Groundwater Dynamics near the Saltwater–Freshwater Interface in an Island of Seto Inland Sea
Author:
Tomozawa Yusuke1, Onodera Shin-ichi1ORCID, Saito Mitsuyo1ORCID, Asai Kazuyoshi2
Affiliation:
1. Graduate School of Advanced Science and Engineering, Hiroshima University, 1-7-1 Kagamiyama, Higashihiroshima 739-8521, Japan 2. Geo-Science Laboratory Co., Ltd., 1-608, Ueda Honmachi, Tenpaku-ku, Nagoya 468-0007, Japan
Abstract
Groundwater dynamics near the saltwater–freshwater interface were investigated in an island of the Seto Inland Sea, using multiple tracers (δD, δ18O, Cl−, SF6, and 14C) at two coastal groundwater monitoring wells at depths of 10–40 m. The groundwater recharge area and age were also estimated using these tracers. Additionally, bedrock groundwater at a depth of 40 m at the 2.7 m altitude was brackish and considered to be near the saltwater–freshwater interface, and a mixture of seawater (2–3.5%) and fresh groundwater (97–98%) was estimated by the Cl− concentration. Based on the δ18O of fresh groundwater estimated from the seawater mixing ratio, the recharge area was estimated to range from near to above the summit; however, this region is unlikely to be the actual recharge area, as the groundwater may be old freshwater that was recharged during a previously colder period. Groundwater dating using SF6 and 14C suggests that the fresh groundwater originated during the last glacial period (assumed 20,000 years ago) and that the 40 m deep bedrock groundwater is a mixture of old water (0–28%), 30 m deep groundwater (76–100%), and stagnant seawater (1–3%).
Subject
Water Science and Technology,Aquatic Science,Geography, Planning and Development,Biochemistry
Reference47 articles.
1. Onodera, S., Saito, M., and Kitaoka, K. (2018). Water Environment in Seto Inland Sea Catchments: Sato Water, Kibito Publishing. (In Japanese). 2. Groundwater vulnerability on small islands;Holding;Nat. Clim. Change,2016 3. Species and potential sources of phosphorus in groundwater in and around Mataram City, Lombok Island, Indonesia;Ioka;SN Appl. Sci.,2021 4. Impact of citrus agriculture on the quality of water resource in a small steep Island, Seto Inland Sea, Japan;Kimbi;Int. J. Geomate,2021 5. Kimbi, S., Onodera, S., Ishida, T., Saito, M., Tamura, M., Tomozawa, Y., and Nagasaka, I. (2022). Nitrate contamination in groundwater: Evaluating the effects of demographic aging and depopulation in an island with intensive citrus cultivation. Water, 14.
|
|