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Abstract. While semiarid forests frequently colonize rocky substrates, knowledge is scarce on how roots garner resources in these extreme habitats. The Sierra San Miguelito Volcanic Complex in central Mexico exhibits shallow soils and impermeable rhyolitic-rock outcrops, which impede water movement and root placement beyond the soil matrix. However, rock fractures, exfoliated rocks and soil pockets potentially permit downward water percolation and root growth. With ground-penetrating radar (GPR) and electrical resistivity tomography (ERT), two geophysical methods advocated by Jayawickreme et al. (2014) to advance root ecology, we advanced in the method development studying root and water distribution in shallow rocky soils and rock fractures in a semiarid forest. We calibrated geophysical images with in situ root measurements, and then extrapolated root distribution over larger areas. Using GPR shielded antennas, we identified both fine and coarse pine and oak roots from 0.6 to 7.5 cm diameter at different depths into either soil or rock fractures. We also detected, trees anchoring their trunks using coarse roots underneath rock outcroppings. With ERT, we tracked monthly changes in humidity at the soil–bedrock interface, which clearly explained spatial root distribution of both tree species. Geophysical methods have enormous potential in elucidating root ecology. More interdisciplinary research could advance our understanding in belowground ecological niche functions and their role in forest ecohydrology and productivity.

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Rincon de Parangueo is a Quaternary maar that had a perennial lake until the 1980s. The lake was gradually desiccated as a consequence of drawdown in the Salamanca-Valle de Santiago regional aquifer and now functions as a playa-lake. In contrast with the features observed in other crater-lakes in the region (La Alberca, Cíntora, and San Nicolás), which also dried up at the same time, the bottom of the Rincón crater displays clear evidence of active deformation associated with mass movement of lake sediments towards the depocenter inside the crater. The most conspicuous topographic feature is a 10 -12 m high scarp parallel to the former lake coast. The scarp is produced by an annular shaped normal fault system, down towards the depocenter. Evidence of active mass movement is observed along the topographic scarp. Rotational slides associated with rollover anticlines and local grabens produced by antithetic faults are common on the eastern and northern parts of the scarp. Planar slides with open folds at their base occur at western part of the lake basin.Evaporites (trona, thermonatrite, eitelite, halite, and silvite) are abundant in the playa-lake sediments. Their presence makes us believe that a mass removal process is acting as a consequence of salt dissolution and infiltration of the brine towards the aquifer. This process, probably in conjunction with lake sediment compaction and/or diatreme subsidence, may explain the significantly higher fault displacement rate observed inside the crater ( ≈ 50 cm/year ) in comparison with active faults elsewhere in the Salamanca-Valle de Santiago aquifer ( ≈ 6 cm/year ).Keywords: drawdown, maar, evaporite, stromatolite, landslide. Resumen

Groundwater occurrence in semi-arid regions is variable in space and time due to climate patterns, terrain features, and aquifer properties. Thus, accurate delineation of Groundwater Potential Zones (GWPZs) is essential for sustainable water resources management in these environments. The present research aims to delineate and assess GWPZs in a semi-arid basin of San Luis Potosi (SLP), Mexico, through the integration of Remote Sensing (RS), Geographic Information System (GIS), and Analytic Hierarchy Process (AHP). Seven thematic layers (geology, lineament density, land use and land cover, topographic wetness index (TWI), rainfall, drainage density, and slope) were generated in raster format. After the AHP procedure and rank assignment, the thematic layers were integrated using the raster calculator to obtain the GWPZs map. The results indicated that 68.21% of the area is classified as low groundwater potential, whereas 26.30% is classified as moderate. Validation was done by assessing the water residence time data from 15 wells distributed in the study area. Furthermore, the Receiver Operating Characteristics (ROC) curve was obtained, indicating a satisfactory accuracy prediction (AUC = 0.677). This study provides valuable information for decision-makers regarding the conservation and sustainable management of groundwater resources.

Most agricultural soils in semi-arid regions present a deficiency of organic matter (SOM). In order to improve this soil, wastewater is used due to its high organic carbon content. The objective of the present work was to characterize the dissolved organic matter in five residual water samples and ten soil samples from the agricultural area of the municipality of San Luis Potosí by 3D fluorescence spectroscopy. The changes in some physical and chemical properties of the soil were also analyzed. The soil samples were collected at different depths to observe the anthropogenic organic matter presence, their retention in the soil profile, their fluorescence intensity changes and their migration into the aquifer. Temperature, electrical conductivity, dissolved oxygen, oxidation-reduction potential and total dissolved solids were determined in situ. The major anions and cations: Na3-, SO4 2-, NO 3-, NO2 -, were analysed in laboratory. The results show the great contribution of organic matter (>2020 mg/L) in the residual water used for irrigation, as well as, the low content of SOM. The physical and chemical results indicate that the high electrical conductivity of the water, represents a risk of salinization for soils, but not of short term sodicity. The 3D fluorescence spectra of the soil profile, shows the presence of humic and fulvic acids, aromatic proteins and products of microbial degradation. The latter observed in that depth where there is a greater percentage of clay.Palabras clave: fluorescencia 3D, proteínas aromáticas, ácidos húmicos, ácidos fúlvicos, contaminación de suelo RESUMEN La mayoría de los suelos agrícolas en regiones semiáridas presentan una deficiencia de materia orgánica (MOS) y para compensarla se recurre al uso de agua residual por R.M. Fuentes Rivas et al. 576 su alto contenido de carbono orgánico. El objetivo del presente trabajo fue caracterizar la materia orgánica disuelta con espectroscopía de fluorescencia 3D, en cinco muestras de agua residual y 10 de suelo de la zona agrícola del municipio de San Luis Potosí. Se analizaron los cambios de algunas propiedades físicas y químicas del suelo y del agua. Las muestras se colectaron a diferentes profundidades para observar la presencia de materia orgánica, su retención a lo largo del perfil de suelo y su migración hacia el acuífero. La temperatura, la conductividad eléctrica, el oxígeno disuelto, el potencial de oxido-reducción y los sólidos totales disueltos se determinaron in situ. En laboratorio fueron analizados los aniones y cationes mayoritarios: Na . Los resultados muestran el gran aporte de materia orgánica del agua residual empleada para el riego, así como, el bajo contenido de MOS. Los resultados físicos y químicos indican que la alta conductividad eléctrica del agua representa un riesgo de salinización para los suelos, pero no de sodicidad a corto plazo. Los espectros de fluorescencia 3D del perfil del suelo evidencian la presencia de ácidos húmicos, acidos fúlvicos, proteínas aromáticas y productos de degradación microbian...