Taking advantage of the convenient facilities in the Dongshan Branch, the subterranean Estuary Monitoring system (SEMS) includes 4 permanent monitoring wells, whose obvious aquifers lie at 85.9 to 100.30 meter, 50.50-59 meter, 37.6- 3.3 meter, and 19.7-19.8 meter separately; and some convenient equipment, such as BUOY automatically liting system, OS305 Plus CTD, and Sampling and data integration system. Long-term observations can be carried out to monitor groundwater temperature, salinity, water level, dissolved oxygen, oxidation/reduction potential, dissolved inorganic carbon, total alkalinity, nutrients, and natural submarine groundwater discharge tracers, such as Ra and Rn. The aim of SEMS is to study the effect of climate change on the interaction of groundwater and seawater in subterranean estuaries and associated impacts on biogeochemical cycles of elements in the coastal ocean.