The San Luis Potosí valley is an endorheic basin that contains three aquifers: a shallow unconfined aquifer of alluvial material and two deep aquifers, free and confined. The groundwater contamination documented for the shallow aquifer generates contamination of the deep unconfined type aquifer, from which part of the population’s drinking water needs are met. This study records incipient anthropogenic contamination of two types: biogenic and potentially toxic trace elements. The studied contaminants include fecal coliform bacteria, total coliform, nitrate, and potentially toxic elements such as: manganese (Mn), mercury (Hg), arsenic (As), and cadmium (Cd). This contamination in some locations exceeds the permissible limit for human consumption. Some major consequences to health, including severe illness, may be caused by the trace elements. The present results give a first signal about the contamination of the deep unconfined type aquifer due to anthropogenic activity in the valley. This is a priority issue because this aquifer supplies drinking water, and in the short or medium term it will have an effect on public health.
mays, Avena sativa, y Cicer arietinum. El polen de la familia Quercus sp., propio de la zona montañosa, se detectó en las muestras de tres puntos de la zona de recarga y siete puntos de la zona de descarga. ABSTRACT Extensive outcrops of folded limestone rocks forming mountainous systems with intense karst development are found in areas of centralMexico. An important part of the water supply in these areas is derived from aquifers controlled by the karst system. We analyzed the underground flow between the towns of Joya de Luna (in an elevated part of the mountain) and Guaxcamá, topographically lower, to establish if there is a connection between these zones, and corroborate if the water infiltrated in the upper part is captured in lowland springs. A new method is proposed to qualitatively assess the hydraulic connectivity between the recharge and discharge zones in a karst and fractured system using pollen grains as tracers. Deuterium and oxygen-18 isotopic data were used to compare and evaluate the suitability of this method; in addition, excess deuterium was used as a factor in the hydrogeological analysis. Through a survey of the vegetation present within a 5 km radius in both zones, the pollen families existing in the recharge zone Joya de Luna and the discharge zone in Guaxcama were documented, and a database with 41 pollen species was generated for morphological characterization. Subsequently, 135 groundwater samples with suspended pollen grains were collected from 5 water wells in the recharge zone and 10 water springs in the discharge zone. The species analysis showed that pollen grains of Zea mays, Avena sativa, Cicer arietinum y Quercus sp., characteristic only of the recharge zone, were also present in water samples collected in the discharge area. The pollen-based results were consistent with those obtained with isotopic data; they allowed identifying two routes with hydraulic connection, G1
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