Water quality was evaluated at sites of the Jose Antonio Alzate Dam, the rivers Lerma, Tejalpa and Temoaya in the State of Mexico, Mexico. The variables measured included pH, conductivity, temperature, dissolved oxygen (DO), ammonia, nitrates, sulfates, sulfides and metal concentrations (Cu and Pb). Chemical speciation for dissolved metals in the aqueous phase was obtained using measured concentrations and the software MINEQL+ (4.5); metal partition coefficients was also obtained using dissolved and particulate concentrations of metals. Hydraulic behavior of the studied water bodies was investigated and the fate of Cu and Pb ions was simulated. The simulation results indicate that the Lerma River provides the majority of organic matter and metal contaminants as a result of a poor oxygen saturation velocity, and showed a slight improvement when the Lerma River is subjected to its tributaries Tejalapa and Temoaya Rivers. Under the reducing conditions predominating along the dam and from the results of aqueous phase chemical speciation, it was found that sulfide metal-associated species are the ones that predominate. It was demonstrated that in general, the rivers Tejalapa and Temoaya presented the best water quality. The Lerma River oxygen saturation improves after the rainy season, but it worsens during the dry season. Due to irregular topography, the small slope prevailing in the Lerma River, and the almost nonexisting water flow, zones with different characteristics are formed within the dam. The sedimentation contributes in the generation of local eddies causing the existence of a small diffusive flow. The order of partition coefficient was Pb > Cu. Cu presented the highest risk levels in the dissolved phase
The José Antonio Alzate Dam in the State of Mexico, Mexico, receives wastewaters from domestic, industrial, and agricultural activities through the Lerma River. Chemical and physicochemical characteristics of the water were determined. Sediment has been studied in order to define the importance of its influence on the reservoir's state as a whole. The quantification of the metals, Cd, Cu, and Pb in total forms and the geochemical distribution and the chemical mobility of these metals in sediment have been established using a chemical sequential extraction scheme. The three metals showed a common characteristic, being more abundant in fraction F6 (residual), but the other fractions of the geochemical distribution were variable depending on the metal. First, the contamination level was evaluated with the results of the total metals, using the criteria of EPA, Thomas and Murdoch, and the Ontario Ministry of Environment for sediment in water bodies. Subsequently, the risk was assessed using the same criteria but considering the results of sequential extractions, where the geochemical distribution of each metal allowed a better understanding of metal portions with more influence on the risk, in which Cu and Pb presented low risk, but not Cd.
Due to the problem of contamination in the Jose Antonio Alzate dam, located in the State of Mexico, Mexico, the partition coefficient, the contamination degree, and the ecological risk index of nine metals were calculated in order to establish the water quality in different areas of the Alzate dam. The sampling sites were selected according to the river flow into the dam, via three sampling programs, the physical-chemical parameters were measured in situ, and the samples were collected to measure metals in the dissolved phase and also as suspended particulate matter. Thomann's model was used to calculate the partition coefficient. Håkanson's methodology was used to determine the degree of contamination and the ecological risk index. Finally, the water quality criteria for the dissolved metals were calculated. The results for suspended particulate matter suggest a moderate risk of metal contamination in the dam. Copper and lead in dissolved form exceeded the values of water quality criteria.
ResumenLa descarga de aguas residuales a los sistemas acuáticos, sin previo tratamiento, es un problema generalizado en México; como es el caso del río Lerma en donde se sustituyó el aporte de agua limpia proveniente del sistema lagunar Almoloya-Lerma-San Bartolo, ubicado en el valle de Toluca Estado de México, por el agua residual del valle. Los intentos por limpiarla antes de su descarga han resultado infructuosos y esto ha causado que el río presente condiciones sépticas en todo su recorrido, incluyendo el primer cuerpo receptor que es la presa José Antonio Alzate (PJAA) creando condiciones peligrosas para la salud y limitando el uso de esta agua. En el presente trabajo se evalúa la eficiencia de tratamiento de un sistema lagunar aerobio experimental (SLE). Este sistema de tratamiento se construyó con 5 mamparas, las cuales formaron 6 canales internos. Ésta se operó en forma continua por espacio de 26 semanas, suministrándole en forma constante agua del Río Lerma. Se encontró que la eficiencia de reducción promedio, de la materia orgánica reportada como DBO 5 fue de 83%, removida en el primer canal después de 7 días de retención hidráulica. Esto comprobó que los canales no se comportan como lagunas en serie. Con los datos obtenidos, se aplicaron ecuaciones de diseño, obteniéndose el factor de decaimiento de la materia orgá-nica "k" y el valor de dispersión "d" específicos para el tipo de tratamiento y las condiciones ambientales del sitio. De esta forma, se calculó la superficie de la PJAA requerida para ser modificada en un sistema de tratamiento, basado en la eficiencia
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