N. Ceniceros

Universidad Nacional Autónoma de México, Ciudad de México, The Federal District, Mexico

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Publications (29)36.68 Total impact

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    ABSTRACT: El Chichón volcano has an eruptive record of at least 12 major eruptions in the Holocene, the latest one in March-April 1982 causing the worst volcanic disaster in the history of Mexico. After about 6 centuries of quiescence, this eruption destroyed a large dome and opened a 1 km wide crater. A lake, formed within the crater shortly after the eruption, has been an important source of information about the evolution of the post-eruptive processes. The fluctuations of the crater lake water physicochemical parameters, observed since 1983, have allowed identifying hydrothermal waters and H2S-rich gases, influenced by tectonic and meteorological effects, as the main contributors to its composition. Here we propose some methods to help assessing the state of the volcano derived from the relative contribution of these factors as an easy to implement volcanic surveillance method in potentially active volcanoes with crater lakes, or other volcano-influenced water sources.
    No preview · Article · Sep 2014 · Journal of Volcanology and Geothermal Research
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    ABSTRACT: The influence of the Cerro Prieto Geothermal Field (CPGF) on groundwater quality of the close-by agricultural area was evaluated by means of chemical and isotopic determinations. According to irrigation standards, concentrations of As, Cd, Pb, Crtot, Cr(VI), Cu, Cd, Hg, B in agricultural wells showed the suitability of the water for irrigation. Iron was below irrigation limits in all but one well. However, chloride levels were above those limits in 83 out of 87 collected samples. Isotopic determinations of δ2H, δ18O, δ34S, δ13C, and spatial concentration trends of elements related with geothermal brines and toxic metals and metalloids did not indicate an influence of the CPGF to groundwater in the nearby agricultural area. Isotopic values of δ2H, δ18O showed the occurrence of evaporation processes and infiltration of canal's irrigation water to geothermal water reservoirs and to groundwater in the agricultural zone. High chloride concentrations might be associated with these processes.
    No preview · Article · Mar 2014 · Renewable Energy
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    ABSTRACT: The geochemistry and mineralogy of samples collected along depth profiles from an As-rich tailing deposit with abundant calcite was studied to determine the processes that influence the mobility of Fe, Zn, Cu, Ni, Cd, As, Sb, Cr and Tl. In spite of their near neutral pH, almost all of them are acid potential generators. Total concentrations decreased as: Fe > As > Zn > Pb > Cu > Sb > Cd > Cr > Ni > Tl. Soluble contents were lower and followed a slightly different order. Mobility decreased as: Tl > Cd, Zn, Cu, Sb, Ni, As > Fe, Pb > Cr. Higher soluble concentrations of Fe, Cu, Zn, As, Pb, and Ni were found in low-pH samples and of Sb and Tl in near-neutral samples. Sulfide oxidation processes are developing in the tailing’s dam. These processes do not have a trend with depth but occur mainly in acid layers. Near neutral layers formed by primary sulfides and calcite probably correspond to wastes produced from the processing of ore coming mainly from pods within the skarn, and acid layers with abundant secondary minerals from material mined from chimneys and mantos. The presence of calcite influences speciation, neutralizes acid mine drainage (AMD), and decreases the mobility of most toxic metals and metalloids (TMMs). However, a hard-pan layer was not observed in the studied profiles. Retention of TMM within tailings probably occurs through the formation of low solubility metal carbonates and from elevation of pH that promotes Fe hydroxides precipitation that may retain As, Sb and metals. Calcite occurrence promotes As, Cd, Cu, Fe, Zn, Pb, Cd and Cr retention, does not play a role on Tl and Ni mobilization, and increases Sb release.
    No preview · Article · Nov 2012 · Applied Geochemistry
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    ABSTRACT: An experimental study to evaluate the potential of using indigenous limestones in a passive system to treat acid mine drainage, at a mining zone of Mexico was carried out. Chemical and mineralogical characteristics of four types of native rocks (KIT1, KIT2, KSS, QZ) showed distinct CaCO(3) contents. Synthetic aqueous leachates from an old tailings impoundment had a pH of 2.18, 34mg/L As, 705mg/L Fe(total), and 3975mg/L SO(4)(2-). To evaluate dissolution behavior of rocks, kinetic batch experiments with an acid Fe-rich solution were performed. Decaying kinetic constants adjusting H(+) concentration to a first order exponential process were: KIT1 (k=2.89), KIT2 (k=0.89) and KSS (k=0.47). Infrared spectrum and XRD of precipitates showed schwertmannite formation. To determine As and heavy metals (Fe, Cd, Zn, Al) removal from the synthetic leachates, batch experiments using KIT1 were developed. Arsenic decreased from 34.00mg/L to 0.04mg/L, Fe and Al were totally removed, and concentrations of Zn and Cd decreased 88% and 91% respectively. Analyses by IR and SEM-EDS indicate that co-precipitation with Fe-Hydroxides formed upon leachate interaction with limestone is the main As removal process. Chamosite, identified by XRD may participate in the removal of Al, SiO(2) and a fraction of Fe.
    No preview · Article · Jul 2012 · Journal of hazardous materials
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    ABSTRACT: Real-time volcanic hazard assessment requires the integrated interpretation of data obtained with different monitoring methods, particularly when people may be at risk. One of the methods rendering earliest precursory variations reflecting the internal state of a volcano is the geochemical analysis of gases, ground or lake waters related to volcanic systems, and volcanic ash. At Popocatépetl volcano, Central México, chemical fluctuations of the soluble cover of volcanic ash particles has proved to reflect diverse characteristics of the eruption types. Chloride, sulfate and fluoride concentrations of ash leachates have been consistently measured within the current eruptive episode beginning in December 1994. Particularly, main anions presented diverse relative concentrations in periods of dome extrusions, contrasting with hydrothermal activity or quiescence. Multivariate statistical analysis revealed that higher proportions of fluoride in the leachates corresponded to new dome emplacements and relatively higher sulfate concentrations to hydrothermal ashes, although these results may be ambiguous at times. However, different sulfur isotopic ratios were measured in sulfate from ashes erupted during periods dominated by hydrothermal activity to those emitted during dome emplacement. Additionally, ascent of fresh magma was reflected on high fluoride concentrations jointly with low 34S-SO4 isotopic values. It is thus recommended to maintain persistent analyses of ash-leachates from on-going eruptions as a monitoring tool at active volcanoes.
    No preview · Article · Apr 2012
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    ABSTRACT: Ash emitted by volcanic eruptions, even of moderate magnitude, may affect the environment and the health of humans and animals through different mechanisms at distances significantly larger than those indicated in the volcanic hazard maps. One such mechanism is the high capacity of ash to transport toxic volatiles like fluoride, as soluble condensates on the particles' surface. The mobilization and hazards related to volcanic fluoride are discussed based on the data obtained during the recent activity of Popocatépetl volcano in Central Mexico.
    Full-text · Article · Jul 2011 · Natural hazards and earth system sciences
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    ABSTRACT: Monitoring volcanic activity and assessing volcanic risk in an on-going eruption is a problem that requires the maximum possible independent data to reduce uncertainty. A quick, relatively simple and inexpensive method to follow the development of an eruption and to complement other monitoring parameters is the chemical analysis of ash leachates, particularly in the case of eruptions related to dome emplacement. Here, the systematic analysis of , Cl− and F− concentrations in ash leachates is proposed as a valuable tool for volcanic activity monitoring. However, some results must be carefully assessed, as is the case for S/Cl ratios, since eruption of hydrothermally altered material may be confused with degassing of incoming magma. Sulfur isotopes help to identify SO4 produced by hydrothermal processes from magmatic SO2. Lower S isotopic values correlated with higher F− percentages represent a better indicator of fresh magmatic influence that may lead to stronger eruptions and emplacement of new lava domes. Additionally, multivariate statistical analysis helps to identify different eruption characteristics, provided that the analyses are made over a long enough time to sample different stages of an eruption.
    No preview · Article · Aug 2010 · Applied Geochemistry
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    ABSTRACT: In 1982, a series of eruptions resulted in the worst disaster linked with volcanic activity in México. The characteristics of the phenomena together with a lack of prevention measures resulted in approximately 2000 deaths. An important aspect to prevent disasters is a thorough knowledge and monitoring of the potentially destructive natural phenomena. Monitoring the activity of dormant or active volcanoes by various methods is thus a key measure to estimate the hazard and design adequate risk reduction measures. Despite of the 1982 volcanic disaster, until only a few years, hydrogeochemical monitoring was the only regular surveillance of El Chichón post-eruptive activity. The first samples of the crater-lake water were collected by Casadevall et al. in 1983. Since 1985, a systematic sampling and chemical analyses program has been carried out by the Geophysics Institute in collaboration with local authorities from the State of Chiapas. Chemical analyses of main ions and Rare Earth elements (REE) are performed in the Laboratorio de Química Analítica and Laboratorio ICP-MS of the Instituto de Geofísica, UNAM. Results are interpreted considering the physico-chemical changes that may be recognized as precursors of volcanic activity. The problem is difficult because at least two main water reservoirs feed the crater lake; besides, dissolution of acid volcanic gases, water-rock interactions and geochemical processes among dissolved species have resulted in a complex chemical behavior of the lake-water along the years. The calculated degree of neutralization, pH values, and chloride and sulfate concentrations of samples taken at different dates result in a classification of the volcano as active or inactive according to the method developed by Varekamp. A pH of 0.5, very high conductivity and a temperature of about 50°C characterized the first years following the eruptions. An overall decrease on the temperature and ionic concentrations, along with a less acid pH (around 2.5) have been measured during the last 20 years. However, important changes on the individual concentrations of the main ions have also been observed within this time. These changes show the dynamics of the lake and the relative influence of the water sources, volcanic gases and geochemical processes on the water samples. On the other hand, the lack of REE elements concentration variations reflects some volcanic stability in the period 2006 to 2008. These observations have led to the identification of specific precursory hydrogeochemical parameters, that contribute to the dynamic hazard assessment of El Chichón.
    No preview · Article · Feb 2010
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    ABSTRACT: Samples along depth profiles were taken from an old tailings deposit at an historical Mexican mining zone. Determination of total and soluble TMM (Cd, Pb, Zn, Fe, As, Cu, Ni) contents, mineralogy, pH, conductivity and acid base accounting allowed estimating the geochemical processes influencing metal's mobility. Besides, geochemical modeling was applied to determine speciation and saturation indexes of minerals. Concentration trends with depth were not observed but the lowest pH layers contained the highest soluble TMM concentrations. Presence of calcite influences speciation and decreases the mobility of TMM. Retention of TMM within tailings occurs through the formation of low solubility metal carbonates and the elevation of pH promoting iron hydroxides precipitation that may retain As and metals. Total and soluble concentrations and toxicity indicate that As represents the highest environmental risk among the studied TMM.
    No preview · Article · Jan 2010
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    ABSTRACT: In the historical mining zone of Zimapán, México, unprotected tailings deposits are supplying contaminants to the local fluvial system. This research was conducted to assess the environmental hazard of these wastes and river sediments by determining the input, transport and seasonal variability of arsenic, cadmium, lead and zinc, and their speciation by an operationally defined scheme of decreasing lability: F1, fraction soluble in deionized water; F2, associated to carbonates; F3, oxides and hydroxides of iron; F4, sulfides and organic matter; F5, residual. Higher total concentrations of Cd, Pb and Zn were present in sediments in the dry season regarding the rainy season. In the dry season, As and Pb were principally associated with the more stable F3 and F5 fractions, whereas Cd was in F2 and F5, and Zn in F3, F2 and F5. In the rainy season the association was mainly F3 for As, while F2 and F3 contained most Cd, Pb and Zn. This fractionation indicates that the environmental hazard of Cd, Pb and Zn enhances upon a pH decrease due to their proportion in the carbonatic fraction, and shows a mobility increase during the rainy season.
    No preview · Article · Oct 2009 · Environmental Geology
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    ABSTRACT: Water chemistry of crater lakes, maars and water reservoirs linked to some Mexican volcanoes within and outside the Mexican Volcanic Belt has been determined for several years and examined regarding environmental and volcanic factors. All the analyzed lakes are relatively small with a maximum depth of 65 m, and are located in regions with different climates, from semi-arid to very humid, with altitudes ranging from 100 to more than 4000 m a.s.l. Crater lakes in active volcanoes (El Chichón, Popocatépetl) have very low pH, moderate to high temperatures and major ion concentrations varying with the level of volcanic unrest. Lakes in sub-arid and temperate-arid regions (like maars in Puebla and Guanajuato states) show high alkalinity and pH, with bicarbonate/carbonate, chloride, sodium and magnesium as predominant ions. Lakes located in humid climates (Central Michoacán and Veracruz state) have low mineralization and near-neutral pH values. In general, conservative dissolved ions and conductivity appear to be mostly controlled by precipitation/evaporation and by the ionic concentration of groundwater inputs. Calcium, magnesium, sulfate concentrations and pH are strongly influenced by volcanic-rock or volcanic gas interactions with water. The influence of low-level volcanic activity on crater lakes may be obscured by water–rock interactions, and climatic factors. One of the aims of this paper is to define the relative influence of these factors searching for a reference frame to recognize the early volcanic precursors in volcano-related lakes.
    Full-text · Article · Dec 2008 · Journal of Volcanology and Geothermal Research
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    ABSTRACT: The main ions, silica, boron and sulfide were analyzed by standard methods in samples from waters of several springs and a shallow well located around Popocatépetl volcano. Analyses of several chemical components allowed a geochemical monitoring of Popocatépetl activity from 1995 to 2004. Most samples were dilute and immature cold waters and only silica minerals were oversaturated in the springs and well water. The ratios of chemical species indicated water–rock interaction with plagioclases, evaporites and ferromagnesian minerals. The chemistry of the spring with the highest conductivity indicated water interaction with limestones. A small, increasing trend of silica and magnesium concentrations over the nine year period at all sampled sites seems to reflect the increase on the alteration processes, mainly of ferromagnesium minerals. Interaction of immature waters and volcanic CO2 with the silicate minerals may dissolve silica and magnesium, resulting in the observed slow concentration increase in most spring waters. The influence of volcanic activity was reflected as changes of different nature in the water chemistry, which may have been derived from direct interaction of diffuse volcanic gases with the aquifers, or by the opening of new pathways for water and gases through the reactivation of the fault system. It is likely that short-period fluctuations of the water chemistry, like those observed in the concentrations of chloride, boron, and, sometimes, fluoride and sulfate, reflect the interaction of highly-volatile magmatic gases with water. Longer term trends, like those observed in sulfate and CO2 may reflect slow accumulation by scrubbing of fault-transported or diffuse gases that would otherwise show large variations in open vents. Their further concentration reduction signals the decline of the source magma-mixing process. Not all sampled sites responded well to volcanic influence; the spring at Axocopan best correlated with the changes of volcanic activity. The fluctuations of water chemistry played a significant role in the assessment of the volcanic hazard. The most relevant chemical monitoring parameters, jointly with others, were used by decision makers in managing the Popocatépetl activity.
    No preview · Article · Feb 2008 · Journal of Volcanology and Geothermal Research
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    ABSTRACT: A discussion on groundwater-As pollution in Mexico in the framework of mining activities, and the research developed in one particular contaminated location are presented. More research is needed to ascertain the sources and fate of As at many other contaminated sites. Groundwater contamination in Zimapán, Central Mexico, is the result of both natural (ore) and anthropogenic (smelters and tailings’ impoundments) processes. Arsenic released from arsenopyrite oxidation within tailings contaminates the shallow aquifer in spite of the sorption and formation of secondary minerals that retain some of the As. Alteration and dissolution of As-minerals in mineralized zones contaminate a deeper limestone aquifer. Arsenic is transported through faults and fractures to potable water wells and springs. In the town of Zimapán, treatment with ferric sulfate proved to be adequate to remove As from the contaminated municipal water. Another low-tech treatment technique using shaly limestone also removed most of the As.
    No preview · Article · Dec 2007 · Trace Metals and other Contaminants in the Environment
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    ABSTRACT: Arsenic concentrations exceeding drinking-water standards have been measured in groundwater of various areas of Mexico. This is a relevant public health problem since groundwater supplies most drinking water of the country. Although a natural source has been proposed as the cause of water contamination at most sites, the specific processes releasing As have only been identified in a few aquifers. The geological characteristics of Mexico including volcanic, geothermal, and highly mineralized zones constitute favorable environments for As occurrence. Furthermore, As-abundance in bedrock has lead Mexico to be one of the major world As-producers. As-bearing minerals like arsenopyrite, scorodite, mimetite, adamite, tennantite and nickeline can be found in several zones. Besides, arsenic may be a minor component of Fe, Ag, Cu, Pb, Zn, and Au ores. While thousands of people have been chronically exposed to As, arsenic-related health effects have been documented only for residents at some Mexican locations, like Comarca Lagunera, Zimapan, and Acambaro. Water-rock interactions may release As to water in mining areas, but ore extraction and processing produce surface wastes that can also release As to groundwater. Investigations developed in two historical mining zones revealed different As contents in groundwater. At Zimapan, a semi-arid area about 250 km NE of Mexico City, abundant arsenopyrite and hydrogeological conditions produced high As concentrations in deep wells exploited for drinking water supply. Oxidation and dissolution of As-bearing minerals mainly arsenopyrite, scorodite and tennantite released As to the fractured deep limestone aquifer. In addition, mining operations polluted shallow wells. In contrast, low levels of As were detected in wells near mine tailings in the warm sub-humid zone of Taxco, Guerrero. To explain those differences, the mineralogy and the geochemical processes occurring in tailings at both areas were studied. Results showed that besides As levels in processed ore, mineralogy of the ore deposits is one of the main causes of different degrees of As release. Precipitation of secondary minerals like gypsum, goethite, K-jarosite and hematite produced a cemented layer that retains As in the active oxidation zone of the tailings at Taxco. Formation of beundantite also reduces As dispersion. At Zimapan, the relative proportion of pyrite and calcite leads to differences on As mobility, evidenced by mineralogy and geochemical fractionation of As in tailings. Geology of the substrate under the tailings also affects the pollution levels of shallow wells. Granular alluvial material permits a greater mobilization of As at Zimapan than in Taxco, where presence of limonites and calcareous lutites results in low As groundwater contents. Economically and technical affordable treatment methods have been tested to clean the water. At Zimapan, addition of local limestone proved to remove a high proportion of As; flocculation with iron salts was also suitable to treat polluted water.
    No preview · Article · May 2007
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    ABSTRACT: Water-sediment geochemical processes influencing As, Pb, Zn, Cu and Fe mobilization were investigated in a river within the historic mining area of Taxco, Mexico. Tailings wash off and acid mine drainage have led to concentrations of metals in sediments well above the regional background. Zinc and lead associate with the carbonate fraction, followed by Fe oxi-hydroxides. Arsenic and Fe concentrate in the residual fraction, followed by organic matter/sulphide and Fe oxi-hydroxides. Metals are mainly transported as particulates in the water. Calcium, silicate and iron minerals are oversaturated in the river water. Limestones play a key role in the contaminant behaviour. Principal components analysis indicated that Zn, Cu and Pb may be released to the water following small changes in physico-chemical and/or hydrogeological conditions. Application of straightforward analytical techniques jointly with geochemical and statistical evaluation, is an affordable alternative to clarify the environmental impact of mining wastes in developing countries.
    No preview · Article · Jan 2007
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    ABSTRACT: The distribution and fate of arsenic in various environmental reservoirs have been studied in Zimapán, México. Natural arsenic in groundwater is released by oxidation and dissolution of arsenic-bearing minerals. Mining wastes (tailings and smelter particulates) pollute some of the shallow wells. Tailings contain high concentration of As. However, As mobility is limited by oxidation-reduction, sorption, and formation of secondary minerals. Sequential extraction showed that As is mainly retained in the residual and Fe/Al oxyhydroxides fractions. Arsenic occurs also in beudantite and K-jarosite. High arsenic concentrations are found in soils and river sediments near tailings, slag piles and mineralized areas. Due to the semi-arid climate, few crops are grown in this area. Nevertheless, wild flora has grown on tailing and slag piles, and As-rich soils. Arsenic is absorbed from these As-rich substrates and translocated to the stem, leaves, flowers and fruits. The concentrations and fate of arsenic varies depending on the arsenic source.
    No preview · Article · Jan 2005
  • H. Muñoz · M.A. Armienta · A. Vera · N. Ceniceros
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    ABSTRACT: Nitrate concentrations in groundwater from the Huamantla Valley, Tlaxcala, were investigated in relation with environmental and hydrogeological parameters. Two groundwater-sampling campaigns were performed in the study area. Nitrate concentration was measured by potentiometry with an ion selective electrode. Parametric and non-parametric variance analyses were applied to assess nitrate concentration depending to location, water use, and agricultural practices. Average nitrate concentration was almost twice higher in the dry season (second sampling period) than in the rainy season (first sampling period). Four lenses in the first, and seven in the second sampling campaigns, were detected above the World Health Organization NO 3- drinking water limit of 44.29 mgL -1. Statistical significative differences were not found between nitrate content and static water level. Nitrate concentration was found to depend on location (low-plain or mountain) and agricultural practice (irrigation or seasonal).
    No preview · Article · Jul 2004 · Revista Internacional de Contaminacion Ambiental
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    ABSTRACT: Mining in Mexico has produced important economic benefits since pre-Hispanic times. On the other hand, tailings and rock wastes constitute potential pollution sources in many zones of the country. Taxco, about 150 km south-west of Mexico City, is one of the historical mining zones of Mexico. The environmental behaviour of metals from tailings in a branch of the Taxco river was investigated. Several communities use the Taxco river water along its flow. Samples were taken from tailings, river-waters and sediments. Field determinations included conductivity, pH, Eh, temperature and alkalinity of the water. Mineralogical and chemical analyses were performed in tailings and sediments. Water analyses included main ions, and metals in acidified filtered and unfiltered samples. Quartz, jarosite, pyrite, chalcopyrite, Fe oxihydroxides, gypsum, clay and silica minerals were identified in the tailings. All samples had an acid pH (2·50–4·16) and high concentrations of Pb (up to 2750 mg/kg), Zn (up to 690 mg/kg) and As (up to 3530 mg/kg). Mineralogical and chemical characteristics of tailings indicated occurrence of sulphide oxidation. Higher metal concentrations were found in unfiltered, acidified water samples than in filtered water samples in the year 2000: Fe (up to 21·2 mg/l), Zn (up to 13·4 mg/l) Pb (up to 0·115 mg/l) and As (up to 0·035 mg/l). Zn, Fe and Pb reached much higher concentrations in the dry season than in the rainy season. The Taxco river water does not comply with Mexican drinking water standards. High concentrations of Pb (up to 5280 mg/kg) and Zn (up to 33,500 mg/kg) were measured in sediments. Pb and Zn in sediments accumulated downflow in the dry season. A more uniform distribution was found in the rainy season. Results showed that metals are released from tailings as a result of sulphide oxidation and rain-water erosion. Metals are then transported by the river-water mainly in particulate form and, after settling, increase the concentration of metals in the sediments.
    No preview · Article · Mar 2004 · Applied Earth Science IMM Transactions section B
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    ABSTRACT: Se investigó la influencia de diversos parámetros ambientales e hidrogeológicos en los contenidos de nitratos del agua subterránea del Valle de Huamantla, Tlaxcala. Se realizaron dos muestreos que incluyeron el 17 y 22 % de los pozos del área de estudio. Las concentraciones de nitrato se determinaron por potenciometría con electrodo de ión selectivo. Estadísticamente, por análisis de varianza paramétrica y no paramétrica, se analizó la existencia de diferencias en las concentraciones de nitrato con relación a la ubicación, el uso del agua y el tipo de agricultura que se practica donde se encuentran los pozos. La concentración promedio de nitrato en la temporada de sequía (segundo muestreo) resultó casi el doble respecto a la registrada en la temporada de lluvias (primer muestreo). En el primer muestreo se detectaron cuatro lentes y en el segundo siete, donde la concentración sobrepasó la norma de 44.29 mgL-1 de NO3 - establecida por la World Health Organization (1985) para el agua potable. No se encontraron diferencias estadísticas de las concentraciones de nitratos con relación a la profundidad del nivel estático, pero la ubicación ( localización del pozo en el valle o en la montaña) y el tipo de agricultura (temporal o de riego) sí influyeron en las mismas.
    Full-text · Article · Jan 2004
  • N. Ceniceros · M. A. Armienta · S. Ramos · O. Cruz · A. Aguayo
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    ABSTRACT: The geochemistry of the crater lake of the El Chichón volcano has been studied since 1983. Results have been used to analyze post-eruptive processes and assessing volcanic risk. Chemical analysis has included pH, temperature, principal ions, fluoride, Iron , sulfide, boron and Silica. From 1985, all determinations have been performed at the Analytical Chemistry Laboratory of the Geophysics Institute (National University of Mexico). Such analysis were made following the standard methods, as given in APHA (1989), e.g. UV-visible, emission, and atomic absorption spectroscopy, potentiometric and volumetric techniques.. The El Chichón crater lake water showed an increasing pH from 1983 to 1986 (from 0.56 to 2.33), from then pH has fluctuated around the later value (in August 2002 pH was 1.98). Conductivity showed a high fluctuations with a general decreasing trend, ranging between 83800 uS/cm (1983, Casadevall et al., 1984) and close to 2000 uS/cm (December 1998). Water-type has changed along these years: The Chichon water could be classified as acid, calcium-chloride in 1983; in 1991 changed to Sulfate-mixed and since 1992, it has been mostly of sodium chloride type, except for a few dates when it could be classified as sulfate-mixed or calcic type. Since 1985, cation concentrations produced by environmental rock dissolution decreased in the same manner. A decreasing trend with time was observed also in anions of a potential magmatic origin like sulfate, chloride and fluoride. Molar concentrations of chloride have been mostly greater than sulfate concentrations (up to two orders of magnitude) and have varied without any observed correlation. Oxidation-reduction processes may explain the large sulfate concentration changesSulfate shows large. The geochemical modeling programs (MINTEQA2, PHREEQCE) showed saturation indices close to equilibrium for gypsum and anhydrite suggesting that sulfates also can be derived from other processes such as dissolution-precipitation. Application of this programs proved to be useful to determine temporal changes in species predominance, mainly of sulfur, calcium, and magnesium. A high correlation between Boron and Chloride (r=0.97) suggests a common origin for such species, probably derived from volcanic gas dissolution. Global geochemical variations in the last twenty years showed a decrease in magmatic contribution in the crater lake, an increase of hydrometeorological regime and a stabilization in the geothermal system.
    No preview · Article · Apr 2003