The Cuatro Cienegas basin in the Chihuahuan desert is a system of springs, streams, and pools. These ecosystems support >70 endemic species and abundant living stromatolites and other microbial communities, representing a desert oasis of high biodiversity. Here, we combine data from molecular microbiology and geology to document the microbial biodiversity of this unique environment. Ten water samples from locations within the Cuatro Cienegas basin and two neighboring valleys as well as three samples of wet sediments were analyzed. The phylogeny of prokaryotic populations in the samples was determined by characterizing cultured organisms and by PCR amplification and sequencing of 16S rRNA genes from total community DNA. The composition of microbial communities was also assessed by determining profiles of terminal restriction site polymorphisms of 16S rRNA genes in total community DNA. There were 250 different phylotypes among the 350 cultivated strains. Ninety-eight partial 16S rRNA gene sequences were obtained and classified. The clones represented 38 unique phylotypes from ten major lineages of Bacteria and one of Archaea. Unexpectedly, 50% of the phylotypes were most closely related to marine taxa, even though these environments have not been in contact with the ocean for tens of millions of years. Furthermore, terminal restriction site polymorphism profiles and geological data suggest that the aquatic ecosystems of Cuatro Cienegas are hydrologically interconnected with adjacent valleys recently targeted for agricultural intensification. The findings underscore the conservation value of desert aquatic ecosystems and the urgent need for study and preservation of freshwater microbial communities.Cuatro Cienegas ͉ terminal restriction site polymorphism ͉ 16S clone library ͉ water conservation ͉ microbial ecology

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En este trabajo se analizó el comportamiento geohidrodinámico del acuífero Campo Durazno en su primera unidad geohidrológica, por medio de un modelo que explica su interconexión con el entorno. La metodología que se aplicó fue con base en 36 fuentes de abastecimiento, de los cuales se monitorearon aspectos hidráulicos, geohidrológicos y ambientales. Se realizaron diferentes pruebas en campo y en laboratorio para la determinación de los parámetros químicos e hidráulicos que son la base del modelo. Por medio del modelo propuesto se determinó la dirección del flujo subterráneo; el balance hidrológico indicó una recarga superficial nula, lo que permitió corroborar que la unidad en estudio está en equilibrio en forma hidráulica y geohidrológica. En calidad del agua, se determinaron parámetros físico-químicos en las tres zonas (recarga, transición y descarga), siendo las zonas de transición y descarga las más elevadas en concentraciones de Na+ y SO4- según la normativa nacional e internacional para consumo de agua potable; su presencia se debe probablemente a fuentes de contaminación industrial localizadas en la zona. La geohidrodinámica de la unidad hidrogeológica somera permite concluir que es necesario implementar un plan de gestión ambiental a corto plazo para la conservación sostenible del acuífero.

This paper examines the relationships between recent shallow seismicity and exploitation of fluids in the northern Burgos Basin where cumulative seismic events recorded in the State of Nuevo Leon reach a total of 304 earthquakes between 2006 and 2016. In detail, 2 to 5 yearly events occurred from 2006 to 2011; but a later remarkable increase was evident as follows: 89 in 2012, 69 in 2013, 75 in 2014, 31 in 2015 and 27 in 2016. This behavior doesn’t match the random fluctuations from natural seismicity rates. A statistical analysis allowed us to determine that the sequence of earthquakes after 2011 could be related to the activity of exploratory wells in the Burgos Basin, which were drilled down to the Pimienta (Upper Jurassic) and Agua Nueva (Upper Cretaceous) shale gas plays. The epicenters located in the State of Nuevo Leon, in the municipalities of China, General Terán, Montemorelos and Los Ramones, were associated with the Upper Jurassic Pimienta and Upper Cretaceous Agua Nueva shale gas fields. Only 17 earthquakes had magnitudes ranging from 4.0 - 4.5 Richter  magnitude and those were associated with the exploratory wells Anhelido-1, Arbolero 1, Batial-1, Durian-1, Kernel-1, Mosquete-1,  Neritas-1, Nuncio-1, Serbal-1 and  Tangram-1. The hypocenters correspond to the depth at which the Pimienta and Agua Nueva Formations lie; hence, sharp changes in the minor shock frequencies were considered as indicators of induced seismicity related to hydraulic fracturing for fluid extraction. The scatterplot of the frequency and magnitude of events for 2009-2014  shows slopes between -7.0963 to -1.1538 that were considerably more negative than the   natural seismicity values which span from 0.75 to 0.9.  The slopes for 2012, 2013 and 2014 are negatives (-7.0963, -0.3656 and -0.1333), respectively. These dramatic changes in increasing of the minor shock sequences in the Burgos Basin allow us to be considered as indicators of induced seismicity due to fluid exploitation. This  interpretation is based on the frequency and magnitude of shocks which achieve values  of hydraulic fracturing-induced   earthquakes associated with anthropogenic fracking,  similar to other seismicity data obtained in different parts of the world where this Technique is applied.

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