Geochemical tracers for the groundwater and streams in mountainous regions of central Taiwan
Date Issued
2015
Date
2015
Author(s)
Chuang, Jin-Lun
Abstract
Total amount of natural groundwater resources in Taiwan has been estimated as 17,332 Mm3 of which ca. 72% is distributed in mountainous region, and less than 30% distributed in plain area. Therefore, mountainous region is a potential area which contains abundant water resources in Taiwan. We expect to distinguish the characters of different groundwater aquifers and the mixing relationship between groundwater and stream which could help to build hydrological circulating model of groundwater in mountainous region of Taiwan and offer important information for managing water resources. In this study, 11 groundwater samples are collected from the monitoring wells of the CGS funded project (An integrated investigation of groundwater resources in Taiwan mountainous area: Phase I) and, 20 river samples in Dajia Basin, Liwu Basin, Meilun Basin and Hualien Basin are also collected. In addition to the major ions and hydrogen/oxygen isotopes of water samples, we applied noble gases (helium, radon) and strontium isotopic ratio as tracers of groundwater flow and sources in study area. Most of the hydrogen and oxygen isotopic values fall on the local meteoric water line of Taiwan. It revealed that groundwater source in studied area is mainly from the precipitation. Besides, the geochemical data show that the groundwater and stream water samples in this study are mostly belonging to the category of Ca(HCO3)2 type and NaHCO3 type. It appears that the water compositions are mainly controlled by both processes of carbonate dissolution and silicate weathering. Furthermore, local hydro-geological condition plays an important role to differentiate the geochemical characters of groundwater in different aquifers. If the hydro-geological conditions are similar, different groundwater aquifers would show similar geochemical characters. According to the geochemical characters, we can differentiate four types of groundwater aquifer: (1) recharging by rainfall and runoff infiltration quickly, (2) recharging quickly and effecting by radiogenic regolith in situ (3) recharging slowly with more aquitards, and (4) deeper groundwater migrating along fractures or fault in studied areas. Furthermore, we can suggest that the results of terrigenic helium-4 concentration, dissolved radon concentration, and tritium-helium dating are useful tools to distinguish geochemical characters of groundwater from different aquifers. The results show that the influx of tributaries did not play an important role for the main stram in Liwu Basin. We obtain similar results of groundwater discharging percent into stream by different geochemical tracers (radon and strontium isotopic ratio) estimation. We received a relative low groundwater discharge percent of about 9.72~12.7% to stream base flow at Liwu river (LW-03 site), due to high amount of rainfall occurred in 2013. Nevertheless, we got a much higher groundwater discharge percent of about 43.5~45.2% into stream in 2014, which may be due to less rainfall during this year. Furthermore, the influx of tributaries may be more important for Dajia Basin, because we obtained different fractions of groundwater discharging to stream estimating by radon and strontium isotopic ratios. There was about 3.00% and 58.1% groundwater discharged to Dajia river (DJ-3 site) by radon and strontium isotopic ratios respectively. At DJ-8 site, there was 0.30% and 54.7% groundwater contributed Dajia river by radon and strontium isotopic ratios respectively. Above of all, this study reveals that the noble gases are considered as sensitive tracers for differentiating the characteristics of groundwater aquifer in mountainous region of Taiwan due to their unique geochemical characteristics. Besides, dissolved radon and strontium isotopic ratio are very useful tracers for understanding the relationship between groundwater and stream in the basins if there are less tributaries. The tracers could be used for others basin in Taiwan, and offer essential information, helping to build hydrological circulating model of groundwater in mountainous region of Taiwan.
Subjects
Geochemical tracers
groundwater in mountainous regions
noble gas
strontium isotopic ratio
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-R01224110-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):05f4e8aa49cd2da575a7c9b34dc1a64a