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[AHW18-12] Spatial evaluation of submarine groundwater discharge (SGD) by mass balances approach on an island scale
Keywords:submarine groundwater discharge, spatial variation, mass balances approach, island scale
Submarine groundwater discharge (SGD) is defined as subsurface water flow at continental margins from the seabed to the coastal ocean. As a component of the hydrological cycle, SGD plays an important role in the overall coastal water budget, which can rival or even exceed surface runoff in some coastal areas. In addition, because it often contains higher nutrients than river water, SGD delivers comparatively large quantities of nutrients to coastal ecosystems. In the present research, we aimed to examine the spatial variation of SGD based on mass balances approach on an island scale.
The study area is Ikuchijima Island in Seto Inland Sea, southern Japan. The regional climate is mild, with an annual mean precipitation of 1,100 mm and temperature of 15.6 °C. The whole island is characterized by steep slopes and is widely covered by citrus farms with more than 40% of the island. To evaluate the spatial distribution of SGD on an island scale, we performed a radon (222Rn) and nutrient monitoring survey along the coastline of Ikuchijima Island. Large variability in SGD was observed, with significant discharges seen in areas of steeper topography and much lower discharges from low-lying areas. Topographic influences are likely to be the major driver of spatial variability in SGD. Based on a 222Rn mass balance model, the SGD rates were estimated to range from 8.38 cm d-1 to 17.02 cm d-1, with an average of 12.98 cm d-1. Estimated nutrient loading through the SGD were comparable to or even higher than that from local streams. It suggests SGD is an important source of nutrients to coastal ecosystems in the area.
Acknowledgments
This research was supported by JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito) and Fostering Joint International Research (A) (No. 20KK0262, PI: Mitsuyo Saito).
The study area is Ikuchijima Island in Seto Inland Sea, southern Japan. The regional climate is mild, with an annual mean precipitation of 1,100 mm and temperature of 15.6 °C. The whole island is characterized by steep slopes and is widely covered by citrus farms with more than 40% of the island. To evaluate the spatial distribution of SGD on an island scale, we performed a radon (222Rn) and nutrient monitoring survey along the coastline of Ikuchijima Island. Large variability in SGD was observed, with significant discharges seen in areas of steeper topography and much lower discharges from low-lying areas. Topographic influences are likely to be the major driver of spatial variability in SGD. Based on a 222Rn mass balance model, the SGD rates were estimated to range from 8.38 cm d-1 to 17.02 cm d-1, with an average of 12.98 cm d-1. Estimated nutrient loading through the SGD were comparable to or even higher than that from local streams. It suggests SGD is an important source of nutrients to coastal ecosystems in the area.
Acknowledgments
This research was supported by JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito) and Fostering Joint International Research (A) (No. 20KK0262, PI: Mitsuyo Saito).