A meta-analysis of groundwater contamination by nitrates at the African scale (original) (raw)
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Spatial and statistical assessment of factors influencing nitrate contamination in groundwater
Journal of Environmental Management, 2008
The weights of evidence (WofE) modeling technique has been used to analyze both natural and anthropogenic factors influencing the occurrence of high nitrate concentrations in groundwater resources located in the central part of the Po Plain (Northern Italy). The proposed methodology applied in the Lodi District combines measurements of nitrate concentrations, carried out by means of a monitoring net of 69 wells, with spatial data representing both categorical and numerical variables. These variables describe either potential sources of nitrate and the relative ease with which it may migrate towards groundwater. They include population density, nitrogen fertilizer loading, groundwater recharge, soil protective capacity, vadose zone permeability, groundwater depth, and saturated zone permeability. Once conditional dependence problems among factors have been solved and validation tests performed, the statistical approach has highlighted negative and positive correlations between geoenvironmental factors and nitrate concentration in groundwater. These results have been achieved analysing the calculated statistical parameters (weights, contrasts, normalized contrasts) of each class by which each factor has been previously subdivided. This has permitted to outline: the overall influence each factor has on the presence/ absence of nitrate; the range of their values mostly influencing this presence/absence; the most and least critical combination of factor classes existing in each specific zone; areas where the influence of impacting factor classes is reduced by the presence of not impacting factor classes. This last aspect could represent an important support for a correct land use management to preserve groundwater quality. r
Earth
Groundwater is a useful source of water for various uses in different places. The major challenge in the use of this resource is how to manage and protect it from contamination. The current study was conducted in Morogoro Municipality to identify vulnerable groundwater areas by using DRASTIC-LU/LC model. The study applied eight input parameters, i.e., depth to water table, net recharge, aquifer media, soil media, topography, impact of vadose zone, hydraulic conductivity and land use/land cover patterns, which were overlaid in GIS to generate groundwater vulnerable map. The model used rating (R = 1–10) and weighting (W = 1–5) techniques to assess the effect of each parameter on groundwater contamination. The DRASTIC-LU/LC Vulnerability Index map was classified into low- (area = 29.2 km2), moderate- (area = 120.4 km2) and high-vulnerability zones (area = 124.4 km2). Nitrate analysis was conducted using the cadmium reduction method (DR 890) to assess the validity of the model and it wa...
Tracking Sources and Fate of Groundwater Nitrate in Kisumu City and Kano Plains, Kenya
Water
Groundwater nitrate (NO3−) pollution sources and in situ attenuation were investigated in Kisumu city and Kano plains. Samples from 62 groundwater wells consisting of shallow wells (hand dug, depth <10 m) and boreholes (machine drilled, depth >15 m) were obtained during wet (May–July 2017) and dry (February 2018) seasons and analyzed for physicochemical and isotopic (δ15N-NO3−, δ18O-NO3−, and δ11B) parameters. Groundwater NO3− concentrations ranged from <0.04 to 90.6 mg L−1. Boreholes in Ahero town showed significantly higher NO3− (20.0–70.0 mg L−1) than boreholes in the Kano plains (<10.0 mg L−1). Shallow wells in Kisumu gave significantly higher NO3− (11.4–90.6 mg L−1) than those in the Kano plains (<10.0 mg L−1). About 63% of the boreholes and 75% of the shallow wells exceeded the drinking water WHO threshold for NO3− and NO2− (nitrite) during the study period. Mean δ15N-NO3− values of 14.8‰ ± 7.0‰ and 20.7‰ ± 11.1‰, and δ18O-NO3− values of 10.2‰ ± 5.2‰ and 13.2‰ ±...
Journal of Water and Health, 2007
By 2010 Africa's urban population will have grown to over 420 million with on-site sanitation the predominant excreta disposal option. The use of on-site sanitation has important public health benefits but can result in large faecally derived loadings of nitrogen and chloride to groundwater resources. Nitrate is of particular concern, with elevated concentrations linked to potentially serious health problems. N and Cl can derive from natural sources so it is important to quantify the additional impact of human activities. Several authors have used empirical relationships between nitrate and chloride concentrations to assess the extent to which excreta influences groundwater quality. However, these relationships have assumed fixed loadings from excreta. Relationships between N and Cl have been extended here by adding country-specific estimates of average annual per capita nitrogen and chloride content of, and loading from, excreta. The results are compared with groundwater monito...
Journal of Environmental Health Science and Engineering, 2019
Purpose This study was conducted to assess the capability of the lumped parameter model (LPM), an efficient model due to its analytical nature and the limited data requirements, to estimate health risks from nitrate in groundwater in arid and semi-arid climates. Methods To assess the capability of LPM, two scenarios were established: one for estimation of hazard quotient (HQ) via monitoring nitrate concentration in groundwater and the other using the LPM. After nitrate was monitored in 148 randomlyselected wells, a modified LPM was used to estimate water volume and nitrate concentration, which ultimately led to the development of a model for estimating HQ. The performances of LPM were assessed using the coefficient of determination, percentage standard deviation, and root mean square error. To compare health risk maps Kriging, Spline, Inverse distance weighted, and natural neighbor models were run using geographical information system (GIS). Results Linear analysis revealed a strong correlation between HQ values estimated in LPM and monitoring scenarios in arid climate compared to semi-arid (r = 0.962, n = 22, p = 0.00), suggesting that the LPM was more accurate in predicting nitrate concentration in the arid climate. Uncertainty analysis showed that LPM outputs were sensitive to several parameters, especially leakage from cesspits, which are involved in the sources and sinks of nitrate in the groundwater. In addition, it was found that the natural neighbor was the most appropriate model with the lowest errors for preparing health risk maps from nitrate. Conclusions The obtained results revealed that LPM can be effectively used to estimate nitrate concentration in groundwater in arid climates and thereby LPM is an appropriate model to estimate health risk from nitrate in this climate.
Environmental Earth Sciences, 2016
A multi-isotope approach and mixing model were combined to identify spatial and seasonal variations of sources, and their proportional contribution to nitrate in the Hutuo River alluvial-pluvial fan region. The results showed that the NO 3 À concentration was significantly higher in the Hutuo River valley plain (178.7 mg/L) region than that in the upper and central pluvial fans of the Hutuo River (82.1 mg/L and 71.0 mg/L, respectively) and in the river (17.0 mg/L). Different land use types had no significant effect on the groundwater nitrate concentration. Based on a multi-isotope approach, we confirmed that the main sources of groundwater nitrate in different land use areas were domestic sewage and manure, followed by soil nitrogen, ammonia fertilizer, nitrate fertilizer and rainwater, and there were no significant spatial or seasonal variations. Combining d 15 NeNO 3-, d 18 O eNO 3 and d 37 Cl results can increase the accuracy of traceability. Nitrification could be the most important nitrogen migration and transformation process, and denitrification did not significantly affected the isotopic composition of the nitrate. The SIAR model outputs revealed that the main nitrate pollution sources in groundwater and river water were domestic sewage and manure, accounting for 55.9%e61.0% and 22.6% (dry season), 50.3% e60.4% and 34.1% (transition season), 42.7%e47.6% and 35.6% (wet season 2016) and 45.9% e46.7% and 38.4% (wet season 2017), respectively. This work suggests that the random discharge and disposal of domestic sewage and manure should be the first target for control in order to prevent further nitrate contamination of the water environment.
Assessing Groundwater Nitrate Pollution in Yaoundé, Cameroon: Modelling Approach
2013
Groundwater flow modelling and mass transport simulation were carried out to determine the Nitrate and Total Dissolved Solid (TDS) migration within the shallow unconfined aquifer of the upper Anga’a river watershed of Yaoundé city, Cameroon. The MODFLOW code calibrated for February 2008 groundwater levels was used to simulate the steady state distribution of hydraulic head. Simulated hydraulic heads were similar to observed values along the watershed in model validation. The nitrate and TDS transport were described by the convection equation and solved using MT3D. The pollutant fate andtransport model (MT3D) reproduced the spatial pattern of observed nitrate concentrations in model calibration and validation. Groundwater and plume velocities were 0.26 and 0.21 m per day respectively. Simulating the contaminant migration from the recharge area shows that the plume may take more than 50 years travel time to reach the central part of the basin from which decision analysis can be made for generating key criteria to secure any water quality from contamination. The application of groundwater modelling tool in this study has shown excellent perspectives for monitoring and protecting aquifer system from spatial and temporal pollutant migration that addresses the concern of changing natural groundwater recharge, population growth and economic development in the study region.
Environmental Science and Pollution Research, 2021
Groundwater resources in arid and semiarid regions are the most and sometimes the only water resource used for agricultural, industrial, and urban water supply. Irregular and immense application of nitrogen fertilizers in the lands under cultivation and nitrate leakage from livestock farming have affected the groundwater quality. In such areas, nitrate is one of the main pollutants in the groundwater. In this study, the temporal and spatial trend of nitrate contamination in 31 wells in Fasarud Plain, southern Iran, from April 2017 to March 2018 were assessed. To survey the geochemical quality of the plain, a geographic information system to expand geographic location maps and spatial distribution maps of nitrate concentration and nitrate pollution index (NPI) was applied. Nitrate concentrations ranged between 2.43 and 96 mg L-1. Results indicated that nitrate temporal trend was increased significantly in most of the wells, and the spatial trend of area percentage of nitrate class 3 (not permissible limit of more than 50 mg L-1) was positive. The greatest quantities of this variable in groundwater samples detected in northern, western, and eastern areas of the plain have a direct relation with the fertilization of agricultural lands. Generally, by ending the irrigation season, nitrate concentration and NPI reduced temporally in the samples and the percentage area of nitrate class 3 decreased gradually, again beginning the agricultural season, the NPI, nitrate concentration, and percentage area of nitrate class 3 began to increase. Overall, the change of nitrate concentration and distribution of agricultural regions have illustrated that nitrate originated from nitrogenous inorganic fertilizers applied within irrigation periods.
Modeling of Groundwater Nitrate Contamination Due to Agricultural Activities—A Systematic Review
Water
Groundwater nitrate contamination is a significant concern in agricultural watersheds worldwide with it becoming a more pervasive problem in the last three decades. Models are great tools that are used to identify the sources and spatial patterns of nitrate contamination of groundwater due to agricultural activities. This Systematic Review (SR) seeks to provide a comprehensive overview of different models used to estimate nitrate contamination of groundwater due to agricultural activities. We described different types of models available in the field of modeling groundwater nitrate contamination, the models used, the input requirements of different models, and the evaluation metrics used. Out of all the models reviewed, stand-alone process-based models are predominantly used for modeling nitrate contamination, followed by integrated models, with HYDRUS and LEACHM models being the two most commonly used process-based models worldwide. Most models are evaluated using the statistical m...