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The irrigation schedule in arid areas has to be efficient in order to reduce losses due to evaporation and deep infiltration. Irrigation optimization poses the need to establish with precision the value of actual evapotranspiration (ETa), and the crop coefficient (Kc). The water soil availability can be increased using hydrogel and organic matter amendments, and their effects could vary ETa and Kc. The aim of this study was to determine the ETa, and Kc of an experimental site with lysimeters on the Spanish Mediterranean coast cropped with a turf grass variety, Agrostis stolonifera ‐L‐93, under field conditions, and amended with hydrogel and organic matter. Reference evapotranspiration (ET0) was determined from meteorological data (FAO‐Penman‐Monteith equation). ETa was calculated from the water balance, and Kc was obtained by dividing ETa by ET0. Kc was calculated and compared on a yearly, monthly and daily basis. In summer, the differences between amendments become manifest:Unamended lysimeter (100% sand) had Kc values (0.92‐1.16), similar to organic matter amended lysimeter (0.99‐1.17). Maximum and minimum Kc values for the hydrogel amended lysimeters (1.04‐1.52) were higher than those from the other because of the ability of this compound to retain water, which facilitated evapotranspiration. Finally, hydrogel helped to maintain the turf grass quality.

The problematic that commonly arises when protecting springs that supply water for human consumption requires a methodological process to prioritize springs that are used for this purpose according to their greatest need for protection from contamination and exploitation processes. To this end, the stages included in the present study were: a) regionalization of the study area (State of Mexico, Mexico) considering physical variables, which included precipitation, hydrogeological functioning, and geoforms; b) selection of the springs used for human supply that have the greatest exploitation flows, as registered in the Public Water Rights Record; and c) prioritization of springs to be protected based on a multi-criteria evaluation (MCE), considering criteria such as exploitation flow, land use, population to be supplied, conservation of spring water collection systems, existence of alternative supply sources, and marginalization index of nearby populations. Regionalization enabled identifying regions that were homogeneous in terms of the characteristics of the springs and their physical environment. Six of those regions with the largest territorial areas were selected, where 88% of the springs used for human consumption were located. Within each selected region, the springs that were representative of exploitation flow were identified, and a total of 23 were included. Lastly, MCE permit to identify six springs (one in each region) that were priorities for protection. The prioritization of the springs to be protected in each of the six regions selected will facilitate the future application of protection methods based on the physical characteristics of the springs and their physical and socioeconomic environments. Considering also the characteristics of groundwater flow in the feeding areas of the springs.

Purpose The intensive cultivation of turfgrass requires a high quantity of water and fertilizer. The fertilizers can leach and reach groundwater or be transported by run-off to water surface. It is necessary to improve irrigation and fertilization techniques to guarantee water and fertilizer optimal use and avoid contamination. The objectives were to analyze water flow and nitrate transport using the HYDRUS-1D and explore the effect of organic matter and hydrogel on the nitrate leaching. Materials and methods The experimental site was divided into 4 plots, each with an approximate area of 40 m2 and a volume of 10 m3 . The substrate is composed of sand, which is superimposed on a gravel layer where drainage pipes are installed to collect the leachates. The plots were constructed with different amendments in order to evaluate their influence on water flow and contaminant transport. The plot 1 contains organic matter (OM) and hydrogel (HG). The plot 2 contains OM. The plot 3 was constructed with only HG and the plot 4 with only sand. Results and discussion The results’ simulation indicated that the plot P1 retained water and, accordingly, retained the nitrate leached (2% of total applied nitrogen). The plot P4 drained a greater volume of water and nitrate leached (12% of total applied nitrogen). The greatest differences between the predicted and observed data occurred after 650 h, which appears to confirm the difficulty of modeling relatively long time periods. During this period, there may be changes in the hydraulic parameters that affect water flow. The simulations of nitrate transport indicated that the model partially represents the observed data. This may be due to aspects not considered in the model, such as moisture retention, piston flow, and preferential flow, which favor the leaching of more or less nitrates. Conclusions The use of hydrogel appears to be a good option for controlling leaching and, therefore, can be recommended, for example, in intensive crop fields or greenhouse crops.

15 p. - Supplementary data to this article can be found online at https://doi.org/10.1016/j.apgeochem.2020.104866. - The data used to support the findings of this study are available from http://repositori.uji.es/xmlui/handle/10803/620641., [EN] The southern part of the Plana de Castellón aquifer (Spanish Mediterranean coast) has experienced persistent seawater intrusion over the last 50 years. The salinisation process is related to the lateral advance of the saline wedge and saline upconing as a result of intensive local groundwater pumping. In this context, managed aquifer recharge (MAR) was performed to aid in the recovery of this coastal aquifer. The artificial recharge water (ARW) was characterised by very low mineralisation, as evidenced by a mean electrical conductivity of 330 μS/cm, whereas native groundwater (NGW) was brackish, with EC values of approximately 3000–3500 μS/cm. The dynamics of the injected water and physicochemical changes to groundwater during the MAR event were evaluated using a combination of hydrogeochemical methods. EC, chloride ions, nitrate ions, and stable water isotopes (oxygen-18 and deuterium) were used as tracers to quantify the presence of injected water in groundwater (mixing ratios). Hydrochemical analysis (of major cations and anions) was used to determine changes to water characteristics and hydrogeochemical processes associated with the mixing of ARW and NGW and water-rock interactions. The injection significantly reduced groundwater salinity: EC and major ions rapidly and continuously declined after the first days of recharge. Percentage decreases in electrical conductivity of 80–90% and 30% were detected at 80 and 450 m from the recharge wells (values of 350–550 μs/cm), respectively. The principal process occurring in the aquifer during injection was dilution due to the displacement of NGW and mixing of ARW and NGW. Carbonate and sulfate mineral dissolution, cation exchange, and redox reactions were also identified, and their magnitudes were estimated. In quantitative terms, cation exchange was the most important geochemical process occurring during the MAR event., This study formed part of the project “Facing seawater intrusion recharging coastal aquifers with regenerated water”, financed by The Coca-Cola Foundation (Atlanta, USA), with the support of Coca-Cola Iberian Partners.

The urban area of Puebla Valley aquifer is seated in Puebla City and neighbor municipalities. Puebla is the fourth largest city in Mexico, where there are significant industrial zones and a large population. Water needs are almost exclusively met by groundwater, which has brought intense exploitation of groundwater resources and water quality degradation. The present study investigates the hydrogeochemical changes in groundwater, particularly focuses on the chemical changes produced by upwelling mineralized water. These concentrations may represent potential risks to the health of the population. The groundwater presented five types of families Ca-HCO3, Mg-HCO3, Mix-HCO3, HCO3-Ca-SO4 and Ca-SO4. The high concentrations of sulphates, calcium and magnesium are reflected in high TDS and Total Hardness. The samples collected showed detectable concentrations of F−, Fe, Mn, Ba, Sr, Cu, Zn, B and Li. The limitations for its use as drinking water are given by the high values of TDS, sulphates, total hardness and Mn. Geochemical modeling using Geochemist's Workbench (GWB) and PHREEQC software enabled the computation of the saturation index of mineral phases with ions in solution and speciation ions. Groundwater was initially in equilibrium with calcite; however, due to the changes in hydrogeological conditions, gypsum and dolomite are being dissolved until new equilibrium conditions are met. The additional calcium and carbonate in the water causes calcite to become oversaturated and to precipitate. Evidence of dedolomitization reactions and common ion effect is illustrated by concurrent increases in calcium and magnesium concentrations in the groundwater.

Previous studies performed on the volcanic-sedimentary aquifer of the Tenancingo Valley (Mexico) reports high concentrations of Fe, Mn, and NO 3 − , and water from several wells receives purification treatments due to presence of Fe and Mn. These studies have not achieved conclusive results regarding the origin of Fe and Mn, nor have hydrogeochemical evaluations of the aquifer been performed. The present study aimed to evaluate the physicochemical characteristics of the water and identify the geochemical processes that determine presence of Fe and Mn in groundwater. This characterization was based on physicochemical data from well and spring samples (16 samples) during dry and rainy seasons (June and November 2012, respectively). The EC, temperature and pH ranged from 125 to 793 μS cm − 1 , 14.5 to 24.9 °C and 6.5 to 8.5 pH units, respectively. The Eh values ranged from − 219 to 327 mV, indicating the existence of both reducing and oxidizing zones. Presence of Fe and Mn was detected in both springs and wells; concentrations were higher in well, exceeding 4 mg Fe L − 1 and 0.5 mg Mn L − 1 . Content of Si ranged from 12 to 47 mg L − 1 . A model of the hydrogeochemical behavior of the aquifer was created to highlight the following: i) processes involved in water-rock interactions, including fluctuations in silicate levels that determine anionic and cationic content of water, and ii) redox reactions as the major control processes of Fe and Mn. Water quality for human use is restricted by Fe and Mn content and pH. For irrigation use, significant limitations were not presented.

The authors gratefully aknowledge the support received from Consejo Nacional de Ciencia y Tecnologia (CONACyT) through project no. 248327

The Ixtapan de la Sal–Tonatico hot springs are located in the geological setting of the Trans-Mexican Volcanic Belt, on the border of the Morelos–Guerrero Basin, which is carbonated region with limestone and silicic rocks. The temperature, electrical conductivity and pH of the thermal waters are 25.7–37.2 °C, 9520–13,920 µS/cm and 5.90–6.88, respectively. The hydrochemical family is NaCl (Cl− mean concentration of 2198 mg/L and Na+ mean concentration of 1396 mg/L). The minor and trace elements that are notable for their high concentrations are B (19.69–23.58 mg/L), Li (6.09–8.06 mg/L), Sr (4.80–6.18 mg/L) and As (0.30–1.97 mg/L). Isotope data (δ18O, δ2H) show δ18O enrichment of the thermal waters, which may be a result of isotopic exchange with the host rock at high temperatures, although the value was very small, which may be due to mixing with groundwater near the surface. The water samples were oversaturated with calcite, dolomite and quartz, verified in the field by the presence of precipitated rocks (travertines). The samples were undersaturated with chalcedony, silica gel, cristobalite, celestite and strontianite. Several chemical geothermometers and the results from multicomponent equilibrium suggest a reservoir temperature between 90 and 130 °C. Meanwhile, a temperature of 129 °C was estimated with the Cl–enthalpy mixing model. According to the conceptual model of the functioning of this system, considering that flow is characterized by the heating of water at deep zones due to the high geothermal gradient caused by recent tectonic activity. This water rises to the surface through fractures and faults. As it rises, thermal water mixes in different proportions with Ca-HCO3 groundwater.

This work presents the use of multi-criteria decision analysis (MCDA) as a decision tool to facilitate the process of prioritization of drinking wells that would need more protection before contamination risk. In this study, three aspects of the protection of the groundwater quality were taken into account: natural, anthropic and technical. From these aspects, elements more representative were selected, which can be quantified with available and easily accessible information. Considering those elements, selection criteria were defined which have been represented by: population distribution indicator, human development index, land use, index for aquifer vulnerability to contamination, well age and well yearly pumping rate. The developed method has been applied to drinking supply wells located in the Toluca Valley aquifer (Mexico), and implied the generation of the thematic maps of the defined selection criteria. For the MCDA, the values of each map were converted to the same scale, each criterion was weighted in function of its importance according to the objective and there were aggregated by the way of a lineal combination. The obtained result is a map that shows the level of protection priority of the supply wells. This map can offer information to the stakeholder in a relative short time and contribute to accelerate the actions aimed to protect the quality of the vital underground liquid.

The Sierra Huautla (Morelos State, Mexico) is a biological reserve with historical mines of Ag and Pb. In this area, waters used by inhabitants are contaminated by arsenic (As). An integrated environmental survey was realized both in waters and sediments to better constrain the source and the mobility of As and other trace elements. Two areas of interest were selected: (1) the Nexpa River ecosystem to determine the local geochemical background, and (2) the Huautla area, affected by past mining activities. This study allowed the definition of the local geochemical baseline in sediments or in waters, demonstrated uncontaminated by TE in the Nexpa area, except for As in the dissolved phase or for Cd in Suspended Particulate Matters (SPM). In the Huautla area, TE contents in water were higher than the World Health Organization (WHO) limits for Al, As and Mn in unfiltered waters, and only for As in the dissolved phase. Speciation analyses revealed arsenic to be present only as the toxic-inorganic arsenate species, As(+V). In SPM, Ag, As, Cd and Zn concentrations were higher than Sediment Quality Guidelines (SQG). The different geochemical indice (EF: 5, PLI: 3, EF: Igeo: 5–3) demonstrated that SPM were significantly contaminated and consistute an health risk for Huautla inhabitants exposed to As-contaminated waters and TE-rich SPM. The combination of mineralogy, chemistry, C and S stable isotopes with thermodynamic modeling indicate dissolutions of minerals from local geological formations, sorption-desorption phenomena from clays and oxy-hydroxides, and the weathering responsible for the transport of the TE-rich SPM (1.8 wt% for 17% of the total TE concentration). Moreover, the past mining activity would be a source of the contamination only for As in waters from flooded mines.

Golf courses represent an agricultural activity wherein grass is intensively cultivated using large quantities of fertilizers. In the present study, nitrogen and phosphorus leaching was analyzed over two years in an experimental green under actual field conditions. The green contained four plots with distinct amendments (P1: hydrogel + peat, P2: peat, P3: hydrogel, and P4: no amendment). The applied doses of nitrogen ranged from 5 to 103 kg/ha and of phosphorus from 9 to 31 kg/ha. The irrigation level varied as a function of the rainfall regime and the water requirements of grass; overall water intake varied from 1550 to 2080 mm/year. Daily, leached water volume was calculated, and samples were taken for chemical analysis. Nitrogen and phosphorus mass balances were calculated for different periods based on the collected data. The plot amended with peat and hydrogel (P1) had reduced water flow; the percentage of drainage water varied from 8.4 to 29%. As a result, the dissolution and leaching of nitrogen (N) and phosphorus (P) were the lowest in comparison to the other plots. According to the calculated mass balances, the lowest leaching values were also recorded in this plot (P1), ranging from 0.5 to 6.3% for N and from 0.8 to 20.9% for P. The plot without amendment (P4) drained the most water (25.9–44.8%) and leached the highest quantities of N and P, ranging from 9.1–45.7%, and 6–35.9%, respectively. The use of double amendments (hydrogel and peat) therefore represented optimal operating conditions for the green. Moreover, a relationship was found between increasing rates of fertilization and increasing percentages of N and P leaching as well as between higher irrigation levels and greater leaching.

The objective of this investigation was to use multicriteria analysis to analyze and model the main criteria that influence the optimal design of a network to monitor groundwater levels. The multicriteria analysis was performed using a GIS (IDRISI Selva). The Toluca Valley aquifer (Mexico) was chosen as the case study. The definition and importance of the criteria (factors and constraints) that influence the design of the monitoring network were based on available information and consultations with experts in the topic. The factors considered were: rate of decline in groundwater levels, decline in groundwater levels, rise in groundwater levels, cracks, vertical hydraulic gradient, and density of wells. The Analytical Hierarchy Process (AHP) was used to weight the factors, resulting in a consistency ratio of 0.08. The weighted linear combination (WLC) method was then applied which resulted in a map identifying the locations of the priority areas to be monitored. The results show that 1.0 % of the study region corresponds to very high priority monitoring areas, 1.8 % to high priority areas, another 1.8 % to medium priority, 4.4 % to low priority and 91 % to very low priority monitoring areas. The proposed method can be used by government and public and private organizations to determine monitoring strategies that support water resources management.

This study evaluated the impact of an abandoned Ag mine on the quality of surface and groundwater. The mining site of Huautla is in south Morelos State, central Mexico. Ag–Pb–Zn and Au–Cu sulfide ores were mined in the district. The ores were characterized by the presence of Ag, galena (PbS), sphalerite (ZnS), and stromeyerite (CuAgS). Ag was the metal of greater interest. Other metals included Cu, Pb, Zn, and Au. Mining activities stopped in the early 1990s when the market price of Ag decreased; the abandoned mines then were flooded by rising groundwater levels. Because of the urgent demand for water by the inhabitants in the area, this water has been used as drinking water and as waterholes for livestock. Water sampling points included abandoned mines (America, Pajaro, Santiago, Tlachichilpa, and San Francisco), dams, and dug wells. The greatest concentrations of As and other toxic chemical elements (Fe, Mn, Pb, Cd, F) were detected in groundwater samples from flooded mines. The presence of these elements was related to the rock–water interaction process. The oxidation of sulfides appears to be the cause of increased metal concentrations in groundwater samples from flooded mine. Other possible water–rock interaction processes that can control the presence of arsenic in groundwater were the adsorption of arsenic in iron oxyhydroxides, the adsorption in carbonates, and/or coprecipitation with calcite. In the case of the San Francisco and America mines, the oxidation conditions, low correlation of As with SO4 2− and Fe2+, and concentrations of silica indicate that the presence of As in the groundwater could be due also to competition for adsorption sites.

The Toluca Valley is located on the high plains of Mexico, where there are significant industrial zones and large populations. Water needs are almost exclusively met by groundwater, which has brought about intense exploitation of the aquifer and indication of some contamination. The present study investigates the effect of urbanization, related to industrialization of the region, on groundwater in the central portion of the Toluca Valley aquifer--a zone with high population density and where the largest industrial park is located. A general decline in the groundwater level has been found over the years, at a rate of as much as 2.5 m/year. The appearance of a large drawdown cone was identified, indicating changes in the direction of groundwater flow. Also identified was the presence of several ground fissures, the location of which coincided with the drawdown cone. In hydrochemical terms, the water type is sodium-magnesium bicarbonate and this characteristic has not changed over time, although it has been possible to detect the presence of larger quantities of sulfates (up to 117 mg/L) and nitrates (up to 47 mg/L) in recent years, likely associated with contamination from industrial and urban wastewater. Factor analysis made it possible to identify ions that would characterize natural processes involving the acquisition of salts (HCO3 (-), Na(+), Mg(2+), and Si), as well as anthropic activities (SO4 (2-), NO3 (-), Cl(-), Ca(2+), and K(+)).

Arsenic (As) in groundwater for domestic use poses a worldwide threat to public health, most notably in rural areas. The aims of this study were: first, determine groundwater composition in a mining area in central Mexico (Huautla); second, assess As exposure through human groundwater consumption and; third, develop and test a household filter to obtain drinking water for these rural communities. From the 17th century through the 1990s, mines in the area produced Ag-galena and sphalerite from volcanic rock. Groundwater flooded the mines when they were abandoned due to low silver prices. Local households now use the water to meet domestic needs. Water from the mines was found to have high As content (0.04–0.26 mg L −1 ) and Fe, Mn, Pb and Cd were also above Mexican drinking water standards and WHO guidelines. All the population in the Huautla community was exposed to the metalloid through water used in food preparation. The best As removal was obtained with a filter using oxidized commercial fiber (HCl 2N as oxidant). Concentrations in the effluent were below Mexican drinking water standards (0.025 mg As L −1 water) during the 105-day (2520 h) filter operation, with a maximum As removal efficiency of 95.4%. The household filter was simple, low-cost and may be very attractive for As removal in rural areas in developing countries.

Wastewater biosolids are large potential sources of macronutrients for agriculture, conservation and restoration of soils; there are, however, few studies on phosphorus (P) release in soils amended with biosolids. Biosolids and vermicomposted biosolids were tested in concentrations (5–30 g amendment kg−1 soil) equivalent to 18–100 Mg ha−1. Desorption of P was determined by successive extractions for 65 days. Soil P was low, and biosolid and vermicompost addition released 8 and 6 times more P, respectively, than soil alone. To describe the release of P, zero-, first- and second-order equations, simple Elovich and power functions and the parabolic diffusion law were compared based on their coefficient of determination (r 2) and standard error (SE). In all treatments, the power function and especially the parabolic diffusion law were the best fit, with 0.898–0.996 r 2 and 0.022–0.732 SE. The general behavior of the kinetic parameters mostly depended on the amendment doses. Eutrophication posited to start beyond 16 mg P kg−1 soil was more likely allayed by a maximum vermicompost dose of 50 Mg ha−1, higher than the 36 Mg ha−1 maximum biosolid dose. The higher vermicompost P addition and lower P release could favor gradual and longer-term P absorption by plants and may reduce leaching or runoff P losses.

The Valley of Puebla aquifer (VPA), at the central region of Mexico, is subject to intensive exploitation to satisfy the urban and industrial demand in the region. As a result of this increased exploitation, a number of state and federal agencies in charge of water management are concerned about the problems associated with the aquifer (decline of groundwater table, deterioration in water quality, poor well productivity and increased pumping and water treatment costs). This study presents a groundwater management model that combines “MODFLOW” simulation with optimization tools “MODRSP”. This simulation–optimization model for groundwater evaluates a complex range of management options to identify the strategies that best fit the objectives for allocating resources in the VPA. Four hypothetical scenarios were defined to analyze the response of the hydrogeological system for future pumping schemes. Based on the simulation of flow with the MODFLOW program, promising results for the implementation of the optimization of water quantity were found in scenarios 3 and 4. However, upon comparison and analysis of the feasibility of recovery of the piezometric level (considering the policy of gradual reductions of pumping), scenario 4 was selected for optimization purposes. The response functions of scenario 4 were then obtained and optimized, establishing an extraction rate of 204.92 millions of m3/year (Mm3/year). The reduction in groundwater extraction will be possible by substituting the volume removed by 35 wells (that should be discontinued) by the same volume of water from another source.

In this contribution, we describe the formation and evolution of the upconing process in a Mediterranean coastal aquifer. The study area has experienced severe salinization over the last 40 years because of intensive exploitation of groundwater. We used historical and current records of piezometric levels and chloride concentrations to trace the development of the salinization of the aquifer. We defined the 3D shape of the saline wedge from the spatial distribution of chloride concentrations and vertical well logs of electrical conductivity using monitoring network data. Upconing first appeared in the early 90s and has continued until the present day. In this study, we examined the intensity of the upconing process. Dry periods and the associated increases in pumping caused the advance of seawater intrusion. The sharp reduction in groundwater withdrawals over the last 10 years has caused the saline wedge to move backwards, although the ongoing pumping and the climate conditions mean that this retreat is quite slow., Grupo de Investigación de Acuíferos Costeros, Universitat Jaume I, España, Unidad de Valencia, Instituto Geológico y Minero de España, España, Centro Interamericano de Recursos del Agua, Facultad de Ingeniería, Universidad Autónoma del Estado de México, México

The impact of intensive aquifer exploitation has been observed in numerous places around the world. Mexico is a representative example of this problem. In 2010, 101 out of the 653 aquifers recognized in the country, showed negative social, economic, and environmental effects related to intensive exploitation. The environmental effects include, among others, groundwater level decline, subsidence, attenuation, and drying up of springs, decreased river flow, and deterioration of water quality. This study aimed at determining the hydrochemical changes produced by intensive aquifer exploitation and highlighting water quality modifications, taking as example the Valle de Toluca, Salamanca, and San Luis Potosi aquifers in Mexico's highlands. There, elements such as fluoride, arsenic, iron, and manganese have been detected, resulting from the introduction of older groundwater with longer residence times and distinctive chemical composition (regional flows). High concentrations of other elements such as chloride, sulfate, nitrate, and vanadium, as well as pathogens, all related to anthropogenic pollution sources (wastewater infiltration, irrigation return flow, and atmospheric pollutants, among others) were also observed. Some of these elements (nitrate, fluoride, arsenic, iron, and manganese) have shown concentrations above Mexican and World Health Organization drinking water standards.

The need to protect groundwater resources against quality deterioration due to anthropogenic activities is unquestionable. The concept of aquifer pollution vulnerability maps and of wellhead protection areas (WHPA) as protection tools is not new; however, in spite of the elapsed time, their use has been increased as a result of the increase in economic development—and everything that this entails—and the increase in prohibitive costs of treating contaminated water or of the decontamination of aquifers. The study’s objective was to establish an integrated method that defines, first of all, the areas of highest vulnerability in the aquifer, and second, within these areas, the wells that most urgently need protection. To identify these wells, additional criteria were taken, such as well constructive data, pumped volume, and the region’s socioeconomic characteristics (social exclusion index). Once the wells were ranked, several of them were chosen as a pilot study to compare different methods for the delineation of WHPA based on calculated fixed radius and analytical methods and, this way, identify which method or methods best adapt to the characteristics of the study area. The Minkin analytical method proved to offer the best results since it protects well on both sides and achieves a balance in the well’s upgradient distances. It is also worth mentioning that the delimitation of the WHPAs in the study area was limited in respect to hydrogeologic and technical data.

With the increasing population, urbanization and industry in the arid area of Tecate, there is a concomitant increase in contaminants being introduced into the Tecate River and its aquifer. This contamination is damaging the usable groundwater supply and making local residents and commercial enterprises increasingly dependent on imported water from the Colorado River basin. In this study we apply a suite of chemical and isotopic tracers in order to evaluate groundwater flow and assess contamination trends. Groundwater recharge occurs through mountain-block and mountain-front recharge at higher elevations of the ranges. Groundwater from the unconfined, alluvial aquifer indicates recent recharge and little evolution. The increase in salinity along the flow path is due to interaction with weathering rock-forming silicate minerals and anthropogenic sources such as urban wastewater, residual solids and agricultural runoff from fertilizers, livestock manure and/or septic tanks and latrines. A spatial analysis shows local differences and the impact of the infiltration of imported waters from the Colorado River basin. The general trend of impaired water quality has scarcely been documented in the last decades, but it is expected to continue. Since the groundwater system is highly vulnerable, it is necessary to protect groundwater sources.

The agricultural activities practice often demands an intensive application of fertilizers. Phosphate and nitrogen fertilizers are the most employed in the corn growing areas of the central Mexico highlands. The first ones presents an uranium content ranging from 50 to 200 mg. kg−1 depending on the origin of the phosphate rock used in its production. It is crucial to analyze the rainwater, surface water, soil water at several depths, groundwater and soil to determine the simultaneous behavior of phosphate, nitrate and uranium, and their leaching in a specific agricultural land. Uranium concentration, 16 mg. kg−1, in the soil water was higher than that in the surface water and groundwater. The different concentrations are due to an unequal uranium distribution in the environment. The phosphate concentration, 37.4 mg. kg−1, diminished throughout the profile of the soil due to a sorption–precipitation process. The nitrates were leached toward groundwater after the application of fertilizers, but the nitrate concentration in it did not exceed the limit for drinking water.

The final use that may be given to biosolids that result from the treatment of residual municipal waters depends on their physicochemical and microbiological characteristics. Their organic matter content and wealth of essential elements may allow their use for agricultural fertilization purposes. The objective of this research project was to evaluate the physicochemical interactions between soil treated with biosolids and compost from municipal residual waters, and the nutritional parameters of broad bean seeds (Vicia faba L.). The studied area is located in the central region of the Mexican Republic. The biosolids were treated with aerated static pile composting. The experimental work was performed in the area surrounding the East Toluca Macroplant, where nine 2 × 3 m plots were defined and distributed in a Latin square; 3 plots were used as controls (without conditioning), 3 were conditioned with 4.5 Mg ha−1 of biosolids on a dry base, and 3 were conditioned with the same amount of compost. The parameters determined for biosolids, compost, and soil were: pH, electrical conductivity (EC), organic matter (OM), total nitrogen, available phosphorus, cation exchange capacity (CEC), exchangeable cations (Ca, Mg, Na and K), total and available heavy metals (Cd, Cr, Cu, Ni and Zn); for the plant: height reached, green seeds productivity and yield per treatment (ton ha−1); for the seeds: humidity, ashes, fiber, fats, protein, starch and total and available heavy metals (Cd, Cr, Cu, Ni and Zn). pH was slightly acid in soil treated with biosolids (6.71). OM and CEC did not represent significant differences. Total concentrations of Cr, Zn, Ni and Cu in soil presented significant differences (p < 0.05) between treated soil and the control, Cd was not detected. Cu was the most available metal in soil treated with compost (15.31%), Cd and Cr were not detected. The plants had higher growth rates with biosolids (112.22 cm) and compost (103.73 cm); higher green broad bean productivity and higher seed yield, especially in plots containing biosolids, which had rates three times higher than the control. In regards to broad bean seeds, content of ashes, fiber, fats, protein, starch and heavy metals (Cu, Ni and Zn), there were no significant differences between the treatments. Cd and Cr were not detected. In conclusion, it has been proven that the use of biosolids and compost studied in this broad bean crop do not involve an environmental risk, and thus give way to a solution to the problem of final disposition of biosolids in the region.

There are several environmental processes occurring under aquifer overexploitation conditions. These processes include groundwater table decline, subsidence, attenuation and drying of springs, decrease of river flow, and increased pollution vulnerability, among others processes. Some of these effects have been observed on the Upper Basin of the Lerma River. The Lerma River begins in the SE of the Valley of Toluca at 2,600 m asl, in the wetland known as Lagoons of Almoloya del Río. This wetland is made up of a group of lagoons, which are an important aquatic system from an environmental point of view. The water inflow of this wetland is a discharge of springs, which occur between the fractured volcanic material of the mountain range and granular volcanic-continental deposits of the Valley of Toluca aquifer. The intensive exploitation of the Valley of Toluca aquifer to supply urban and industrial water to Mexico City and Toluca began in 1950 and is responsible for a steady decline of piezometric levels of 1-3.5 m/yr. Other effects of this exploitation--the drying of the wetland, the decrease of river flow and the land subsidence--caused serious ecological and social impacts. The authorities declared this aquifer as overexploited in order to reduce the exploitation and preserve the availability of water resources in this important region.

Phosphate fertilizers contain approximately 200 mg.kg-1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1-50 mg.kg-1) and phosphates (22-33 mg.kg-1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg.l-1 and phosphates between 1 and 0.3 mg.l-1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved.

Irrigation with treated wastewater was carried out in an experimental site in Castellon (eastern part of Spain). By using water soil samplers at different depths some physico-chemical parameters (conductivity, pH, major ions, nitrogen species, BOD, COD, and organic matter) were controlled to identify the processes affecting the self-cleaning power of the vadose zone. Modeling of these processes has been carried out by means of the NETPATH software. Two intervals have been considered, the first one from 15 to 180 cm in depth and the second one from 180 to 240 cm, in which ionic exchange processes affecting Na+, Ca2+, Mg2+, and K+, calcite precipitation, and dolomite and gypsum dissolution are active. The main differences between the intervals are modifications of CO2 interchange and the behavior of sodium. As a result of the synergic effect of different processes involved there is a good level of purification.

The high salinization in some sectors of the Castellon Plain aquifer (Spain) has been erroneusly attributed to seawater intrusion, because of the high and increasing contents of chloride ions. However, recent studies of this aquifer have shown that the chemical characteristics of groundwaters are the result of three different components: intruding seawater, freshwater from rainfall infiltration and saline water with a characteristic sulphate-calcium-magnesium facies, derived from bordering aquifers. The division into sectors according to hydrochemical features, in addition to the inclusion as variables of both certain minor ions and the ionic deviations of the theoretical mixing of freshwater and seawater, have provided a clear characterization of the salinization processes affecting the aquifer. The present study shows the application of statistical methods to the characterization of the salinization processes in the coastal aquifer of the Castellon Plain. The application of these statistical methods (cluster analysis and principal components analysis) has lead to the corroboration of the hypotheses developed from the previous hydrochemical study. Inclusion of specific variables (certain minor ions and ionic-Δ) into the PCA enhances a definition of the degree of the salinization processes.

This work proposes a method to estimate increased energy consumption of pumping caused by a drawdown of groundwater level and the equivalent energy consumption of the motor-pump system in an aquifer under intensive exploitation. This method has been applied to the Valley of Toluca aquifer, located in the Mexican highlands, whose intensive exploitation is reflected in a decline in the groundwater level of between 0.10 and 1.6 m/year. Results provide a summary of energy consumption and a map of energy consumption isopleths showing the areas that are most susceptible to increases in energy consumption due to pumping. The proposed method can be used to estimate the effect of the intensive exploitation of the Valley of Toluca aquifer on the energy consumption of groundwater extraction. Finding reveals that, for the year 2006, groundwater extraction in the urban zone required 2.39 times more energy than the conditions observed 38 years earlier. In monetary terms, this reflects an increase of USD$ 3 million annually, according to 2005 energy production costs.

A method based on neutron activation analysis was developed for the determination of fractions of milligrams of 2,4-D (2,4-dichlorophenoxy acetic acid) in aqueous solution in laboratory tests. The indirect determination of 2,4-D was based on the quantification of chlorine,38Cl, produced by neutron activation. The range of application was 0.01–100 mg l−1. No loss of38Cl by chemical effects of the nuclear reaction was found. The advantages of the proposed method include high precision and sensitivity of determination. Results were compared with those obtained by UV-Vis spectrophotometry, where concentrations less than 1 mg·l−1 were not detected.

The use of organic wastes in agriculture may increase the production of crops by incorporating organic matter and nutrients into the soil, and by improving its physical characteristics; however, this use may cause environmental problems such as the leaching of certain ions. The objective of this study was to establish possible nitrogen and phosphorus leaching under real field conditions in Phaeozem soils. The experimental work was performed in a corn (Zea mays L.) field where three plots were conditioned with inorganic fertilizer, three plots with 4.5 Mg ha−1 of biosolids on dry basis, and three plots with the same amount of composted biosolids. The quality of biosolids and composted biosolids complied with the Mexican Official Standards. Soil water samples were collected with suction cups during two agricultural cycles and were analysed. Soil samples were also taken and analysed. The N–NO3 concentrations in soil water fluctuated between 0.9 and 98 mg L−1 in the composted biosolid treatment, between 0.7 and 64 mg L−1 in the biosolid treatment, and between 1 and 61 mg L−1 in the inorganic fertilizer treatment. The maximum concentration of N–NO2 and N–NH3 in soil water was 1.02 and 2.65 mg L−1, respectively. The greatest percentage of nitrogen leached is produced when inorganic fertilizer is used (37.4% and 24.0% N leached in the first and second years, respectively), followed by composted biosolids (17.1% and 13.5% N leached in the first and second years, respectively) and last by biosolids (11% for both years). This difference could be related to the form in which nitrogen is present in the fertilizers, while commercial fertilizer is as inorganic nitrogen, organic wastes are basically presented as organic nitrogen. The maximum PO 4 3 - concentration in soil water was 1.9 mg L−1 in the composted biosolid treatment, 1.7 mg L−1 in the biosolid treatment and 0.9 mg L−1 in the inorganic fertilizer treatment. The estimated percentage of leached phosphorus was less than 1% for all treatments. The minimum leaching that occurred seemed to be due to a sorption–precipitation process.

El acuífero del Valle de Toluca, localizado en el Altiplano Mexicano, se encuentra sometido a una intensa explotación para cubrir las necesidades de agua en el propio valle, así como parte de las de Ciudad de México. Los altos niveles de explotación han provocado el descenso del nivel piezométrico, problemas de subsidencia, disminución de caudales en ríos y desecación de manantiales. Este estudio pretender determinar en qué grado esta intensiva extracción del agua subterránea es capaz de afectar y modificar el quimismo del agua. Para ello se han empleado técnicas estadísticas y datos históricos de los principales parámetros físico-químicos. Se ha podido comprobar que existen algunos cambios en el quimismo, ya que, inicialmente, el agua extraída del acuífero estaba ligada en gran medida a un flujo local (recarga por agua de lluvia y por alimentación lateral desde otros acuíferos) mientras que ahora el quimismo es característico de un flujo regional, puesto de manifiesto por aguas de tipo bicarbonatado sódico. Adicionalmente, también se ha producido un aumento del contenido de nitratos, aunque sólo de forma ocasional se sobrepasa el límite para agua potable (50 mg NO3– L–1). The Valle de Toluca aquifer, located in the Highlands of Mexico, is subject to intensive exploitation to meet the water demand in the valley, as well as for part of Mexico City. This intensive exploitation has produced a decline in groundwater level, land subsidence problems and a decrease in river and spring flows. This study is aimed at determining the extent to which the intensive groundwater abstraction is able to affect and modify the chemical characteristics of the water, using statistical techniques and historical data on the main physico-chemical parameters. Some changes in the chemical characteristics have been verified; initial water abstractions were mainly derived from a local flow zone (rainwater recharge and lateral flows from other aquifers), but currently the chemical characteristics are those of a regional flow zone, revealed by waters of sodium bicarbonate type. An increase in nitrate content has also occurred, although only occasionally is the limit for potable water (50 mg NO3- L-1) exceeded. The authors would like to thank the CONACyT (Consejo Nacional de Ciencia y Tecnología de México, Project 0391) and the Universidad Autónoma del Estado de México (Project 1067) for their financial support.

Guadalupe Reservoir, on the San Cayetano river, feeds into the Lerma river about 18 km north of Toluca in the State of Mexico, Mexico. On August 9, 1995, more than 6000 Israeli carp (Cyprinus carpio v. specularis and rubrofruscus) died within a week in this reservoir. We investigated the cause of the fish mortality and we determined whether the reservoir could be used again for carp culture. Five days after the accident the residual chlorine was 4 times higher than the maximum permissible amount. Ammonia nitrogen, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were also above the recommended levels. Six months later, the amount of some contaminants in the water, such as chlorine, were back to normal ranges of water quality criteria for aquaculture. Ammonia, BOD and COD concentrations were lower to those found in the previous analyses but remained higher than the recommended levels. Most probably, residual chlorine was the cause of carp mortality as the chlorine level was very high when the fishes died.