14:15 〜 14:30
[AHW22-12] Investigation of Submarine Groundwater Discharge in Northwestern Coastal Taiwan through Radium Isotopes
キーワード：Submarine groundwater discharge, Radium apparent age, Source of groundwater, Radium isotopes, Stable isotopes, Taoyuan-Chungli Tableland
Characterization of submarine groundwater discharge (SGD) is complex due to that it is controlled not only by the permeability of seabed/coastal aquifer, but also by several driving forces, such as tidal pumping, the nearshore circulation, the saline circulation, the variation of seasonal discharge. Therefore, the understanding of seasonal/temporal variation of SGD in the hydrological contrasting conditions are important. This study collected water samples around northwestern coastal Taiwan to analysis 223Ra and 224Raex, δ18O, and δD in the dry season (May-October) and the wet season (November-April) in the serious drought year (2021) of Taiwan. A couple of short-lived radium isotopes (223Ra and 224Raex) in four stations was applied to calculated the radium apparent age in the coastal seawater. The apparent age in the dry season (6.48 ± 2.63 days) was slightly higher than that in the wet season (4.69 ± 2.40 days). Based on the mass balance model of 224Raex, the SGD in wet season and dry season were 848.85 ± 181.70 and 314.16 ± 69.09 cm d-1, respectively.
In addition, the good correlation of stable isotopes (δ18O and δD) of groundwater for the shallow groundwater (≦ 20 m) and the deep groundwater (> 20 m) (R2 = 0.95, n = 11) as well as the correlation between 224Raex and 223Ra (224Raex = 31.81 × 223Ra - 3.42, R2 = 0.87, n = 11 for the shallow groundwater; 224Raex = 26.91 × 223Ra + 4.98, R2 = 0.95, n = 5 for deep groundwater) shows that they have the similar sources, which probably originated the deep aquifer. The high quantities of SGD during the abnormal drought conditions in this area were higher than those in the Asia coastal area, demonstrating the high potential of SGD and indicating the deep groundwater, acting as regional flow, plays an important role to contribute SGD in the coastal area. These results contribute to make a better decision in the management of water resources.
In addition, the good correlation of stable isotopes (δ18O and δD) of groundwater for the shallow groundwater (≦ 20 m) and the deep groundwater (> 20 m) (R2 = 0.95, n = 11) as well as the correlation between 224Raex and 223Ra (224Raex = 31.81 × 223Ra - 3.42, R2 = 0.87, n = 11 for the shallow groundwater; 224Raex = 26.91 × 223Ra + 4.98, R2 = 0.95, n = 5 for deep groundwater) shows that they have the similar sources, which probably originated the deep aquifer. The high quantities of SGD during the abnormal drought conditions in this area were higher than those in the Asia coastal area, demonstrating the high potential of SGD and indicating the deep groundwater, acting as regional flow, plays an important role to contribute SGD in the coastal area. These results contribute to make a better decision in the management of water resources.