Hydrogeochemistry of Shallow Groundwater and Suitability to Irrigation: The Case of the Karfiguéla Paddy Field in Burkina Faso

Abstract

Shallow groundwater is often exposed to multiple sources of pollution that can make it unsuitable for certain uses. Complete hydrogeochemical studies are necessary for the better management of these resources. Well water samples were collected on the extent of Karfiguéla paddy field for physico-chemical parameters, such as pH, EC, TDS, Na+, Ca2+, Mg2+, K+, NH4+, NO3−, NO2−, SO42−, CO32−, Cl−, and HCO3−, and metallic trace elements analyses as a case study. Due to the alluvial nature of aquifer deposits and the short residence time of groundwater, physical parameters and ion concentrations are low and within the recommended guideline values for irrigation water of the Food and Agriculture Organization (FAO) of the United Nations. However, Cd presents concentrations above 10 µg/L, the limit recommended by the FAO, while NO3− presents a slight to moderate risk. Piper and Stiff diagrams showed two types of water, Ca·Mg·HCO3 and Ca·Mg·SO4·Cl. Saturation indices revealed the under mineralization of natural minerals. Gibbs and bivariate diagrams, correlations and factorial analyses indicated that groundwater mineralization is mainly controlled by anthropogenic agricultural activities (60.05%), calcite and magnesite alteration (15.01%) and CO2 dissolution process (9.05%). Irrigation water suitability parameters, such as sodium adsorption ratio (SAR), sodium percentage (%Na), potential salinity (PS), the Kelly ratio (KR), residual sodium carbonate (RSC) and irrigation coefficient (Ka), confirmed that the shallow groundwater is 100% good for irrigation, while NO3− and permeability index (PI) indicated that it is permissible. However, according to magnesium hazard (MH), the groundwater is 100% unsuitable for irrigation and could lead to soil alkalinity.

Keywords

• hydrogeochemistry
• shallow groundwater
• anthropogenic pollution
• irrigation
• paddy field