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Nogueira, G.; Stigter, T.Y.; Zhou, Y.; Mussa, F.; Juizo, D. |
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Understanding groundwater salinization mechanisms to secure freshwater resources in the water-scarce city of Maputo, Mozambique |
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Journal Article |
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Year |
2019 |
Publication |
Science of The Total Environment |
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661 |
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723-736 |
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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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0048-9697 |
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THL @ christoph.kuells @ Nogueira2019 |
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34 |
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Author |
Panagopoulos, G. |
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Title |
Application of major and trace elements as well as boron isotopes for tracing hydrochemical processes: the case of Trifilia coastal karst aquifer, Greece |
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Journal Article |
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2009 |
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Environmental Geology |
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58 |
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5 |
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1067-1082 |
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0943-0105 |
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Greece |
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THL @ christoph.kuells @ Panagopoulos2009 |
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36 |
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Stigter, T.Y.; van Ooijen, S.P.J.; Post, V.E.A.; Appelo, C.A.J.; Carvalho Dill, A.M.M. |
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A hydrogeological and hydrochemical explanation of the groundwater composition under irrigated land in a Mediterranean environment, Algarve, Portugal |
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1998 |
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Journal of Hydrology |
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208 |
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3 |
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262-279 |
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In the Campina de Faro, in the south of Portugal, agricultural practices have a large impact on groundwater composition. These practices involve pumping of water for irrigation from combinations of large diameter, shallow wells (noras) and small diameter, deep boreholes (furos). Excess irrigation water returns to the aquifer and mixes with water from the regional groundwater flow system. This irrigation return flow is concentrated by strong evapotranspiration and by flushing of fertilisers. The concentration increase induces cation exchange, whereby Ca on the soil exchanger is replaced by Na. The mixing in the aquifer allows application of a mixing cell model which may then be used to calculate transmissivities from the Cl mass balance. The calculations are complicated by the time-variant behaviour of Cl and the method is adjusted to calculate the change of chloride in time. Results from the calculations appear to be in good agreement with hydrochemical observations. |
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0022-1694 |
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THL @ christoph.kuells @ Stigter1998 |
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38 |
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Wigley, T.M.L.; Plummer, L.N. |
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Title |
Mixing of carbonate waters |
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1976 |
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Geochimica et Cosmochimica Acta |
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40 |
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9 |
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989-995 |
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When mineral solutions of different compositions are mixed, the molalities and activities of individual ions in the mixture are often non-linear functions of their end-member values. This non-linearity is particularly significant in determining mineral saturation levels. Mixtures of saturated solutions may be either undersaturated or supersaturated depending on the end-member compositions and the physical conditions in which end-members and their mixtures exist. In carbonate solutions important non-linear effects occur due to redistribution of carbonate species. In extreme cases this causes mixture pH to be below both the end-member pH values. A simple but precise computer program (WATMIX) has been developed for calculating mixture composition for closed and open system mixing of arbitrary end-members. A number of mixing examples are considered which allow one to isolate three important processes leading to non-linear behaviour: the algebraic effect, the δPCO2 effect, and the ionic strength effect. |
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0016-7037 |
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THL @ christoph.kuells @ Wigley1976 |
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40 |
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Zhou, X.; Li, C. |
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Hydrogeochemistry of deep formation brines in the central Sichuan Basin, China |
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1992 |
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Journal of Hydrology |
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138 |
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1 |
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1-15 |
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Subsurface brines are abundant in the Sichuan Basin, China. Five brine-bearing aquifers have been identified within rocks of Triassic age in the central part of the basin. These are of two types: brine-bearing clastic and brine-bearing carbonate aquifers. Brines in this region have high total dissolved solids and chemical species that are different from those of evaporatively concentrated seawater. Deep formation brines in clastic aquifers, in which evaporites do not exist, are characterized by high concentrations of Ca, Sr, Ba, Br and I, low concentrations of Mg and K, and lack of SO4, and are dominated by the NaCaCl type. Brines in carbonate aquifers, which have interbeds of evaporites, are characterized by high total dissolved solids, low concentrations of Ca, Mg and SO4, and lack of Ba, and are of the NaCl type. The brines in clastic aquifers originate from connate continental sedimentary waters mixed with marine waters; membrane filtration through shales has played an important part in modifying the chemical compositions and increasing the salinity of the brines. Those in carbonate aquifers are bittern marine sedimentary waters, with chemical compositions mainly controlled by precipitation of evaporites. |
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0022-1694 |
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Asia |
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THL @ christoph.kuells @ Zhou19921 |
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41 |
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