[AHW20-P25] Observation for the groundwater inflow to the lagoons connected to Lake Biwa
Keywords:Groundwater inflow, Connected lagoons, Lake Biwa
The field campaign was conducted in December 2017 for two lagoons (Noda-Numa and Hasu-Ike) located on northeastern shore of Lake Biwa. The volume of inflow and outflow, water temperature, electric conductivity, chlorophyll-a and radon (222Rn) concentration were measured in these lagoons. 222Rn is a radioactive element of uranium (238U) series with 3.8 day of half-life. 222Rn is a useful tracer of groundwater discharge because it generally enriched in groundwater than surface water. Water samples were collected at the inlet, outlet and near the center of the lagoons and natural springs and groundwater wells around the lagoons. Also bottom sediment samples were collected in the lagoons. These samples have been analyzed for nutrients (nitrogen, phosphorus and silicate) and stable isotope ratios of oxygen and hydrogen (δ18O and δD) for water.
δ18O and δD for water were plotted on the different meteoric lines between Noda-Numa an Hasu-Ike. This result suggests these water are originated from different watersheds with different groundwater flow systems. Besides, these values were lower at the inlet than the center and outlet of the lagoons and was lowest in the groundwater around the lagoons. These results suggest the presence of groundwater inflow to these lagoons and the signal decreased from the inlet to the outlet.