Estimation of natural background and source identification of nitrate-nitrogen in groundwater in parts of the Bono, Ahafo and Bono East regions of Ghana

Abstract

The identification of the chemical status of groundwater is a prerequisite for sustainable management and development of groundwater resources. A better assessment of the chemical status of the groundwater requires the knowledge and understanding of the natural background concentrations to establish threshold values of chemical pollutants in groundwater. The aim of this study is to estimate the natural background levels, the threshold value (TV) of nitrate-nitrogen (NO3) − -N) and to identify its source in the groundwater in the Bono, Ahafo and Bono East regions of Ghana. A total of 165 groundwater samples were taken from the crystalline and sedimentary aquifers in the study area. iterative outlier removal technique and a Gaussian mixture model were then used to assess the natural background and threshold nitrate-nitrogen concentrations in the groundwater. Chloride data was then used to trace the NO3 - source in the groundwater. The estimated NBL of NO3 − -N in the area ranges from [0.001–3.9] mg/L, with an expected value of 1.25 mg/L and calculated TV of 6.95 mg/L. The data suggest that NO3 − –N concentrations are homogeneous across all the lithologies underlying the study area. The results showed that agricultural, domestic, and denitrification contribute significantly to the loading of NO3 − –N concentration in the groundwater. The estimated threshold range of NO3 − –N provides the baselinenitrate-nitrogen concentration for future studies in the region. However, the results are inconclusive, and we recommend using isotopic detection. 15N-NO3 − and 18O-NO3 − ) in future studies through comprehensive and sustainable regional monitoring of the aquifer system in order to further limit the source of nitrate and nitrogen in the groundwater system.