Spatial distribution of nitrate health risk associated with groundwater use as drinking water in Merida,Mexico

Water containing nitrate levels above 45 mg/l is not recommended for human consumption and its prolonged intake is associated with various health conditions. In Merida city, Mexico, the only source for water supply is a karstic aquifer, but the absence of sewerage and drainage networks makes it highly vulnerable to anthropogenic contamination. In this work, the concentration and spatial distribution of nitrate in the Merida's karstic aquifer were assessed by statistical and geostatistical techniques. The sources of nitrate contamination were tracked by making statistical correlations between nitrate concentrations and key ions; the potential risk to human health was also estimated by using the Hazard Index (HI). A total of 177 groundwater samples were collected from the four water supply systems serving Merida, during 2012 and 2013. Nitrate concentrations from collected samples varied between 15.51 and 70.61 mg/l, with maximum and minimum concentrations per sampling point ranging from 47.47 to 70.61 mg/l and from 15.51 to 17.32 mg/l, respectively. Significant positive correlations (P < 0.05) between nitrates and chlorides, sulphates and potassium were found, which may indicate potential contamination from domestic wastewater and agricultural activities. The spatial distribution of nitrate concentrations in the aquifer revealed an increase in nitrates following a trajectory South–North West, towards central and northwestern zones within Merida Metropolitan Area. From the health risk analysis, it was found that infants exposed at current nitrate levels are at a higher risk (HI_MAX = 1.40) than adults (HR < 1.0) and therefore, there is a clear need for implementing effective strategies to protect groundwater quality and to better manage and control nitrate pollution sources.     

Groundwater Assessment for Current and Future Water Demand in the Daka Catchment,Northern Region,Ghana

The use of untreated surface water for domestic purposes has resulted in the infection of some people by guinea worm and other water borne diseases in the Northern Region of Ghana. The aim of this study is to assess the current groundwater quantity and quality conditions in the 7,820 km² Daka catchment and project the water demand in 2025. Results of groundwater analyses generally show good water quality for domestic use. Borehole analyses indicate that the catchment’s groundwater system can be characterized by a regolith aquifer underlain by a deeper fractured rock aquifer in some areas. The current per capita water demand is estimated at 40 l/day although 60 l/day is the desired amount, indicating that with the current population of 363,350, the projected water demand for the communities is 21,800 m³/day. With a projected population of 555,500 in 2025, an expected 33,300 m³/day of water is required. The estimated optimum potential groundwater available for use in the catchment is 154 × 10⁶ m³/year (4.24 × 10⁵ m³/day). However, the current total groundwater abstraction is only 8,876 m³/day or 2% of the optimum. In comparison, the projected total current and 2025 water demands are only 5 and 8%, respectively, of the optimum potential groundwater available for use in the catchment. In addition, only 1,780 m³/day (0.65 × 10⁶ m³/year) or 0.06% of the average annual flow of 1,016 × 10⁶ m³/year of the Daka River is treated for domestic use. These figures reveal that a significantly very large water resource potential exists for both surface and groundwater development in the Daka catchment. It is suggested that their development should proceed conjunctively.     

Understanding the origin and fate of nitrate in groundwater of semi-arid environments

Though nitrate enrichment in groundwater is a worldwide phenomenon and mainly related to human impact, processes leading to nitrate enrichment in scarcely inhabited semi-arid regions are not yet well understood. In those regions, elevated nitrate concentrations put additional pressure on the scarce water resources, as they pose a serious health risk. This study applies a multidisciplinary approach (hydrogeology, isotope hydrology, and geochemistry) to understand the origin and fate of nitrate in groundwater of the semi-arid Kalahari of Botswana. Our investigations suggest that nitrate in groundwater of the study area is of natural origin, leached from a pool in the unsaturated zone that was actively involved in the soil nitrogen cycle. The presence of active (minor) recharge was found, showing that nitrate may be transported into the groundwater under the present conditions. Yet, slow travel times of replenishing water and the low recharge amounts render the thick unsaturated zone into a long-term reservoir for nitrate. Being only little influenced by reactive processes, nitrate has a high persistency in the observed groundwater system. Concentration increases induced by the present land-use do not yet appear to affect the groundwater quality but may within decades.     

Environmental and political implications of Vietnam's water vulnerabilities: A multiscale assessment

Vietnam's low‐lying areas of the Lower Mekong Basin are prone to floods, salt water inundation, and riparian competition with upstream neighbours. Vietnam's opening to the global economy, accompanied by industrialization and a rapidly growing population, impose multiscale (global, regional, local) stresses on urban and rural water systems resulting in water contamination and groundwater overdraft. Water vulnerability is a function of both natural and social hazards and depends on the scope of capital investment, political and ideological institutions, managerial capacity and governance. Water distribution and riparian ecosystem health are also hydropolitical issues related to dam‐building activity by Vietnam and its transboundary neighbours, Laos, Cambodia and particularly China, whose territory contains the source of the Mekong River. A multiscale assessment of Vietnam's interlinked water vulnerabilities indicates that the resilience of the country's social‐ecological water system rests on peaceful resolution of regional transboundary conflicts based on shared economic interests and on improved managerial practices of local authorities.     

Hydrogeochemistry of Groundwater and Its Suitability for Drinking and Agricultural Use in Nahavand,Western Iran

Groundwater is the major source of drinking water in Nahavand city. However, the groundwater quality at the agricultural areas has been deteriorating in recent years. Ground water quality monitoring is a tool which provides important information for water management and sustainable development of the water resources in Nahavand. Hydrochemical investigations were carried out in an agricultural area in Nahavand, western Iran, to assess chemical composition of groundwater. In this study, 64 representative groundwater samples were collected from different irrigation wells and analyzed for pH, electrical conductivity, major ions, and nitrate. The results of the chemical analysis of the groundwater showed that concentrations of ions vary widely and the most prevalent water type is Ca–Mg–HCO₃, followed by other water types: Ca–HCO₃, Ca–Na–HCO₃, and Na–Cl, which is in relation with their interactions with the geological formations of the basin, dissolution of feldspars and chloride and bicarbonate minerals, and anthropogenic activities. Thirty-seven percent of the water samples showed nitrate (NO₃ ⁻) concentrations above the human affected value (13 mg L⁻¹). The phosphorous (P) concentration in groundwater was between 0.11 and 0.90 mg L⁻¹, with an average value of 0.30 mg L⁻¹, with all of the samples over 0.05 mg L⁻¹. The most dominant class C2-S1 (76.5%) was found in the studied area, indicating that sodicity is very low and salinity is medium, and that these waters are suitable for irrigation in almost all soils. Agronomic practices, such as cultivation, cropping, and irrigation water management may decrease the average NO₃ ⁻ concentration in water draining from the soil zone.     

张掖盆地地下水硝酸盐污染与人体健康风险评价

地下水是张掖盆地的重要水资源,其硝酸盐污染尚未得到足够重视。对张掖盆地2004、2015年地下水硝酸盐浓度进行了系统分析,并采用美国环境保护署（USEPA）推荐的健康风险评价模型评估了地下水硝酸盐的健康风险。结果表明：自2004年以来张掖盆地地下水硝酸盐污染日趋严重。2015年硝酸盐浓度最高已达到283.32 mg·L^-1,17.61%的采样点硝酸盐氮浓度超过GB5749-2006《生活饮用水卫生标准》中饮用地下水限量值（20 mg·L^-1）。研究区人群经皮肤接触途径摄入硝酸盐的健康风险在可接受水平,而饮水摄入硝酸盐的健康风险较高,总风险中饮水途径引起健康风险的贡献率占99.40%,远大于皮肤接触途径。儿童经饮水摄入和皮肤接触两种途径的健康风险均显著高于成人,分别为成人的1.544倍和1.039倍。32.39%的采样点地下水硝酸盐对儿童的健康风险超出了可接受水平,14.79%的采样点地下水硝酸盐对成人的健康风险不可接受。甘州区城区、临泽县北部边缘及高台县城区周围硝酸盐浓度最高,这些区域内所有人群都面临硝酸盐引发的高健康风险,其余区域硝酸盐引发的健康风险相对较低。     

Geochemistry of groundwater in front of a warm‐based glacier in Southeast Greenland

Groundwater in front of warm‐based glaciers is likely to become a more integrated part of the future proglacial hydrological system at high latitudes due to global warming. Here, we present the first monitoring results of shallow groundwater chemistry and geochemical fingerprinting of glacier meltwater in front of a warm‐based glacier in Southeast Greenland (Mittivakkat Gletscher, 65° 41′ N, 37° 48′ W). The groundwater temperature, electrical conductivity and pressure head were monitored from August 2009 to August 2011, and water samples were collected in 2009 and analyzed for major ions and water isotopes (δD, δ¹⁸O). The 2 yrs of monitoring revealed that major outbursts of glacier water during the ablation season flushed the proglacial aquifer and determined the groundwater quality for the next 2–8 weeks until stable chemical conditions were reached again. Water isotope composition shows that isotopic fractionation occurs in both groundwater and glacier meltwater, but fractionation due to evaporation from near‐surface soil moisture prior to infiltration has the most significant effect. This study shows that groundwater in Low Arctic Greenland is likely to possess a combined geochemical and isotopic composition, which is distinguishable from other water sources in the proglacial environment. However, the shallow groundwater composition at a given time is highly dependent on major outbursts of glacier water in the previous months.     

三峡库区梁滩河流域水化学与硝酸盐污染

运用水化学和水质分析技术,测定了三峡库区梁滩河流域地表水体和地下水体中的水化学组成和硝酸盐氮含量,揭示了梁滩河流域地表水和地下水水体的水化学组成和硝酸盐污染的空间分布规律、来源及循环过程。结果表明:梁滩河流域地表水的硝酸盐污染表现为沿着地表径流从上游到下游呈现出加重的趋势,这种污染趋势与养殖业、生活和工农业废污水的沿程直接排放有着直接关系;而地下水硝酸盐污染呈现出流域上游和下游较轻、而中游东侧支流区域较重的空间分布特征,这种空间分布特征与地表水体中氨氮和有机氮的含量、地表水与地下水之间的补给排泄关系、厚层土壤包气带的存在以及土地利用状况等因素有着密切的关系。     

Trends and occurrences of nitrate in the groundwater of the West Bank, Palestine

Groundwater is the major source of water to the Palestinians. Efficient management of this resource requires a good understanding of its status. This understanding necessitates a characterization of the quality of the utilizable volumes. This paper focuses on the assessment of nitrate concentrations in the aquifers of the West Bank, Palestine. A preliminary statistical analysis is carried out for the spatial and temporal distributions of the nitrate concentrations. GIS is utilized to facilitate the analysis and to efficiently account for the spatiality of nitrate concentrations. The analysis was carried out at different spatial levels and key parameters including soil type, watersheds, depth, population, and rainfall. It is observed that elevated nitrate concentrations in the groundwater greatly coincide with increasing rainfall, particularly in the last few years. Results confirm that the annual mean nitrate concentration in the Western groundwater basin has an increasing trend over the period from 1982 to 2004 indicating its vulnerability to contamination. This result can be attributed to the agricultural activities along with the high groundwater recharge. However, leaking septic and sewer systems are considerably causing nitrate contamination of groundwater in populated areas. Overall, the recommendations call for an immediate intervention to manage the quality problems in the West Bank aquifers.     

地下水硝酸盐污染研究综述

地下水为重要的资源,一旦受污染,将难以更新与恢复。近年来,地下水硝酸盐污染问题正日益受到国内外研究者的关注。关于这方面的研究主要在以下方面：地下水硝酸盐的转化过程与机理;地下水硝酸盐污染的来源以及避免污染的方法措施;地下水硝酸盐氮、亚硝酸盐氮的确定方法;如何减少或者除去地下水中的硝酸盐;另外还有一些地下水硝酸污染与人体健康的研究等。在综述有关文献的基础上,提出未来地下水硝酸盐污染的三个方向：水与硝酸盐运移的耦合;界面过程;人文影响与全球角度。     

Economic Development Threatens Groundwater in Puerto Rico: Results of a Field Study

Abstract

This report addresses the question of groundwater quality in a context of economic development and heterogeneous land use. Seven wells, each actively producing for the public water supply, and together providing 37 percent of the total aquifer production of four municipios, were tested in three topographic basins. Major land use categories, including agriculture, urbanization, and industry, were identified throughout the basins. Well samples were drawn three times during a six-month period and analyzed for a set of 15 water quality parameters including biological indicators. The most common pollutants detected were heavy metals, nitrate, arsenic, and semivolatile organic compounds. Wells surrounded by agricultural and commercial activities were contaminated by nitrate, mercury, lead, and phthalates. Wells in mixed residential and industrial settings had concentrations of semivolatile organic compounds and lead. The presence of noxious chemicals in the public water supply, even in relatively small amounts, threatens the viability of the groundwater reservoir. Both operational and policy aspects of water quality should be discussed in the context of urban and economic development.     

Groundwater vulnerability mapping: A GIS and fuzzy rule based integrated tool

Contamination of groundwater has become a major concern in recent years. Since testing of water quality of all domestic and irrigation wells within large watersheds is not economically feasible, one frequently used monitoring strategy is to develop contamination potential maps of groundwater, and then prioritize those wells located in the potentially highly contaminated areas for testing of contaminants. However, generation of contamination potential maps based on groundwater sensitivity and vulnerability is not an easy task due inherent uncertainty. Therefore, the overall goal of this research is to improve the methodology for the generation of contamination potential maps by using detailed landuse/pesticide and soil structure information in conjunction with selected parameters from the DRASTIC model. The specific objectives of this study are (i) to incorporate GIS, GPS, remote sensing and the fuzzy rule-based model to generate groundwater sensitivity maps, and (ii) compare the results of our new methodologies with the modified DRASTIC Index (DI) and field water quality data. In this study, three different models were developed (viz. DI_fuzz, VI_fuzz and VI_{fuzz_ped}) and were compared to the DI. Once the preliminary fuzzy logic-based (DI_fuzz) was generated using selected parameters from DI, the methodology was further refined through VI_fuzz and VI_{fuzz_ped} models that incorporated landuse/pesticide application and soil structure information, respectively. This study was conducted in Woodruff County of the Mississippi Delta region of Arkansas. Water quality data for 55 wells were used to evaluate the contamination potential maps. The sensitivity map generated by VI_{fuzz_ped} with soil structure showed significantly better coincidence results when compared with the field data.     

荒漠地区包气带氯离子与硝酸盐的空间分布特征

荒漠地区包气带中的Cl^-、NO₃^-与生态环境有密切联系,与地下水安全有直接联系。主要以荒漠地区包气带Cl^-、NO₃^-为研究对象,通过对Cl^-、NO₃^-在包气带及不同土壤类型中的分布特征进行研究,表明强烈的蒸散发作用使Cl^-、NO₃^-呈活塞式分布,同时植物对水分的吸收以及对NO₃^-的优先吸收使NO₃^-表现出不同的分布特征。土壤中的NO₃^-可能被植物优先吸收并遵循营养循环,使表层土壤中出现极大值,随后逐渐减小。靠近表层土壤出现NO₃^-峰值和较高的NO₃^-/Cl^-原子比率反映了蓝藻菌活跃的固N作用;相对较大的NO₃^-/Cl^-原子比率伴随着较低的Cl^-说明在干旱地区稀疏的植被覆盖条件限制了对NO₃^-的吸收作用。不同的土壤类型中,Cl^-、NO₃^-表现出不同的分布特征,在粘性土壤中,NO₃^-、Cl^-浓度随含水率的减小而减小。     

Groundwater Quality Assessment in a Hyper-arid Region of Rajasthan,India

Groundwater is an important source of livelihood in regions where rainfall is scanty, surface water sources are absent, and all domestic and agricultural needs are fulfilled with groundwater. This study deals with groundwater quality assessment in a hyper-arid region using multivariate statistical analysis. A total of 43 samples were collected and analyzed using principal component analysis and hierarchical cluster analysis to model the relationship and interdependence among the various physicochemical variables contributing to groundwater quality in the study area. The results of the statistical techniques showed that the variables are in strong correlation with each other. Cluster analysis proved to be a good tool to ascertain the spatial similarity between the contributing variables. The methodology adopted in the present study has been found to be effective and can be utilized to establish strong water quality monitoring network in similar areas.

     

多层抽水试验地下水位动态与同位素浅析——以衡水试验为例

针对不同深度含水层,揭示其富水性,探讨地下水资源可恢复性、可利用性和浅层劣质水改造利用可能性。以国土资源部衡水地下水试验场为依托,在详细调查试验场影响区地下水开发利用状况、监测地下水年动态基础上,开展分层抽水试验和水化学同位素采样。通过对大量抽水水位动态数据过程、局部流场特征和水化学同位素的分析,得出结论:该区农业为影响地下水水位的主控因素;含水层系统承压性、补给强度从下到上分别呈减弱、增强趋势,除浅层外各含水层渗透性较强;各含水层渗流强度及方向不同等。提出实现地下水可持续开发利用建议:对浅层地下咸水适时进行抽咸换淡、混灌轮灌改造利用;170m、300m强含水层作为工农业用水主要开采层,深层地下水主要用于生活用水;按照水量平衡、分质用水原则开发地下水。     

珠江口东岸地区海水入侵三维溶质数值模拟研究

在建立水文地质概念模型的基础上,运用FEFLOW软件建立珠江口东岸地区海水入侵三维溶质模型,并利用研究区水位和水质的动态观测资料对模型进行识别和校正。运用模型进行情景模拟,预测现状开采条件下地下水的水质演化趋势。预测2010年,第四系含水层海水入侵面积为115.98km2,基岩裂隙含水层海水入侵面积为89.36km2,2020年,第四系含水层海水入侵面积为106.83km2,基岩裂隙含水层海水入侵面积为82.76km2。预测结果表明:在现状开采条件下,第四系和基岩裂隙含水层海水入侵程度有所缓解,海水入侵面积逐渐减少,Cl-高浓度区域逐渐变小。     

Managing the Murray‐Darling Basin

Within the Murray‐Darling Basin lie Australia's most important water and land resources as well as some of the country's most serious resource management problems. This paper summarises the importance of the resource‐based industries, especially agriculture. The major agricultural and water resource problems are outlined, with most attention being paid to salinity. Critical to the problems and their solution are the institutional arrangements for the management of this large interstate river basin. The River Murray Waters Agreement, dating from 1914, has had limited success in tackling the basin's problems, because of its limited geographical and functional scope, especially in the area of water quality. The growing severity of the latter problems, especially salinity, resulted in the 1987 signing of the Murray‐Darling Basin Agreement to promote and coordinate the management of the basin's water, land and environmental resources. As it is concerned with the basin as a whole, its success is dependent on the full cooperation of the Commonwealth and three state governments involved.     

Characterization of Mechanisms and Processes Controlling Groundwater Recharge and its Quality in Drought-Prone Region of Central India (Buldhana,Maharashtra) Using Isotope Hydrochemical and End-Member Mixing Modeling

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO₃ facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ²H, δ¹⁸O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

     

Rural-urban spatial inequality in water and sanitation facilities in India: A cross-sectional study from household to national level

A major obstacle for the developing nations to meeting the United Nation's Sustainable Development Goals (SDG: 2015–2030) for WaSH (Water-Sanitation-Hygiene) is the appalling rural-urban inequality in infrastructural facilities that lead to regional/spatial differences in livelihood. In India, where about 70% of the population dwells in villages, rural-urban inequality can pose steep challenges to the authorities in their motto of ensuring improved water and sanitation for all. Cognizant of the need, the present study aimed to map nationwide rural-urban spatial inequalities for various WaSH infrastructural facilities along a four-tier administrative hierarchy: household-district-state-national. Cross-sectional data for district-wise percentages of rural and urban households having access to (i) latrine facility within premises, (ii) treated tap water, (iii) improved water source, and (iv) at-home water source were obtained from the Census of India database for 2011. A variety of metrices (Bray-Curtis Dissimilarity Index (BCDI), Gini coefficient, Moran’I, LISA) were used to characterize underlying spatial patterns. Rural-urban spatial inequality in 'treated tap water' appeared as the most spatially variable WaSH parameter across the nation. Results indicated that governmental claims of having met the Millennium Development Goal (MDG) for ‘improved’ water source require a thorough reappraisal, especially for rural India, as majority of these so called improved sources thrive on groundwater (hand pump+tube well), which is heavily contaminated by co-occurrences of multiple pollutants (fluoride, arsenic, nitrate, salinity), which have grave human health effects, and thus questioning the fundamental premise of 'safe water'. About 54% of the rural households in India rely on groundwater sources as compared to <20% urban households. In addition, about 67% of rural, against about 12% urban, households still ‘indulge’ in open defecation practices, which calls for stringent management actions coupled with strategic awareness campaigns. Rural-urban inequality in WaSH facilities appeared most alarming across the central Indian states of Chattisgarh, Bihar, Jharkhand, Odisha, Madhya Pradesh and Rajasthan. Overall, spatial heterogeneity in the rural-urban inequality appeared a daunting challenge for the authorities, urging for spatially-optimized policy reforms instead of enacting nationwide uniform policy measures.     

京津以南河北平原地下水位下降驱动因子的定量评估

自1970年代以来,在自然因素和人为活动的交互影响下,京津以南河北平原地下水位持续下降并产生了一系列地质环境问题,严重影响了该区域社会经济的可持续发展。本文从降水、地表径流、气温等自然因素及地下水超采、水利工程修建、农作物产量水平提高、耗水型作物面积扩大等人为因素初步分析了京津以南河北平原地下水位下降的主要原因;通过建立投影寻踪回归模型,定量评价了各因素对地下水位下降的影响,确定了各影响因素对地下水位下降的相对贡献率。结果表明:地下水开采是引起地下水位下降的最主要因素,对地下水位下降的相对贡献率为54.7%,其中工业、农业、生活用水对地下水位下降的相对贡献率分别为6.6%、43.7%和4.4%;其次是降水和地表径流,其相对贡献率分别为25.6%和19.7%。