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1.
This paper reviews the development of multi-purpose geochemical mapping and the progress of research in applied environmental geochemistry and health at Imperial College over the past 40 years. With funding from the research councils, UK government, EU, industry and NGOs, research has provided the basis for postgraduate training in areas ranging from the applications of geochemistry to plant, agricultural livestock and wildlife nutrition, to evaluating contamination from metalliferous mining and smelting, understanding the chemical nature of the urban environment and relationships between geochemistry and human health and disease. Examples include (1) the influence of Mo in marine black shales on the Cu nutrition of grazing cattle and sheep, (2) the importance of soil ingestion on trace element intake and metabolism and metal exposure in farm livestock, (3) the impacts of soil contamination from historical metalliferous mining and smelting on agriculture and human exposure to metals, including potential health problems from Cd at Shipham and from As in SW England, (4) the growth of urban geochemistry and the importance of Pb in the urban environment, (5) the health impacts due to Hg losses from the informal sector Au mining in Brazil, and (6) health issues relating to F- excess and Se deficiency in China.  相似文献   

2.
为了研究陕西省泾惠渠灌区地下水污染特征及人体健康风险状况,采集地下水样品进行分析测定,首先运用单因子指数法进行污染评价,再利用GIS获取主要污染物As、Cr （Ⅵ）和NO3--N的空间分布特征,最后借鉴美国环境保护署的人体健康风险评价模型对灌区地下水污染物的人体健康风险做出评价。结果表明：研究区地下水中As、Cr （Ⅵ）、NO3--N的质量浓度均超标,As对成人的致癌风险最高达3.50×10-4,明显超出限值1.00×10-4,长期暴露对当地居民带来罹患癌症的健康风险较高;As、Cr （Ⅵ）、NO3--N的非致癌风险从大到小排序为Cr （Ⅵ）、NO3--N、As,其中Cr （Ⅵ）对儿童的非致癌风险最高,达8.693 7,远超限值1.000 0,危害性最大。空间分布特征方面,As的致癌风险区域面积比例最高,为42.82%,As、Cr （Ⅵ）、NO3--N的非致癌风险区域面积比例分别高达69.19%、69.06%和66.55%,水安全问题突出。  相似文献   

3.
The effectiveness of aquifer remediation is typically expressed in terms of a reduction in contaminant concentrations relative to a regulated maximum contaminant level (MCL), and is usually confirmed by sparse monitoring data and/or simple model calculations. Here, the effectiveness of remediation is re-examined from a more thorough risk-based perspective that goes beyond the traditional MCL concept. A methodology is employed to evaluate the health risk to individuals exposed to contaminated household water that is produced from groundwater. This approach explicitly accounts for differences in risk arising from variability in individual physiology and water use, the uncertainty in estimating chemical carcinogenesis for different individuals, and the uncertainties and variability in contaminant concentrations within groundwater as affected by transport through heterogeneous geologic media. A hypothetical contamination scenario is developed as a case study in a saturated, alluvial aquifer underlying an actual Superfund site. A baseline (unremediated) human exposure and health risk scenario, as induced by contaminated groundwater pumped from this site, is predicted and compared with a similar estimate based upon pump-and-treat exposure intervention. The predicted reduction in risk in the remediation scenario is not an equitable one—that is, it is not uniform to all individuals within a population and varies according to the level of uncertainty in prediction. The importance of understanding the detailed hydrogeologic connections that are established in the heterogeneous geologic regime between the contaminated source, municipal receptors, and remediation wells, and its relationship to this uncertainty is demonstrated. Using two alternative pumping rates, we develop cost-benefit curves based upon reduced exposure and risk to different individuals within the population, under the presence of uncertainty.  相似文献   

4.
Arsenic (As) is a toxic metalloid found to be an important groundwater contaminant of mainly natural geogenic origin worldwide particularly in large deltas and along major rivers in poor regions of South- and East-Asia. Excessive and long-term human intake of toxic inorganic As with food and water is causing arsenicosis, which is disfiguring, disabling, and leading to potentially fatal diseases like skin- and internal cancers. It is estimated that more than 100 million people mainly in developing countries are at risk. The arsenicosis situation in affected countries has been named the largest chemical threat to public health ever experienced and arsenicosis is spreading to regions where near-sterile well water loaded with As has replaced microbial suspect surface water containing lower As concentrations. This review provides an overview of the state of the art knowledge on the water and food As intake and exposure, and how the As chemistry in water and food may influence chosen mitigation strategies. Although reports on severe health effects from exposure to As in water are abundant there are several weak points in our knowledge on causes and prevalence of arsenicosis in order to devise effective mitigation. The main mitigation strategies focus on drinking water based on exploration of As-free water and As removal from extracted water, whereas mitigation strategies on cooking water and reducing exposure through food are quite often overlooked. The experiences of adopted low cost methods for lowering the human intake of As in rural areas are critically evaluated in terms of public acceptance, sustainability and impact on arsenicosis.  相似文献   

5.
Anthropogenic sources of carbon from landfill or waste leachate can promote reductive dissolution of in situ arsenic (As) and enhance the mobility of As in groundwater. Groundwater from residential-supply wells in a fractured crystalline-rock aquifer adjacent to a Superfund site in Raymond, New Hampshire, USA, showed evidence of locally enhanced As mobilization in relatively reducing (mixed oxic-anoxic to anoxic) conditions as determined by redox classification and other lines of evidence. Redox classification was determined from geochemical indicators based on threshold concentrations of dissolved oxygen (DO), nitrate (NO 3 – ), iron (Fe2+), manganese (Mn2+), and sulfate (SO 4 2– ). Redox conditions were evaluated also based on methane (CH4), excess nitrogen gas (N2) from denitrification, the oxidation state of dissolved As speciation (As(III) and As(V)), and several stable isotope ratios. Samples from the residential-supply wells primarily exhibit mixed redox conditions, as most have long open boreholes (typically 50–100?m) that receive water from multiple discrete fractures with contrasting groundwater chemistry and redox conditions. The methods employed in this study can be used at other sites to gauge redox conditions and the potential for As mobilization in complex fractured crystalline-rock aquifers where multiple lines of evidence are likely needed to understand As occurrence, mobility, and transport.  相似文献   

6.
The interactions between groundwater and surface water have been significantly affected by human activities in the semi-arid Hailiutu catchment, northwest China. Several methods were used to investigate the spatial and temporal interactions between groundwater and surface water. Isotopic and chemical analyses of water samples determined that groundwater discharges to the Hailiutu River, and mass balance equations were employed to estimate groundwater seepage rates along the river using chemical profiles. The hydrograph separation method was used to estimate temporal variations of groundwater discharges to the river. A numerical groundwater model was constructed to simulate groundwater discharges along the river and to analyze effects of water use in the catchment. The simulated seepage rates along the river compare reasonably well with the seepage estimates derived from a chemical profile in 2012. The impacts of human activities (river-water diversion and groundwater abstraction) on the river discharge were analyzed by calculating the differences between the simulated natural groundwater discharge and the measured river discharge. Water use associated with the Hailiutu River increased from 1986 to 1991, reached its highest level from 1992 to 2000, and decreased from 2001 onwards. The reduction of river discharge might have negative impacts on the riparian ecosystem and the water availability for downstream users. The interactions between groundwater and surface water as well as the consequences of human activities should be taken into account when implementing sustainable water resources management in the Hailiutu catchment.  相似文献   

7.
《Applied Geochemistry》2006,21(1):83-97
Groundwater in the Gwelup groundwater management area in Perth, Western Australia has been enriched in As due to the exposure of pyritic sediments caused by reduced rainfall, increased groundwater abstraction for irrigation and water supply, and prolonged dewatering carried out during urban construction activities. Groundwater near the watertable in a 25–60 m thick unconfined sandy aquifer has become acidic and has affected shallow wells used for garden irrigation. Arsenic concentrations up to 7000 μg/L were measured in shallow groundwater, triggering concerns about possible health effects if residents were to use water from household wells as a drinking water source. Deep production wells used for public water supply are not affected by acidity, but trends of progressively increasing concentrations of Fe, SO4 and Ca over a 30-a period indicate that pyrite oxidation products extend to the base of the unconfined aquifer. Falling Eh values are triggering the release of As from the reduction of Fe(III) oxyhydroxide minerals near the base of the unconfined aquifer, increasing the risk that groundwater used as a drinking water source will also become contaminated with high concentrations of As.  相似文献   

8.
The concentration of trace metals was measured in groundwater samples collected from Malwa region of Punjab, India. The samples were analyzed by using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). The results were compared with permissible limits prescribed by various health and environmental protection agencies. The concentrations of trace metals such as Mn, Se, Mo, Cd, Sb and Pb were higher than their respective permissible limits at some sampling sites. The total hazard index (HItotal) (summing the hazard index through ingestion and dermal routes) at all the sampling sites exceeded or nearing unity, indicating the presence of non-carcinogenic health effects from ingestion of groundwater and dermal contact with groundwater. The results reveal that the total excess lifetime cancer risk (ELCRtotal) of metals exposure was in accordance with the acceptable lifetime risks for carcinogens in drinking water.  相似文献   

9.
Modelling cumulative impacts of basin-scale coal seam gas (CSG) extraction is challenging due to the long time frames and spatial extent over which impacts occur combined with the need to consider local-scale processes. The computational burden of such models limits the ability to undertake calibration and sensitivity and uncertainty analyses. A framework is presented that integrates recently developed methods and tools to address the computational burdens of an assessment of drawdown impacts associated with rapid CSG development in the Surat Basin, Australia. The null space Monte Carlo method combined with singular value decomposition (SVD)-assisted regularisation was used to analyse the uncertainty of simulated drawdown impacts. The study also describes how the computational burden of assessing local-scale impacts was mitigated by adopting a novel combination of a nested modelling framework which incorporated a model emulator of drawdown in dual-phase flow conditions, and a methodology for representing local faulting. This combination provides a mechanism to support more reliable estimates of regional CSG-related drawdown predictions. The study indicates that uncertainties associated with boundary conditions are reduced significantly when expressing differences between scenarios. The results are analysed and distilled to enable the easy identification of areas where the simulated maximum drawdown impacts could exceed trigger points associated with legislative ‘make good’ requirements; trigger points require that either an adjustment in the development scheme or other measures are implemented to remediate the impact. This report contributes to the currently small body of work that describes modelling and uncertainty analyses of CSG extraction impacts on groundwater.  相似文献   

10.
Groundwater is an important and often exclusive water resource in arid and semi-arid regions. The aim of the present paper was to gain insight into the processes and conditions that control the deterioration of groundwater quality in the semi-arid Kalahari of Botswana. Measurements of 3He, 4He, 20Ne, 22Ne, and of 14C of dissolved inorganic carbon (DIC) were combined with existing isotopic and hydrochemical data to investigate groundwater from the Ntane Sandstone Aquifer, which is affected by high nitrate concentrations of non-anthropogenic origin. All groundwater samples revealed neon concentrations in excess to air-saturated water, which we attributed to the addition of excess air during recharge. Neon concentrations ranged from values close to air saturation for 14C DIC rich samples (up to 80.5%MC) up to values of 90% in excess to air-saturated water for lower 14C DIC contents (2.6-61.3%MC). A strong linear correlation of excess Ne with nitrate concentrations suggests an intimate connection between groundwater quality and the processes and conditions during groundwater recharge. Low groundwater recharge rates under present-day semi-arid conditions are associated with low amounts of excess Ne and elevated nitrate concentrations. In contrast to this, higher excess Ne values in groundwater of lower 14C DIC and nitrate contents indicate that the high quality groundwater end-member presumably is related to higher groundwater table fluctuations during wetter climatic conditions in the past. We attribute the decline in groundwater quality with respect to nitrate to a decreasing rate and temporal variability of groundwater recharge, and to concurrent changes in biogeochemical activities following a transition to a drier climate during the Holocene. Under such conditions, a much stronger decrease in groundwater recharge compared to the release of nitrate from soil organic matter may result in elevated nitrate concentrations in the vadose zone and groundwater. This implies a strong impact of climate change on the transport of solutes like nitrate through the vadose zone which needs to be considered in predictions of future groundwater quality.  相似文献   

11.
宁夏固原市原州区高氟地区氟对人体健康的影响   总被引：1，自引：0，他引：1  
近年来随着人们生活质量的提升,对健康的关注度也不断提高,氟中毒性地方病越来越受到人们的重视。在关注氟污染源分析及暴露途径研究的同时,开展氟暴露途径评价健康风险研究也十分必要。据调查,固原市原州区彭堡镇地区表层土壤氟含量高于当地区域背景值,本文针对当地存在氟超标导致地方病的实际情况,重点采集了固原市原州区彭堡镇地区表层土壤、地层岩石、农作物、地下水等样品,主要采用电感耦合等离子体发射光谱法（ICP-OES）、原子荧光光谱法（AFS）等分析方法对相关元素进行分析测试,研究固原市原州区彭堡镇高氟区氟超标对人体健康的影响,并运用健康风险评价模型对人体健康风险进行评价。评价结果表明：谷物和蔬菜氟暴露途径健康风险指数HQ<1,没有非致癌风险。当地人体氟暴露风险主要途径为饮用地下水摄入,相关的健康风险指数HQ>1,这表明通过饮用氟超标的地下水,可能具有潜在的非致癌风险。年度总健康风险为1.69×10-8,低于国际辐射防护委员会（ICRP）建议的最大可接受年健康风险水平5.0×10-5,属于人类可接受的风险水平。根据氟健康风险评价结果,本文提出该地区饮用水安全性方面还需多给予关注。  相似文献   

12.
某金矿区农田土壤重金属污染的人体健康风险   总被引：8，自引：0，他引：8  
环境重金属污染的人体健康效应是当今社会最为关注的重大环境问题。某金矿区矿业活动导致土壤、地下水、农作物中重金属元素存在不同程度的累积或超标。通过土壤、地下水、蔬菜及粮食作物的样品采集,人群暴露问卷调查,获得了暴露人群的膳食结构参数。以农田土壤中7种重金属元素的综合污染分区内的土壤、地下水、蔬菜、小麦玉米等样品中的重金属元素的平均含量为依据,采用USEPA推荐的人体健康风险评价模型,计算了经口食入、皮肤接触等暴露途径对成年人的健康风险概率。研究表明,研究区存在因重金属导致的不可接受的人体健康高非致癌风险和致癌风险。总体而言,土壤重金属污染愈重地区,区内人体健康风险愈高。地下水中的Cr元素、土壤综合污染区内的Hg元素、污染区内的蔬菜及粮食是危害人体健康的重要因素。因此,禁饮Cr含量高的地下水、禁食污染区内的农作物、修复土壤重金属污染、调整农作物种植结构是保护研究区人群健康的重要环境管理工作。  相似文献   

13.
The importance or otherwise of rice as an exposure pathway for As ingestion by people living in Bengal and other areas impacted by hazardous As-bearing groundwaters is currently a matter of some debate. Here this issue is addressed by determining the overall increased cancer risk due to ingestion of rice in an As-impacted district of West Bengal. Human target cancer health risks have been estimated through the intake of As-bearing rice by using combined field, laboratory and computational methods. Monte Carlo simulations were run following fitting of model probability curves to measured distributions of (i) As concentration in rice and drinking water and (ii) inorganic As content of rice and fitting distributions to published data on (i) ingestion rates and (ii) body weight and point estimates on bioconcentration factors, exposure duration and other input variables. The distribution of As in drinking water was found to be substantially lower than that reported by previous authors for As in tube wells in the same area, indicating that the use of tube well water as a proxy for drinking water is likely to result in human health risks being somewhat overestimated. The calculated median increased lifetime cancer risk due to cooked rice intake was 7.62 × 10−4, higher than the 10−4–10−6 range typically used by the USEPA as a threshold to guide determination of regulatory values and similar to the equivalent risk from water intake. The median total risk from combined rice and water intake was 1.48 × 10−3. The contributions to this median risk from drinking water, rice and cooking of rice were found to be 48%, 44% and 8%, respectively. Thus, rice is a major potential source of As exposure in the As-affected study areas in West Bengal and the most important exposure pathway for groups exposed to low or no As in drinking water.  相似文献   

14.
More than 2.5 billion people on the globe rely on groundwater for drinking and providing high-quality drinking water has become one of the major challenges of human society.Although groundwater is considered as safe,high concentrations of heavy metals like arsenic(As) can pose potential human health concerns and hazards.In this paper, we present an overview of the current scenario of arsenic contamination of groundwater in various countries across the globe with an emphasis on the Indian Peninsula.With several newly affected regions reported during the last decade, a significant increase has been observed in the global scenario of arsenic contamination.It is estimated that nearly 108 countries are affected by arsenic contamination in groundwater(with concentration beyond maximum permissible limit of 10 ppb recommended by the World Health Organization.The highest among these are from Asia(32) and Europe(31), followed by regions like Africa(20), North America(11), South America(9) and Australia(4).More than 230 million people worldwide, which include 180 million from Asia, are at risk of arsenic poisoning.Southeast Asian countries, Bangladesh, India, Pakistan,China, Nepal, Vietnam, Burma, Thailand and Cambodia, are the most affected.In India, 20 states and 4 Union Territories have so far been affected by arsenic contamination in groundwater.An attempt to evaluate the correlation between arsenic poisoning and aquifer type shows that the groundwater extracted from unconsolidated sedimentary aquifers, particularly those which are located within the younger orogenic belts of the world, are the worst affected.More than 90% of arsenic pollution is inferred to be geogenic.We infer that alluvial sediments are the major source for arsenic contamination in groundwater and we postulate a strong relation with plate tectonic processes, mountain building, erosion and sedimentation.Prolonged consumption of arsenic-contaminated groundwater results in severe health issues like skin, lung, kidney and bladder cancer; coronary heart disease;bronchiectasis; hyperkeratosis and arsenicosis.Since the major source of arsenic in groundwater is of geogenic origin, the extend of pollution is complexly linked with aquifer geometry and aquifer properties of a region.Therefore, remedial measures are to be designed based on the source mineral, climatological and hydrogeological scenario of the affected region.The corrective measures available include removing arsenic from groundwater using filters, exploring deeper or alternative aquifers, treatment of the aquifer itself, dilution method by artificial recharge to groundwater, conjunctive use, and installation of nano-filter, among other procedures.The vast majority of people affected by arsenic contamination in the Asian countries are the poor who live in rural areas and are not aware of the arsenic poisoning and treatment protocols.Therefore, creating awareness and providing proper medical care to these people remain as a great challenge.Very few policy actions have been taken at international level over the past decade to reduce arsenic contamination in drinking water, with the goal of preventing toxic impacts on human health.We recommend that that United Nations Environment Programme(UNEP) and WHO should take stock of the global arsenic poisoning situation and launch a global drive to create awareness among people/medical professionals/health workers/administrators on this global concern.  相似文献   

15.
 The most appropriate and widely used source of drinking water for the populations of the upper regions of Ghana is groundwater. In general, groundwater quality is acceptable except for some parts of the Bolgatanga and Bongo Districts, where there are occurrences of elevated levels of natural groundwater fluoride. Concentrations of groundwater fluoride in excess of the World Health Organization (WHO) maximum guideline value (1.5 mg/l) in the Bongo area have been known since 1978. However, the effect of fluoride on people ingesting the water did not receive public and medical attention until October 1993, when health personnel were asked to investigate the cause of stained teeth in school children. The investigation established that 62% of the total population of school children in the Bongo area had dental fluorosis. Against this background, a study was initiated to understand the geochemistry, genesis, and distribution of fluoride in relation to the geology of the area. Groundwater fluoride in the upper regions ranges from 0.11 to 4.60 ppm, with the highest concentrations associated with the fluorine-enriched Bongo coarse-grained hornblende granite and syenite suite. The source of groundwater fluoride within the Bongo granitoids is dissolution of the mineral fluorite and dissolution of and anion exchange with micaceous minerals and their clay products. Applying the WHO recommended guideline values for fluoride in drinking water reveals that 49% of wells in the area deliver water below the optimum level of 0.5 mg/l F–; these populations are thus prone to dental caries. Twenty-eight percent of the wells fall within the optimum interval for good dental health (0.5–1.5 mg/l F–). Twenty-three percent of the wells have concentrations above the recommended maximum guideline limit of 1.5 mg/l F–; this population is susceptible to dental and possibly skeletal fluorosis. Climatic conditions of the area suggest that the individual water consumption is in the order of 3 to 4 l which is higher than the WHO estimate of 2 l/adult/day. In addition, dietary intake for the upper region population is probably higher than WHO baseline values (0.2–0.5 mg/day). This implies that a much higher population is susceptible to developing dental and skeletal fluorosis than originally suspected. Geochemical symbol plot maps help geochemists understand factors controlling the distribution and uptake of fluoride in the upper regions, but they are of minimal value to health officials responsible for planning epidemiological studies and dental health education programs in the region. By casting fluoride data into contoured 'geochemical health-risk maps' using intake interval guidelines more closely aligned to regional climatic and dietary conditions, health officals can better judge the impacts (regional and population based) of fluoride on segments of the population, such as various sex and age groups. Received: 11 March 1997 · Accepted: 17 June 1997  相似文献   

16.
This study aims to investigate the hydrochemical characteristics of shallow aquifer in a semi-arid region situated in northwest Algeria, and to understand the major factors governing groundwater quality. The study area is suffering from recurring droughts, groundwater resource over-exploitation and groundwater quality degradation. The approach used is a combination of traditional hydrochemical analysis methods of multivariate statistical techniques, principal component analysis (PCA), and ratios of major ions, based on the data derived from 33 groundwater samples collected in February 2014. Results show that groundwater in the study area are highly mineralized and collectively has a high concentration of chloride (as Cl?). The dominant water types are Na-Cl (27%), Mg-HCO3 (24%) and Mg-Cl (24%). According to the (PCA) approach, salinization is the main process that controls the hydrochemical variability. The PCA analysis reveal the impact of anthropogenic factor especially the agricultural activities on the groundwater quality. The PCA highlighted two types of recharge: Superficial recharge from effective rainfall and excess irrigation water distinguished by the presence of nitrate and lateral recharge or vertical leakage from carbonate formations marked by the omnipresence of HCO3?. Additionally, three categories of samples were identified: (1) samples characterized by good water quality and receiving notable recharge from carbonate formations; (2) samples impacted by the natural salinization process; and (3) samples contaminated by anthropogenic activities. The major natural processes influencing water chemistry are the weathering of carbonate and silicate rocks, dissolution of evaporite as halite, evaporation and cation exchange. The study results can provide the basis for local decision makers to ensure the sustainable management of groundwater and the safety of drinking water.  相似文献   

17.
The Nauset Marsh estuary is the most extensive (9.45 km2) and least disturbed salt marsh/estuarine system within the Cape Cod National Seashore, even though much of the 19 km2 watershed area of the estuary is developed for residential or commercial purposes. Because all of the Nauset watershed is serviced by on-site individual sewage disposal systems, there is concern over the potential impact of groundwater-derived nutrients passing from these systems to the shallow receiving waters of the estuary. The purpose of this study was to determine whether denitrification (the bacterial conversion of nitrate to gaseous nitrogen) in estuarine sediments could effectively remove the nitrate from contaminated groundwater before it passed from the watershed to the estuary. Rates of denitrification were measured both in situ and in sediment cores, in areas of active groundwater discharge, in relatively pristine locations, and in areas situated down-gradient of moderate to heavily developed regions of the watershed. Denitrification rates for 47 sediment cores taken over an annual cycle at 5 stations ranged from non-detectable to 47 μmol N2 m−2 h−. Mean denitrification rates were positively correlated with sediment organic content, and varied seasonally due to changes in sediment organic content and to the effect of water temperatures on sediment oxygen penetration depths. There was no correlation between observed denitrification rates and corresponding nitrate concentrations in groundwater. A comparison of in situ denitrification rates (supported by groundwater nitrate) with denitrification rates observed in sediment cores (supported by remineralized nitrate) showed that groundwater-driven denitrification rates were small, and not in excess of denitrification rates supported by remineralized nitrate. Most of the denitrification in Nauset sediments was apparently fueled by remineralized nitrate through coupled nitrification/denitrification. Denitrification did not contribute significantly to the direct loss of nitrate from incoming groundwater at Nauset Marsh estuary. Groundwater flow was rapid, and much of it occurred in freshwater springs and seeps through very coarse, sandy, well-oxygenated sediments of limited organic content. There was little opportunity for denitrification to occur during groundwater passage through these sediments. These results have important management implications because they suggest that the majority of nitrogen from contaminated groundwater crosses the sediment/water interface and arrives at Nauset Estuary, where it is available to primary producers. Preliminary budget calculations suggest that while denitrification was not an effective mechanism for the direct removal of nitrate in contaminated groundwater flowing to Nauset Marsh estuary, it may contribute to significant nitrogen losses from the estuary itself.  相似文献   

18.
Bob Bolin  Timothy Collins  Kate Darby   《Geoforum》2008,39(3):1494-1511
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19.
Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.  相似文献   

20.
Evaluation of potential radiation doses and health risk to future populations is the primary goal of post-closure performance assessments. This article summarizes current methods used to estimate radiation doses and health risks following emplacement of high-level waste in a geologic repository. The methods described use the radionuclide concentrations in groundwater, surface water, or the atmosphere estimated by the release and transport analyses methods described in previous articles. Methods are described here to estimate (1) transfer of radionuclides from water or air to humans by various exposure pathways, (2) radiation dose received by individuals and populations from each exposure pathway, and (3) population health risks.  相似文献   

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