Abstract
The basin of Rio de la Sabana is the largest tributary of the Tres Palos coastal lagoon in Southwest Mexico, east of Acapulco. This lagoon and its upstream basin areas have become a high priority area for the preservation of coastal and marine environments. To obtain information about water quality as affected by urban expansion since 2002, fourteen physicochemical parameters (temperature, pH, electrical conductivity, dissolved oxygen, ammonium, nitrate, nitrite, sulphate, phosphate), biochemical (biological and chemical oxygen demand, methylene blue active substances) and bacteriological parameters (total and fecal coliforms) were determined. This sampling was done for dry and rainy season conditions at seven locations (S1, S2, S3, …, S7) along the river, spaced 3 to 6 km apart to a total of 30.4 km. The results were grouped into four zones: (Z1) reference, (Z2) transition, (Z3) polluted, (Z4) recovery. The Alborada (S5) and Tunzingo (S6) sites, adjacent to dense high-class residential areas (Z3), had the greatest pollution charges in both seasons, while the La Poza (S7) site near the Tres Palos lagoon (Z4) showed a decrease in pollution. All parameters correlated with increasing head- to down-river sampling distance by following linear (pH, DO) or curvilinear patterns (all other parameters). Using sampling location and dry versus rainy sampling season as multivariate regression (predictor) variables led to least-squares capturing: 1) 66% to 95% of the T(°C), pH, DO, and PO3-4 variations, and 2) 57% to 96% of the log-linear variations of the other parameters. Among the parameters, T(°C), DO, and PO3-4 were not significantly affected by sampling season, while pH became so after deleting two higher than usual pH values at the S5 and S6 locations during the dry season.
Highlights
Accelerated urbanization processes are causing water-quality disruptions within rivers and streams across watersheds and regions
This article focuses on assessing water quality changes along a 30.4 km stretch of Rio de la Sabana as it flows east of Acapulco into the coastal Tres Palos lagoon (Figure 1)
The data for the 14 water quality parameters are listed in Table 3 and are plotted in Figure 2 by sampling location and season, with best-fitted Equation (1) results overlaid
Summary
Accelerated urbanization processes are causing water-quality disruptions within rivers and streams across watersheds and regions. Apart from noticing enhanced levels of water pollution and reduced biological viability in natural waterways, surficial water quality evaluations are needed to provide quantitative information for sustainable water-resource management [2] [3] [4]. Since these evaluations need to address a host of sampled water quality indicators, it is necessary to determine how these indicators are patterned and vary across space and time in a predictive manner as advocated by, e.g., [5]-[10]. During the last two decades, the mid-low part of this sub-basin has experienced an accelerated population growth, which has led: 1) to serious water pollution and environmental degradation issues towards the river and to the coastal lagoons at Tres Palos and Puerto Marques [12] [13]; 2) to increased vulnerability to health risks across the new and flood-prone de la Sabana Valley settlements [13]
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