Significance of isotopic and geochemical methods to determine the evolution of inland brackish and bitter water: An example from the Zuli river in the upper reaches of the Yellow River,China

With the increasing demand for water resources, the utilization of marginal water resources of poor-quality has become a focus of attention. The brackish water developed in the Loess Plateau is not only salty but also famous for its ‘bitterness’. In the present work, multi-isotope analysis (Sr, B) was combined with geochemical analysis to gain insight into the hydrogeochemical evolution and formation mechanisms of brackish water. These results demonstrate that groundwater in the headwater is influenced by carbonate weathering. After the confluence of several tributaries in the headwater, the total dissolved solids (TDS) of water is significantly increased. The dissolution of evaporates is shown to be the main source of salinity in brackish water, which also greatly affects the strontium isotopic composition of water. This includes the dissolution of Mg-rich minerals, which is the main cause of the bitterness. Furthermore, the release of calcium from the dissolution of gypsum may induce calcite precipitation and incongruent dissolution of dolomite, which also contributes to the enrichment of magnesium. The highly fractionated boron isotopic values observed in the upstream groundwater were explained by the absorption with clay minerals. The inflow of brackish groundwater is the source of river water. Then evaporation further aggravates the salinization of river water, with water quality evolving to saline conditions in the lower reach. When the river reaches the valley plain, the ⁸⁷Sr/⁸⁶Sr ratios decreases significantly, which is primarily related to erosion of the riverbanks during runoff. These results indicate that water resource sustainability could be enhanced by directing focus to mitigating salinization in the source area of the catchment.     

Hydrological characterization and connectivity of proglacial lakes to a stream,Adygine ice-debris complex,northern Tien Shan

ABSTRACT

In this study, we characterized the glacial meltwater flow through a proglacial area with a focus on proglacial lakes, their hydrological regime and their connection to the stream. The studied lakes – the Adygine ice-debris complex, northern Tien Shan – showed a distinct development throughout an ablation season: at Lake 2, the mean daily water-level fluctuation amplitude increased from 0.07 m to 0.18 m (June, August), then dropped to 0.07 m in September. Glacial meltwater flows through the lakes and further downstream through a rock glacier rather fast, moving at 0.085 m s^?1. However, based on the low dye recovery in the stream (0.03%), only a small portion of water was routed efficiently. The complexity of the site’s drainage system was supported by varying isotopic composition of water in the tarns situated on the rock glacier, with Tarn a (δ²H: –36.08‰; δ¹⁸O: –6.25‰) being the most enriched and Tarn c (δ²H: 78.68‰; δ¹⁸O: 11.9‰) the most depleted in heavy isotopes.     

Using hydrochemical,stable isotope,and river water recharge data to identify groundwater flow paths in a deeply buried karst system

The deeply buried river‐connected Xishan karst aquifer (XKA) in western Beijing, China, has been suffering from diminishing recharge for several decades, which in turn leads to the disappearing of spring water outflows and continuously lowering of groundwater level in the area. Thus, it is important to correctly recognize the groundwater recharge and flow paths for the sustainable development of the XKA. To investigate these issues, the hydrochemical and isotopic compositions are analysed for both surface water and groundwater samples collected over an area of about 280 km². Results show that (a) the river water is characterized by high Na contents; (b) the δ²H and δ¹⁸O values in the river water are distinctively higher than those of groundwater samples, after experiencing the long‐time evaporative enrichment in the upstream reservoir; (c) the Sr concentrations and ⁸⁷Sr/⁸⁶Sr ratios of groundwater clearly indicated the interaction between water and carbonate minerals but excluded the water–silicate interaction; and (d) the groundwater samples in the direct recharge area of the XKA have the lowest Na concentrations and the δ²H and δ¹⁸O values. Based on the large differences in the Na contents and ¹⁸O values of groundwater and surface water, a simple two‐component mixing model is developed for the study area and the fractions of the river water are estimated for groundwater samples. We find that the distribution pattern of the river water fractions in the XKA clearly shows a change of directions in the preferential flow path of the groundwater from its source zone to the discharge area. Overall, our results suggest that the recharged surface water can be a useful evidence for delineating the groundwater flow path in river‐connected karst aquifer. This study improves our understanding of the heterogeneity in karst groundwater systems.