Hydrogeochemistry Characteristics of Groundwater in the Nandong Karst Water System, China

Abstract

The hydrogeochemical characteristics of groundwater are an important element in the study of the spatial and temporal variation of groundwater resources, which is crucial to water resources utilization, ecological environmental protection, and human development. Water samples were collected at eight observation of Nandong Karst Water System (NKWS) sites in each month of 2019, and the main ions and isotopes of the water samples were examined. The hydrogeochemistry characteristics of groundwater and its differences with surface water were explored by using the methods of multivariate statistics, Gibbs model. Results showed that the water chemistry types of groundwater were mainly HCO3 – Ca and HCO3 –Ca· Mg. The analysis of hydrogen and oxygen isotope showed that the initial recharge source of surface water and groundwater were atmospheric precipitation, and the measured hydrogen and oxygen isotopes of surface water were heavier due to the strong evaporation effect. The natural and anthropogenic processes contributed to the chemical composition of surface water and groundwater in the study area. However, the main factor affecting the quality of surface water and groundwater was the input of anthropogenic contaminants. In terms of natural factors, the main chemical ions of surface water and groundwater were mainly controlled by water–rock action originating from weathering and hydrolysis of rocks and soils. Ca2+, Mg2+, and HCO− 3 mainly originated from natural dissolution of carbonate rocks. K+, Na+, SO2− 4, and Cl− were partly from atmospheric precipitation. For human activities, Na+ and Cl− were partly from domestic water for local residents. SO2− 4 in surface water mainly came from mining. NO− 3 in groundwater mainly came from chemical fertilizers, and NO− 3 in surface water were mainly from human waste and domestic sewage.

Nonenzymatic hydrolysis of 1,2:3,4‐diepoxybutane: A kinetic study including pH, temperature, and ion effects

“…The most prevalent anion (nucleophile) in the surface water, groundwater, and soil water is HCO 3 − and its typical concentration ranges between 100 and 1000 mg L −1 (0.0016–0.016 M). The other major anions, SO 4 2− , NO 3 − , Cl − , H 2 PO 4 − /HPO 4 2− , are present at the concentrations below 0.005 M, 39–42 which are lower than those analyzed in Table 3. Also, SO 4 2− and NO 3 − exhibit very low basicity as they derive from relatively strong acids.…”

“…In addition, the pH of surface water, groundwater, and soil water (pH 4-9) falls into the region of the neutral DEB hydrolysis (Figure 2), making the pH and temperature the crucial factors governing the compound stability. 39,[41][42][43][44] The results of our prediction shown in Table 4 reveal that depending on the temperature of fresh waters that are met in the environment, the halflife of DEB ranges from 2 days at 30 • C to 31 days at 0 • C. Therefore, a complete disappearance of DEB, expressed as 7 half-lives, will take from 14 to 218 days, respectively. It is here worth noting that due to the low molecular weight (86 Da) and good hydrophilic-lipophilic balance (logP of −0.4), DEB easily permeates biological membranes and distributes throughout the body, for example, to the aqueous humor of the eye.…”

“…Therefore, it can be anticipated that the general catalysis from anions in natural fresh waters will have negligible contribution into the DEB hydrolysis. In addition, the pH of surface water, groundwater, and soil water (pH 4–9) falls into the region of the neutral DEB hydrolysis (Figure 2), making the pH and temperature the crucial factors governing the compound stability 39,41–44 . The results of our prediction shown in Table 4 reveal that depending on the temperature of fresh waters that are met in the environment, the half‐life of DEB ranges from 2 days at 30°C to 31 days at 0°C.…”

“…Also, SO 4 2− and NO 3 − exhibit very low basicity as they derive from relatively strong acids. In addition, CO 3 2− anions, which rendered the strongest acceleration of the DEB hydrolysis, are present in the mentioned waters at submicromolar concentrations 39–42 . Therefore, it can be anticipated that the general catalysis from anions in natural fresh waters will have negligible contribution into the DEB hydrolysis.…”

“…In addition, CO 3 2− anions, which rendered the strongest acceleration of the DEB hydrolysis, are present in the mentioned waters at submicromolar concentrations. [39][40][41][42] Therefore, it can be TA B L E 3 Contribution of the specific and general catalysis to the hydrolysis of 1,2:3,4-diepoxybutane (DEB) in the acetate, phosphate, and carbonate buffers of different pH and concentration at 60 • C. anticipated that the general catalysis from anions in natural fresh waters will have negligible contribution into the DEB hydrolysis. In addition, the pH of surface water, groundwater, and soil water (pH 4-9) falls into the region of the neutral DEB hydrolysis (Figure 2), making the pH and temperature the crucial factors governing the compound stability.…”