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| Titel |
Analysis of dissolved gas and fluid chemistry in mountainous region of Goaping river watershed in southern Taiwan |
| VerfasserIn |
Kai-Wen Tang, 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 |
250124028
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| Publikation (Nr.) |
 EGU/EGU2016-3392.pdf |
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| Zusammenfassung |
| Annual rainfall in Taiwan is up to 2500 mm, about 2.5 times the average value of the world.
However due to high topographic relief of the Central Mountain Range in Taiwan,
groundwater storage is critical for water supply. Mountain region of the Goaping river
watershed in southern Taiwan is one of the potential areas to develop groundwater recharge
model. Therefore the target of this study is to understand sources of groundwater and
surface water using dissolved gas and fluid chemistry. Four groundwater and 6
surface water samples were collected from watershed, 5 groundwater and 13 surface
water samples were collected from downstream. All samples were analyzed for
stable isotopes (hydrogen and oxygen), dissolved gases (including nitrogen, oxygen,
argon, methane and carbon dioxide), noble gases (helium and radon) and major
ions.
Hydrogen and oxygen isotopic ratios of surface water and groundwater samples aligned
along meteoric water line. For surface water, dissolved gases are abundant in N2 (>80%) and
O2 (>10%); helium isotopic ratio is approximately equal to 1 RA (RA is 3He/4He ratio of
air); radon-222 concentration is below the detection limit (<200 Bq/m3); and concentrations
of major anions and cations are low (Na+ <20 ppm, Ca2+ < 60 ppm, Cl− <2
ppm). All these features indicate that surface waters are predominately recharged by
precipitation.
For groundwater, helium isotopic ratios (0.9∼0.23 RA) are lower and radon-222
concentrations (300∼6000 Bq/m3) are much higher than the surface water. Some samples
have high amounts of dissolved gases, such as CH4 (>20%) or CO2 (>10%), most likely
contributed by biogenic or geogenic sources. On the other hand, few samples that have
temperature 5∘ higher than the average of other samples, show significantly high Na+
(>1000 ppm), Ca2+ (>150 ppm) and Cl− (>80 ppm) concentrations. An interaction between
such groundwater and local hot springs is inferred.
Watershed and downstream samples differ in dissolved gas species and fluid chemistry for
groundwater and surface water. The higher hydrogen and oxygen isotopic ratios for surface
water from downstream are most probably caused by evaporation. Low radon-222
concentrations of some groundwater from downstream may represent sources from different
aquifers. Therefore, we conclude that surface water from downstream are recharged
directly from its watershed, but groundwater are influenced by the local geological
environment.
Keywords: groundwater, dissolved gas, noble gas, radon in water, 3He/4He |
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