Origin and formation mechanism of salty water in Zuli River catchment of the Yellow River

Abstract

The Zuli River is one of the branches of the upper Yellow River, as an inland catchment with semiarid climate in northwestern China, and the formation, evolution, and development of brackish water at such a large scale have remained unclear. This study aims to find clues about the origin and formation mechanism of salty water through multiple methods of hydrochemistry and isotope hydrology. The results show that groundwater is dominantly recharged by precipitation, and the river water was mainly recharged by groundwater discharge. The relatively high tritium content of groundwater (>5.0 TU) clearly suggests the occurrence of a modern recharge and rapid circulation. The dissolution of evaporate minerals, followed by incongruent dissolution of carbonate minerals (dolomite), constituted the main processes controlling groundwater salinization. In addition, the intense evaporation and unreasonable use of fertilizers further increase the TDS of the river, which should be the primary external mechanism of water salinization. • Practitioner points• The authors aimed to find clues about the formation mechanism of salty water in an inland catchment of the Yellow River. • The results of this research shows that the dissolution of dissolved minerals constituted the main processes controlling groundwater salinization. In addition, the intense evaporation and unreasonable use of fertilizers, which should be the primary external mechanism of water salinization. • This work would provide a theoretical basis for government to develop rational utilization of brackish water resources in the study area, which is also significant for understanding the mechanism of water salinization in an inland mountain watershed and even in similar inland watersheds around the world.

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.

“…The Boron isotope ratios of the river water samples displayed a broader range (17.45 (Table 1) The strata of the mountain area in the headwater of the Zuli River are mainly composed of a set of marine carbonate rocks (Zhan et al, 2010). In our previous study, groundwater was considered as recharged by precipitation in the headwaters based on the analysis of stable isotopes data (δ 2 H, δ 18 O) (Liu et al, 2019). The groundwater in the headwater region is characterized by higher strontium concentration and 87 Sr/ 86 Sr ratios relative to those determined for precipitation (strontium concentrations: (0.002-0.3mg/l), 87 Sr/ 86 Sr ratio:0.7078-0.7092 (Bullen et al, 1996))( Table 1).…”

“…Current knowledge typically attributes the salinization of groundwater in most inland areas to the mixing of old groundwater in deep strata (Herrera et al, 2018), which usually means the salinity of groundwater originated from long periods of water-rock interactions (Petrides, Cartwright, & R.Weaver, 2006;Skrzypek, Dogramaci, & F.Grierson, 2013). However, our recent study showed that even under the rapid renewal of groundwater, the fresh groundwater from the headwaters still evolves into brackish water with rapid salinization (Liu et al, 2019). Several hypotheses have been advanced in previous studies as to the source of salinity in brackish water.…”

“…Thick layers Silurian carbonate rocks are deposited in this area ( Fig.3a), affected by large-scale tectonic activity, joints and fissures were developed in the strata of headwater. Additionally, karstic features have developed, and fissure water and bedrock fissure water are present in the fracture zone (Liu et al, 2019).…”

“…According to the previous work, the upstream groundwater is recharged by groundwater in headwater and precipitation. And the tritium data shows a rapid circulation of groundwater (less than 40 years) in the upstream area (Liu et al, 2019). Groundwater still evolves to brackish water from headwater to the upstream area under such a rapid replenishing, which is rare in most similar inland areas around the world.…”

“…Our previous study showed that groundwater recharge in the Zuli River catchment is produced by the infiltration of precipitation in the headwaters (Liu, Tan, Shi, Xu, & I.Elenga, 2019). During this recharging process, the upstream groundwater undergoes rapid salinization.…”