Fig 1.
Simple geomorphological map of the Yuncheng Basin, China.
(Areas: I, mountain bedrock areas; II, Emei high platform; III, Kaolao low platform; IV, loess hilly regions; V, piedmont plain; VI, alluvial plain; VII, fluvial depressions; VIII, Yellow River terrace). → groundwater flow direction; pentagram, surface water; triangle, shallow groundwater; circle, deep groundwater; Line AB, location of cross-section in Fig 2.
Fig 2.
Box plots of the groundwater concentrations of the major ions in the Yuncheng Basin.
(a), shallow groundwater; (b), deep groundwater. The concentrations of Ca, Mg and NO3- refer to the right axis.
Table 1.
Major physicochemical properties of water samples taken in the Yucheng Basin.
(units, mg/L, except for the well depth, temperature, pH and isotope data).
Fig 3.
Schematic diagram of the distribution of major aquifers, hydrochemical facies and ion concentrations in groundwater.
Q1, Lower Pleistocene; Q2, Middle Pleistocene; Q3, Upper Pleistocene.
Fig 4.
Piper diagrams of groundwater samples from the Yuncheng Basin.
Subgroups: (a) shallow groundwater—A′, samples from the northeastern areas; B′, samples from the southern mountain areas; and C′, samples from the western areas; (b) deep groundwater—A, samples from the northeastern areas; B, samples from the southern mountain areas; C, samples from the western areas; and D, samples from the Emei high platform areas. Symbols: triangle, shallow groundwater; circle, deep groundwater.
Fig 5.
(a) Plots of TDS versus Na/(Na+Ca) and (b) TDS versus Cl/(Cl+HCO3) illustrating the dominant processes that control the groundwater chemistry in the study area.
Triangle, shallow groundwater; circle, deep groundwater.
Fig 6.
Cross-plots of the TDS and major ions in groundwater.
Triangle, shallow groundwater; circle, deep groundwater; TSG, trend line for shallow groundwater; TDG, trend line for deep groundwater.
Fig 7.
Molar ratio bivariate plots of (a) Na-normalized Ca and HCO3 and (b) Na-normalized Ca and Mg.
The dashed circles represent the ranges of approximate compositions of the silicate and carbonate end members, and a dashed box represents the evaporite end member. Most deep groundwater samples fell in the area of silicate end member area, indicating that the majority of ions originated from silicate mineral weathering. Triangle, shallow groundwater; circle, deep groundwater; solid red dot, Salt Lake saline water.
Fig 8.
Scatterplot of δ18O versus δD for selected water samples.
Triangle, shallow groundwater; circle, deep groundwater; X-shape, surface water; Subgroup A, groundwater recharged by high-altitude precipitation in the mountain areas; Subgroup B, groundwater recharged by rainwater in a lower altitude area; Subgroup C, waters subjected to evaporation; Subgroup D, groundwater affected by extensive water-rock interactions.
Fig 9.
Distribution of fluoride in groundwater with depth along profile AB in the Yuncheng Basin.
Areas of circles or triangles represent the concentration of fluoride in groundwater, as in Fig 1. triangle, shallow groundwater; circle, deep groundwater.
Fig 10.
Scatterplot of the fluoride concentration versus the concentrations of major ions, the TDS content and the pH of groundwater in the Yuncheng Basin.
Δ, shallow groundwater; ○, deep groundwater.
Fig 11.
SEM and XRD analyses of rock/sediment samples from the Yuncheng Basin.
(a) XRD pattern of a rock sample, (b) XRD pattern of a sediment sample, (c) SEM pattern of a rock sample, (d) SEM pattern of a sediment sample and chemical components of point one in Fig 8d. Biotite/micas were identified as major fluoride-bearing minerals in both rock and sediment samples.
Table 2.
Summary of the major minerals in sediments (n = 50) from the Yuncheng Basin.
Table 3.
Fluoride content (mg/kg) in rock/sediment samples (n = 3) from the Yuncheng Basin.
Fig 12.
Bivariate plots of the major ions in groundwater.
(a) Ca + Mg versus HCO3; (b) Ca versus HCO3; (c) Mg versus HCO3; (d) Ca + Mg versus K+Na; (e) (Ca+Mg)-(SO4+HCO3) versus K+Na-Cl. triangle, shallow groundwater; circle, deep groundwater.
Fig 13.
A bivariate plots of SIDolomite/SICalcite versus SIGypsum in shallow groundwater (a) and deep groundwater (b).
Meaning of symbols: the green solid triangle, SIDolomite of shallow groundwater; the blue hollow triangle, SICalcite of shallow groundwater; the big solid red triangle, SIFluorite of shallow groundwater; the small solid red circle, SIDolomite of deep groundwater; the big hollow red circle, SICalcite of deep groundwater; the big solid red circle, SIFluorite of deep groundwater.
Table 4.
Percentages of fluoride species in selected fresh and saline groundwater samples (calculated by PHREEQC).
Table 5.
Fluoride content in selected pesticides/fertilizer/solid waste samples in the study area.