Estimating SGD flux in the Pingtung Plain coastal area using Radon and Radium isotopes

• Main Authors: Yao-Li Chang, 張堯禮
• Other Authors: Chih-Chieh Su
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/37498123863131171081

碩士 === 國立臺灣大學 === 海洋研究所 === 103 === This study aims to estimate the submarine groundwater discharge (SGD) flux in Pingtung coastal zone with radioisotope tracers. For SGD fluxes estimation, radon and radium isotopes in river and estuary waters were measured in dry and wet seasons, and coastal investigations were conducted by using Ocean Researcher 3 in May (OR3-1768) and September (OR3-1799) 2014. Delayed Coincidence Counter (RaDeCC) and RAD7 instruments were used for measuring the short-lived radium isotopes (224Ra, 223Ra) and 222Rn. The analysis results of river and spring samples in Pingtung Plain showed the variation of radon-in-water activities may reflect short-term regional rainfall events. In wet season, radon-in-water activities in shallow groundwater can reached up to 26000 dpm/100 L or more. In contrast, the 224Ra activities were less than 4 dpm/100 L. Owing to radium isotopes activities are controlled by the dissolution time and lithology of aquifer, activities of long-lived radionuclides in rivers and springs were generally higher than the short-lived radionuclides. In the downstream of Gaoping River, 224Ra activities are significantly increased with rainfall which implied the deep groundwater input by the rise of water table. Marine investigation results showed the rainfall in plain area will increased activities of radon-in-water and 224Ra in surface waters by 1.5 times, but on the other hand, the variation of 226Ra activities in coastal bottom waters will be reflected on precipitation in mountain range. In May 2014, the main SGD output occurred in the bottom layer, the estimated flux of SGD is 26890 m3/day, which is five times higher than the surface flux. However, the SGD output in September is mainly on the surface layer, and the flux (981295 m3/day) is eight times higher than the bottom.