WATER SALINITY RISK ASSESSMENT USING THE SODIUM ADSORPTION RATIO (SAR) IN WATER FROM A DAM USED FOR IRRIGATION PURPOSES

Water quality evaluation is an important parameter to classify the use of water. The objective of this study was to evaluate the risk conditions of using water from the La Vega dam for irrigation purposes. The La Vega dam is located at 9 km south of Teuchitlán town and 5 km south of the Ameca River in Jalisco México. The main dam water sources are fountains and municipal wastewater (to the north), the Salado River (to the south-east), and seasonal agricultural runoff. This water body is supplying approximately 90% of the water for irrigation for about 5,314 ha of sugar cane farming and others relatively minor agricultural products. Besides irrigation, fishing is an important activity to support families from the surrounding areas.

Forty-five water samples were collected from inflows, along the dam and the irrigation net. To evaluate the risk by using the water from the La Vega dam for irrigation, the Sodium Adsorption Ratio (SAR) was calculated, this includes the concentration of sodium, calcium and magnesium. The SAR values results demonstrated a low salinity risk (3.60) at the north inflows and in the north dam area. However the risk increases to medium (13.2) at the center and south of the dam and along the distribution net. The Salado River was identified as the main pollution source, where high sodium, calcium and magnesium concentrations were detected (SAR value was 366).

Moreover, the results demonstrated also high boron (13.3 mg/L) and arsenic (0.19 mg/L) concentrations in the Salado River. As a conclusion, the Salado River is the main pollution contributor to the La Vega dam, highly increasing the SAR and boron values and the risk to use the dam water for irrigation purposes. Moreover, the sugar cane plants have apparent leaf burns, which is typical of boron toxicity. Research continues to determine the seasonal pollution variability and boron toxicity evaluation on sugar cane after 35 years of irrigation with water from the La Vega dam.