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| Titel |
Geochemical Characteristics of Aquifer system in Taichung Area, Central Taiwan |
| VerfasserIn |
Jui-Fen Tsai, Cheng-Hong Chen, Tsung-Kwei Liu |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124314
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| Publikation (Nr.) |
 EGU/EGU2016-3732.pdf |
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| Zusammenfassung |
| For understanding the relationship between water bodies and host rocks and getting more
information for groundwater in Taichung area, Central Taiwan, we systematically analyzed
the stable isotopes (hydrogen and oxygen), helium isotopes and radon concentrations of
dissolved gases from 54 groundwater, 39 river and 4 rain samples collected from Taichung
Basin in wet and dry seasons of the year 2015.
In the δ18O vs. δD plot, all samples present a linear trend similar to local meteoric water,
indicating a meteoric origin. However, river samples are relative lighter than rain samples, it
appears that the rivers are mainly recharged from precipitation of high-elevation areas with a
lighter isotopic composition. Because the seasonal isotopic variation of river samples is
significant, we calculated relative contribution of precipitation by seasons using the mass
balance equation. Results show that the precipitation in the rainy season is the major source
of groundwater.
The helium isotopic ratio in dissolved gases of most groundwater samples are close to
1 RA (RA = 3He/4He ratio of air), except the sample from Wu-Feng well that
exhibits 0.3 RA. This sample also has an older C-14 age (∼27000 yrs.) than others
(<200 yrs.), implying that the dissolved helium is likely affected by radiogenic
4He of surrounding rocks. The average concentration of radon for groundwater in
the northern section of Taichung Basin is 20.3 Bq/L, which is higher than that of
the southern section (14.5 Bq/L). Variations of radon concentrations in the two
sections may be related to the different drainage systems (Paleo-Dajia River vs. Wu
River), in which sediments from Paleo-Dajia River may contain higher uranium
concentrations. On the other hand, water in rivers usually contains undetectable radon
(<0.37 Bq/L) because it rapidly escapes to the atmosphere. However, river samples
from the central part of basin have radon concentrations ranging between 1 and 3
Bq/L, reflecting that the sampling sites are in the vicinity of points of groundwater
inflow.
This study illustrates the utility of hydrogen and oxygen isotopes to trace the groundwater
source and determine the seasonal contribution ratios of precipitation to groundwater
recharge, and demonstrates the advantage of using dissolved gas to investigate the
groundwater-host rocks interaction.
Key words: Central Taiwan, groundwater, dissolved gas, helium isotope, hydrogen and
oxygen isotopes, water radon |
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