Impact of the Morón stream on water quality of the Reconquista River (Buenos Aires, Argentina)

Resumen

The Reconquista River basin is located in an urban area where 2.5 10⁶ inhabitants and 4,242 industries are settled. The confluence with the Morón stream shows the largest anthropogenic impact. The effect of the Morón stream on the water quality of the Reconquista River was evaluated in relation to its organic, mineral and metal contribution. Bimonthly samplings were carried out in the Reconquista River upstream (GOR), and downstream (SMT) from the confluence with the Morón stream and in the latter (MOR). Dissolved oxygen, pH, conductivity, temperature, transparency, nutrients, major ions, suspended solids, particulate and total organic carbon, Kjeldahl nitrogen, total phosphorus and heavy metals were determined in water samples. Discharge ratios between the Reconquista and Morón streams were estimated based on chloride concentrations. The samplings were ordered from the Principal Component Analysis in: GOR, SMT and MOR according to a growing gradient of organic and mineral contamination. This gradient has a spatial component (related to the discharge point of the Morón stream) and one related with the flow of the Reconquista River. Mean levels of heavy metals were higher than the thresholds for aquatic life protection. The most important were: lead, zinc, copper and mainly chromium, all of them related to industrial activity. Their concentrations responded to an irregular and intermittent discharge. Sometimes, metal levels at SMT and GOR were higher than at MOR, indicating other sources of contamination besides the Morón stream.