ABSTRACT
FECAL CONTAMINATION OF GROUNDWATER IN A SMALL RURAL DRYLAND WATERSHED IN CENTRAL CHILE

Mariela Valenzuela1*, Bernardo Lagos2, Marcelino Claret3, María A. Mondaca4, Claudio Pérez3, and Oscar Parra1.
 
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.
Keywords: biological contamination, bacteria, water quality, environmental pollution.
1 Universidad de Concepción, Centro de Ciencias Ambientales EULA, Casilla 160-C, Concepción, Chile. * Corresponding author (marvalenz@udec.cl). 2 Universidad de Concepción, Facultad de Ciencias Físicas y Matemáticas, Av. Esteban Iturra s/n - Barrio Universitario, Concepción, Chile. 3 Instituto de Investigaciones Agropecuarias, Centro Regional de Investigación Quilamapu, Av. Vicente Méndez 515, Chillán, Chile. 4 Universidad de Concepción, Facultad de Ciencias Biológicas, Casilla 160-C, Concepción, Chile.