3:30 PM - 4:45 PM
[AHW16-P17] Assessment of the spatial distribution of submarine groundwater and associated nutrients discharge along the Ikuchi Island coastline, Seto Inland Sea, Japan
Keywords:Submarine groundwater discharge (SGD), Radon, Nutrients , Ikuchi Island
To analyze the spatial distribution of SGD and associated nutrients, we performed a continuous 222Rn and conductivity (EC) monitoring survey on a boat along the shoreline during December 22th, 2015. The total SGD flux was estimated to be 8.60×106 m3 yr-1 based on the 222Rn mass balance, which was in reasonable agreement with results obtained from the Darcy’s law (8.53×106m3 yr-1) and water balance calculation (8.55×106 m3 yr-1). A strong pattern in the spatial distribution of SGD was observed, with the highest values (>2.5 cm d-1) located along the western part of the island due to the steepest topography and much lower population. The results from a nutrient analysis of the groundwater indicated that the associated nutrient fluxes loading through the SGD pathway were 109.6×106, 2.980×106, and 439.8×106 g yr-1 for DIN, DIP and DSi, respectively, which were comparable to or even higher than the levels observed in the local streams. Therefore, adequate attention should be paid to the importance of SGD as one source of nutrients during the eutrophication controls process in this area.