Índices de calidad del agua para uso agrícola y contaminación del río Santiago, México

Abstract

Santiago River water is used for irrigation in its lower basin in the State of Nayarit. The quality of the river water is affected by wastewater discharges, tributaries, hydroelectric dams, rainy and dry seasons. Sampling sites were established in the riverbed, before and after each source of impact, and sampling was carried out in each season. pH, EC, Ca2+, Mg2+, Na+, K+, CO32-, HCO3-, Cl-, SO42-, B, P-PO43- and N-NO3-were determined. A descriptive space-time analysis was performed using water quality indices and diagrams for agricultural use, geochemical diagrams and pollution indicators. The pH and EC values in the dry season averaged 7.8 and 1034 µS cm-1 and in the rainy season 6.7 and 414 µS cm-1. During the dry season at site 5, values of 8.92 mg P-PO4 3-L-1, 28.43 mg N-NO3-L-1 and EC of 1699 µS cm-1 were obtained. At site 11, values of 0.80 mg P-PO4 3-L-1, 0.10 mg N-NO3-L-1 and EC of 395 µS cm-1 were obtained. It was found that in the river waters, the Ca2+ and Mg2+ ions predominated during the rainy season, Na+ during the dry season, and HCO3-in both seasons. According to the Gibbs diagram, the dominant process is rock weathering. It was concluded that the discharge of wastewater affects the water quality of the Santiago River and the tributaries and hydroelectric dams contribute to improve it, and that the river waters are suitable for agricultural use in the lower basin in Nayarit.