Dados da Submissão

Título

Groundwater assessment for drinking and irrigation in the Cedro Basin, Pernambuco, NE Brazil: GIS and quality indices

Texto do resumo

The Cedro Basin is one of the inland basins of NE Brazil, which contains the only long-term source of groundwater for drinking, irrigation, industry, etc for the population in the homonymous municipality. The basin is constituted by two main hydrogeological units (Brejo Santo and Mauriti [aquifer] formations). In this research, 104 groundwater samples from the Mauriti Formation deep wells, depths between 80 and 130 m, have been examined for physical-chemical investigation. Physical parameters and major ions, viz., pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH) as CaCO3, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), chloride (Cl−), and sulfate (SO42−), bicarbonate (HCO3−), nitrate (NO3−), iron (Fe), and manganese (Mn) were analyzed using standard procedures. Groundwater is predominantly fresh (TDS varying from 122 to 2294 ppm; avg. 455.5 ppm, std. dev. of 333), soft (total hardness = 69 to 1676 ppm; avg. 242 ppm, std. dev. of 148), and weakly acid to alkaline with pH ranging from 6 to 8.3 (avg. 7.6, std. dev. 0.4). The major cations occur in the order: Ca2+ (avg. 46 ppm) > Na+ (avg. 40 ppm) > Mg2+ (avg. 30 ppm) > K+ (avg. 2 ppm) > Fe (avg. 0.015 ppm) > Mn (avg. 0.001 ppm). Insomuch as the major anions follow the order: HCO3− (avg. 224 ppm) > Cl− (avg. 91 ppm) > SO42− (avg. 11 ppm) > NO3− (avg. 8 ppm). The main water types from the Mauriti Formation are Ca–Mg–HCO3 with subordinate Na–HCO3 and Ca–Mg–Cl. The analyzed parameters allowed obtain the water quality indexes for drinking and irrigation. Furthermore, selected parameters and calculated index values in a GIS-based (ArcGIS Desktop 10.7) environment produced interpolated maps to reveal groundwater spatial variability. The analyzed samples are within the World Health Organization (WHO) and Brazilian standard-allowed limits, and are suitable for human consumption, which is compatible with the calculated Drinking Water Quality Index (DWQI) between 14 and 113 with an expressive number of 97% belonging to the excellent category. Similarly, irrigation ion-based indices such as salinity (EC), Sodium Absorption Ratio (SAR), Soluble Sodium Percentage (SSP), Residual Sodium Carbonate (RSC), Kelley Ratio (KR), Magnesium Hazard (MH), and Permeability Index (PI) showed that most groundwater is suitable for irrigation uses. The several thematic maps constructed revealed that only a few pockets are declining in quality.

Palavras Chave

Cedro Basin; Drinking and Irrigation evaluation; GIS-based techniques