Hydrochemistry characteristics and evolution of karst spring groundwater system in Jinan

Jinan is the capital city of Shandong Province, famous for the landscape of springs in China, for spring is of unique nature in both quantity and quality. It is an important carrier of Jinan’s profound historical and cultural connotation, and an important part of a historical and cultural city. The formation of spring in Jinan is influenced by topography and karst hydrogeological condition. Its unique karst geological conditions provide a space for pooling and flowing of groundwater. The karst landforms well develop over the mountainous area in the south, which accumulates a large amount of precipitation that subsequently becomes karst groundwater. In the north, intrusive igneous rocks with low permeability forms relatively no-flow boundary. Therefore, the karst groundwater flows along bedding planes and discharge as a number of springs in the city. In terms of genesis, the springs in Jinan belong to the erosion-contact type. In this paper, the research area is the Baotu spring hydrogeology unit. The chemistry and environment characteristics of the karst groundwater in Baotu spring area were analyzed, and the regional distribution characteristics, time variation and mutual transformation relationship of each chemical index were revealed. The current situation and evolution of groundwater environment in Jinan area were studied. Result shows that the hydrochemical types of karst groundwater in Jinan from southeast to northwest along the flow field are，HCO3?SO4-Ca→HCO3?SO4-Ca?Mg→HCO3-Ca→HCO3-Ca?Mg. In terms of karst groundwater environment, the concentration of NO〖_3^-〗 in groundwater has generally increased. The Total Hardness and TDS content exceed the groundwater quality standard of class Ⅲ. According to the investigation, the main cause of deterioration of the karst groundwater environment is the extensive use of chemical fertilizers, pesticides and the discharge of pollutants in agricultural planting areas in the southern mountainous areas.