共查询到20条相似文献，搜索用时 15 毫秒
1.
Current knowledge on groundwater microbial pathogens and their control 总被引：12，自引：2，他引：10
Received, January 1999/Revised, July 1999, August 1999/Accepted, October 1999 相似文献
2.
Received: 10 May 1999 / Accepted: 16 October 1999 相似文献
3.
Influence of dissimilatory metal reduction on fate of organic and metal contaminants in the subsurface 总被引：5，自引：0，他引：5
Geobacter become dominant members of the microbial community when Fe(III)-reducing conditions develop as the result of organic contamination,
or when Fe(III) reduction is artificially stimulated. These results suggest that further understanding of the ecophysiology
of Geobacter species would aid in better prediction of the natural attenuation of organic contaminants under anaerobic conditions and in
the design of strategies for the bioremediation of subsurface metal contamination.
Received, May 1999/Revised, October 1999/Accepted, October 1999 相似文献
4.
Received: 9 November 1998 / Accepted: 6 October 1999 相似文献
5.
Francis H. Chapelle 《Hydrogeology Journal》2000,8(1):41-46
2 (methanogenesis). In aquifers contaminated by anthropogenic contaminants, an excess of available organic carbon often exists,
and microbial metabolism is limited by the availability of electron acceptors. In addition to changes in groundwater chemistry,
the solid matrix of the aquifer is affected by microbial processes. The production of carbon dioxide and organic acids can
lead to increased mineral solubility, which can lead to the development of secondary porosity and permeability. Conversely,
microbial production of carbonate, ferrous iron, and sulfide can result in the precipitation of secondary calcite or pyrite
cements that reduce primary porosity and permeability in groundwater systems.
Received, January 1999/Revised, July 1999, August 1999/Accepted, October 1999 相似文献
6.
Prediction uncertainty of plume characteristics derived from a small number of measuring points 总被引：1，自引：0，他引：1
A small number of measuring points may inflict a bias on the characterisation of flow and transport based on field experiments
in the unsaturated zone. Simulation of pure advective transport of a Gaussian plume through a setup of 30 regularly placed
measuring points revealed regular temporal fluctuations about the real spatial moments. An irregular setup predicted both
irregular fluctuations and larger discrepancies from the real value. From these considerations, a regular setup is recommended.
Spatial moments were sensitive to the plume size relative to the distance between individual measuring points. To reduce prediction
errors of the variance, the distance between the measuring points should be less than twice the standard deviation of the
examined plume. The total size of the setup should cover several standard deviations of the plume to avoid mass being lost
from the monitored area. Numerical simulations of a dispersing plume (comparing calculations based on 9000 nodes with 30 measuring
points) revealed that vertical and horizontal centres of mass were predicted well at all degrees of heterogeneity, and the
same was the case for horizontal variances. Vertical variances were more susceptible to prediction errors, but estimates were
of the same order of magnitude as the real values.
Received, October 1998/Revised, June 1999, October 1999/Accepted, November 1999 相似文献
7.
S. A. Hayward A. K. A. Pryde R.F. de Dombal M. A. Carpenter M. T. Dove 《Physics and Chemistry of Minerals》2000,27(4):285-290
Calculations of the Rigid Unit Modes (RUMs) allowed in the nepheline structure are used to explain the diffuse scattering
previously seen in electron diffraction experiments. The RUM calculations also show that the modulation wavelength for incommensurate
nephelines is essentially determined by the framework topology. X-ray diffraction is used to measure the intensity of the
diffuse scattering as a function of temperature. The diffuse intensity increases sharply at 308 K. This effect is interpreted
as being due to the softening of a phonon mode, indicating a phase transition. Measurements of this phase transition below
the transition temperature are made using hard mode infrared spectroscopy.
Received: 17 February 1999 / Revised, accepted. 15 October 1999 相似文献
8.
The reliable yield of a water-supply well depends on many different factors, including the properties of the well and the
aquifer; the capacities of the pumps, raw-water mains, and treatment works; the interference effects from other wells; and
the constraints imposed by abstraction licences, water quality, and environmental issues. A relatively simple methodology
for estimating reliable yields has been developed that takes into account all of these factors. The methodology is based mainly
on an analysis of water-level and source-output data, where such data are available. Good operational data are especially
important when dealing with wells in shallow, unconfined, fissure-flow aquifers, where actual well performance may vary considerably
from that predicted using a more analytical approach. Key issues in the yield-assessment process are the identification of
a deepest advisable pumping water level, and the collection of the appropriate well, aquifer, and operational data. Although
developed for water-supply operators in the United Kingdom, this approach to estimating the reliable yields of water-supply
wells using operational data should be applicable to a wide range of hydrogeological conditions elsewhere.
Received, September 1998/Revised, May 1999, September 1999/Accepted, October 1999 相似文献
9.
macroscale processes that perturb general groundwater chemistry and therefore mineral–water equilibria; and microscale interactions, where attached organisms locally perturb mineral–water equilibria, potentially releasing limiting trace nutrients
from the dissolving mineral.
In the contaminated unconfined glacio-fluvial aquifer near Bemidji, Minnesota, USA, carbonate chemistry is influenced primarily
at the macroscale. Under oxic conditions, respiration by native aerobic heterotrophs produces excess carbon dioxide that promotes
calcite and dolomite dissolution. Aerobic microorganisms do not colonize dolomite surfaces and few occur on calcite. Within
the anoxic groundwater, calcite overgrowths form on uncolonized calcite cleavage surfaces, possibly due to the consumption
of acidity by dissimilatory iron-reducing bacteria. As molecular oxygen concentration increases downgradient of the oil pool,
aerobes again dominate and residual hydrocarbons and ferrous iron are oxidized, resulting in macroscale carbonate-mineral
dissolution and iron precipitation.
Feldspars, in contrast, weather exclusively at the microscale near attached microorganisms, principally in the anoxic region
of the plume. Native organisms preferentially colonize feldspars that contain trace phosphorus as apatite inclusions, apparently
as a consequence of the low P concentration in the groundwater. These feldspars weather rapidly, whereas nearby feldspars
without trace P are uncolonized and unweathered. Feldspar dissolution is accompanied by the precipitation of secondary minerals,
sometimes on the bacterial cell wall itself.
These observations suggest a tightly linked biogeochemical system whereby microbial processes control mineral diagenesis at
many scales of interaction, and the mineralogy and mineral chemistry influence microbial ecology. Only the macroscale interaction,
however, is easily observable by standard geochemical methods, and documentation of the microscale interactions requires microscopic
examination of microorganisms on mineral surfaces and the locally intense diagenetic reactions that result.
Received, May 1999/Revised, October 1999/Accepted, October 1999 相似文献
10.
Wetlands play an important role in water conservation, environmental protection, and biodiversity conservation. Remote sensing is an economical and efficient technique for wetland monitoring which can limit disturbance in sensitive areas and support wetland conservation. In this paper, we used three phases of Thematic Mapper/Enhanced Thematic Mapper plus (TM/ETM+) remote sensing images from October 1989, October 1999, and October 2009 to study wetlands in Xingzi County. The images were segmented using the object-oriented remote sensing image interpretation software eCognition Developer 8.64, then segmented images were classified by slope, digital elevation model (DEM) data, Normalized Difference Vegetation Index (NDVI), Specific Leaf Area Vegetation Index (SLAVI), and Land and Water Masks (LWM) index to produce land type classification maps. Land use change information was obtained by analyzing the superposition of two classification maps of the wetland area from different years. The results showed that landscape patches in Xingzi County displayed fragmentation in their spatial distribution over time. Based on an index of changes in landscape patches, the fastest growing landscape type is grassland, while the fastest decreasing type is irrigated land. Dominant driving factors of changes in Xingzi County’s wetland landscape are population growth and policy changes. 相似文献
11.
Modeling microbial processes in porous media 总被引：8，自引：1，他引：7
The incorporation of microbial processes into reactive transport models has generally proceeded along two separate lines
of investigation: (1) transport of bacteria as inert colloids in porous media, and (2) the biodegradation of dissolved contaminants
by a stationary phase of bacteria. Research over the last decade has indicated that these processes are closely linked. This
linkage may occur when a change in metabolic activity alters the attachment/detachment rates of bacteria to surfaces, either
promoting or retarding bacterial transport in a groundwater-contaminant plume. Changes in metabolic activity, in turn, are
controlled by the time of exposure of the microbes to electron acceptors/donor and other components affecting activity. Similarly,
metabolic activity can affect the reversibility of attachment, depending on the residence time of active microbes. Thus, improvements in quantitative analysis of active
subsurface biota necessitate direct linkages between substrate availability, metabolic activity, growth, and attachment/detachment
rates. This linkage requires both a detailed understanding of the biological processes and robust quantitative representations
of these processes that can be tested experimentally. This paper presents an overview of current approaches used to represent
physicochemical and biological processes in porous media, along with new conceptual approaches that link metabolic activity
with partitioning of the microorganism between the aqueous and solid phases.
Received, January 1999 · Revised, June 1999, July 1999 · Accepted, October 1999 相似文献
12.
Irina Gaus 《Hydrogeology Journal》2000,8(2):218-229
Pesticides are a potential threat to the quality of extracted groundwater when the water-supply area is used for agricultural
activities. This problem is discussed for the water-supply area of Sint-Jansteen, The Netherlands, where measured pesticide
concentrations in the extracted water regularly exceed EU limits (0.1 μg/L). Groundwater samples taken from the aquifer within
the water-supply area show low contamination, but samples taken from the extracted water occasionally contain pesticides,
making the water inadequate for drinking-water purposes. The more intense contamination of the extracted water is caused by
the change in the natural groundwater flow pattern near the extraction wells. In this area, pesticide use cannot be avoided
easily, and an approach is given to differentiate pesticide use in the area according to expected travel time toward the wells
and the chemical characteristics of the pesticides. A groundwater flow model for the area is developed and the effects of
groundwater extraction on the natural flow pattern are evaluated. Using particle tracking, the travel-time zones are determined.
Combining these results and the degradation behavior of certain pesticides led to an optimal scheme to integrate agricultural
activities and groundwater extraction in the area. This is illustrated for five different types of pesticides (atrazine, simazine,
bentazone, MCPA, and mecoprop).
Received, October 1998/Revised, July 1999, September 1999/Accepted, November 1999 相似文献
13.
In this study a non-hydrostatic version of Penn State University (PSU) -- NationalCenter for Atmospheric Research (NCAR) mesoscale model is used to simulate thesuper cyclonic storm that crossed Orissa coast on 29 October 1999. The model isintegrated up to 123 h for producing 5-day forecast of the storm. Several importantfields including sea level pressure, horizontal wind and rainfall are compared with theverification analysis/observation to examine the performance of the model. The modelsimulated track of the cyclone is compared with the best-fit track obtained from IndiaMeteorological Department (IMD) and the track obtained from NCEP/NCAR reanalysis. The model is found to perform reasonably well in simulating the track and in particular, the intensity of the storm. 相似文献
14.
High-impact mesoscale weather events, occurring in different parts of India in all seasons, lead to major weather- and climate-related
disasters. Several research groups and operational weather forecasting centres in India have adopted mesoscale models for
research and operational usage. This paper reviews the work done by different groups with respect to two specific events,
(1) unprecedented locally heavy rainfall near Mumbai (Santa Cruz) on 26 and 27 July 2005 and (2) the Orissa super-cyclone
of 29 and 30 October 1999 from its incipient stage on 24 and 25 October 1999. Considerable variability in the prediction of
the intensity and location of mesoscale heavy rainfall, as well as in the intensity and path of the super-cyclone, are found.
In order to reduce uncertainty in dynamical prediction, it is necessary that the model dynamics, physics, resolution, boundary
conditions and availability of data on land–ocean surface processes are tuned separately to the specific event types, such
as heavy monsoon rainfall, tropical cyclone genesis and movement and severe local thunderstorms, as the processes controlling
such types of events may require suitable treatments for their proper simulations through appropriate dynamics, physics and
resolution. 相似文献
15.
H. Lemmens M. Czank G. Van Tendeloo S. Amelinckx 《Physics and Chemistry of Minerals》2000,27(6):386-397
Using minimum exposure techniques, it is feasible to perform high resolution electron microscopy on the α-cristobalite phase
of (Si0.9 Ge0.1)O2, which is extremely radiation sensitive. Such images reveal atomic scale information of twins and tridymite-like stacking
faults on (1 1 1)β planes, as well as of domain boundaries resulting from the β→α transition. Polytype structures are formed in certain cases.
Morphological features suggest that the phase transformation cristobalite → tridymite proceeds by means of a zonal dislocation
mediated synchro-shear process on (1 1 1)β planes; the geometry of this process is analyzed.
Received: 13 June 1999 / Accepted: 30 October 1999 相似文献
16.
1999—2008年中国地区雪密度的时空分布及其影响特征 总被引：3，自引：2，他引：1
利用1999—2008年地面积雪观测资料,对全国范围内的雪密度时空分布特征进行分析.结果表明,西北和东北是我国主要的积雪区,从10月到翌年4月基本都有雪存在.全国雪密度每月的最高值从10月份开始到1月份一直南移,从1月份到4月份不断北移.最大密度发生在1月份江南地区的湖南和江西的交界处.江南地区积雪持续时间短,变化明显,属于瞬时性积雪.东北和新疆地区的雪密度也相对较高,积雪持续时间长,雪密度变化相对平稳,大部分属于季节性积雪.在东北和西北地区选取9个站点进行雪密度的变化研究,可以看出:从11月中旬到3月上旬是雪密度稳定期,10月到11月上旬和3月中旬到4月是雪密度非稳定期.对西北和东北的降水、气温、雪深和雪密度做相关分析,表明:雪深是西北和东北地区雪密度的主要贡献因子. 相似文献
17.
Since the discovery of a depletion of the stratospheric ozone layer over Antarctica in 1979, scientific attention has been directed towards the effects of increased doses of ultraviolet radiation on phytoplankton in other ecosystems. Little is known about the effects of ultraviolet-B (280–320 nm) radiation (UVBR) on temperate estuarine phytoplankton. Freshly collected phytoplankton samples from Central San Francisco Bay were exposed to ambient UVBR in quartz bottles and monitored for biomass and nutrient uptake rates for comparison with phytoplankton dispensed into bottles made of polycarbonate that effectively filtered out the UVBR to evaluate response to natural UVBR exposure. Short-term (10–12 h) exposure experiments were carried out monthly from October 1998 to October 1999. No significant effect of UVBR on chlorophylla concentrations was found but a clear deleterious effect of UVBR on nutrient uptake was observed. 相似文献
18.
Rio Tinto estuary (Spain): 5000 years of pollution 总被引：6，自引：0，他引：6
R.A. Davis Jr. A. T. Welty J. Borrego J. A. Morales J. G. Pendon J. G. Ryan 《Environmental Geology》2000,39(10):1107-1116
Mining of massive sulfide deposits in southwestern Spain extending back to the Copper and Bronze Ages has resulted in the
pollution of the Rio Tinto fluvial-estuarine complex, the site of Columbus' departure for the New World in 1492. Additional
sources of potential pollution include the large industrial complex at Huelva near the lower portion of the estuary. Extensive
analysis of surface sediment samples and cores has established that there are no geographic trends in the distribution of
the pollutants, which include Cu, Fe, Pb, Zn, Ti, Ba, Cr, V and Co. These data have, however, demonstrated that tidal flux
within the estuary carries phosphorus and perhaps other elements from the industrial complex at Huelva to the tidal limit
of the system, several kilometers upstream from the discharge site. Radiometric analysis of short cores shows that sedimentation
rates over at least the past couple of centuries have been about 0.3 cm/year. These data and that from a single deep core
demonstrate that the estuary was polluted from mining activity long before the large-scale operations began in the late nineteenth
century.
Received: 3 May 1999 · Accepted: 18 October 1999 相似文献
19.
Increasing sediment loads entering the Lake Tanganyika ecosystem are hastening the need for improved understanding of the linkages between catchment characteristics and influent sediment transport and loading. Sediment loads of two catchments at the southern end of the lake were estimated for October 1998–December 1999, and catchment characteristics determined using GIS. It was found that both sediment yields and loads were higher from the catchment of the Lunzua River (19.8 t km?2 and 20,114 t, respectively) compared with that of the Kalambo (4.1 t km?2 and 12,197 t) in 1999. These differences were both attributed to the smaller size and higher road density of the Lunzua catchment, and suggest that previous recommendations regarding the positioning of underwater lake reserves fail to take into account the low sediment retention capacity of small mountainous rivers. Differences between the study rivers in the transport of suspended sediments, organic matter, and bedload sediments into the lake were also found, the latter determined by the novel application of the 'McLaren Model'. 相似文献
20.
Pit lakes form when open-pit mining operations are discontinued and dewatering ceases. The increase in open-pit metal mining
since the 1970s will lead to the formation of numerous pit lakes over the next 50 years. Many of these lakes will develop
acid sulfate conditions with high levels of dissolved metals. Approaches to remediation of these conditions that have been
recommended include the addition of lime or other alkaline materials and the stimulation of sulfate-reducing bacteria. However,
prevention rather than remediation is probably the preferable approach. Measures to prevent oxidation of mining waste and
wall rocks, including measures to fill pits quickly with water, to inhibit the activity of acidophilic sulfur-oxidizing bacteria,
and to promote anoxic conditions at the lake bottoms may minimize the formation of acids and dissolved metals.
Received: 26 August 1999 · Accepted: 29 October 1999 相似文献