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Bahir, M., Ouhamdouch, S., & Carreira, P. M. (2018). Geochemical and isotopic approach to decrypt the groundwater salinization origin of coastal aquifers from semi-arid areas (Essaouira basin, Western Morocco). Environmental Earth Sciences, 77(13), 485.
Abstract: In arid and semi-arid areas, the groundwater is the main source of water supply and agricultural activity. Overexploitation of coastal aquifers and pollution vulnerability are among the main problems related to groundwater resources assessment and management in these zones. In fact, in the last decades, these resources have been threatened by a degradation of their quality and quantity that furthers natural and anthropic effects, such as climate change, seawater intrusion and overexploitation. However, the protection and management of these resources requires knowledge of the origin of their mineralization. In this study, the Essaouira basin is selected as a typical example. Stable isotopes (18O and 2H) together with geochemical data were used to identify the groundwater salinization origin in the coastal aquifers of the Essaouira basin. The results of both the approaches show that the groundwater mineralization is due to: (1) the dissolution of salt minerals, (2) the ion exchange phenomena, (3) seawater intrusion, and (4) sulphate reduction. Also, the recharge is supported by fast infiltration of oceanic precipitation without significant evaporation.
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Siarkos, I., & Latinopoulos, P. (2016). Modeling seawater intrusion in overexploited aquifers in the absence of sufficient data: application to the aquifer of Nea Moudania, northern Greece. Hydrogeology J., 24, 2123–2141.
Abstract: In many coastal areas, overexploitation of groundwater resources has led both to the quantitative degradation of local aquifers and the deterioration of groundwater quality due to seawater intrusion. To investigate the behavior of coastal aquifers under these conditions, numerical modeling is usually implemented; however, the proper implementation of numerical models requires a large amount of data, which are often not available due to the time-consuming and costly process of obtaining them. In the present study, the investigation of the behavior of coastal aquifers under the lack of adequate data is
attempted by developing a methodological framework consisting of a series of numerical simulations: a steady-state, a false-transient and a transient simulation. The sequence and the connection between these simulations constitute the backbone of the whole procedure aimed at adjusting the various model parameters, as well as obtaining the initial conditions for the transient simulation. The validity of the proposed methodology is tested through evaluation of the model calibration procedure and the estimation of the simulation errors (mean error, mean absolute error, root mean square error, mean relative error) using the case of Nea Moudania basin, northern Greece. Furthermore, a sensitivity analysis is performed in order to minimize the error estimates and thus to maximize the reliability of the models. The results of the whole procedure affirm the proper implementation of the developed methodology under specific conditions and assumptions due to the lack of sufficient data, while they give a clear picture of the aquifer’s quantitative and qualitative status. |
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Di Lorenzo, T., & Galassi, D. M. P. (2013). Agricultural impact on Mediterranean alluvial aquifers: do groundwater communities respond? Fundamental and Applied Limnology/Archiv für Hydrobiologie, 182(4), 271–282.
Abstract: In Mediterranean countries agricultural development heavily depends on groundwater availability due
to arid and semi-arid climate and poor surface-water resources. Agriculture represents one of the most relevant pressures which generate impacts in alluvial aquifers by means of fertilizers and pesticides usage and groundwater overexploitation. Until now, very few studies have addressed the ecological response of groundwater fauna to groundwater contamination and overexploitation due to agricultural practices. We investigated a Mediterranean alluvial aquifer heavily affected by nitrates contamination and groundwater abstraction stress due to crop irrigation. The aim of this study was to evaluate the sensitivity of groundwater communities to (a) groundwater nitrate contamination, (b) groundwater abstraction due to irrigation practices, and (c) saltwater intrusion. The present work suggests that nitrate concentration lower than 150 mg l –1 is not an immediate threat to groundwater biodiversity in alluvial aquifers. This conclusion must be carefully considered in the light of the total lack of knowledge of the effects of long-term nitrate pollution on the groundwater biota. Moreover, local extinctions of less tolerant species, prior to monitoring, cannot be ruled out. Conversely, species abundances in ground water are affected by groundwater withdrawal, but species richness may be less sensitive. This result is attributable to the disappearance of saturated microhabitats and to the depletion of fine unconsolidated sediments, reducing the surface available to bacterial biofilm, which represent the trophic resource for several groundwater invertebrates and where the main aquifer self-purification processes, such as denitrification, take place. Saltwater intrusion seems not to affect groundwater species at the values measured in this coastal aquifer. |
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Kim, Y., Lee, K. - S., Koh, D. - C., Lee, D. - H., Lee, S. - G., Park, W. - B., et al. (2003). Hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer: a case study in Jeju volcanic island, Korea. Journal of Hydrology, 270(3), 282–294.
Abstract: In order to identify the origin of saline groundwater in the eastern part of Jeju volcanic island, Korea, a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions. The total dissolved solid contents of groundwaters are highly variable (77–21,782mg/l). Oxygen, hydrogen, sulfur, and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater. Strontium isotopic compositions and Br/Cl and I/Cl ratios strongly suggest that the source of salinity is modern seawater intrusion. Hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation-exchange reactions. The highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions. These properties enhance the salinization of groundwater observed in the study area. Based on the Cl, Br, and δ18O data, seawater was determined to have intruded inland some 2.5km from the coastline. Considering the poor correlation of sampling depth and Cl concentrations observed, the position of seawater-freshwater interface is not uniformly distributed in the study area, due to heterogeneities of the basaltic aquifers.
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Vengosh, A., Spivack, A. J., Artzi, Y., & Ayalon, A. (1999). Geochemical and boron, strontium, and oxygen isotopic constraints on the origin of the salinity in groundwater from the Mediterranean coast of Israel. Water Resources Research, 35(6), 1877–1894.
Abstract: In order to identify the origin of the salinity and formation of saline plumes in the central part of the Mediterranean coastal aquifer of Israel, we determined the elemental and boron, strontium, and oxygen isotopic compositions of fresh and brackish groundwater (C1 up to 1500 mg/L). We distinguish between two key anthropogenic sources: (1) sewage effluents used for irrigation with high Na/C1, SO4/C1, and B/C1 ratios and low Br/C1 ratios relative to seawater ratios, low ;5•B values (0-10%o) and high ;5•80 values (>-4%0); and (2) imported water from the Sea of Galilee that is artificially
recharged tothe aquifer with high Br/C1 (3 x 10 -3) and ;5•80 values (-1%o) and a low 87Sr/86Sr ratio of 0.70753. The brackish groundwater from the saline plumes have relatively low Na/C1 ratios (0.5-0.8) and high Ca/Mg, Mg/C1, and Ca/(SO 4 q- HCO3) (> l) ratios relative to seawater ratios; marine SO4/C1 and Br/C1 ratios;5•B values of 24.8-49.9%0; 18 87 86 ;50 of -2.95%0 to -4.73%0; and Sr/ Sr ratios of 0.708275-0.708532. The composition of most of the investigated groundwater from the saline plumes differs from those of the 87 86 anthropogenic sources, imported water, fresh uncontaminated groundwater (Sr/ Sr of 0.70866, ;5•B of 20-30%o), and saline water from the adjacent Eocene aquitard. Only in ß 18 areas of artificial recharge does local groundwater have high Br/C1 and ;50 values that are typical to the Sea of Galilee. The linear relationships between chloride and most of the ions, including Band Sr, the relatively high ;5•B (>30%0) and low ;5•80 (<-4%0) values, and the chemical signature of the saline plumes (e.g., marine Br/C1 and SO4/C1 ratios), suggest that (1) mixing processes control the chemical composition of the brackish water within the aquifer, and (2) the saline postulated end-member has a chemical composition that resembles modified seawater with a marine and higher ;5•B values, and a 87Sr/86Sr ratio of <0.7083. We propose that most of the salinization phenomena and the formation of saline plumes in the inner parts of the coastal aquifer are derived from upconing of underlying natural saline water bodies and enhanced by overexploitation and draw-down of the overlying fresh groundwater. |