Chemical Characteristics and Evolutionary Patterns of Groundwater in the Daqing River Plain Area of Haihe Basin

BACKGROUND: Groundwater is closely related to surface water. Groundwater over-extraction has triggered a series of negative ecological effects in the Daqing River basin. The evolution of groundwater chemical characteristics is influenced by both natural and anthropogenic factors. The analysis of groundwater chemical characteristics can indicate the meteorological-hydrological and water-rock interaction during groundwater runoff, thus reflecting the groundwater circulation path, groundwater system characteristics and evolution laws, etc. It also helps to monitor groundwater dynamics and prevent the occurrence of groundwater pollution.OBJECTIVES: To clarify the chemical characteristics and evolution of groundwater in the plain area of the Daqing River basin, which will be important for the rational development and utilization of water resources in the basin. METHODS: 47 water samples from the shallow aquifer groups and 32 water samples from the deep aquifer groups were collected to analyze the main anions（Cl-, SO■, NO■） and cations(K+, Na+, Ca2+, Mg2+). The water chemistry characteristics and evolution laws were studied by using the water chemistry type, Gibbs model and ion ratio relationship. On-site portable water quality analyzer（HACH-HQ40d） was used to test pH（accuracy 0.01）, total dissolved solids（TDS, accuracy 0.01） and other parameters, and groundwater samples were collected after the indicators were stabilized. All samples were sent to the laboratory at low temperature and stored in a refrigerator at 4℃, and groundwater alkalinity was determined by titration on the same day. Seven days later, the samples were sent to the Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences for testing of major anions（Cl-, SO■, NO■） and major cations(K+, Na+, Ca2+, Mg2+) using inductively coupled plasma-optical emission spectrometry（iCAP6300）. The anion and cation charge balance error was less than 5%, and the anion and cation test accuracy was 0.01mg/L.RESULTS: The test results showed that the largest deviation was in the water sample from Hanbao Village, Liu Lizhuang Town, Anxin County, Baoding City, Hebei Province, which was from the shallow aquifer groups, and the maximum TDS reached 6015.00mg/L. The TDS of the shallow aquifer groups ranged from 254.10 to 6015.00mg/L, with an average of 664.14mg/L, a large coefficient of variation and a large variation in TDS, indicating that the shallow aquifer groups were affected by meteor