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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...

Origen de la calidad del agua del acuífero colgado y su relación con los cambios de uso de suelo 9 Resumen La historia de la ciudad San Luis Potosí se remonta al siglo XVI. Con el descubrimiento de yacimientos de oro y plata y la presencia de cuerpos de agua en el valle, fue fundada la ciudad San Luis Minas del Potosí, dando lugar a los dos primeros usos de suelo, urbano y minero. A partir del siglo XVII, el uso de suelo agrícola se desarrolló en huertos y fue relegado a la periferia de la zona urbana en el transcurso del tiempo. Finalmente el uso de suelo industrial surgió de manera importante en la segunda mitad del siglo XX. En la actualidad los tres usos de suelo existentes dentro del Valle de San Luis Potosí son el urbano, agrícola e industrial. A través de una campaña de muestreo hidrogeoquímico en octubre de 2008, con 44 muestras de norias y 3 de manantiales dentro del valle, se evaluaron parámetros físico-químicos, cationes, aniones y elementos traza. En los tres usos de suelo en la zona de estudio fueron detectados niveles importantes de nitratos, sulfatos, cloruros, conductividad eléctrica, coliformes totales y fecales; sin embargo, en la zona urbana existen anomalías puntuales de metales pesados principalmente de mercurio, bario, estroncio, cadmio, plomo, fósforo y plata, relacionadas a las antiguas actividades mineras y a la industria activa en la zona. Mientras que en la zona agrícola, la presencia de metales está asociada a los canales a cielo abierto que también reciben agua del Tanque Tenorio y éste a su vez de la zona industrial. En la zona industrial se detectaron grandes anomalías de tipo puntual en casi todos los metales pesados analizados; la principal fuente de estos contaminantes corresponden a un terreno industrial activo. Este trabajo está enfocado a evaluar el impacto que ha generado la actividad antropogénica sobre el acuífero colgado del Valle de San Luis Potosí desde inicios de la fundación de la ciudad hasta la actualidad, utilizando la calidad del agua como herramienta de análisis. Palabras clave: Cambio de uso de suelo, calidad del agua, acuífero colgado, actividad minera, contaminación.

Groundwater quality and availability are essential for human consumption and social and economic activities in arid and semiarid regions. Many developing countries use wastewater for irrigation, which has in most cases led to groundwater pollution. The Mezquital Valley, a semiarid region in central Mexico, is the largest agricultural irrigation region in the world, and it has relied on wastewater from Mexico City for over 100 years. Limited research has been conducted on the impact of irrigation practices on groundwater quality on the Mezquital Valley. In this study, 31 drinking water wells were sampled. Groundwater quality was determined using the water quality index (WQI) for drinking purposes. The hydrogeochemical process and the spatial variability of groundwater quality were analyzed using principal component analysis (PCA) and K-means clustering multivariate geostatistical tools. This study highlights the value of combining various approaches, such as multivariate geostatistical methods and WQI, for the identification of hydrogeochemical processes in the evolution of groundwater in a wastewater irrigated region. The PCA results revealed that salinization and pollution (wastewater irrigation and fertilizers) followed by geogenic sources (dissolution of carbonates) have a significant effect on groundwater quality. Groundwater quality evolution was grouped into cluster 1 and cluster 2, which were classified as unsuitable (low quality) and suitable (acceptable quality) for drinking purposes, respectively. Cluster 1 is located in wastewater irrigated zones, urban areas, and the surroundings of the Tula River. Cluster 2 locations are found in recharge zones, rural settlements, and seasonal agricultural fields. The results of this study strongly suggest that water management strategies that include a groundwater monitoring plan, as well as research-based wastewater irrigation regulations, in the Mezquital Valley are warranted.

Land use changes are currently one of the indisputable factors in the alteration of processes and cycles of the aquifer system in the San Luis Potosí Valley. Due to its importance, is considered indispensable to investigate this detrimental factor of aquifers. The aim of this research is to use a numerical flow model to analyze the impact that land use changes have had on the aquifer. A finite differences numerical model was adapted to the size and hydrological properties of the aquifer system. It consisted of a regular grid with 30 columns and 34 rows with constant spacing of 1000 meters. It has two layers; the first includes the shallow aquifer and the second, the deep aquifer. The initial hydraulic head of the model corresponds to 1986 and was verified for 1995 and 2007. The model shows the development of a drawdown cone (central valley) extending toward the industrial area (southern valley). Piezometric water levels revealed a decrease of 0.6 to 1.6 meters annually during a period from 1977 to 2007. This work demonstrates that it is the consequence of land use changes and of the incessant overall decline in groundwater reserves. Based on the flow model, population growth projections and water use change, the calculated predictions indicate that by 2021, the total established volume of 136 Mm 3 /year for consume will be reached. The flow model of the San Luis Potosí Valley aquifer system shows a clear effect of the risks associated with aquifer mining.

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In Soconusco, Chiapas, in spite of the high availability of surface water, it is resorting to the use of groundwater. Knowledge about the quality of surface or groundwater used to irrigate crops in that region is low. This paper aims to contribute to the knowledge of the quality of groundwater for agricultural use through the characterization of the spatial variability. Assuming a random spatial distribution of 45 samples which were collected in situ were determined: acidity and alkalinity (pH), electrical conductivity (EC), Total Dissolved Solids (TDS), cations and anions and trace elements; in addition to the agricultural index: Sodium Adsorption Ratio (SAR), Residual Sodium Carbonate (RSC), Soluble Sodium Percentage (SSP), Sodium Percentage (% Na), Kelly Ratio (KR), Magnesium Adsorption Ratio (MAR), Permeability Index (PI), Effective Salinity (ES), Salinity Potential (SP) and Osmotic Potential (OP). In general, SSP, % Na, KR, PI are low, there is only one anomalous point (9) with high values at W of the study area. Similarly, PS, ES, Cl, Na and SAR are low except point 16 and conversely, RSC and pH are high, except at this point located in the center of the study area. The results allow us to infer that the water in that aquifer presents no problems or sodicity toxic ions. In 27 sites sampled values above 250 µmhos/cm were found at 25°C, classified as medium to high risk of salinity, unsuitable for agricultural use. Analysis of the combined effect of the presence of sodium (SAR) and salinity (EC or TDS) shows that 27 of analyzing sites have restricted water medium at very high for use in irrigation.

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