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Dynamic responses of photosystem II in the Namib Desert shrub, Zygophyllum prismatocarpum, during and after foliar deposition of limestone dust 总被引:1,自引:0,他引:1
van Heerden PD Krüger GH Kilbourn Louw M 《Environmental pollution (Barking, Essex : 1987)》2007,146(1):34-45
The effects of limestone dust deposition on vegetation in desert ecosystems have not yet been reported. We investigated these effects in a succulent shrub from the Namib Desert at a limestone quarry near Skorpion Zinc mine (Namibia). Effects of limestone dust were determined in Zygophyllum prismatocarpum (dollar bush) plants with heavy, moderate and no visible foliar dust cover by means of chlorophyll a fluorescence measurements. Limestone dust deposition decreased overall plant performance through loss of chlorophyll content, inhibition of CO(2) assimilation, uncoupling of the oxygen-evolving complex and decreased electron transport. Importantly, dynamic recovery occurred after termination of limestone extraction at the quarry. Recovery was accelerated by rainfall, mainly because of dust removal from leaves and stimulation of new growth. These results indicate that limestone dust has severe effects on photosynthesis in desert shrubs, but that recovery is possible and that, in arid environments, this process is modulated by rainfall. 相似文献
2.
Immink Harmke Louw Robbie Garlick Amy Vosper Samuel Brent Alan 《Environment, Development and Sustainability》2022,24(8):10005-10025
Environment, Development and Sustainability - Concerns about the impact of climate change and the need for stabilising a global temperature rise to below 2 degrees Celsius are driving the... 相似文献
3.
Robert Louw Joop van Ham Heiko Nieboer 《Journal of the Air & Waste Management Association (1995)》2013,63(8)
It is proposed that peroxyacetyl nitrate and its homologues are formed in polluted air via hydrogen abstraction from the corresponding aldehyde by nitrogen trioxide, followed by (a relatively fast) combination of the resulting acyl radical with oxygen and NO2. This mechanism provides a simple explanation for the formation of nitric acid, HNO3, as well. Nitrogen trioxide should be able to abstract hydrogen atoms from hydrocarbons, since the H-ONO2 bond strength is about 100 kcal/mole. 相似文献
4.
Isabel W.C.E. Arends Jan G.P. Born W.Ren Ophorst Peter Mulder Robert Louw 《Chemosphere》1989,18(9-10):1965-1970
Pyrolysis (800–900°C, ca. 5 s) of benzene/HC1 mixtures leads to chlorobenzene (1) even in a reducing environment of H2 and/or CH4. With added oxygen, 1 is formed even at 550°C; such slow combustions also yield chlorinated phenols and dibenzofurans. 相似文献
5.
van Dijk HF de Louw MH Roelofs JG Verburgh JJ 《Environmental pollution (Barking, Essex : 1987)》1990,63(1):41-59
To obtain an insight into the effects of a high ammonium deposition on trees young, coniferous trees were planted in pots in a greenhouse and treated with artificial ammonium-enriched rainwater. Application of 480 kg ammonium N ha(-1) year(-1) resulted in an increase of the shoot/root ratio. The biomass of fine roots strongly declined, as did the numbers of mycorrhizae. The fructification of the mycorrhizal fungi was totally inhibited. The nitrogen content of the needles was enhanced, but the levels of potassium, magnesium and calcium decreased sharply. The phosphorus content remained almost unaffected. Much of the nitrogen was stored as arginine. The levels of leaf pigments also increased. Within one year of treatment many of the trees died. The trees that were treated with 48 kg ammonium-N ha(-1) year(-1) did not show any signs of deterioration. 相似文献
6.
The slow combustion of benzene/phenol gives rise to dibenzofuran (DBF) as major product of incomplete combustion, with negligible proportions of dibenzo-p-dioxin (DBD), or benzofuran (BF). Contrary to a recent proposal that acetylene growth reactions, e.g. BF-->DBF, are important in dioxin formation, co-combustion of benzene/phenol with acetylene--around 550 degrees C--did not alter this product pattern. Also, BF was identified as a product from degradation of DBF. 相似文献
7.
Hydrodehalogenation of chlorobenzene on activated carbon and activated carbon supported catalysts 总被引:1,自引:0,他引:1
Chlorinated aromatic compounds in (waste) gases can be removed and/or dehalogenated by passing over a bed of activated carbon (AC) in a hydrogen containing atmosphere. Dehalogenation of the model compound chlorobenzene (PhCl) to HCl is complete at 490 degrees C--rather than the approximately 900 degrees C needed for the mere gas-phase reaction--but part of the benzene moieties is retained on the AC, resulting in its rather rapid deactivation, apparently due to a large decrease in surface area. Therefore, <1 mmol PhCl per gram of 'catalyst' could be processed. At 600 degrees C chlorobenzene yields 100% of both HCl and benzene, but still the AC lost most of its activity in time. Performances are compared of three different commercial ACs. As a HCl-washed AC is just as active, metals are not involved. This acid-washed AC was used as a support for 10 wt% Ni or Fe catalysts. While Fe did not show appreciable activity, results with Ni are promising. The yields of HCl and benzene from PhCl are approximately 100% already at T<400 degrees C, and T(50%) congruent with 260 degrees C, over 200 degrees C lower than with AC alone. There is no appreciable decrease of activity after having injected >20 mmol PhCl per gram of catalyst at partial conversion. 相似文献
8.
Hanneke J. M. Meijer Arike Gill Perry G. B. de Louw Lars W. Van Den Hoek Ostende Julian P. Hume Kenneth F. Rijsdijk 《Die Naturwissenschaften》2012,99(3):177-184
Since 2005, excavations at Mare aux Songes, Mauritius, have revealed the presence of a very rich, ∼4,200-year-old fossil bone
bed including dodo (Raphus cucullatus) bones and bone fragments. The recently excavated dodo assemblage comprises at least 17 individuals and is characterised
by the presence of small and fragile skeletal elements, a dominance of leg elements and an absence of juveniles. The hydrology
of the area suggests that dodos, like many other species, were probably lured to Mare aux Songes by the presence of freshwater
during times of drought. The most likely scenario for the origin of the fossil deposit is that animals became trapped in the
sediment in repeated miring events, which would favour the conservation of hindlimbs. Such a scenario is fully in accordance
with the taphonomic characteristics of the bone assemblage. 相似文献
9.
Pathways from chlorinated phenols as precursors to PCDD/Fs are discussed with focus on the effect of (poly)chlorination on thermochemistry and rate in the displacement of chlorine from a chlorophenol molecule by a (chloro)phenoxy radical (reaction (A) as a key example). Through measurements on the respective methylethers (anisoles) the O-H bond of 2,4,6-TCP turns out to be 5 kcal/ mol, and that in PCP 4 kcal/mol, less strong than O-H in phenol itself. On this basis it is concluded that-in contrast with earlier proposals--displacements such as in reaction (A) are at least as slow as reaction (B) of phenoxy radical with chlorobenzene. PhO. + PhCl -->PhOPh + Cl. reaction B Compared with condensation of two (chloro)phenoxy radicals, such radical/molecule reactions are therefore an insignificant pathway to dioxins in incinerators. 相似文献
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