Hydrochemical and isotopic characteristics of springs in Beijing and their implications

Field tests on temperature, dissolved oxygen, electric conductivity, redox potential, values of pH and total dissolved solid of spring waters were carried out in Beijing, and chemical and isotopic components in waters such as K+, Na+, Ca2+, Mg2+, Cl-, SO42-, HCO32-, NO3-, D, 18O, Sr2+ and 87Sr/86Sr were also tested in labs. Springs in Beijing were classified into four types based on their formation mechanisms, and a comparative analysis between data obtained during this investigation and those obtained during the past 30 years were also made. The results indicate that most of the second kind springs and 60% of the first kind springs existent in early 1980s have disappeared, runoffs from the survived thirteen springs have decreased sharply, which is mainly attributed to the decreasing precipitation and the exploitation of groundwater. Quality analysis of spring waters obtained shows that qualities of most spring waters are good, and physical and chemical indexes of these waters have changed slightly compared with those 30 years ago, which implies that qualities of these spring waters have not been obviously impacted by human activities. These spring waters only participate in shallow groundwater circulation, and detention of these waters is comparatively short, suggesting strong renewability. These springs are recharged by infiltration precipitation, and have close dynamic interconnections with other shallow groundwater. Sr ions in spring waters are derived from weathering of carbonate rocks.