Geochemical mechanisms controlling the isotopic and chemical composition of groundwater and surface water in a sector of the Pampean plain (Argentina)

Identifying the factors controlling surface water and groundwater chemical characteristics and irrigation suitability in the Yarkant River Basin, northwest China

This study investigated the geochemical processes and the suitability for irrigation purposes of surface water and groundwater in the Yarkant River Basin, northwest China. The results showed that the surface water was moderately alkaline and neutral to slightly alkaline in the groundwater. The mean values for most ions in the groundwater were higher than those in the surface water. Geochemical method and hydrogen and oxygen isotope revealed that hydrochemical were mainly affected by dissolved evaporite minerals, ion exchange processes, and anthropogenic activities. Still, the geochemical processes of in surface water and groundwater were different. Additionally, three and four factors were extracted by factor analyses of surface water and groundwater, respectively, which distinguished the hydrochemical from natural origins and anthropogenic activities in more detail. The surface water and some groundwater in the south of the study area were suitable for irrigation processes. However, many groundwaters in the north were unsuitable for irrigation, because of their high sodium levels and salinity. The study results provide a theoretical basis for the sustainable utilization of regional water resources.

Assessment of cation exchange as conditioning processes of water chemistry in freshwater lenses

Freshwater lenses are groundwater sources of limited dimensions that can be usually found in a variety of climates worldwide. These aquifers' quality is important for socioeconomic development, being cation exchange one of the most important geochemical processes that can change the water geochemistry. This study aims to assess the cation exchange processes that determine the chemistry of freshwater lenses in a multilayer aquifer type, considering the center-east of the Pampean Region (Argentina) as a case study. Water samples were taken from the freshwater lenses at different depths to analyze major ions in the laboratory. In addition, geological profiles were made along with the extraction of sediment samples for X-ray diffractometry (XRD) and laboratory tests to analyze the cation exchange capacity. The results show that water stored in the lenses has a vertical facies variation from Ca-HCO₃ to Na-HCO₃ . According to the laboratory results, the change of water facies mainly occurs in the clayey sediments that divide the carbonate bioclastic material above and the loessic sediment below, being cation exchange the most important process. PRACTITIONER POINTS: Cation exchange is the main geochemical process regulating groundwater chemistry. Hydrochemical changes determine the quality of freshwater lenses. Na/Ca exchange is mainly regulated by the groundwater flow into the bioturbated clay. Batch exchange tests were also carried out to quantify the Na/Ca exchange processes.

Transport of Tl(I) in water-saturated porous media: Role of carbonate, phosphate and macromolecular organic matter

Understanding the transport behaviors of thallium (Tl) in porous media is of considerable interest for both natural soils and artificial filtration removal of Tl. In this context, the transport behaviors of Tl(I) in water-saturated sand columns under different conditions were systematically investigated. It was found that, in addition to the effects of pH and ionic strength (IS), the transport of Tl(I) depended on the carbonate, phosphate and macromolecular organic matter as well. Tl(I) broken the columns more difficultly under higher pH and lower IS conditions. Moreover, the adsorption of carbonate and phosphate on sand surfaces may increase the retention of Tl(I) in columns. As for macromolecular organic matter, humic acid (HA) facilitated Tl(I) transport, especially under neutral and alkaline conditions (7.0 and 9.8), which was possibly associated with Tl-complexes formation and competed adsorption between Tl(I) and HA. However, bovine serum albumin (BSA) impeded Tl(I) transport for the reason that deposited BSA might provide more adsorption sites for Tl(I), though Tl(I) had a slight effect on BSA transport. In order to evaluate the mechanisms of transport, a dual-sites non-equilibrium model was applied to fit the breakthrough curves of Tl(I). Retardation factor (R) values of individual Tl(I) transport from model calculations were found to be higher than that of Tl(I) transport with HA and lower than that of Tl(I) transport with BSA. The fraction of instantaneous sorption sites (β) was found to decrease with increasing pH, implying nonequilibrium sorption is a main sorption mechanism of Tl(I) with pH increasing. The fundamental data obtained herein demonstrated that carbonate, phosphate and macromolecular organic matter significantly influenced the Tl(I) migration and could lead to the leaking or bindings of Tl(I) at Tl-occurring sites.