Research on microbiological groundwater quality was conducted in Chile in a rural watershed that has almost no other water source. Forty-two wells were randomly selected and levels of indicator bacteria -total coliforms (TC), fecal coliforms (FC), and fecal streptococci (FS) -were repeatedly measured during the four seasons of 2005. The aim of this study was to characterize microbiological groundwater quality, relate indicator levels to certain watershed features and management characteristics which are likely to affect water quality. The dynamics of seasonal temporal contamination was determined with statistical analyses of indicator organism concentrations. Nonparametric tests were used to analyze relationships between bacterial indicators in well water and other variables. TC, FC, and FS were found in all samples indicating the wells had been contaminated with human and animal fecal material. The frequency distribution of microorganisms fitted a logistic distribution. The concentrations appeared to be temporal and levels varied between seasons with higher concentrations in winter. The cause of contamination could be linked to the easy access of domestic animals to the wells and to the permeable well casing material. Local precipitation runoff directly influenced the bacterial concentrations found in the wells.
Consumption of water contaminated with nitrates is associated with important health effects such as methemoglobinemia and gastric cancer. Intensive agriculture, which uses large quantities of N fertilizer, is the main source of nitrates in water systems. There are several strategies to reduce leaching and increase Nitrogen Use Efficiency (NUE). An experiment was conducted with spring wheat (Triticum aestivum L.) under sprinkler irrigation (center pivot) to determine if adjusted N applications using precision agriculture tools and plant demand resulted in a lower groundwater nitrate load. Evaluated treatments were: producer fertilization (Pr), precision agriculture (Pa), chlorophyll meter (Sm), and control without N (W/N). The ceramic capsule methodology was used to evaluate N leaching losses that were sampled after each irrigation (six) and drainage water was also estimated. Differences among treatments in terms of N loss and grain yield were not significant (p > 0.05). However, N balance showed significant differences (p < 0.01) in soil residual N among treatments. A regression between applied and residual soil N after harvest showed that N, applied as fertilizer, explained 98% of residual soil N variation, which would probably be leached in the following winter since the soil would be bare. It was concluded that NUE can be improved to result in a lower environmental load by using precision agriculture tools and considering plant N demand.
Objetivos. Evaluar el riesgo asociado a la contaminación con nitrato de pozos noria de suministro de agua potable rural en la zona de RESUMENLa contaminación de las aguas subterráneas es un problema creciente de la salud pública, pues restringe la disponibilidad de agua potable para la población. En Chile, el agua subterrá-nea para consumo humano representa más del 40% del volumen total de agua consumido en las zonas urbanas y el 76% en las zonas rurales (1).El nitrato es uno de los contaminantes mas frecuentes de las aguas subterráneas y su presencia puede asociarse a problemas de salud humana, especialmente en grupos sensibles como los lactantes. Estos, al ingerir fórmulas lácteas preparadas con agua con altas concentraciones de nitrato, pueden presentar metahemoglobinemia o «síndrome del niño azul» (2, 3). A pesar de que esto ha sido recientemente cuestionado (4), las normativas relativas a la calidad del agua y los métodos de análisis de riesgo consideran esta hipótesis dentro de su fundamentación, pues están concebidos para proteger la salud humana (2, 3).
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