Analysis of the Seasonal Variation of Groundwater Quality in a Highly Cultivated Catchment, Northern Benin

Abstract

This study assesses groundwater quality in the Dassari watershed, a highly cultivated catchment area in Northern Benin, West Africa. Four sampling campaigns were conducted and the groundwater samples were analyzed using the standardized methods of the American Public Health Association. Descriptive and multivariate statistics were applied to describe and group the water samples into categories. The water samples were also compared to the World Health Organization (WHO) norms and those of the Republic of Benin. Boxplot comparison method and variance analysis were used to analyze the seasonal variation of groundwater parameters in both rainy and dry seasons. The hydro-chemical facies of the sampled groundwater were investigated through Piper and Chadha diagrams, and the general type of groundwater in the catchment was found to be as calcium-rich and magnesium-rich water based on the identification of the dominant cations. The major anion in the samples was Hydro-carbonate HCO3-, thus the groundwater in the study catchment can be considered as carbonate-rich water. Comparing the concentrations of analyzed parameters to WHO and the Republic of Benin guidelines for drinking water, the whole catchment was found to have potable groundwater. Comparing the nitrate concentration in the samples to a natural limit of 10 mg/L, we show that all samples had a nitrate concentration above that limit, thus indicating an anthropogenic pollution due to high fertilizer use. However, these concentrations are still under the permissible limit of WHO (50 mg/L). The analysis of the seasonal change in hydro-chemical parameters revealed no significant change at 5% level of these parameters from rainy season to dry season. In the Dassari catchment, groundwater is still potable although we found a slight sign of pollution due to high fertilizer use.