Environmental Imprints on the Temporal Changes of the Chemistry of Geothermal Water from Some Low-Temperature Geothermal Fields in the North China Plain

Abstract

The North China Plain, located to the north of the Yellow River, is a great sedimentary basin with extensive accumulation of Tertiary and Quaternary deposits, that region contains more than 30 low-temperature geothermal sites. The total areas of all discovered thermal anomalies are about 7,000 km2. Only a few sites have been exploited such as in Beijing, Xiaotangshan, Tianjin, Tanggu, Xiongxian, Shenzhou, etc.. Depths of the geothermal wells range from 500 m to 2,000 m, and the wellhead water temperatures vary from 45Åé to 75Å

é. The chemical composition and temporal changes of the lowtemperature water in the North China Plain are affected by the annual climatic environment, the artificial environment, and the paleoclimatic environment. In Tanggu areas, the temporal changes in extraction amount of hot water, the rate of land subsidence and the fluoride contents, show a strong correlation with each other. In Xiaotangshan areas, the chemical composition of hot waters also show relation with the extraction amount. The chemical composition of hot water in Tanggu areas is positively related to the annual precipitation amount. In Xiaotangshan areas, the chemistry changes with a lag behind that of precipitation of about 4 months. Based on the 14C and oxygen isotopic data from hot water in North China Plain, a curve has been completed showing the paleoclimatic dry-cold or wet-warm changes since last glacial period. Understanding the effect of the regional environment on the chemistry of geothermal water would certainly be a great help to establish the models of geothermal field and of manage it properly for sustainable development.