Assessing the inconsistency between groundwater vulnerability and groundwater quality: the case of Chapala Marsh, Mexico     

J. A. Ramos Leal  C. Noyola Medrano  F. O. Tapia Silva  J. T. Silva García  L. R. Reyes Gutiérrez 《Hydrogeology Journal》2012,20(3):591-603

Aquifer systems present intrinsic properties such as vulnerability, which is identified as the potential risk of groundwater pollution by contaminants generated by human activity. When there are surface sources of pollution, usually there is a direct relationship between high vulnerability and decreased water quality. Nevertheless, this relationship is not observed in all aquifers and so the causative circumstances of inconsistencies between aquifer vulnerability and water quality have been investigated. This work addresses the vulnerability assessment of the Chapala Marsh area, Mexico, using SINTACS analysis. The Chapala Marsh aquifer is characterized by a granular structure and a fractured recharge zone; there are natural and anthropogenic sources of pollution. The results show discrepancies between the vulnerability indices and groundwater quality, as indicated by the existence of vulnerable areas with good water quality and vice versa. This is because the SINTACS method works well when contaminants have only vertical movement. For scenarios with lateral movement of contaminants, the method of geographic weighted regression (GWR) is used to model the influence of potential sources of contaminants on the water quality.  相似文献   

Cloud condensation nuclei (CCN) concentration in the Brazilian northeast semi-arid region: the influence of local circulation     

Gerson P. Almeida  Stephan Borrmann  João B. V. Leal Junior 《Meteorology and Atmospheric Physics》2014,125(3-4):159-176

Ground-based aerosol instrumentation covering particle size diameters from 25 nm to 32 µm was deployed to determine aerosol concentration and cloud condensation nuclei (CCN)-activation properties at water vapor supersaturations in the range of S = 0.20–1.50 % in the remote Brazilian northeast semi-arid region (NEB) in coastal (maritime) and continental (inland) regimes. The instruments measured aerosol number concentration and activation spectra for CCN and revealed that aerosol properties are sensitive with respect to the sources as a function of the local wind circulation system. The observations show that coastal aerosol total number concentrations are above 3,000 cm^?3 on average, exhibiting concentration peaks depending on the time of the day in a consistent daily pattern. The variation on aerosol concentration has also influences on the fraction of particles active as CCN. At 1.0 % water vapor supersaturation, the fraction can reach as high as 80 %. Inland aerosol total concentrations were about 1,800–1,900 cm^?3 and did not show much diurnal variation. The fraction of particles active as CCN observed inland depend on the history of the air masses, and was much higher when air masses were originated over the sea. It was found that (NH₄)₂SO₄ and NaCl are the major soluble inorganic fraction of the aerosols at the coast. The major fraction of NaCl was present in the coarse mode, while ammonium sulfate dominates the inorganic fraction at the submicron range, with about 10 % of the total aerosol mass at 0.32 µm. Inorganic compounds are almost absent in particles with sizes around 0.1 μm. The study suggests that the air masses with high concentration of CCN originate at the sea. The feasible explanation lies in the fact that the NEB’s beaches have a particular morphology that produces a wide surf zone and creates a large load of aerosols when combined with strong and permanent winds of the region.  相似文献   

Tree-ring growth variability in the Austrian Alps: the influence of site, altitude, tree species and climate     

Sofia Leal  Thomas M. Melvin  Michael Grabner  Rupert Wimmer  Keith R. Briffa 《Boreas: An International Journal of Quaternary Research》2007,36(4):426-440

We present an extensive new network of ring-width chronologies, comprising data from 100 sites within the Austrian Eastern Alps, made up of multiple tree species. Principal components analysis and cluster analysis were used to identify five separate high-frequency tree-growth signals from these data. Tree-growth variability at these sites is explained by site altitude and species differences that moderate the effects of the annually varying climatic forcing on tree growth. Recently developed, two-century long gridded climate data sets for the Greater Alpine Region were used to assess the relationship between climate and tree growth. Tree growth at low altitudes is controlled mainly by spring-summer moisture availability. At high altitudes precipitation is no longer a limiting factor and growth is mostly determined by summer temperature. In the intermediate altitudinal range, we did not find any direct relationships with specific climatic variables. High-altitude chronologies suitable for reconstructing past temperatures and low-altitude chronologies suitable for reconstructing past precipitation were identified.  相似文献   

Aquifer vulnerability and groundwater quality in mega cities: case of the Mexico Basin   总被引：1，自引：0，他引：1  

Jose Alfredo Ramos Leal  C. Noyola Medrano  F. O. Tapia Silva 《Environmental Earth Sciences》2010,61(6):1309-1320

The aquifer system in the Metropolitan Zone of the Mexican Basin is comprised by a higher, middle, and a lower aquifer, separated by less permeable elements. This study integrated a geographical database from which aquifer vulnerability values were obtained using the SINTACS method. The results show the lowest vulnerability values in the lacustrine zone of the basin, where most of the urban area is settled. The medium vulnerability indices are at the edges of the basin and are associated with tuffs, pyroclasts and alluvial deposits. The highest vulnerability values are in the ranges bordering the basin. High water quality values are toward the limits of the basin and in the recharge zones while lower quality water is in the Tlahuac and Iztapalapa zones. The results of this study enable a cause–effect relationship to be established between potential sources of contamination and groundwater quality indices only for Tlahuac and Iztapalapa, a notable finding since most of the urban area is settled over low and very low vulnerability zones.  相似文献   

Cloud condensation nuclei from biomass burning during the Amazonian dry-to-wet transition season   总被引：1，自引：0，他引：1  

Jorge Alberto Martins  Fábio Luiz T. Gonçalves  Carlos A. Morales  Gilberto F. Fisch  Francisco Geraldo M. Pinheiro  João Bosco V. Leal Júnior  Carlos J. Oliveira  Emerson M. Silva  José Carlos P. Oliveira  Alexandre A. Costa  Maria Assunção F. Silva Dias 《Meteorology and Atmospheric Physics》2009,104(1-2):83-93

Aircraft measurements of cloud condensation nuclei (CCN) during the Large-Scale Biosphere–Atmosphere Experiment in Amazonia (LBA) were conducted over the Southwestern Amazon region in September–October 2002, to emphasize the dry-to-wet transition season. The CCN concentrations were measured for values within the range 0.1–1.0% of supersaturation. The CCN concentration inside the boundary layer revealed a general decreasing trend during the transition from the end of the dry season to the onset of the wet season. Clean and polluted areas showed large differences. The differences were not so strong at high levels in the troposphere and there was evidence supporting the semi-direct aerosol effect in suppressing convection through the evaporation of clouds by aerosol absorption. The measurements also showed a diurnal cycle following biomass burning activity. Although biomass burning was the most important source of CCN, it was seen as a source of relatively efficient CCN, since the increase was significant only at high supersaturations.  相似文献   

西藏丁青弧前蛇绿岩的地球化学特征   总被引：9，自引：4，他引：9  

刘文斌  钱青等 《岩石学报》2002,18(3):392-400

丁青蛇绿岩位于班化湖－丁青－怒江蛇绿岩带的东段，其地幔岩出露规模是该带中最大的。本文报道的丁青蛇绿岩主要由地幔橄榄岩、堆晶岩、辉长岩和斜长花岗岩组成。蛇绿岩剖面上覆硅岩中的放射虫化石是早株罗世和晚三叠世诺利克期的，中侏罗统砂岩和砾岩不整合覆盖在蛇绿岩之上，由此确定丁青蛇绿岩是晚三叠－早侏罗世的，在中株罗世之前侵位，丁青蛇绿岩属于玻安岩系，玻安岩的特点是富Si、Mg和大离子亲石元素（LILE），贫高场强元素（Ti、P、Zr、Y、Yb和Nb）。丁青蛇绿岩的堆晶岩、辉长岩和辉绿岩均具“U”型REE分布，暗示丁青玻安岩是由于亏损的地幔源岩和来自消减带的水和流体两组分的混合形成的。丁青玻安岩的地球化学特征类似西太平洋第三纪玻安岩，而明显不同于MORB的地球化学性质， 表明丁青玻安岩应当形成于洋内岛弧的弧前环境，属于弧前蛇绿岩。  相似文献   

Biomonitoring with benthic macroalgae and direct assay of heavy metals in seawater of the Oporto coast (northwest Portugal)   总被引：2，自引：0，他引：2  

M.C.Fernanda Leal  M.Teresa Vasconcelos  Isabel Sousa-pinto  João P.S. Cabral 《Marine pollution bulletin》1997,34(12):1006-1015

The concentrations of dissolved Cd, Cu, Hg and Pb in seawater and algae (Enteromorpha spp. and Porphyra spp.) were determined in parallel on three beaches located in the Oporto coast (Portugal), during 8 successive months, comprising periods of low and high biological productivity. The concentrations of dissolved metals in seawater varied markedly during the sampling period and exhibited seasonality. The concentrations of Cd were high in autumn and winter, but low in spring. The concentrations of Cu and Hg were high in autumn, low in winter and peaked in May. The concentrations of Pb were low in autumn and winter, and also peaked in May. It is likely that biological activity was, at least partially, responsible for the observed seasonal changes. The mean concentrations of dissolved metals in seawater were similar to those reported for polluted and industrialized european coastal areas. Metal concentration factors, calculated month-to-month for each alga, metal and site, varied markedly during the sampling period, indicating that concentration factors based on single or few determinations could be misleading. On the contrary, mean concentration factors (calculated by dividing the mean metal concentration in the algae by the mean metal concentration in seawater) were relatively constant at all three sites, indicating that in the Oporto coast, Enteromorpha spp. can be used to estimate the mean concentration of dissolved Cd, Cu and Hg in seawater, and Porphyra spp., the mean concentration of Cd, Cu and Pb. However, considering that future estimates of the concentrations of these metals in seawater should be based on determinations of the metal contents in Enteromorpha spp. and Porphyra spp. carried out on several occasions spanning a considerable period of time, the use of these algae as monitors of heavy metal pollution can have limited practical advantages over the direct assay of the metals in seawater.  相似文献   

Evidence for Strong Copper(I) Complexation by Organic Ligands in Seawater     

M. Fernanda C. Leal  Constant M. G. Van Den Berg 《Aquatic Geochemistry》1998,4(1):49-75

Thiols like glutathione and cysteine form such stable complexes with copper(I) that they preclude the presence of copper(II). Conventionally seawater is titrated with copper(II) whilst monitoring the labile or reactive copper concentration by voltammetry or with other techniques, to determine the concentration of copper(II) binding complexing ligands in seawater. Titrations of seawater to which copper(I) binding ligands have been added reveal that the copper(I) binding ligands are detected when seawater is titrated with copper(II). The copper(II) in seawater is reduced to copper(I) within 2 to 40 minutes depending on the nature of the copper(I) binding ligand. The titrations of seawater with copper(II) thus give a response to the presence of copper(I) binding ligands indiscernible from that for copper(II) binding ligands. The stoichiometry of the detected apparent ligand concentrations for given concentrations of glutathione and cysteine suggest that 2 : 1 (thiol : Cu) complexes are formed. This was confirmed using voltammetry of free glutathione. Values of 21.2 and 22.2 were found for log _CuL for glutathione and cysteine respectively (for the reaction of Cu + 2L CuL₂). The complex stability is similar to that of natural organic species in the oceanic water column. The high stability of the copper(I) complexes was apparent from values of 32.1 and 32.6 for log Cu(I)L2 (for the reaction Cu⁺ + 2L CuL₂) for the copper(I) complexes with glutathione and cysteine in seawater. Glutathione and other thiols are common in the marine system including the water column. It is therefore possible that at least some of the ligands detected in seawater, and previously assumed to be copper(II) binding ligands, are in fact strongly complexed as copper(I). The copper(I) oxidation state may thus be stabilised in seawater.  相似文献   

Towards a universal optimization of the performance of sand storage dams in arid and semi-arid areas by systematically minimizing vulnerability to siltation: A case study in Makueni,Kenya     

Josep de Trincheria  Walter Filho Leal  Ralf Otterpohl 《国际泥沙研究》2018,33(3):221-233

Sand storage dams are hydraulic retention structures that increase the volume of coarse sediments in seasonal sandy streams by exclusively blocking the bedload transport during runoff events. However,siltation of fine grain particles, which are transported as part of the suspended load, is a major factor causing sand storage dams to perform poorly. Therefore, this study aimed to evaluate the hydrological performance and cost-efficiency of 30 sand storage dams. This study also aimed to increase the understanding of critical factors which may affect the performance and lead to siltation of sand storage reservoirs. The analysis was based on a physical survey of 30 sand storage dams that were built in onestage in southeastern Kenya. Most of the study sites had the capacity to produce sand. However, the reservoirs suffered from severe siltation, which caused generalized low annual yields, reduced supply capacities, and low cost-efficiency. It is argued that the main factors for the poor performance were the high inter-and intra-annual variability of bedload transport, which coupled with the construction of onestage spillways, led to siltation of the reservoirs. Thus, large volumes of fine grain particles accumulated in the reservoirs during runoff events with bedload layer heights lower than the height of the one-stage spillways. To systematically maximize the robustness to the inherent variability of bedload transport, and ensure optimal performance levels by systematically minimizing siltation, spillways should be built in stages of reduced height. Thus, the lower the stage height, the higher the probability of maximizing the accumulation of coarse sediment. It is estimated that a multi-stage construction process with stage heights of 20 cm would have produced a performance 26 times higher. This implies that the 30 reservoirs would have had the capacity to supply 8516 people as compared to the current supply capacity of 330 people. Improvements in the performance of sand storage dams can greatly assist attempts to link this technology with income-generating activities for agropastoralists in arid and semi-arid areas.  相似文献   

Season‐based rainfall–runoff modelling using the probability‐distributed model (PDM) for large basins in southeastern Brazil          下载免费PDF全文

Rong Zhang  Luz Adriana Cuartas  Luiz Valerio de Castro Carvalho  Karinne Reis Deusdará Leal  Eduardo Mário Mendiondo  Narumi Abe  Stephen Birkinshaw  Guilherme Samprogna Mohor  Marcelo Enrique Seluchi  Carlos Afonso Nobre 《水文研究》2018,32(14):2217-2230

Southeastern Brazil is characterized by seasonal rainfall variability. This can have a great social, economic, and environmental impact due to both excessive and deficient water availability. During 2014 and 2015, the region experienced one of the most severe droughts since 1960. The resulting water crisis has seriously affected water supply to the metropolitan region of São Paulo and hydroelectric power generation throughout the entire country. This research considered the upstream basins of the southeastern Brazilian reservoirs Cantareira (2,279 km²; water supply) and Emborcação (29,076 km²), Três Marias (51,576 km²), Furnas (52,197 km²), and Mascarenhas (71,649 km²; hydropower) for hydrological modelling. It made the first attempt at configuring a season‐based probability‐distributed model (PDM‐CEMADEN) for simulating different hydrological processes during wet and dry seasons. The model successfully reproduced the intra‐annual and interannual variability of the upstream inflows during 1985–2015. The performance of the model was very satisfactory not only during the wet, dry, and transitional seasons separately but also during the whole period. The best performance was obtained for the upstream basin of Furnas, as it had the highest quality daily precipitation and potential evapotranspiration data. The Nash–Sutcliffe efficiency and logarithmic Nash–Sutcliffe efficiency were 0.92 and 0.93 for the calibration period 1984–2001, 0.87 and 0.88 for the validation period 2001–2010, and 0.93 and 0.90 for the validation period 2010–2015, respectively. Results indicated that during the wet season, the upstream basins have a larger capacity and variation of soil water storage, a larger soil water conductivity, and quicker surface water flow than during the dry season. The added complexity of configuring a season‐based PDM‐CEMADEN relative to the traditional model is well justified by its capacity to better reproduce initial conditions for hydrological forecasting and prediction. The PDM‐CEMADEN is a simple, efficient, and easy‐to‐use model, and it will facilitate early decision making and implement adaptation measures relating to disaster prevention for reservoirs with large‐sized upstream basins.  相似文献