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Nogueira, G., Stigter, T. Y., Zhou, Y., Mussa, F., & Juizo, D. (2019). Understanding groundwater salinization mechanisms to secure freshwater resources in the water-scarce city of Maputo, Mozambique. Science of The Total Environment, 661, 723–736.
Abstract: In this study hydrochemical, isotopic and multivariate statistical tools are combined with a recharge analysis and existing geophysical data to improve understanding of major factors controlling freshwater occurrence and the origins of high salinities in the multi-layered coastal aquifer system of the Great Maputo area in Mozambique. Access to freshwater in this semi-arid area is limited by an inefficient public supply network, scarce surface waters, long droughts and an increasing population growth. Groundwater has a large potential to enhance water security, but its exploitation is threatened by both coastal and inland salinization mechanisms that are poorly understood. A GIS approach is utilized to classify potential recharge zones based on hydrogeological properties and land use/cover, whereas potential recharge rates are estimated through a root zone water balance method. In combination with water stable isotope data results reveal that extreme rainfall events provide the most relevant contributions to recharge, and interception and evaporation play an important role in the low recharge areas. Hierarchical clustering of hydrochemical and isotopic data allows the classification of six water groups, varying from fresh to brackish/salt waters. Corresponding scatter plots and PHREEQC modelling show evaporation and mixing with seawater (up to 5%) as major processes affecting salinity in the area. The co-occurrence of high alkalinity and Cl concentrations, in combination with piezometric and geo-electrical data, suggests that: 1) inland brackish/salt groundwater is caused by mixing with seawater trapped within clay layers; and 2) brackish/salt surface waters result from seepage of brackish groundwater into rivers and wetlands, followed by evaporation, hence increasing salinity and δ18O values. Mixing with small fractions of trapped seawater as main salinity source, rather than halite dissolution, is further corroborated by Br/Cl ratios of brackish/salt water samples near the ocean ratio. Cation exchange upon salinization is mainly observed in the semi-confined aquifer, while freshening takes place in the phreatic aquifer, particularly in areas presenting high recharge rates.
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Dhar, A., & Patil, R. S. (2011). Fuzzy uncertainty based design of groundwater quality monitoring networks. J. Environ. Res. Develop., 5(3a), 683–688.
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Guerzoni, S., Molinaroli, E., & Chester, R. (1997). Saharan dust inputs to the W. Mediterranean Sea: depositional patterns, geochemistry and sedimentological implications. Deep-Sea Res, 44(3-4), 631–654.
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Giménez-Forcada, E. (2014). Space/time development of seawater intrusion: A study case in Vinaroz coastal plain (Eastern Spain) using HFE-Diagram, and spatial distribution of hydrochemical facies. Journal of Hydrology, 517, 617–627.
Abstract: A new method has been developed to recognize and understand the temporal and spatial evolution of seawater intrusion in a coastal alluvial aquifer. The study takes into account that seawater intrusion is a dynamic process, and that seasonal and inter-annual variations in the balance of the aquifer cause changes in groundwater chemistry. Analysis of the main processes, by means of the Hydrochemical Facies Evolution Diagram (HFE-Diagram), provides essential knowledge about the main hydrochemical processes. Subsequently, analysis of the spatial distribution of hydrochemical facies using heatmaps helps to identify the general state of the aquifer with respect to seawater intrusion during different sampling periods. This methodology has been applied to the pilot area of the Vinaroz Plain, on the Mediterranean coast of Spain. The results appear to be very successful for differentiating variations through time in the salinization processes caused by seawater intrusion into the aquifer, distinguishing the phase of seawater intrusion from the phase of recovery, and their respective evolutions. The method shows that hydrochemical variations can be read in terms of the pattern of seawater intrusion, groundwater quality status, aquifer behaviour and hydrodynamic conditions. This leads to a better general understanding of the aquifers and a potential for improvement in the way they are managed.
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Pacheco, F. A. L., & Szocs, T. (2006). “Dedolomitization reactions” driven by anthropogenic activity on loessy sediments, SW Hungary. Applied Geochemistry, 21(4), 614–631.
Abstract: In the Szigetvár area, SW Hungary, shallow groundwaters draining upper Pleistocene loess and Holocene sediments are considerably contaminated by domestic effluents and leachates of farmland fertilizers. The loess contains calcite and dolomite, but gypsum was not recognized in these sediments. The anthropogenic inputs contain significant amounts of Ca and SO4. The Ca from these anthropogenic inputs is promoting calcite growth, with concomitant consumption of carbonate alkalinity, undersaturation of the system with respect to dolomite, and dolomite dissolution; in brief, is driving “dedolomitization reactions”. Geochemical arguments supporting the occurrence of “dedolomitization reactions” in the area are provided by the results of mass balance and thermodynamic analyses. The mass balances predicted the weather sequence dolomite\textgreatercalcite\textgreaterplagioclase\textgreaterK-feldspar, at odds with widely accepted sequences of weatherability where calcite is the first mineral in the weathering sequence. The exchange between calcite and dolomite can be a side effect of “dedolomitization reactions” because they cause precipitation of calcite. The thermodynamic prerequisites for “dedolomitization reactions” are satisfied by most local groundwaters (70%) since they are supersaturated (or in equilibrium) with respect to calcite, undersaturated (or in equilibrium) with respect to dolomite, and undersaturated with respect to gypsum. The Ca vs. SO4 and Mg vs. SO4 trends are also compatible with homologous trends resulting from “dedolomitization reactions”.
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