Physicochemical characteristics, buffer capacity and determination of the environmen- tal base line of the River Grande, San Luis, Argentina

Abstract

The purposes of the study were to determinate the physicochemical characteristics of the River Grande (Province of San Luis, Argenti- na), study its buffer capacity and establish the environmental base line. Physicochemical parameters were obtained in three sample areas (RG1, RG2 and RG3) during 1997, 1998 and 1999. The values found for the different parameters were (rate values for each case are indicated): conductivity 213. 14 – 158. 47 uS/cm; hardness 115.51 – 103.65 mg/L CaCO₃ ; total alkalinity 131.61 – 82.28 mg/L CaCO₃ ; pH of 7.78 – 7.67; Na 26.46 – 16.08 mg/L; Ca 36.62 – 31.91 mg/L; Mg 5.83 – 5.80 mg/L; HCO₃^- 151.47 – 94.70 mg/L; SO4 = 14.41 – 12.83 mg/L; Cl- 29.87 – 27.59 mg/L; NO3 - 0.43 – 0.27 mg/L; PO4 3- 25.65 – 10.31 ppb; DQO 358 – 4.05 mg/L O2 . Results suggest that the analyzed water is adequate for various uses, such as recreational, aquatic life and human consumption; the values of the analyzed parameters did not exceed, in any case, the values recommended by international entities. The different analyzed parameters did not show significant differences in relation to sample seasons (rainy and dry) but to conductivity and DQO (P < 0.05). According to its main ions, the water can be classified as containing calcium bicarbonate, being HCO₃^- the main responsible for the base acid equilibrium. The values of buffer index for different pH values were calculated. The low bicarbonate concentration shows the limited buffer capacity of the system which in turn involves a high intrinsic vulnerability. This physicochemical characterization is considered as the ‘base environmental condition of the system’ due to the limited anthropogenic influence and the constant concentrations obtained in the analyzed parameters.