ANÁLISIS DE TENDENCIAS DE VARIABLES INDICADORAS DE CALIDAD DE AGUA PARA EL RIACHUELO (CUENCA MATANZA-RIACHUELO, ARGENTINA)

Abstract

The Matanza-Riachuelo river is a clear and extreme example of the “urban river syndrome” and an emblematic case of environmental pollution in Argentina. Analysis of water quality data trends for the Riachuelo (in the Matanza-Riachuelo river lower basin) was performed by using water quality monitoring data generated by the Environmental Protection Agency of the Buenos Aires City Government. Data was collected in three monitoring points along the river from 2008 to 2016. The Mann-Kendall non-parametric statistical test was applied to the time series available for six parameters, five physicochemical and one microbiological, and the monthly rainfall data for the Buenos Aires City area. Trend analysis showed an improvement in the quality of Riachuelo’s surface water, reflected by increasing levels in dissolved oxygen (upstream the river mouth) and decreasing levels in biological oxygen demand, total ammonia nitrogen and chloride. Non-biodegradable organic matter, in contrast, showed an increasing trend. Monthly rainfall also experienced an increment while Escherichia coli numbers did not show a defined pattern. Increasing stormwater runoff may have determined the trends observed in the time period considered. Nonetheless, the quality of Riachuelo’s water remained severely degraded with 50 % of the dissolved oxygen, and biological and chemical oxygen demands values below 2 mg/L and above 15 and 50 mg O2/L, respectively. E. coli numbers were similar to those recorded in raw sewage.