11:15 AM - 11:30 AM
[ACG42-07] Estimating of the environment of Submarine Groundwater Discharge(SGD) in Otsuchi Bay and Funakoshi Bay, using carbon stable isotope of shell of bivalves.
Keywords:submarine groundwater discharge(SGD), carbon stable isotope, Pacific oyster(Crassostrea gigas), mussel(Mytilus coruscus), Otsuchi Bay, Funakoshi Bay
The average 222Rn concentrations were 228.9±22.4 (Bq/m3) in Otsuchi Bay and 115.0±18.4 (Bq/m3) in Funakoshi Bay, respectively. The contribution rates of SGD in coastal areas estimated from δ13CDIC were 17.4±5.7% in Otsuchi Bay, and 9.0±1.6% in Funakoshi Bay, and those in offshore area were from 0.2±0.3% to 4.0±0.6% in Otsuchi Bay. The contribution rates of SGD in coastal areas estimated from δ13CSHELL of C. gigas and M. coruscus were 21.9±2.4 and 10.5±11.4% in Otuchi Bay, respectively, and 3.2±3.3 and 6.9±8.8% in Funakoshi Bay, respectively. Thus, the contribution rates estimated from the bivalves in Otsuchi Bay are higher than those in Funakoshi Bay. The contribution rates of SGD in offshore area estimated from δ13CSHELL of M. coruscus was from 0±10.5% to 12.4±2.8% in Otsuchi Bay. These results suggested that SGD contributes to the biological products in not only coastal areas but also offshore area in Otsuchi Bay. However, we did not divide the source of freshwater into SGD and riverine water. It is necessary to develop the three source model to evaluate the contribution rate of SGD.