Genetic analysis and assessment of hydrochemical characteristics of waters in Laizhou-Pingdu area, Shandong

Groundwater (or phreatic water) and surface water are important water sources for industry and household in Laizhou-Pingdu area, Shandong, East China. To investigate the hydrochemical characteristics and water quality in this region, 39 groundwater samples and 41 surface water samples were collected systematically. Their hydrochemical characteristics and influencing factors were analyzed using mathematical statistics, the Piper trilinear diagrams, Gibbs diagrams, and ion ratios. In addition, a comprehensive water quality was evaluated using water quality index, sodium adsorption ratio, and sodium percentage methods for drinking and irrigation water in this region. The results show that both groundwater and surface water are weakly alkaline. The major hydrochemical types of groundwater in the southern shallow hilly area are HCO₃⁻·SO₄²⁻-Ca²⁺·M²⁺ and HCO₃⁻·SO₄²⁻·Cl⁻-Ca²⁺·Mg²⁺. In the coastal plain, groundwater is primarily Cl⁻-Na⁺ and Cl⁻-Ca²⁺, while surface water is mainly SO₄²⁻-Na⁺·Ca²⁺ and HCO₃⁻·SO₄²⁻-Na⁺·Ca²⁺·Mg²⁺. Rock weathering is the main factor on the hydrochemical characteristics of surface water and groundwater in the southern shallow hilly area, whereas groundwater in the coastal plain is influenced by evaporation concentration-seawater processes. Human activities have a certain impact on hydrochemical components, and the extremely high value of Cl⁻ in coastal plain groundwater indicate that seawater intrusion in some areas is intensified. The use of nitrogen fertilizers in agricultural activities and sewage discharge are the primary causes of NO₃⁻ pollution, which is not suitable for direct drinking. The evaluation of irrigation water quality show that in overall, surface water and groundwater in the southern shallow hilly area have good quality, and reasonable use for irrigation will not cause salinity or alkalinity damage to plants and soil. However, groundwater quality in the coastal plain is relatively poor, and introducing high-quality surface water is advised.