal compensation point and the choice between these two measurement techniques should depend on the scales to which the measurements apply and the processes to be studied. 相似文献