[Hydrochemical Characteristics and Formation Mechanism of Groundwater in the Western Region of Hepu Basin, Beihai City].

Beihai City is a typical coastal city where groundwater provides a strong support for social and economic development. Studies on the hydrochemical characteristics and formation mechanism in Beihai City play an important role in the scientific management of water resources and coastal ecological environment protection. In this study, we revealed the main hydrogeochemical processes controlling groundwater quality by means of groundwater survey and water sample collection in the western region of Hepu Basin, Beihai City, combined with hydrochemistry and isotope theories and methods. The results showed that groundwater had the remarkable features of low pH value and low mineralization degree. For pore water, hydrochemistry type by primarily NO3 type water and concentrations of Na+ and Cl- were modestly increased along the flow path. Ca-HCO3, Ca-Cl·HCO3, Ca·Na-HCO3, and Na-Cl·HCO3 types were predominant in fissure water. The groundwater was of meteoric origin, hydrogeochemical evolutions were mainly affected by water-rock interactions, cation exchange, and anthropogenic activities. Na+, K+, and Cl- were mainly derived from evaporite and silicate rocks; Ca2+, Mg2+, HCO3-, and SO42- were from carbonatite and evaporite; and NO3- principally arose from anthropogenic activities. This study suggests that the groundwater pollution prevention and control should be carried out as soon as possible in the area where the NO3 type water occurs to avoid the further deterioration of water quality.

[Comprehensive Classification Method of Urban Water by Remote Sensing Based on High-Resolution Images].

Urban water is a significant part of the urban ecosystem. Therefore, a comprehensive evaluation method of the water environment was proposed based on domestic high-resolution images. The relationships between the spectral characteristics and water quality parameters of urban water were analyzed based on sampling in Nanjing, Wuxi, Changzhou, and Yangzhou from 2017 to 2019. An index named the U-FUI (urban Forel-Ule index) suitable for urban water based on GF-2 images was proposed to achieve the classification of urban water on the basis of the international standard chroma conversion model and the Forel-Ule index. Independent verification data showed that the recognition accuracy of the classification model could reach 72%. The results indicated that urban water can be classified into six classes from Ⅰ to Ⅵ, which represent water colors of blue, light green, dark green, yellow, yellowish brown, and dark grey, respectively, according to the U-FUI. Among them, the water quality of U-FUI Ⅰ water is good, but is rarely distributed in urban water. The concentrations of chlorophyll-a in U-FUI Ⅱ-Ⅲ water are higher than those of the other classes; the concentrations of total suspended solids, particularly inorganic suspended solids, of U-FUI Ⅳ-Ⅴ water are higher than those of the other classes; and the water quality of U-FUI Ⅵ water is poor and the water quality parameters are different from those of the other classes. Meanwhile, the method was successfully applied to the GF-2 image of Nanjing on April 9, 2018. The results showed that the urban water in Nanjing is mainly composed of U-FUI Ⅱ-Ⅳ water, whereas the distribution of U-FUI Ⅰ, Ⅴ, and Ⅵ water is lower in the city. The spatial distribution characteristics were consistent with the results of in-situ sampling in the same period.

[Hydrogeochemical Investigations of Groundwater in the Lingbei Area, Leizhou Peninsula].

Groundwater is an important source of water supply in the Leizhou Peninsula. In August 2018, five surface water samples, 18 shallow pore water samples, 14 middle-deep pore water samples, and 27 pore fissure water samples were collected in the Lingbei area, the northern part of the Leizhou Peninsula. Major ion concentrations, as well as H, O isotope composition (of δ18O and δ2H) were analyzed. The results show that groundwater pH values, total hardness, concentrations of K+, TDS, Cl-, and SO42- are low, while H2SiO3(aq) and NO3- concentrations are relatively high. For pores and fissures water, hydrochemical types are mainly Mg-Ca-HCO3, Mg-Ca-HCO3-Cl, and Cl- loadings are significantly increased along the flow path. Ca-Cl, Na-Ca-HCO3-Cl, and Na-Ca-Mg-HCO3-Cl types predominate in shallow pore water. For middle-deep pore water, the types are primarily Mg-Ca-HCO3, Na-Ca-Mg-HCO3, K-Na-HCO3-SO4, and concentrations of K+, Na+, Cl-, and SO42- are modestly increased along the flow path. We find that the groundwater is of meteoric origin, groundwater Cl- and Na+ originate from marine atmospheric precipitation, Mg+, Ca2+, and HCO3- are mainly derived from silicate weathering, and NO3- principally arises from chemical fertilizer. Shallow pore water and fissure pore water are affected by evaporation concentration, whereas cation exchange is important for middle-deep pore water. The milligram equivalent ratio of nitrate in groundwater reaches 28.3%. After taking into account the nitrate, 50.85% of the sampling water is NO3 type, and displays a pollution trend. Our results contribute to the sustainable utilization of groundwater in the study area and other similar areas.