Tracing submarine groundwater discharge into Dapeng Bay Southwestern Taiwan by Ra isotopes

• Main Authors: Jun-Chen Huang, 黃浚宸
• Other Authors: 蘇志杰
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/6r2w6e

碩士 === 國立臺灣大學 === 海洋研究所 === 106 === River discharge is a major pathway for transporting terrestrial materials to the ocean, including nutrients and trace elements, and their fluxes have been widely studied. Although not as obvious as river, the underground flow across the seabed to the coastal ocean, referred to as submarine groundwater discharge (SGD), now has been recognized as a significant contribution to the coastal ocean. However, little is known and studied about SGD in Taiwan. The Dapeng Bay, located at the Pingtung Plain where is characterized by abundant groundwater resource, is a shallow lagoon with only one outlet for exchanging water with the ocean. Although the water in the Dapeng Bay mainly consists of seawater with domestic, fishing, and agricultural waste waters, the reported hydrogeological conditions in the Pingtung Plain indicate a potential of SGD in the Dapeng Bay. Therefore, this study purposed to investigate SGD in the Dapeng Bay by using naturally occurring radionuclides, Radium (224Ra, 228Ra, and 226Ra), as tracers and further to understand its seasonal variation. Our results show that high Ra water was observed at the inner part of Dapeng Bay. The high activity at high tide and low one at low tide indicates that the study area is highly influenced by tidal activity. As well, Ra activities in the Dapeng Bay water is much higher than offshore seawater, indicating the possibility of SGD input. Based on mass balance model of Ra, we estimated the SGD flux is 9.18×104-9.16×105 m3/day, accounting for 1~9.5 % of the total volume of the Dapeng Bay.