Groundwater quality, as major source of freshwater, is an important factor in sustainable development and water resources management. Due to increase in water demand in developing countries and overexploitation, groundwater quality has decreased in many aquifers in the world. One of the most important factors which decrease the groundwater quality is salinization. The aim of this study is to comprehensively review the sources and mechanisms of salinization. Based on our review, the major sources of groundwater salinization consist of marine sources (e.g., connate saline groundwater, marine transgressions, incidental flooding by seawater, lateral seawater intrusion and seawater sprays), natural continental sources (e.g., evaporation, soluble minerals, membrane effects and geothermal origin), anthropogenic activities and multiplicity sources. Research approaches in groundwater salinization include hydrogeochemical and isotopic tracers, hydrogeochemical models and groundwater dating isotopes (radioisotopes). The simple and clear guideline presented in this paper can be applied to investigate the groundwater salinization by researchers in the world.

An overview on source, mechanism and investigation approaches in groundwater salinization studies

Earth models, seismological, compositional and thermal, are elegantly explained and brought right up to date with an authoritative summary of the literature. The book (264 pages) includes approximately 470 references and an appendix for the PREM (seismic) model for the mantle and core. It is well illustrated, and indexed with some 250 items. The book is well produced, and the text virtually error-free, through one important boob on page 97 has inverted the important concept of liquidus and solidus. The book provides an extremely useful introduction and handy references to researchers working in the earth sciences, physics and materials science. It wiI1 provide an almost essential upgrade to a number of undergraduate courses, including the more traditional geology and geophysics. It is very highly recommended. A. P. JONES

Applied Chemical and Isotopic Groundwater Hydrology

High‐elevation mountains often constitute for basins important groundwater recharge sources through mountain‐front recharge processes. These processes include streamflow losses and subsurface inflow from the mountain block. However, another key recharge process is from irrigation practices, where mountain streamflow is distributed across the irrigated piedmont. In this study, coupled groundwater fluctuation measurements and environmental tracers (¹⁸O, ²H, and major ions) were used to identify and compare the natural mountain‐front recharge to the anthropogenically induced irrigation recharge. Within the High Atlas mountain front of the Ourika Basin, Central Morocco, the groundwater fluctuation mapping from the dry to wet season showed that recharge beneath the irrigated area was higher than the recharge along the streambed. Irrigation practices in the region divert more than 65% of the stream water, thereby reducing the potential for in‐stream groundwater recharge. In addition, the irrigation areas close to the mountain front had greater water table increases (up to 3.5 m) compared with the downstream irrigation areas (<1 m increase). Upstream crops have priority to irrigation with stream water over downstream areas. The latter are only irrigated via stream water during large flood events and are otherwise supplemented by groundwater resources. These changes in water resources used for irrigation practices between upstream and downstream areas are reflected in the spatiotemporal evolution of the stable isotopes of groundwater. In the upstream irrigation area, the groundwater stable isotope values (δ¹⁸O: −8.4‰ to −7.4‰) reflect recharge by the diverted stream water. In the downstream irrigation area, the groundwater isotope values are lower (δ¹⁸O: −8.1‰ to −8.4‰) due to recharge via the flood water. In the nonirrigation area, the groundwater has the highest stable isotope values (δ¹⁸O: −6.8‰ to −4.8‰). This might be due to recharge via subsurface inflow from the mountain block to the mountain front and/or recharge via local low altitude rainfall. These findings highlight that irrigation practices can result in the dominant mountain‐front recharge process for groundwater.

Groundwater recharge sources in semiarid irrigated mountain fronts

Delineating the source and mechanism of groundwater salinization in crucial declining aquifer using multi-chemo-isotopes approaches

Major element concentrations and stable (δ18O and δ2H) and radiogenic (3H and 14C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water–rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ18O and δ2H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO4 and Ca-Na-Cl-SO4. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ18O and δ2H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes ( 18 O, 2 H, 3 H, 14 C) and chemical tracers: a case study of the intermediate aquifer, Sfax, southeastern Tunisia

Abstract Introduction: mediastinal cysts are rare lesions developed from mediastinal structures. They may be acquired like thoracic duct cysts or lymphangiomas or congenital like the bronchogenic cysts, enteric cysts or celomic cysts. These cysts are rare and may cause diagnostic challenges. Aim: to assess the major characteristics of these cysts based on a single institution experience.Methods: the authors performed a descriptive, retrospective study from January 2009 to March 2020 in a single institution. Cystic lesions taking birth from the mediastinum for which gross features, microscopic features were available were included. Results: this study contained 52 mediastinal cysts that were completely resected and no patient presented complications after the surgical resection. The bronchogenic cysts were the most frequent and represented 57.69% of all lesions. Thymic cysts and pericardial cysts represented respectively 40.38% and 1.92% of the cases. The positive diagnosis was based on the microscopic exam. The final diagnosis was concordant with the radiologic findings in 15 cases reaching a rate of 28%.Conclusion: the diagnosis of mediastinal cysts is based on the microscopic analysis of the cystic wall. Pericardial cysts may be suspected based on their characteristic location in the cardiophrenic angle, thymic cyst may be evoked based on their location in the thymic region and bronchogenic cysts are mainly located in the middle mediastinum. Inspite of these most frequent locations, the cysts may be located in any part of the mediastinum and may be difficult to diagnose when the key diagnostic features are absent.

Mediastinal cysts : a 52-case retrospective study

https://doi.org/10.1016/j.ijscr.2022.107160

Mediastinal paraganglioma as a large dumbell tumor: A case report

The origin of groundwater in the Sfax aquifer system was studied using environmental isotopic tracers (δ18O, δ2H, and 3H). In total, 164 water samples were analyzed for stable isotopes: 73 collected from the Sfax shallow aquifer, 63 from the Sfax middle aquifer, and 28 from the Sfax deep aquifer. Recent recharge of the groundwater in the Sfax aquifer was identified using tritium concentrations in 82 groundwater samples from different depths. The isotopic ratios of the shallow aquifer range from −5.55 to −1.59 ‰ for δ18O and from −38.38 to −14.19 ‰ for δ2H, and the isotopic ratios in the middle aquifer range from −6.86 to −2.97 ‰ for δ18O and from −44.18 to −22.38 ‰ for δ2H. The deep aquifer exhibited markedly lower isotopic values, ranging from −6.70 to −5.70 ‰ for δ18O and from −42.40 to −38.89 ‰ for δ2H. The mixing proportions inferred from stable isotopic mass balance calculations suggest that the deep aquifer contributes significantly to the middle aquifer through geologic structures and may reach 100 % in the Menzel Chaker region. The isotopic mass balance model also indicates that the middle groundwater aquifer may contribute up to 100 % of the shallow Plio-Quaternary aquifer, particularly in the western and northeastern parts of the study area, between Bir Ali ben Khalifa and Djebeniana. The tritium data support the existence of recent recharge. The tritium and stable isotope data clearly indicate the presence of mixing processes, especially in the northwestern and coastal portions of the study area. A conceptual model is established, explaining the pressure differences that generate vertical leakage, which is a reasonable mechanism for flow between the aquifers.

Determination of the origins and recharge rates of the Sfax aquifer system (southeastern Tunisia) using isotope tracers

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Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes ( 18 O, 2 H, 3 H, 14 C) and chemical tracers: a case study of the intermediate aquifer, Sfax, southeastern Tunisia

Mediastinal cysts : a 52-case retrospective study

Mediastinal paraganglioma as a large dumbell tumor: A case report

Determination of the origins and recharge rates of the Sfax aquifer system (southeastern Tunisia) using isotope tracers