The geographic location of Yongqing County is optimal, covering the center of the Beijing, Tianjin, and Baoding triangle. However, the economic and social development of Yongqing County in recent years has resulted in negative impacts on groundwater. Therefore, investigating the current status of groundwater chemistry in Yongqing County is of great significance to provide a useful basis for future studies on groundwater quality assessment. The aim of this study is to assess the hydrochemical characteristics and formation mechanisms of the unconfined aquifers of Yongqing County using descriptive statistical and multivariate statistical methods. In addition, ionic ratios, Piper diagram, Gibbs diagrams, and PHREEQC software were used in this study to determine the main factors influencing the hydrochemical characteristics of the unconfined aquifers. The results suggested slightly alkaline groundwater of the unconfined aquifers in the western part of Yongqing County, belonging to the fresh-brackish groundwater type. In addition, the hydrochemistry facies types in the study area are complex, consisting of four facies types, namely HCO3−−Mg·Ca, HCO3−−Na, HCO3−-Na·Ca, and HCO3−-Na·Mg. On the other hand, the main factors influencing the hydrochemical characteristics of groundwater are mineral dissolution followed by some anthropogenic pollution. Rock dominance was the main influencing factor, demonstrated by thedissolution of silicate and carbonate rock minerals. In addition, the alternating adsorption of cations occurring in the aquifer plays a non-negligible effect on the hydrochemical characteristics of the unconfined aquifers in the study area. In fact, the validation results using PHREEQC inverse hydrogeochemical simulations demonstrated consistent conclusions with those mentioned above. According to the findings obtained, the dissolution of carbonate and silicate minerals as well as Na+, K+, and Ca2+ ion exchange in the aquifer are the main factors influencing the hydrochemical characteristics of the unconfined aquifers of Yongqing County. The recommendations suggest put forward in this research are helpful to understand the formation mechanism of hydrochemistry in typical alluvial proluvial plain and provide insights for decision makers to protect the groundwater resources.
This paper studies the spatial distribution characteristics and controlling factors of groundwater chemistry in the Chahannur Basin. One hundred and seventy shallow groundwater samples (50 m shallow) are collected, and seven ions, pH, TDS, TH, iron, manganese, COD, barium and other indicators, are detected. Piper triplex graph, Gibbs model, ion ratio, analysis of variance and Kriging interpolation are used to carry out the research. The results show that bicarbonate water is the main water chemical type in the Chahannur Basin, in which bicarbonate water accounts for 65.23%, chloride water accounts for 15.15% and sulfate water accounts for 19.62%. Bicarbonate water is mainly distributed in the mountainous areas in the north and south of the basin, and the main controlling factor is rock weathering. Sulfate-type water is mainly distributed in the lower reaches of the northern mountains of the basin, and the main controlling factors are rock weathering and evaporation concentration. The chloride water is mainly distributed in the Chahannur Lake area and the shallow groundwater buried area in the central region of the basin. The main controlling factors are evaporation concentration and human influence. Na+ is mainly derived from atmospheric precipitation and rock salt leaching, Ca2+ and Mg2+ are mainly derived from carbonate minerals leaching, and silicate minerals leaching is less. The pH of groundwater in the basin ranges from 6.3 to 9.18, with an average value of 7.50. The TDS in the basin ranges from 227 to 22,700 mg/L, with an average of 1661 mg/L. Iron in the catchment ranges from 0.01 to 15.343 mg/L, with a mean of 0.837 mg/L. The manganese content in the basin ranges from 0.005 to 3.802 mg/L, with an average value of 0.254 mg/L. COD in the basin ranges from 0.71–32.72 mg/L, with an average value of 3.49 mg/L. Barium in the basin ranges from 0.005 to 0.312 mg/L, with an average of 0.075 mg/L. The research results provide basic scientific data support for groundwater hydrochemistry research in the Chahannur Basin and show that the types of water chemistry in the study area are complex and diverse, and although the distribution is still controlled by terrain and geological conditions, the area affected by human activities accounts for a high proportion, so attention should be paid to the impact of human activities on groundwater in this area.
In recent years, the lake area of the Chahannur Basin has been decreasing, leading to an increase in salt dust storms. In order to find out the recharge mechanism of groundwater in the Chahannur Basin, a total of 51 groundwater and surface water samples were collected. Tritium (3H) isotope and Freon (CFCs) were used to estimate the age of groundwater and preliminarily analyze the sources of groundwater recharge. The characteristics of hydrogen, oxygen, and strontium isotopes are used to indicate the characteristics of the water cycle in the Chahannur Basin. The results show that: (1) Two dating methods, tritium isotope (3H) and Freon (CFCs), are suitable for semi-quantitative dating of groundwater in the Chahannur Basin. (2) Hydrogen, oxygen, and strontium isotopes can be used to characterize the groundwater cycle in the Chahannur Basin. (3) The groundwater level around the Chahannur Lake area is low, and the groundwater in the Chahannur Basin flows from the southwest and northwest to the lake area. (4) The groundwater in the Chahannur Basin is mainly replenished by atmospheric precipitation, and the evaporation of groundwater and surface water is strong. The research results provide a basis for the study of measures to prevent the reduction in the Chahannur watershed area.
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