Effect of Ecological Water Supplement on Groundwater Restoration in the Yongding River Based on Multi-Model Linkage

Evaluating the effect of ecological water supplement on groundwater restoration quantitatively could produce positive contributions to both water cycle theory and surface–groundwater conjunctive management. Therefore, in this paper, a groundwater flow numerical model has been established after calculating the river section seepage rate using a fuzzy mathematical method in the Yongding River channel. The simulated results show that the model could accurately reflect the real groundwater dynamic features. Then, a data-driven random forest(RF) model has been established to quantitatively evaluate the contributions of the factors which influence the groundwater level variation. The Nash-Sutcliffe efficiency coefficient(NSE) of the RF model is 0.93. It shows excellent ability to identify the rising zone of groundwater level. The study shows that the infiltration capacity is strong in the upstream area of the Yongding River, and the seepage rate is over 0.7. The lowest seepage rate is 0.19 at the downstream end, while the seepage rate in the middle area is basically between 0.4 and 0.7. From 2018 to 2019, the ecological water supplement of the Yongding River has played a significant role in raising the groundwater level along the river channel. Additionally, its contribution analyzed by the RF model to the change of groundwater level is 25%. Groundwater exploitation is the most important variable affecting the groundwater level variation. The impact depth of groundwater level fluctuation reaches about 10 m. The impact range where the groundwater level average uplifts 1.86 m is 502.13 km2. The influence direction gradually changes from around the ecological water supplement section to along the Yongding River channel. The groundwater level variation along the tangential direction of the Yongding River is slowing down. The groundwater level would entirely uplift with 170 × 106 m3/year ecological water supplement of the Yongding River and 35.77 × 106 m3/year groundwater mining reduction in the downstream area until 2035

High-Arsenic Groundwater in Paleochannels of the Lower Yellow River, China: Distribution and Genesis Mechanisms

High–arsenic (As) groundwater poses a serious threat to human health. The upper and middle reaches of the Yellow River are well–known areas for the enrichment of high–arsenic groundwater. However, little is known about the distribution characteristics and formation mechanism of high-As groundwater in the lower reach of the Yellow River. There were 203 groundwater samples collected in different groundwater systems of the lower Yellow River for the exploration of its hydrogeochemical characteristics. Results showed that more than 20% of the samples have arsenic concentrations exceeding 10 μg/L. The high-As groundwater was mainly distributed in Late Pleistocene–Holocene aquifers, and the As concentrations in the paleochannels systems (C2 and C4) were significantly higher than that of the paleointerfluve system (C3) and modern Yellow River affected system (C5). The high-As groundwater is characterized by high Fe2+ and NH4+ and low Eh and NO3−, indicating that reductive dissolution of the As–bearing iron oxides is probably the main cause of As release. The arsenic concentrations strikingly showed an increasing tendency as the HCO3− proportion increases, suggesting that HCO3− competitive adsorption may facilitate As mobilization, too. In addition, a Gibbs diagram showed that the evaporation of groundwater could be another significant hydrogeochemical processes, except for the water–rock interaction in the study area. Different sources of aquifer medium and sedimentary structure may be the main reasons for the significant zonation of the As spatial distribution in the lower Yellow River

Hydrogeochemical Characteristics and Processes of Shallow Groundwater in the Yellow River Delta, China

The Yellow River Delta is one of the biggest river deltas in China, and the shallow groundwater plays an important role in the development of the local agriculture and ecosystem. However, people are still unclear about the hydrochemical characteristics and mechanisms of the shallow groundwater. In this study, the authors collected and analyzed 81 groundwater samples from the delta plain and piedmont alluvial plain, and explored the hydrochemical features and causes through Piper diagrams, correlation analysis, ionic ratios, and speciation calculations. The results showed that anions were dominated by Cl and HCO3, the concentration of which was much more than that of SO4 and CO3. The groundwater can be divided into various types, including Na–Cl, Ca–Mg–HCO3, Na–HCO3 and Ca–Mg–Cl. This study tested an alternative method–ionic ratios based on the cumulative frequency distribution to characterizing the hydrochemical groups. According to different ion ratios and hydrogeological conditions, three hydrogeochemical zones with different dominant factors have been determined: Weathering—Fresh Water Zone (Zone I), Evaporation—Saline Water Zone (Zone II), and Seawater Mixing Zone (Zone III). As the calculated saturation index show, the calcite and dolomite are saturated, while the halite and gypsum from Zone I to Zone III tend to be saturated. In addition, cation exchange is an important hydrochemical process in the area, and Zone III experiences inverse ironic exchange. In conclusion, this hydrogeochemical zonation would be favorable for water resource management in the Yellow River Delta

Enrichment of High Arsenic Groundwater Controlled by Hydrogeochemical and Physical Processes in the Hetao Basin, China

Based on 447 samples collected from a shallow aquifer (depths from 0 to 150 m) in the Hetao Basin, Northern China, an integrated hydrogeochemical approach was used in this study to conceptualize the enrichment of high arsenic groundwater in the Hetao Basin. An unconventional method of distinguishing hydrogeochemical and physical processes from a dataset was tested by investigating the cumulative frequency distribution of ionic ratios expressed on a probability scale. By applying cumulative frequency distribution curves to characterize the distribution of ionic ratios throughout the Hetao Basin, hydrogeochemical indicators were obtained that distinguish the series of hydrogeochemical processes that govern groundwater composition. All hydrogeochemical processes can basically be classified as recharge intensity of groundwater, evaporation concentration intensity, and reductive degree controlling the spatial distribution of arsenic. By considering the three processes, we found that the concentration of arsenic was more than 10 μg/L when the (HCO3−+CO32−)/SO42− ratio was over 4.1 (strong reductive area). As the evaporation concentration intensity increased, the median value of arsenic increased from 10.74 to 382.7 μg/L in the median reductive area and rapidly increased from 89.11 to 461.45 μg/L in the strong reductive area. As the river recharge intensity increased (with the intensity index increasing from 0 to 5), the median value of arsenic dropped from 40.2 to 6.8 μg/L in the median reductive area and decreased more markedly from 219.85 to 23.73 μg/L in the strong reductive area. The results provide a new insight into the mechanism of As enrichment in groundwater

Distribution and Origin of High Arsenic and Fluoride in Groundwater of the North Henan Plain

BACKGROUND: The North Henan Plain is located in the middle and lower reaches of the Yellow River, and both high arsenic and fluoride groundwater exist. However, the coexistence mechanism of arsenic and fluoride in this sporadic distribution area is unclear.OBJECTIVES: To investigate the spatial distribution characteristics and formation mechanism of arsenic and fluoride in shallow groundwater in the North Henan Plain.METHODS: 332 groups of shallow groundwater samples were collected and analyzed in the North Henan Plain. Atomic fluorescence spectrometry was used to determine arsenic content, and ion chromatography and inductively coupled plasma emission spectroscopy were used to determine the content of fluoride and other cation-anions. Based on the spatial distribution of arsenic and fluoride, combined with hydrochemical diagrams and factor analysis, three main factors affecting the evolution of groundwater in this area were extracted, and the formation mechanism of high arsenic and high fluoride groundwater in this area was discussed.RESULTS: The concentrations of arsenic and fluoride in groundwater were 0.0001-0.1900mg/L and 0.13-4.94mg/L, respectively. The high-arsenic groundwater was mainly distributed in the vertical depth of 15-80m in the front alluvial-diluvial depression of Taihang Mountain and the Yellow River flood fan. The high-fluoride groundwater was mainly distributed in the vertical depth of 7-100m in the modern channel influence zone of the Yellow River. Evaporation and concentration, mineral dissolution/desorption, and redox environment were the main factors controlling the evolution of groundwater in this area. Fluoride had loads of 0.214 and 0.743 in factor F1 (evaporation and concentration) and F2 (mineral dissolution/desorption), respectively. High concentration of[LM]F appeared in groundwater with low concentration of Ca2+, and the concentration of F was positively correlated with ρ(Na+)/[ρ(Na+) +ρ(Ca2+)]. The strong evaporation and concentration in the modern channel influence zone of the Yellow River contributed to the dissolution of fluorine-containing minerals, and the irrigation of the Yellow River water increased the concentration of Na+ in groundwater, which further enhanced the dissolution. Arsenic had a load of 0.728 in factor F3 (redox environment). Arsenic was positively correlated with Fe2+ and NH4+, and negatively correlated with NO3- and SO42-. The lower Eh corresponds to the higher arsenic concentration. The reductive environment in the front alluvial-diluvial depression of Taihang Mountain and the Yellow River flood fan was favorable for the reductive dissolution of arsenic containing iron oxides/hydroxides, resulting in the formation of the high-arsenic groundwater. The desorption of arsenate/arsenite/fluoride in the form of anions on the mineral surface caused by the increase of pH value was favorable for the coexistence of arsenic and fluoride in groundwater. However, the correlation between arsenic and fluoride in groundwater in this area was not significant. The high concentration of calcium ions in the high arsenic region was not conducive to the enrichment of fluoride. In contrast, the weak reducing conditions in the high fluoride region were not conducive to the dissolution of arsenic-containing iron oxides/hydroxides.CONCLUSIONS:The results clarify the coexistence mechanism of arsenic and fluoride in the North Henan Plain, and enrich the theoretical system of co-contamination of groundwater with high arsenic and fluoride

Distribution Characteristics and Formation Mechanisms of Highly Mineralized Groundwater in the Hetao Plain, Inner Mongolia

As the largest artesian irrigation area in northern China, the Hetao Plain is also one of the major grain-producing areas in China. Meanwhile, there is a large amount of highly mineralized groundwater resulting in the soil salinization and desertification in this region. In addition, this study also uses the traditional hydro-geochemical methods to investigate the spatial evolution characteristics and formation mechanisms of highly mineralized groundwater. The results indicate that there is a large amount of highly mineralized groundwater (salinity > 3 g/L) in the shallow aquifer over the Hetao Plain. As far as the spatial patterns are concerned, there are significant spatial differences. In accordance with the structural, paleogeographic, landform, and hydrogeological conditions, the highly mineralized groundwater in the Hetao Plain can be divided into five zones, namely, the front fan depression, the north bank of the Yellow River, Xishanzui, Hasuhai in the Hubao Plain, and Dalad banner on the south bank of the Yellow River. Among them, the highly mineralized groundwater of Xishanzui exhibits the largest value of the salinity > 10 g/L. The main cations are Mg2+ and Na+, while the main anions are Cl− and SO42−. Moreover, the groundwater in the highly mineralized area contains a large amount of I−. According to the analysis of Piper, Gibbs diagrams of groundwater, the proportion coefficients of various components and the indication of isotope, it can be seen that most of the chemical ions in groundwater in the highly mineralized zone come from evaporation-concentration, which are mainly affected by climate, sedimentary environment, hydrogeological conditions and hydrology. The source of high mineralization in Xishanzui are different from other high mineralization regions, and the highly mineralized groundwater in Xishanzui is formed by the infestation of deep underground salt brine. These results can provide scientific basis for the rational allocation of regional water resources and the promotion of water resources development and utilization