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521.
Pisani SO Bruns RE Vasconcellos PC Carvalho LR 《Journal of environmental monitoring : JEM》2003,5(5):795-801
Biogenic hydrocarbon emission rates from individual plant species have been estimated experimentally placing small plants or branches in enclosures and measuring the emission rates of the compounds. All-Teflon chambers (cuvettes) where air samples are drawn through tubes packed with adsorbents, have been commonly used for plant enclosure. Sampling of carbonyl compounds emitted from plants has been done using 2,4-dinitrophenylhydrazine coated particles and the derivative carbonyl compounds have been analyzed by HPLC-UV. In this work, the enclosure technique using a cuvette for measurements of carbonyl compound emissions from plants was evaluated. Blank measurements in an empty cuvette have revealed quite different results for experiments performed under laboratory and field conditions. Rigorous univariate statistical analysis of the data obtained indicate that the analytical procedure to determine carbonyl compounds at trace levels in emission samples using the cuvette may lead to positive artifacts during field sampling. This analysis applied to laboratory measurements showed no difference in the results for the cuvette and external lines. Multivariate statistical calculations point out that solar light intensity accounts for the high carbonyl compound levels, especially for acetaldehyde, in the empty cuvette. 相似文献
522.
Phosphorus chemistry in streams was evaluated at the paired watershed study at the Bear Brook Watershed, Maine. The West Bear catchment has been treated bimonthly since 1989 with 1,800 eq (NH4)2SO4 ha-1 yr-1. East Bear was the untreated reference watershed. During 1993, concentration of total phosphorus (P) in weekly samples from East and West Bear Brook ranged from 0 to 15 g L-1. The median values were 2 and 4 g L-1 for East and West Bear, respectively. During a high discharge event in January of 1995, the concentration of dissolved P remained relatively constant ( 3 g L-1) as pH decreased from 5.63 to 5.08 and from 5.14 to 4.75 in East and West Bear, respectively. The concentration of total P increased to ca. 60 g L-1 during the rising limb of the hydrograph in West Bear, four times the value in East Bear, total P then declined rapidly as discharge remained high followed by an increase. Dissolved Al increased in both streams during the episodic acidification. West Bear, the more acidic, had concentrations of dissolved Al four times those of East Bear (maximum of 1.1 mg L-1 versus 0.25 mg L-1). Acid-soluble particulate Al increased to 0.2 and 4.2 mg L-1 for East and West Bear, respectively, in parallel to total P (but was 102 greater than total P) and then declined in parallel to total P while discharge remained high. Total P, dissolved P, and particulate Al did not relate to pH. Total P and particulate Al and Fe were strongly correlated. Concurrently, base cations remained relatively constant or decreased slightly. Particulate acid-soluble Al exceeded particulate acid-soluble base cations. We hypothesize that the particulate P was occluded in, or adsorbed on, acid-soluble particulate Al(OH)3. This Al(OH)3. This Al(OH)3 precipitates as emerging acidic groundwater degasses CO2 and pH rises. The export of Al and P is greater from the treated watershed because the induced acidification is translocating more Al from soils to the stream. Most of the export of P is related to acid-soluble Al particulate material. 相似文献
523.
Manoj Jha Jeffrey G. Arnold Philip W. Gassman Filippo Giorgi Roy R. Gu 《Journal of the American Water Resources Association》2006,42(4):997-1015
ABSTRACT: The Soil and Water Assessment Tool (SWAT) model was used to assess the effects of potential future climate change on the hydrology of the Upper Mississippi River Basin (UMRB). Calibration and validation of SWAT were performed using monthly stream flows for 1968–1987 and 1988–1997, respectively. The R2 and Nash‐Sutcliffe simulation efficiency values computed for the monthly comparisons were 0.74 and 0.69 for the calibration period and 0.82 and 0.81 for the validation period. The effects of nine 30‐year (1968 to 1997) sensitivity runs and six climate change scenarios were then analyzed, relative to a scenario baseline. A doubling of atmospheric CO2 to 660 ppmv (while holding other climate variables constant) resulted in a 36 percent increase in average annual streamflow while average annual flow changes of ?49, ?26, 28, and 58 percent were predicted for precipitation change scenarios of ?20, ?10, 10, and 20 percent, respectively. Mean annual streamflow changes of 51,10, 2, ?6, 38, and 27 percent were predicted by SWAT in response to climate change projections generated from the CISRO‐RegCM2, CCC, CCSR, CISRO‐Mk2, GFDL, and HadCMS general circulation model scenarios. High seasonal variability was also predicted within individual climate change scenarios and large variability was indicated between scenarios within specific months. Overall, the climate change scenarios reveal a large degree of uncertainty in current climate change forecasts for the region. The results also indicate that the simulated UMRB hydrology is very sensitive to current forecasted future climate changes. 相似文献
524.
Jonn A. Foulk Wayne Y. Chao Danny E. Akin Roy B. Dodd Patricia A. Layton 《Journal of Polymers and the Environment》2006,14(1):15-25
Manufacturing composites with polymers and natural fibers has traditionally been performed using chopped fibers or a non-woven mat for reinforcement. Fibers from flax (Linum usitatissimum L.) are stiff and strong and can be processed into a yarn and then manufactured into a fabric for composite formation. Fabric directly impacts the composite because it contains various fiber types via fiber or yarn blending, fiber length is often longer due to requirements in yarn formation, and it controls the fiber alignment via weaving. Composites created with cotton and flax-containing commercial fabrics and recycled high-density polyethylene (HDPE) were evaluated for physical and mechanical properties. Flax fiber/recycled HDPE composites were easily prepared through compression molding using a textile preform. This method takes advantage of maintaining cotton and flax fiber lengths that are formed into a yarn (a continuous package of short fibers) and oriented in a bidirectional woven fabric. Fabrics were treated with maleic anhydride, silane, enzyme, or adding maleic anhydride grafted polyethylene (MAA-PE; MDEX 102-1, Exxelor® VA 1840) to promote interactions between polymer and fibers. Straight and strong flax fibers present problems because they are not bound as tightly within yarns producing weaker and less elastic yarns that contain larger diameter variations. As the blend percentage and mass of flax fibers increases the fabric strength, and elongation generally decrease in value. Compared to recycled HDPE, mechanical properties of composite materials (containing biodegradable and renewable resources) demonstrated significant increases in tensile strength (1.4–3.2 times stronger) and modulus of elasticity (1.4–2.3 times larger). Additional research is needed to improve composite binding characteristics by allowing the stronger flax fibers in fabric to carry the composites load. 相似文献
525.
In a pilot project performed at a fertilizer manufacturing facility, a one‐step chemical oxidation technique successfully treated urea‐ and ammonium‐contaminated groundwater. The oxidation reaction occurred in an 1,100‐gallon batch reactor. The contaminated inflow was buffered by the metered addition of sodium bicarbonate solution and subsequently treated with sodium hypochlorite in an 8:1 weight ratio of Cl2:N. In an instantaneous reaction, the urea and ammo‐nium‐N were completely oxidized to nitrogen gas that was vented to the atmosphere during mixing. The pH of the reactor discharge was ?6.5. Sodium sulfite was used to reduce residual hypochlorite in the reactor effluent to chloride to provide process water with characteristics suitable for discharge. Oxidation rates were similar with different strengths of hypochlorite; however, a 5 to 6 percent sodium hypochlorite (as Cl2) solution was the most stable. © 2005 Wiley Periodicals, Inc. 相似文献
526.
527.
528.
N. Gruchy F. Vialard E. Blondeel N. Le Meur G. Joly-Hélas P. Chambon M. Till M. Herbaut-Graux A. Vigouroux-Castera A. Coussement J. Lespinasse F. Amblard M. Jimenez L. Lebel Roy Camille F. Carré-Pigeon E. Flori F. Mugneret S. Jaillard C. Yardin R. Harbuz M. Collonge Rame P. Vago M. Valduga N. Leporrier 《黑龙江环境通报》2014,34(12):1133-1138
529.
Economic effects of CO2 fertilization of crops: transforming changes in yield into changes in supply 总被引:1,自引:0,他引:1
Increasing concentrations of atmospheric carbon dioxide CO2 have a beneficial effect on crop production that would tend to offset some of the economic losses that might be generated in some areas by the climatic effects of atmospheric CO2 and other greenhouse gases. Previous estimates of the economic benefits of CO2 fertilization on world crop production, however, were based on the assumption that percent changes in supply are equal to percent changes in yield. This assumption is not valid, however, because it confounds changes in supply with changes in quantity supplied. This error leads to an overestimation of the real economic benefits of CO2 fertilization by 61–166%. The effects of CO2 fertilization on crop production, therefore, will reduce some of the potential damages caused by the climatic impacts of greenhouse gases, but by significantly less than that indicated in earlier research. 相似文献
530.