Nitrate contamination and source apportionment in surface and groundwater in Ghana using dual isotopes (15N and 18O-NO3) and a Bayesian isotope mixing model.

The rising food production to meet the growing human population has led to increased anthropogenic inputs of nutrients such as NO3- in groundwater and aquatic environments. Nitrate concentrations, hydrochemistry, and isotope data (δ18O-H2O, δ2H-H2O, 15N-NO3, and δ18O-NO3) from boreholes (BH), hand dug wells (HDW), and surface water (SW) were analyzed. The objectives of the study were to identify potential nitrate sources and their proportional contributions using an isotope mixing model (SIAR). The results showed that NO3- concentrations in the BH, HDW, and SW were heterogeneous and controlled by localized anthropogenic activities. The hydrochemistry and dual isotope (15N-NO3 and 18O-NO3) identified manure/sewage as the dominant source of NO3- in the groundwater, while the SW showed a complex signature overlapping in the areas of manure/septic, chemical fertilizer, and soil nitrogen. The SIAR analysis showed that sewage/manure contributed about 66%, 68%, and 55% of NO3- in the BH, HDW, and SW, respectively. In the study area, the NO3- source contribution based on the mean probable estimate (MPE) were in the order S&M > SN > CF > P. Shortcomings and the uncertainties associated with the SIAR to guide future studies have also been discussed. The study also highlighted the use of hydrochemistry, environmental isotopes, and Bayesian isotope mixing models for NO3- source identification and apportionment. This is to enable effective planning, farming practices, and sewage disposals to safeguard groundwater quality and control the eutrophication in rivers to meet safe drinking water demand.

Nitrate contamination of groundwater in the Lower Volta River Basin of Ghana: Sources and related human health risks.

A significant population within the Lower Volta River Basin of Ghana relies solely on untreated groundwater (GW) and surface water (SW) for various purposes. However, negative practices associated with increasing human activities pose threats to particularly GW quality in the basin. Using NO3- as a proxy, this study mainly focused on the status of GW contamination, origins of NO3- and potential human health risks through integrated hydrochemistry, correlation analysis, isotopes (15N, δ18O), Bayesian and USEPA human health risk models. Slightly acidic to alkaline GW and SW environments were observed. Electrical conductivity (EC) values above 1000 µS/cm were recorded in 45% of the GW with a maximum of 19370 µS/cm. NO3- in GW ranged from 0.12 to 733 mg/L with average 59.6 mg/L and positively correlated with K+, Ca2+, Mg2+, Cl-, Na+ and EC. In SW, a maximum of 5.3 mg/L of NO3- was observed. Largely, 75% of the GW exceeded local background NO3- value of 2.1 mg/L, while 35% were above the WHO recommended value of 50 mg/L. Bivariate and correlation relationships elucidated human contributions to sources of NO3-, Cl-, SO42- and K+ to GW in the basin. From NO3-/Cl- ratio, 43% of the GW and 21% of SW were affected by effluents and agrochemicals. Values for δ15N-NO3- and δ18O-NO3- ranged from +4.2‰ to +27.5‰ and +4.5‰ to +19.9‰ for GW, and from +3.8‰ to +14.0‰ and +10.7‰ to +25.2‰ for SW. Manure, septic effluents and mineralized fertilizers are sources of NO3- contamination of water in the basin. The Bayesian model apportioned 80% of GW NO3- contamination to sewage/manure. Hazard index indicated 70%, 50% and 48% medium to high-risk levels for infants, children and adults respectively, with 79% high-risk of SW NO2- contamination to infants. Immediate measures for GW and SW quality protection are recommended.

Data Descriptor: Daily observations of stable isotope ratios of rainfall in the tropics.

We present precipitation isotope data (δ2H and δ18O values) from 19 stations across the tropics collected from 2012 to 2017 under the Coordinated Research Project F31004 sponsored by the International Atomic Energy Agency. Rainfall samples were collected daily and analysed for stable isotopic ratios of oxygen and hydrogen by participating laboratories following a common analytical framework. We also calculated daily mean stratiform rainfall area fractions around each station over an area of 5° x 5° longitude/latitude based on TRMM/GPM satellite data. Isotope time series, along with information on rainfall amount and stratiform/convective proportions provide a valuable tool for rainfall characterisation and to improve the ability of isotope-enabled Global Circulation Models to predict variability and availability of inputs to fresh water resources across the tropics.

Groundwater fluoride contamination and probabilistic health risk assessment in fluoride endemic areas of the Upper East Region, Ghana.

Groundwater fluoride contamination has long been recognized as a water-related health issue in some parts of Ghana. However, the extent of fluoride contamination and the related human health risk to the communities in the fluoride endemic areas are not adequately studied. In this paper, fluoride concentrations in existing and newly drilled wells were assessed. Probabilistic non carcinogenic human health risk assessment, uncertainty and sensitivity analysis for three age groups (Group A: 0-10 years; Group B: 11-20 years; Group C: 21-72 years) was also carried out using Monte Carlo simulation technique. The results showed that, 27.27% and 15.38% of the existing wells in the Bongo and Kassena Nankana West districts have fluoride values above the guideline value 1.5 mg L-1 respectively. The non-carcinogenic risk of fluoride associated with oral ingestion recorded a mean Hazard Quotient (HQ) > 1 for younger age group (0-10 years) in all the study areas signifying potential health risk to this age group. Additionally, when the upper 95th percentile is used for the HQ, the oral ingestion for all the age categories recorded an HQ > 1. Sensitivity analyses indicated that fluoride concentration in the drinking water and ingestion rate were the most relevant variables in the model to reduce the potential health effect. The study established the basis for a strong advocacy and public awareness on the effect of water quality on human health and proposed some management strategies to guide future groundwater resources management to reduce the potential health risk to the population.

Tracing stable isotopes (δ²H and δ¹8O) from meteoric water to groundwater in the Densu River basin of Ghana.

This study represents the first attempt to study soil water δ(18)O profiles in Ghana using a mechanical auger. In this paper, the characteristics of δ(18)O and δ(2)H in rain water, surface water, soil water and groundwater have been used to understand the transformation mechanism of rain water to groundwater. Rain waters were sampled in Koforidua and Accra. Surface water and groundwater were sampled from the Densu River and selected boreholes in the basin, respectively. Soil waters were taken from three typical sites, namely, Potroase (POT), Teacher Mante (TM) and Ayikai Doblo (AD) in the northern, middle and southern zone from 0.00- to 6-m depth. The soil water was extracted using vacuum distillation method. The distribution of the stable isotopes of rain water is influenced by rainfall amount with minimal temperature effect. In general, the soil water is of meteoric origin undergoing fractionation-controlled evaporation. In the middle zone, the soil water shows some evidence of recharge from enriched source. The three profiles show similar trend of enriched values in the upper depths with gradual depletions of δ(18)O with depth. The POT profile showed relatively more depleted values suggesting a fast infiltration. In all the three profiles, soil waters below 3 m were found to contribute to groundwater recharge with piston flow as the dominant mechanism. The study also revealed that there is a significant contribution of enrich source to the groundwater system leading to the dilution of the infiltrating water by the large aquifer.

Investigation of the possible sources of heavy metal contamination in lagoon and canal water in the tannery industrial area in Dhaka, Bangladesh.

This study evaluated the heavy metal pollution level of tannery effluent-affected lagoon and canal water in the southwestern Dhaka, Bangladesh. The measured physicochemical parameters (electrical conductivity, chemical oxygen demand, pH, SO²â»4, PO³â»4, Cl-, and NO⁻3) and metals (As, Ca, Cd, Co, Cr, Cu, Fe, K, Mn, Ni, Pb, and Zn) were subjected to principal component (PCA) and hierarchical cluster analyses, and examining correlation matrix as well in order to explain the behavior and sources of the parameters/metals. The mean concentrations of the heavy metals in the lagoon and canal water were very high and, in most cases, exceeded the standard limits recommended by the Bangladesh Government. The following elemental associations were obtained from PCA and CA: Ca-Cd-Cr-Fe-K-Mn-Pb-Zn, Co-Cu-Ni, and As, which could be linked to anthropogenic sources (i.e., processes of the tannery and paint industries with some contributions from the municipal waste system). Potassium, Ca, Cr, Mn, Fe, Zn, As, and Cd occurred as important anthropogenic markers in the lagoons and lower part of the canal. Copper, Co, and Ni were importantly distributed in the lower part of the canal, which also received metal inputs from the municipal waste and other industrial sources, including paint industry. GIS-based factor score maps, generated to show the spatial controls of the major processes affecting surface water hydrochemistry, suggest that the activities of paint and tannery industries and municipal sewage are pervasive processes in the area, whereas the contribution from pesticides (used for tanning and disinfecting hides) has localized effects. This study has provided the evidence that effluents discharged from the tannery and auxiliary industries and urban sewage system are the main sources of heavy metal pollution in the lagoon and canal water systems in the Hazaribagh area of southwestern Dhaka. The high mean concentrations (in mg/l) of Cr (5.27), Pb (0.81), As (0.59), and Cd (0.13) observed in the water samples may have serious public health and potential environmental hazard implications.

The hydrochemistry of groundwater in the Densu River Basin, Ghana.

Hydrochemical analyses of groundwater samples were used to establish the hydrochemistry of groundwater in the Densu River Basin. The groundwater was weakly acidic, moderately mineralized, fresh to brackish with conductivity ranging from of 96.6 microS cm(-1) in the North to 10,070 microS cm( - 1) in the South. Densu River basin have special economic significance, representing the countries greatest hydrostructure with freshwater. Chemical constituents are generally low in the North and high in the South. The order of relative abundance of major cations in the groundwater is Na+>Ca2+>Mg2+>K+ while that of anions is Cl->HCO3->SO4(2-)>NO3-. Four main chemical water types were delineated in the Basin. These include Ca-Mg-HCO3, Mg-Ca-Cl, Na-Cl, and mixed waters in which neither a particular cation nor anion dominates. Silicate weathering and ion exchange are probably the main processes through which major ions enter the groundwater system. Anthropogenic activities were found to have greatly impacted negatively on the quality of the groundwater.