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21.
Claeys M Graham B Vas G Wang W Vermeylen R Pashynska V Cafmeyer J Guyon P Andreae MO Artaxo P Maenhaut W 《Science (New York, N.Y.)》2004,303(5661):1173-1176
Detailed organic analysis of natural aerosols from the Amazonian rain forest showed considerable quantities of previously unobserved polar organic compounds, which were identified as a mixture of two diastereoisomeric 2-methyltetrols: 2-methylthreitol and 2-methylerythritol. These polyols, which have the isoprene skeleton, can be explained by OH radical-initiated photooxidation of isoprene. They have low vapor pressure, allowing them to condense onto preexisting particles. It is estimated that photooxidation of isoprene results in an annual global production of about 2 teragrams of the polyols, a substantial fraction of the Intergovernmental Panel on Climate Change estimate of between 8 and 40 teragrams per year of secondary organic aerosol from biogenic sources. 相似文献
22.
23.
Willy Dierickx 《Irrigation and Drainage Systems》1993,6(4):291-310
Subsurface drainage requires appropriate materials to ensure a proper functioning of the drainage system. The materials normally applied for subsurface drainage are drain pipes and envelopes. Besides a review of the materials used for drain pipes, their hydraulic characteristics — discharge capacity and entrance resistance — have been treated. Much attention is paid to subsurface drainage envelope materials because of practical problems and a serious gap in knowledge, in spite of considerable research efforts. After treating the aim of drainage envelopes, a review of the used materials is given. Practical experience with gravel envelopes, still often used in irrigated areas, shows serious shortcomings. Since organic envelopes are vulnerable to deterioration, the only possible alternative are synthetic envelopes. Their property to retain soil particles is characterized by the so-called filter criteria. Laboratory research and field experiments to evaluate the blocking and clogging aspects of synthetic envelopes are discussed and selection criteria given. 相似文献
24.
The applicability of granular activated carbon (GAC)filtration for the removal of the xeno-estrogenicmicropollutant nonylphenol (NP) is evaluated using batchadsorption data. From the obtained adsorption data, it wasapparent that with contact times of 4 d and 24 hr and GACdosages of 1 and 0.1 g L-1 no saturationof the GAC could be obtained with NP total contaminantloadings up to 10 000 μg L-1.Higher NP concentrations could not be applied due to its lowwater solubility (~5 mg L-1). The influence of temperature(4 or 28 °C) on NP sorption onto GAC was negligible.The results showed that the sorption capacity of GAC for NPwas at least 100 mg g-1 GAC. According to thesedata it can be concluded that a full-scale GACfilter unit will be sufficient to remove environmentallyrelevant NP concentrations of 10 μg L-1.Consequently, the existing GAC treatment technology indrinking water treatment should protect the consumer from theintake of the xeno-estrogenic micropollutant NP via drinkingwater. The sorption capacity of dissolved humic acids (DHA)for NP is considerable at liquid NP concentrations of 10 μgL-1 and the affinity of DHA for GAC is not significant.These observations suggest that interference on removal of NP onGAC, due to the presence of DHA, can be expected at microgramper liter concentrations of NP. They may warrant the removalof humic substances in treatment steps preceding GAC-filtration. 相似文献
25.
Baeyens W. Dehandschutter B. Leermakers M. Bobrov V. A. Hus R. Baeyens-Volant D. 《Water, air, and soil pollution》2003,142(1-4):375-393
Natural geological Hg deposits control the Hg levels inthe upper Katun river. Very high levels of total Hg areobserved in the watercolumn (up to 20 ng L-1) and thesediments (up to 244 μg g-1) close to the depositarea, but almost normal levels (1.8 ng L-1 in the watercolumn and 0.14 μg g-1 in the sediments) are reached60 km downstream of that zone. In general, low dissolvedmethylmercury (MMHg) concentrations were found (0.04–0.05 ngL-1) due to unfavourable methylation conditions. The MMHgconcentrations in the sediments vary from 23.3 ng g-1, inthe vicinity of the geological Hg deposits, to 0.17 ng g-1 60 km downstream.Total Hg levels in Lake Teletskoye (a geological activearea) are slightly increased (1.1–1.8 ng L-1) compared toLake Baikal and fairly constant alover the Lake, suggestingmultiple sources. High mercury concentrations in springs andsoils coincide with high radon concentrations in the samecompartments as well as high soil exhalation fluxes. Theseresults in combination with the fact that Lake Teletskoye islocated in an active fault zone suggest that the Rn and Hgsources may be fault aligned spring waters and deep seatedgases escaping through open cracks. Methylmercuryconcentrations in the Lake (0.03–0.1 ng L-1) werecomparable to the concentrations found in Katun river butrelative to the total Hg burden this means a higher percentage. 相似文献
26.
Leermakers M. Baeyens W. Ebinghaus R. Kuballa J. Kock H. H. 《Water, air, and soil pollution》1997,97(3-4):257-263
Total gaseous mercury (TGM) and rainwater were collected on board of two research vessels (F. S. ALKOR and R.V. BELGICA) positioned 200 km apart in the center of the North Sea Experiment, September 1991. On the F.S. ALKOR (up-wind ship) TGM concentrations ranged from 0.7 to 2.6 ng·m-3 with an average of 1.5 ng·m-3 and on the R. V. BELGICA (down-wind ship) TGM ranged from 0.7 to 1.9 ng·m-3 with an average of 1.2 ng·m-3. An average 20% decrease is observed from the up-wind to the downwind ship, which may largely be affected by entrainment into the free troposphere. An overall removal was 0.5 cm·s-1 for dry periods and varied between 1 to 5 cm·s-1 during rain events. Rainwater concentrations varied between 5 and 25 ng·l-1. Based on these data an annual wet deposition flux of 1.08 ng Hg cm-2 yr1- was estimated for the North Sea. 相似文献
27.
M. Leermakers Y. Gao C. Gabelle S. Lojen B. Ouddane M. Wartel W. Baeyens 《Water, air, and soil pollution》2005,166(1-4):265-286
The techniques of diffusional equilibrium in thin films (DET) and diffusional gradients in thin films (DGT) were used to obtain high resolution pore water profiles of total dissolved and labile trace (mobilizable) metals in the sediments of the Rupel River, Belgium. DGT measures labile metal species in situ by immobilizing them on a resin gel after diffusion through a diffusive gel whereas for DET an equilibrium is established between the DET gel and the pore water. Concentrations of Pb and Zn obtained by DGT were in good agreement with the results obtained by centrifugation, and thus were well buffered by rapid equilibrium with the solid phase, whereas Fe, Mn and Cd were very tightly bound to the sediment phase and large differences were observed between the labile and the total metal concentrations. Cu, Zn, Co and Ni show intermediated behavior. Good correlations were found between the profiles of As and Fe and Mn and Co for DET as well as DGT showing a close link between the geochemical behavior of these elements. Cu, Zn, Pb and Cd are also influenced by the reductive mobilization of Fe and Mn oxides but are also closely linked to the bacterial degradation of organic matter in the surface sediments as to the precipitation of metal sulfides in the deeper layers. 相似文献
28.
Research on mercury (Hg) distribution and speciation was carried out in Lake Baikal, a large, strong-oligotrophic freshwater reservoir in Siberia, Russia, during June 1992 and march 1993. In summer, total Hg in the water column ranged from 0.14 to 0.77 ng Hg/L, with the highest concentrations observed in the central basin of the lake in surface water samples. Labile inorganic Hg was found to be 7 to 20 % of the total Hg content. Highest total Hg concentrations were found in river waters: up to 2 ng Hg/L. Labile methylmercury (MeHg) concentrations ranged from 2 to 38 pg Hg/L in the water column, with the higher concentrations in the central part of the lake, and showing a slight increase in near bottom waters. Labile MeHg makes up 1 to 15 % of the total Hg content in the water column, with larger fractions in deep waters. The slight increase of the MeHg gradient with depth corresponds with the O2 minimum region. Highest MeHg concentrations were observed in river waters (up to 145 pg Hg/L) and in some bays of the lake (up to 160 pg Hg/L). In these high temperature- and phytoplankton-rich water masses, the MeHg-fraction increased up to 35 % of total Hg. Labile MeHg concentrations in water samples taken in winter in the southern basin (under the ice cover), showed slightly higher concentrations than in summer, possibly due to an early spring bloom. In rainwater, total Hg ranged from 3 to 20 ng Hg/L and MeHg from 0.1 to 0.25 ng Hg/L. In snow, a large fraction of total Hg is bound to particulate matter; concentrations of total Hg ranged from 8 to 60 ng Hg/L and labile MeHg from 0.1 to 0.25 ng Hg/L. Atmospheric Hg was found to be 0.73 to 2.31 ng/m3 as gaseous Hg and 0.005 to 0.02 ng/m3 in its particulate form. Spatial distribution patterns of atmospheric Hg show slightly higher concentrations over the central part of the lake and the Selenga river delta. In winter, atmospheric Hg values (measured in the southern region), ranged from 1.2 to 6.1 ng/m3 as total gaseous Hg and 0.02 to 0.09 ng/m3 as total particulate Hg, and are higher than in summer, probably influenced by coal burning and traffic by the local population. MeHg contents in fish ranged from 20 ng Hg/g dry weight in small Cottocomephorus to 300 ng Hg/g dry weight in pike and trout species, which were caught in organic-rich waters. 相似文献
29.
Paul D. Henne Ché Elkin Daniele Colombaroli Stéphanie Samartin Harald Bugmann Oliver Heiri Willy Tinner 《Landscape Ecology》2013,28(5):819-833
Forests near the Mediterranean coast have been shaped by millennia of human disturbance. Consequently, ecological studies relying on modern observations or historical records may have difficulty assessing natural vegetation dynamics under current and future climate. We combined a sedimentary pollen record from Lago di Massacciucoli, Tuscany, Italy with simulations from the LandClim dynamic vegetation model to determine what vegetation preceded intense human disturbance, how past changes in vegetation relate to fire and browsing, and the potential of an extinct vegetation type under present climate. We simulated vegetation dynamics near Lago di Massaciucoli for the last 7,000 years using a local chironomid-inferred temperature reconstruction with combinations of three fire regimes (small infrequent, large infrequent, small frequent) and three browsing intensities (no browsing, light browsing, and moderate browsing), and compared model output to pollen data. Simulations with low disturbance support pollen-inferred evidence for a mixed forest dominated by Quercus ilex (a Mediterranean species) and Abies alba (a montane species). Whereas pollen data record the collapse of A. alba after 6000 cal yr bp, simulated populations expanded with declining summer temperatures during the late Holocene. Simulations with increased fire and browsing are consistent with evidence for expansion by deciduous species after A. alba collapsed. According to our combined paleo-environmental and modeling evidence, mixed Q. ilex and A. alba forests remain possible with current climate and limited disturbance, and provide a viable management objective for ecosystems near the Mediterranean coast and in regions that are expected to experience a mediterranean-type climate in the future. 相似文献
30.
Jan B. A. Arends Evelyne Blondeel Steve R. Tennison Nico Boon Willy Verstraete 《Journal of Soils and Sediments》2012,12(7):1197-1206