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141.
Naumburg E Mata-Gonzalez R Hunter RG McLendon T Martin DW 《Environmental management》2005,35(6):726-740
Although changes in depth to groundwater occur naturally, anthropogenic alterations may exacerbate these fluctuations and, thus, affect vegetation reliant on groundwater. These effects include changes in physiology, structure, and community dynamics, particularly in arid regions where groundwater can be an important water source for many plants. To properly manage ecosystems subject to changes in depth to groundwater, plant responses to both rising and falling groundwater tables must be understood. However, most research has focused exclusively on riparian ecosystems, ignoring regions where groundwater is available to a wider range of species. Here, we review responses of riparian and other species to changes in groundwater levels in arid environments. Although decreasing water tables often result in plant water stress and reduced live biomass, the converse is not necessarily true for rising water tables. Initially, rising water tables kill flooded roots because most species cannot tolerate the associated low oxygen levels. Thus, flooded plants can also experience water stress. Ultimately, individual species responses to either scenario depend on drought and flooding tolerance and the change in root system size and water uptake capacity. However, additional environmental and biological factors can play important roles in the severity of vegetation response to altered groundwater tables. Using the reviewed information, we created two conceptual models to highlight vegetation dynamics in areas with groundwater fluctuations. These models use flow charts to identify key vegetation and ecosystem properties and their responses to changes in groundwater tables to predict community responses. We then incorporated key concepts from these models into EDYS, a comprehensive ecosystem model, to highlight the potential complexity of predicting community change under different fluctuating groundwater scenarios. Such models provide a valuable tool for managing vegetation and groundwater use in areas where groundwater is important to both plants and humans, particularly in the context of climate change. 相似文献
142.
143.
采用氦气碰撞模式和内标法抑制ICP-MS测试地下水中痕量元素的多原子离子干扰和基体效应。探讨He流量、内标元素、宏量离子等因素对测定的影响,结果表明:187Re、208Pb响应值与He流量呈线性下降模型,其他离子为指数下降模型,He流量为2. 5 m L/min~3. 0 m L/min时满足地下水质量分级测定要求;内标元素的响应因子随质量浓度的增大而降低,16. 0μg/L以上时趋于稳定;酸度显著影响测定误差,选用较大质量数的内标元素和保持样品酸度的一致可提高测定的准确度。 相似文献
144.
Integration of traditional and innovative characterization techniques for flux-based assessment of Dense Non-aqueous Phase Liquid (DNAPL) sites 总被引:1,自引:0,他引:1
Nandita B. Basu P. Suresh C. Rao Irene C. Poyer Subhas Nandy Megharaj Mallavarapu Ravi Naidu Greg B. Davis Bradley M. Patterson Michael D. Annable Kirk Hatfield 《Journal of contaminant hydrology》2009,105(3-4):161-172
Key attributes of the source zone and the expanding dissolved plume at a trichloroethene (TCE) site in Australia were evaluated using trends in groundwater monitoring data along with data from on-line volatile organic compound (VOC) samplers and passive flux meters (PFMs) deployed in selected wells. These data indicate that: (1) residual TCE source mass in the saturated zone, estimated using two innovative techniques, is small ( 10 kg), which is also reflected in small source mass discharge ( 3 g/day); (2) the plume is disconnecting, based on TCE concentration contours and TCE fluxes in wells along a longitudinal transect; (3) there is minimal biodegradation, based on TCE mass discharge of 6 g/day at a plume control plane 175 m from source, which is also consistent with aerobic geochemical conditions observed in the plume; and (4) residual TCE in the vadose zone provides episodic inputs of TCE mass to the plume during infiltration/recharge events. TCE flux data also suggest that the small residual TCE source mass is present in the low-permeability zones, thus making source treatment difficult. Our analysis, based on a synthesis of the archived data and new data, suggests that source treatment is unwarranted, and that containment of the large TCE plume ( 1.2 km long, 0.3 km wide; 17 m deep; 2000–2500 kg TCE mass) or institutional controls, along with a long-term flux monitoring program, might be necessary. The flux-based site management approach outlined in this paper provides a novel way of looking beyond the complexities of groundwater contamination in heterogeneous domains, to make intelligent and informed site decisions based on strategic measurement of the appropriate metrics. 相似文献
145.
pH dependence of persulfate activation by EDTA/Fe(III) for degradation of trichloroethylene 总被引:3,自引:0,他引:3
The ability of free ferrous ion activated persulfate (S2O82−) to generate sulfate radicals (SO4−) for the oxidation of trichloroethylene (TCE) is limited by the scavenging of SO4− with excess Fe2+ and a quick conversion of Fe2+ to Fe3+. This study investigated the applicability of ethylene-diamine-tetra-acetic acid (EDTA) chelated Fe3+ in activating persulfate for the destruction of TCE in aqueous phase under pH 3, 7 and 10. Fe3+ and EDTA alone did not appreciably degrade persulfate. The presence of TCE in the EDTA/Fe3+ activated persulfate system can induce faster persulfate and EDTA degradation due to iron recycling to activate persulfate under a higher pH condition. Increasing the pH leads to increases in pseudo-first-order-rate constants for TCE, S2O82− and EDTA degradations, and Cl generation. Accordingly, the experiments at pH 10 with different EDTA/Fe3+ molar ratios indicated that a 1/1 ratio resulted in a remarkably higher degradation rate at the early stage of reaction as compared to results by other ratios. Higher persulfate dosage under the EDTA/Fe3+ molar ratio of 1/1 resulted in greater TCE degradation rates. However, increases in persulfate concentration may also lead to an increase in the rate of persulfate consumption. 相似文献
146.
Tetsuro Agusa Takashi Kunito Pham Thi Kim Trang Pham Hung Viet 《Environmental pollution (Barking, Essex : 1987)》2009,157(2):396-403
This study investigated the status of arsenic (As) exposure from groundwater and rice, and its methylation capacity in residents from the Red River Delta, Vietnam. Arsenic levels in groundwater ranged from <1.8 to 486 μg/L. Remarkably, 86% of groundwater samples exceeded WHO drinking water guideline of 10 μg/L. Also, estimated inorganic As intake from groundwater and rice were over Provisional Tolerable Weekly Intake (15 μg/week/kg body wt.) by FAO/WHO for 92% of the residents examined. Inorganic As and its metabolite (monomethylarsonic acid and dimethylarsinic acid) concentrations in human urine were positively correlated with estimated inorganic As intake. These results suggest that residents in these areas are exposed to As through consumption of groundwater and rice, and potential health risk of As is of great concern for these people. Urinary concentration ratios of dimethylarsinic acid to monomethylarsonic acid in children were higher than those in adults, especially among men, indicating greater As methylation capacity in children. 相似文献
147.
Evidence of groundwater management by aquifer users emerging under Integrated Water Resources Management (IWRM) initiatives is presented, by analyzing the Consejos Técnicos de Aguas (COTAS; Technical Water Councils or Aquifer Management Councils) in the state of Guanajuato, Mexico, established between 1998 and 2000 by the Guanajuato State Water Commission (CEAG). Two contrasting models influenced this attempt to promote user self-regulation of groundwater extractions: locally autonomous aquifer organizations with powers to regulate groundwater extractions versus aquifer organizations with advisory powers only. The COTAS were conceived as locally autonomous IWRM organizations consisting of all aquifer users that would work together to reduce groundwater over-extraction and stabilize aquifer levels, at a later stage. CEAG followed an expedient IWRM approach to develop the COTAS, setting achievable targets for their development and explicitly focusing on active stakeholder participation. The article shows that, due to struggles between the state and federal levels, the COTAS have become advisory bodies that have not led to reductions in groundwater extractions. It concludes that achieving user self-regulation of groundwater extractions requires a fuller delegation of responsibilities to the COTAS which would not be possible without addressing the institutional struggles over water governance at the state and federal levels. 相似文献
148.
Groundwater and water resources management play a key role in conserving the sustainable conditions in arid and semi-arid
regions. Applying some techniques that can reveal the critical and hot conditions of water resources seem necessary. In this
study, kriging and cokriging methods were evaluated for mapping the groundwater depth across a plain in which has experienced
different climatic conditions (dry, wet, and normal) and consequently high variations in groundwater depth in a 12 year led
in maximum, minimum, and mean depths. During this period groundwater depth has considerable fluctuations. Results obtained
from geostatistical analysis showed that groundwater depth varies spatially in different climatic conditions. Furthermore,
the calculated RMSE showed that cokriging approach was more accurate than kriging in mapping the groundwater depth though there was not a distinct
difference. As a whole, kriging underestimated the real groundwater depth for dry, wet, and normal conditions by 5.5, 2.2,
and 5.3%, while cokriging underestimations were 3.3, 2, and 2.2%, respectively; which showed the unbiasedness in estimations.
Results implied that in the study area farming and cultivation in dry conditions needs more attention due to higher variability
in groundwater depth in short distances compared to the other climate conditions. It is believed that geostatistical approaches
are reliable tools for water resources managers and water authorities to allocate groundwater resources in different environmental
conditions. 相似文献
149.
Factor analysis and linear regression model (LRM) of metal speciation and physico-chemical characters of groundwater samples 总被引:2,自引:0,他引:2
An approach is described for viewing the interrelationship between different variables and also tracing the sources of pollution
of groundwater of north Chennai (India). The data set of 43 variables which include major ions, minor ions and trace metal
speciation (Cu, Pb, Cd and Zn) collected during the pre-monsoon and post-monsoon seasons of the year 2000–2001, was subjected
to R-mode factor analysis to comprehend the distribution pattern of the said variables. It was found that first factor measures
salinity and hardness which explained 19.12% of the total variance (comprised of variables EC, TDS, Na+, K+, Ca2+, Mg2+, total hardness, Cl− and SO4
2−) during pre-monsoon, while it was 25.08% during post-monsoon. The second and third factors were attributed to speciation
of zinc and copper ions during both pre-monsoon and post-monsoon. Although there were two more factors, loaded with speciation
parameters of lead and cadmium, the variance of them were less than 10%. From this study it is seen that sea water intrusion,
municipal solid waste disposal are the identified sources of component of pollution. The importance of metal ions is taking
a secondary role and the anthropogenic origin-industrial activity, is the reason in the evaluation of pollution status as
they come in the second, third, fourth and fifth factors. As the trace metal speciation was grouped in separate factors, linear
regression model (LRM) with correlation analysis was applied to check its validity for prediction of speciation and to apply
LRM for rapid monitoring of water pollution. 相似文献
150.
Awareness of groundwater protection has increased substantially in recent decades. In the Province of Quebec, Canada, the Groundwater Catchment Regulation (GWCR) was promulgated in 2002 to protect water quality in public wells. The goal of the present study was to document groundwater protection in the context of emerging regulations and identify factors explaining the propensity of municipalities applying protection strategies. Two types of information were used in this study: data from a questionnaire-based survey conducted among 665 municipalities in the Province of Quebec and complementary information gathered from various sources. Data from the survey revealed that fewer than half of the municipalities have been able to comply with the GWCR, mainly because of financial limitations. Also, close to half of the municipalities have either identified or are expecting land use conflicts to arise between protection areas required by the GWCR and other land usage, with agriculture being the main conflicting activity. Multivariate logistic regression models served to identify factors explaining the likelihood of municipalities to take groundwater protection measures. Those factors were municipality revenue, history of water contamination in distribution systems, land use near wellheads, location of municipalities within a provincial priority watershed and the importance of groundwater use in a region. Results of the study may prove helpful for government authorities in better understanding the groundwater protection issue and in implementing strategies that improve the ability of municipalities to protect groundwater. 相似文献