Quantification of nitrate contamination sources in groundwater from the Anayari catchment using major ions, stable isotopes, and Bayesian mixing model, Ghana.

Nitrate (NO₃⁻) contamination threatens the quality of groundwater in many agricultural areas, and excessive NO₃⁻ consumption may cause adverse human health implications. Determination of NO₃⁻ occurrence and its source of contamination is essential for the effective management of groundwater quality. The characteristics of NO₃⁻ in groundwater from the Anayari Catchment were analysed using hydrogeochemical and stable isotope data. Concentrations of major ions and the isotopic values of δ²H, δ¹⁸O, δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻ of groundwater and δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻ of potential NO₃⁻ source materials (precipitation (P), chemical fertilisers (CF), soil nitrogen (SN), and sewage or manure (S/M)) in the area were determined and used to identify groundwater NO₃⁻ sources. The Bayesian mixing model was applied to estimate the proportional contributions of NO₃⁻ load in boreholes (BH) and hand–dug wells (HDW) in the Catchment. The NO₃⁻ levels were mostly lower than the WHO guideline limit. Correlation analyses indicate that the source of NO₃⁻ was mostly livestock and septic waste. The results from δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻ showed that the contribution of NO₃⁻ from potential sources is in the order of S/M > SN > CF > P, with denitrification influencing the NO₃⁻ concentration in some of the groundwater sources. The Bayesian mixing model demonstrated that by proportion, SN and S/M were the major NO₃⁻ contributors to BH and HDW, respectively. There is a need to institute and enforce proper manure application management strategies to reduce the risk of groundwater contamination from manure nutrients. [ABSTRACT FROM AUTHOR]