Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh,India, Vietnam,and Nepal     

A. van Geen  K. Radloff  Z. Aziz  Z. Cheng  M.R. Huq  K.M. Ahmed  B. Weinman  S. Goodbred  H.B. Jung  Y. Zheng  M. Berg  P.T.K. Trang  L. Charlet  J. Metral  D. Tisserand  S. Guillot  S. Chakraborty  A.P. Gajurel  B.N. Upreti 《Applied Geochemistry》2008

One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.  相似文献   

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   

Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers     

Kathleen A. Radloff  Anya R. Manning  Brian Mailloux  Yan Zheng  M. Moshiur Rahman  M. Rezaul Huq  Kazi M. Ahmed  Alexander van Geen 《Applied Geochemistry》2008

Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1× or (4) 10× the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.  相似文献   

Quantitative sinkhole hazard assessment. A case study from the Ebro Valley evaporite alluvial karst (NE Spain)     

Francisco Gutiérrez  Jesús Guerrero  Pedro Lucha 《Natural Hazards》2008,45(2):211-233

Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km² year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology (precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from an alluvial evaporite karst area (0.81 km²) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability of occurrence of 0.14 sinkholes/km² year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km² year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence. Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes.  相似文献   

Drought and institutional adaptation in the Great Plains of Alberta and Saskatchewan, 1914–1939     

Gregory P. Marchildon  Suren Kulshreshtha  Elaine Wheaton  Dave Sauchyn 《Natural Hazards》2008,45(3):391-411

Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought. These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover, these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective institutional adaptation.  相似文献   

Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia   总被引：3，自引：0，他引：3  

Muh Aris Marfai  Lorenz King 《Natural Hazards》2008,44(1):93-109

Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e., the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land subsidence plays an important role in long-term coastal zone management in Semarang.  相似文献   

Deep-seated gravitational slope deformations and their influence on consequent mass movements (case studies from the highest part of the Czech Carpathians)   总被引：3，自引：0，他引：3  

Jan Hradecký  Tomáš Pánek 《Natural Hazards》2008,45(2):235-253

Gravitational spreading of mountain ridges displays primary disequilibrium of flysch mountain areas of the Czech Carpathians. The progression of various types of mass movements is a product of long-term ridge disintegration and is predisposed by the geological structure of the area and the upper Tertiary-Quaternary morphogenesis of the mountain area. Deep-seated slope deformations are spatially interconnected by the occurrence of some other types of slope deformations (e.g. debris flows, debris slides, slumps, rock avalanches, etc.), which pose a considerable risk for the existence of human society. An important causative factor in these dynamically developing hazardous processes is, among other factors, the way in which land has been used in the last three centuries. Therefore, the occurrence of various types of slope deformations is studied in terms of their relation to deep-seated gravitational deformations and in terms of other limiting factors (structural geological, morphological and climatic factors, manmade impacts, etc.). The paper presents several case studies of slope deformations (Velká Čantoryje Mt, Lysá hora Mt, Ropice Mt and Smrk Mt) in the area of the Outer Carpathians within the territory of the Czech Republic and also adverts to some consequences in terms of the socioeconomic structure of the landscape.  相似文献   

The state of land subsidence and prediction approaches due to groundwater withdrawal in China   总被引：13，自引：6，他引：7  

Ye-Shuang Xu  Shui-Long Shen  Zheng-Yin Cai  Guo-Yun Zhou 《Natural Hazards》2008,45(1):123-135

This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city, and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km² and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km² with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two plains and is about 1,135 km² with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary to predict the future development of land subsidence based on present state. Many researchers proposed several approaches to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction practice, 3D seepage model is the best method presently.  相似文献   

Rain-induced debris and mudflow triggering factors assessment in the Santiago cordilleran foothills,Central Chile   总被引：1，自引：1，他引：0  

Sergio A. Sepúlveda  Cristóbal Padilla 《Natural Hazards》2008,47(2):201-215

Debris and mudflows are some of the main geological hazards in the mountain foothills of the Chilean capital city of Santiago. There, the risk of flows triggered in the basins of ravines that drain the range into the city increases with time due to the city growth. A multivariate statistical study based on the logistic regression method is presented. The model provides equations that allow the computation of combined meteorological triggering factors associated with a probability of rain-induced flow occurrence. Daily rainfall, accumulated rainfall and the snowfall level, traditionally considered as the relevant factors, are analysed for a 25-year period. The results show a strong relevance of the rainfall on the day of the flow event over the other factors. However, the relatively low probabilities returned for some real flow events suggest that the model does not capture all the significant variables and the problem is more complex than as it has been traditionally assumed, and further investigations are needed to develop predictive models of flow triggering.  相似文献