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Han, D., Post, V. E. A., & Song, X. (2015). Groundwater salinization processes and reversibility of seawater intrusion in coastal carbonate aquifers. Journal of Hydrology, 531, 1067–1080.
Abstract: Seawater intrusion (SWI) has led to salinization of fresh groundwater reserves in coastal areas worldwide and has forced the closure of water supply wells. There is a paucity of well-documented studies that report on the reversal of SWI after the closure of a well field. This study presents data from the coastal carbonate aquifer in northeast China, where large-scale extraction has ceased since 2001 after salinization of the main well field. The physical flow and concomitant hydrogeochemical processes were investigated by analyzing water level and geochemical data, including major ion chemistry and stable water isotope data. Seasonal water table and salinity fluctuations, as well as changes of δ2H–δ18O values of groundwater between the wet and dry season, suggest local meteoric recharge with a pronounced seasonal regime. Historical monitoring testifies of the reversibility of SWI in the carbonate aquifer, as evidenced by a decrease of the Cl− concentrations in groundwater following restrictions on groundwater abstraction. This is attributed to the rapid flushing in this system where flow occurs preferentially along karst conduits, fractures and fault zones. The partially positive correlation between δ18O values and TDS concentrations of groundwater, as well as high NO3− concentrations (\textgreater39mg/L), suggest that irrigation return flow is a significant recharge component. Therefore, the present-day elevated salinities are more likely due to agricultural activities rather than SWI. Nevertheless, seawater mixing with fresh groundwater cannot be ruled out in particular where formerly intruded seawater may still reside in immobile zones of the carbonate aquifer. The massive expansion of fish farming in seawater ponds in the coastal zone poses a new risk of salinization. Cation exchange, carbonate dissolution, and fertilizer application are the dominant processes further modifying the groundwater composition, which is investigated quantitatively using hydrogeochemical models.
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Bouchaou, L., Michelot, J. L., Vengosh, A., Hsissou, Y., Qurtobi, M., Gaye, C. B., et al. (2008). Application of multiple isotopic and geochemical tracers for investigation of recharge, salinization, and residence time of water in the Souss–Massa aquifer, southwest of Morocco. Journal of Hydrology, 352(3), 267–287.
Abstract: Groundwater and surface water in Souss–Massa basin in the west-southern part of Morocco is characterized by a large variation in salinity, up to levels of 37gL−1. The high salinity coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies as well as future exploitation. A combined hydrogeologic and isotopic investigation using several chemical and isotopic tracers such as Br/Cl, δ18O, δ2H, 3H, 87Sr/86Sr, δ11B, and 14C was carried out in order to determine the sources of water recharge to the aquifer, the origin of salinity, and the residence time of water. Stable isotope, 3H and 14C data indicate that the high Atlas mountains in the northern margin of the Souss–Massa basin with high rainfall and low δ18O and δ2H values (−6 to −8‰ and −36 to −50‰) is currently constitute the major source of recharge to the Souss–Massa shallow aquifer, particularly along the eastern part of the basin. Localized stable isotope enrichments offset meteoric isotopic signature and are associated with high nitrate concentrations, which infer water recycling via water agricultural return flows. The 3H and 14C data suggest that the residence time of water in the western part of the basin is in the order of several thousands of years; hence old water is mined, particularly in the coastal areas. The multiple isotope analyses and chemical tracing of groundwater from the basin reveal that seawater intrusion is just one of multiple salinity sources that affect the quality of groundwater in the Souss–Massa aquifer. We differentiate between modern seawater intrusion, salinization by remnants of seawater entrapped in the middle Souss plains, recharge of nitrate-rich agricultural return flow, and dissolution of evaporate rocks (gypsum and halite minerals) along the outcrops of the high Atlas mountains. The data generated in this study provide the framework for a comprehensive management plan in which water exploitation should shift toward the eastern part of the basin where current recharge occurs with young and high quality groundwater. In contrast, we argued that the heavily exploited aquifer along the coastal areas is more vulnerable given the relatively longer residence time of the water and salinization processes in this part of the aquifer.
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Cardenal, J., Benavente, J., & Cruz-Sanjulián, J. J. (1994). Chemical evolution of groundwater in Triassic gypsum-bearing carbonate aquifers (Las Alpujarras, southern Spain). Journal of Hydrology, 161(1), 3–30.
Abstract: A hydrochemical study employing modelling techniques, was carried out using samples taken at 65 points (springs and wells) in Triassic carbonate aquifers (Lújar-Gádor Unit, Alpujárride Complex, Betic Cordillera). These aquifers are made up of limestones and dolomites with some gypsum scattered or interbedded. Though the area is semi-arid, recharge is relatively high because of their mountainous nature. The carbonate rocks contain dense microfissuration; the groundwater flow regime is predominantly diffuse. The karstic forms are in general poorly developed. Two main hydrochemical processes have been identified in these aquifers. One is incongruent dissolution of dolomite that determines the chemical composition of the less mineralised water. The other is dedolomitisation (dolomite dissolution together with calcite precipitation caused by dissolution of gypsum), which becomes predominant when the flow encounters interbedded gypsum. This reaction is also frequently associated with low temperature thermalism, and can play a part in more intense local karstification (cavities, sinkholes, high transmisivity in wells) observed in the sectors of these aquifers where gypsum is more abundant. A reaction path model has been used to simulate the geochemical processes through a hypothetical aquifer (with similar lithology to the Alpujárride carbonate aquifers). Successive stages of evolution through the carbonate sequence, represented by different saturation states with respect to calcite, dolomite gypsum and CO2, have been modelled and then compared with the field data.
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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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Kafri, U., Goldman, M., Lyakhovsky, V., Scholl, C., Helwig, S., & Tezkan, B. (2007). The configuration of the fresh–saline groundwater interface within the regional Judea Group carbonate aquifer in northern Israel between the Mediterranean and the Dead Sea base levels as delineated by deep geoelectromagnetic soundings. Journal of Hydrology, 344(1), 123–134.
Abstract: A combined high resolution short offset transient electromagnetic (SHOTEM) and deep sounding, long offset (LOTEM) survey has been carried out along two traverses between the Mediterranean Sea and the Jordan-Dead Sea Rift (DSR). The DSR is located in the study area some 200–250m below sea level. The measurements detected a deep conductor, the top of which exhibited a regular behavior along the both traverses, declining from the Mediterranean to the DSR base level. The geometry of this geoelectric boundary coincides fairly well with the configuration of a supposed fresh/saline groundwater interface as also obtained by both numerical and physical modeling for the known hydrogeological conditions in the study area. Therefore the detected geoelectric boundary is identified with the interface, supporting the hypothesis of current seawater intrusion into the deep regional aquifers between the Mediterranean and the DSR base levels. The intrusion causes the salination of fresh groundwater within the aquifers as well as the salination of the Sea of Galilee.
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