Phytoreduction and volatilization of mercury by ascorbate in Arabidopsis thaliana, European beech and Norway spruce     

Florian Battke  Dieter Ernst  Frank Fleischmann  Stefan Halbach 《Applied Geochemistry》2008

Mercury vapor (Hg⁰) emission from plants contributes to the atmospheric Hg cycle. Young barley (Hordeum vulgare L.) plants grown on a hydroponic cultivation medium containing Hg(II) have previously been shown to increase their Hg⁰ emission significantly by reduction of Hg(II) with endogenous ascorbic acid. Regarding the potential contribution to the Hg cycle from the vast forest-covered areas, it was important to investigate this mechanism in trees. The increase in Hg⁰ emission from young European beech plants cultivated on a HgCl₂ medium exceeded that from controls by ca. tenfold and was proportional to the Hg(II) concentration. From these experiments, a flux of 12.8 μg Hg⁰/h/m² was estimated at an exposure of the roots to 20 μM Hg(II). Mercury vapor release from homogenates of Norway spruce needles exceeded that from European beech leaves by a factor of 2.3–4, i.e. in proportion to the reported AA concentrations; the reduction was maximal at alkaline pH which is typical for AA. The 8.4-fold difference in Hg⁰ release between homogenates from wild-type Arabidopsis thaliana and from its AA-deficient mutant vtc 1-1 also paralleled the reported difference in AA levels of both species. It is concluded that the phytoreduction and vaporization of Hg by AA is an important mechanism as much for Hg detoxification in trees as for Hg emission to the atmosphere. The efficiency of this process seems to result from the optimal coordination of transfer and biochemical transformation of mercuric ions and Hg vapor. There is no evidence for a relevant difference in the mechanisms of biogenic Hg(II) reduction between grass plants and trees.  相似文献   

The hydrochemistry of a semi-arid pan basin case study: Sua Pan,Makgadikgadi, Botswana     

Frank D. Eckardt  Robert G. Bryant  Graham McCulloch  Baruch Spiro  Warren W. Wood 《Applied Geochemistry》2008

This study presents results on the fluid and salt chemistry for the Makgadikgadi, a substantial continental basin in the semi-arid Kalahari. The aims of the study are to improve understanding of the hydrology of such a system and to identify the sources of the solutes and the controls on their cycling within pans. Sampling took place against the backdrop of unusually severe flooding as well as significant anthropogenic extraction of subsurface brines. This paper examines in particular the relationship between the chemistry of soil leachates, fresh stream water, salty lake water, surface salts and subsurface brines at Sua Pan, Botswana with the aim of improving the understanding of the system’s hydrology. Occasionally during the short wet season (December–March) surface water enters the saline environment and precipitates mostly calcite and halite, as well as dolomite and traces of other salts associated with the desiccation of the lake. The hypersaline subsurface brine (up to TDS 190,000 mg/L) is homogenous with minor variations due to pumping by BotAsh mine (Botswana Ash (Pty) Ltd.), which extracts 2400 m³ of brine/h from a depth of 38 m. Notable is the decrease in TDS as the pumping rate increases which may be indicative of subsurface recharge by less saline water. Isotope chemistry for Sr (⁸⁷Sr/⁸⁶Sr average 0.722087) and S (δ³⁴S average 34.35) suggests subsurface brines have been subject to a lithological contribution of undetermined origin. Recharge of the subsurface brine from surface water including the Nata River appears to be negligible.  相似文献   

Weed species diversity on arable land of the dryland areas of central Tanzania: impacts of continuous application of traditional tillage practices     

Riziki S. Shemdoe  Frank M. Mbago  Idris S. Kikula  Patrick L. Van Damme 《GeoJournal》2008,71(2-3):107-115

This paper presents findings from a study that assessed influence of continuous application of a particular traditional tillage practice on weed species richness, diversity and composition and identifies weed species with positive benefits to the communities in semi-arid areas of Mpwapwa district, central Tanzania. In this area farmers apply three different traditional tillage practices which are no-till (NT), shallow tillage (ST) and Ridging System (RT). A total of 36 farm fields were surveyed in 2006/2007 cropping season where 63 weed species from 26 families were identified. Analysis of variance indicated significant differences between practices (p < 0.05), with NT practice having highest weed species richness and diversity. Among the five more prevalent weed species appearing, Bidens lineariloba was observed to exist in all the three practices. Community representatives during focus group discussions indicated 9 weed species out of 63 identified to have beneficial uses. These species are Cleome hirta, Amaranthus graecizans, Bidens lineoriloba, Bidens pilosa, Dactyloctenium aegyptium, Launaea cornuta, Heteropogon contortus, Tragus berteronianus and Trichodesma zeylanicum. Their main uses include leaf-vegetable, medicines, fodder and materials for thatching. From this study NT has highest weed species richness and diversity which therefore suggests that much more time is needed for weeding in this practice compared to other practice which was the farmers’ concern. It was also noted that although weed species have negative effects in crop production and production costs, they still play a vital role in food security and for the health of different people in marginal areas as well as for the complete ecosystem including micro and macrofauna.  相似文献   

Detection of free vertical convection and double-diffusion in groundwater monitoring wells with geophysical borehole measurements     

Susann Berthold  Frank Börner 《Environmental Geology》2008,54(7):1547-1566

Two algorithms for in-situ detection and identification of vertical free convective and double-diffusive flows in groundwater monitoring wells or boreholes are proposed. With one algorithm the causes (driving forces) and with the other one the effects (convection or double-diffusion) of vertical transport processes can be detected based on geophysical borehole measurements in the water column. Five density-driven flow processes are identified: thermal, solutal, and thermosolutal convection leading to an equalization, as well as saltfingers and diffusive layering leading to an intensification of a vertical density gradient. The occurrence of density-driven transport processes could be proven in many groundwater monitoring wells and boreholes; especially shallow sections of boreholes or groundwater monitoring wells are affected dramatically by such vertical flows. Deep sections are also impaired as the critical threshold for the onset of a density-driven flow is considerably low. In monitoring wells or boreholes, several sections with different types of density-driven vertical flows may exist at the same time. Results from experimental investigations in a medium-scale testing facility with high aspect ratio (height/radius = 19) and from numerical modeling of a water column agree well with paramters of in-situ detected convection cells.  相似文献   

CLEARANCE PROBLEMS IN AFRICAN RESEARCH     

Frank E. Bernard  Bobbie J. Walter 《The Professional geographer》1968,20(1):28-32

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Discussion of the Möller radiation chart     

Prof. Wilford G. Zdunkowski  Frank A. Lombardo 《Theoretical and Applied Climatology》1967,15(1-2):141-155

Summary M?ller's assumptions for the carbon dioxide-water vapor overlap region, which lead to the construction of his radiation chart, are reinvestigated in the light of modern theory. A new radiation chart, taking into account the carbon dioxide-water vapor overlap, is constructed using water vapor and carbon dioxide absorption data as furnished byM?ller andElsasser respectively. The results of the radiative fluxes computed from the new chart are compared with equivalent results using the original M?ller and the revised Elsasser radiation diagrams, as well as with measurements.

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Zusammenfassung Die Berechtigung derM?llerschen Annahme zur getrennten Behandlung von Kohlens?ure- und Wasserdampfabsorption zwecks Konstruktion eines atmosph?rischen Strahlungsdiagrammes wird im Lichte der modernen Theorie diskutiert. Ein neues Strahlungspapier wird vorgelegt, das die gleichzeitige Anwesenheit von Kohlens?ure und Wasserdampf im gleichen Spektralbereich berücksichtigt. Dieses beruht auf Wasserdampf- und Kohlens?uredaten, die vonM?ller undElsasser vorgegeben wurden. Nach dem neuen Strahlungsdiagramm berechnete Werte werden mit Me?werten und theoretischen Werten verglichen, die mit dem ursprünglichen M?llerschen und mit dem verbesserten Elsasserschen Strahlungspapier ermittelt wurden.

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Résumé Au vu des théories modernes, on discute l'hypothèse formulée parM?ller et sa justification, hypothèse selon laquelle il est nécessaire de traiter séparément l'absorption du dioxyde de carbone et celle de la vapeur d'eau lors de l'établissement d'un diagramme du rayonnement atmosphérique. On propose alors un nouvel abaque qui tient compte de la présence simultanée du dioxyde de carbone et de la vapeur d'eau dans la même région spectrale. Cet abaque s'appuie sur les valeurs données parM?ller et parElsasser, valeurs valables pour ces deux gaz. On compare le résultat de calculs effectués avec ce nouvel abaque à des mesures et à des valeurs théoriques ces dernières étant basées tant sur les travaux originaux deM?ller que sur l'abaque amélioré deElsasser.

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With 4 Figures  相似文献   

The volcano-magnetic effect     

Frank D. Stacey  Kenneth G. Barr  Geoffrey R. Robson 《Pure and Applied Geophysics》1965,62(1):96-104

Summary A geometrically simple volcano is considered, havig a spherical magma chamber of 2.5 km radius centred at 10 km depth. The Curie point isotherm is assumed to be a plane at 20 km depth, except for the spherical volume which is also non-magnetic. The stress pattern in the vicinity of the spherical chamber, due to regional stress of sufficient intensity to cause an eruptions, is used to calculate the change in magnetization which results from the piezomagnetic effect through the volume of solid rock. The consequent magnetic field anomaly at the surface is then obtaied by numerical integration of the dipole law of force over the stressed volume. For rocks of the type found on the volcanic island of St. Vincent (West Indies), this model gives a maximum local volcano-magnet c effect of about 7 gammas.  相似文献   

Properties of structure and function of cadmium-binding proteins/peptides from Euglena gracilis     

C Daniel Weber  Frank Shaw III  David H Petering 《Marine environmental research》1988,24(1-4)

Euglena gracilis makes two small Cd-binding proteins/peptides (Cd-BP I and Cd-BP II) in response to exposure to Cd²⁺. These proteins migrate slower than mammalian Cd-metallothionein (Cd-Mt) through Sephadex G-75, but like Cd-Mt also contain Zn and are separated into two species when chromatographed over a DEAE column. Both BPs are much less stable than Cd-Mt under acidic conditions. One source of this instability is that at least Cd-BP II contains acid-labile sulfide co-ordinated to the metals. It has been quantitated in Cd-BP II and shown to have a value of 1·25 ± 0·10 S²⁻/Cd. The reactivity of the Cd-binding sites in ligand substitution and thioldisulfide exchange reactions has been assessed. The reactions of Cd-BP I and II with pyridylazoresorcinol (PAR) were slow and displayed complex kinetic behavior. Similarly, both Cd-BPs react slowly and with complicated kinetics with 5,5′-dithiobis-(2-nitrobenzoate).  相似文献   

Direct determination of organic carbon in modern reef sediments and calcareous organisms after dissolution of carbonate     

Mark W. Sandstrom  Frank Tirendi  Alan Nott 《Marine Geology》1986,70(3-4):321-329

An improved method for the direct determination of organic carbon in calcareous marine sediments, organisms and particulate matter is described. Samples are dissolved in phosphoric acid to remove carbonates, purged with oxygen to remove CO₂, and the resulting acidic solution is analysed for total (dissolved and particulate) organic carbon. The method is rapid, involves minimal sample manipulation, and is both accurate (better than ± 2%) and precise (better than ± 0.2 mg organic carbon/g sediment). The method is especially suitable for modern carbonate sediments which have low levels of predominantly acid-soluble organic carbon.  相似文献   

Recovery of thermohaline circulation under CO₂ stabilization and overshoot scenarios   总被引：1，自引：0，他引：1  

Norikazu. Nakashiki  Dong-Hoon Kim  Frank O. Bryan  Yoshikatsu Yoshida  Daisuke Tsumune  Koki Maruyama  Hideyuki Kitabata 《Ocean Modelling》2006,15(3-4):200

In this study we examine the behavior of the thermohaline circulation, as simulated by the Community Climate System Model version 3 (CCSM3), for several centuries following CO₂ stabilization for the SRES B1 and A1B scenarios and for an “overshoot” scenario in which CO₂ levels temporarily reach the same level as in the A1B scenario before declining to an ultimate stabilization level that is identical to the B1 case. While we find no evidence for irreversible changes of the thermohaline circulation in the overshoot experiment, the interplay of the different timescales of the temperature response of the surface and interior ocean does lead to a number of differences in the long-term response of the ocean between it and the B1 stabilization scenario where the same GHG levels are approached by different paths. The stronger initial warming and its slow penetration into the deeper ocean, followed by a transient surface cooling in the overshoot scenario leads to lower static stability, deeper mixing, and a more rapid recovery of the thermohaline circulation than in the B1 stabilization scenario. While the overshoot scenario recovers surface conditions (e.g. SST, sea ice extent) very similar to the B1 scenario shortly after reaching the same GHG levels, the additional accumulation of heat in the interior ocean during the period of higher forcing causes the global mean ocean temperature and steric sea level to remain higher than in the B1 stabilization scenario for at least another several centuries.  相似文献