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The study assesses the extent of nitrate pollution in the Densu Basin, because of its predominance in agriculture and urbanized vicinities, by employing robust techniques to estimate both the natural background and human-induced concentrations. Statistical methods used are the pre-selection method, graphical approach (probability plot), non-parametric approach (kernel density estimation), and parametric approach (Gaussian mixture model). The study shows that the Gaussian mixture model is robust enough in determining the spectral distribution and clustering of the NO3-N concentration in the basin. It estimated the natural background and human-induced concentration at 1.7 ± 1.3 and 9.8 ± 5.6 mg/L, respectively. The results show that the natural background concentration in the basin is more dominant and, hence, conducive for drinking. We found a 26% contribution from anthropogenic sources that had leaked into the natural groundwaters of the Basin. The data suggest multiple sources of NO3-N concentration in the groundwater. [ABSTRACT FROM AUTHOR]

The Lower Volta River Basin of Ghana is an important international and local tourism destination. Communities in the basin depend on shallow aquifer systems, the Volta River, and nearby streams as their sources of water for domestic purposes, cattle watering, and irrigation. Due to increasing human activities and limited information on water quality in the area, a holistic assessment of the quality of the water resources in the basin was conducted using hydrochemistry, δ2H and δ18O, principal components analysis, and selected indices. EC ranged from 141 to 19,370 μS/cm and 60.9–986 μS/cm for shallow groundwater and surface water respectively. NO3− levels above 45–1049.9 mg/l were observed in 45% of analyzed wells. Na–Cl- and HCO3–Ca-dominant facies are identified. Silicate weathering, evaporite dissolution, cation exchange, and salinity are the hydrochemical processes influencing the shallow groundwater in the area. δ2H–δ18O‰ plot showed meteoric shallow groundwater recharge. Ion ratios, EC, and Cl− versus δ18O‰ relationships suggest dissolution and seawater intrusion as causes of groundwater salinity. Hydrochemistry, principal components analyses, and NO3− versus δ18O showed evidence of anthropogenic pollution on water in the basin. All analyzed surface water and 79% of well samples were within suitable range for irrigation. Based on the CCMEWQI model criteria, 85% of the surface water were in good-to-excellent categories while majority of the shallow groundwater were in fair, marginal, and poor categories. The combined approach provided vital information on water quality in the basin. Strategic control measures were proposed. [ABSTRACT FROM AUTHOR]

Fertilizers increase agricultural productivity and farmers' income. However, intensive agriculture frequently overuses fertilizers, which in turn can contaminate surface and groundwater. In this study, hydrochemical and multi-isotope (δ 15N NO3 , δ 18O NO3 and δ 18O H2O) data have been combined to identify nitrate pollution sources in Ghana's Densu River Basin, trace the Nitrogen (N) biogeochemical processes in the basin and apportion the contribution of each pollution source. Surface water NO 3 − ranged from 0.3 to 10.6 mg/L (as N), while groundwater NO 3 − ranged from 0.9 to 34 mg/L. Hierarchical cluster analysis classified the water samples into three spatial categories: upstream, midstream, and downstream, reflecting river and land use patterns. The multi-isotope model considered five primary NO 3 − sources: atmospheric deposition, manure/sewage, NH 4 + in fertilizers, other NO 3 − based fertilizers and soil N. Nitrification was identified as the major biogeochemical process upstream, whereas mixing of sources and denitrification dominate the midstream to downstream sections of the basin. Nitrate source apportioning using a MixSIAR model reveal that N fertilizers (40 %) and soil N (34 %) contribute the most to nitrate pollution upstream of the river. From the midstream to downstream sections, manure/sewage (43 %) become the dominant nitrate source, reflecting the transition from agriculture to peri-urban and urban land use. This study has shown that soil erosion and runoff contribute to nitrate pollution in the Densu River, at levels comparable to N fertilizers, and groundwater across the basin is impacted mainly by manure/sewage. The multi-isotope analyses allowed the partitioning of N sources in other ways not possible using only classical hydrochemical methods. [Display omitted] • Densu Basin nitrate levels steady over the past decade. • HCA classified basin into three groups reflecting land and river use patterns. • Nitrogen isotopes identified five potential nitrate pollution sources. • Nitrification dominant upstream, denitrification dominant midstream and downstream. • MixSIAR apportioned N fertilizers, soil N, manure/sewage as major nitrate sources. [ABSTRACT FROM AUTHOR]