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| Titel |
Old Groundwater, Interbasin Groundwater Flow, Magmatic Solutes, and Hydrologic Fluxes of Carbon in a Lowland Costa Rican Rainforest |
| VerfasserIn |
D. P. Genereux, M. Webb, D. K. Solomon |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030299
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| Zusammenfassung |
| Carbon (C), helium (He), and chloride (Cl) concentrations and isotopes were measured in
groundwater and surface-water in a lowland Costa Rican rainforest at the foot of Volcan
Barva (a 2900 m peak that is one of the largest in the Cordillera Central of Costa Rica).
Results are consistent with the presence and mixing of two distinct groundwaters: (1)
high-solute bedrock groundwater representing interbasin groundwater flow (IGF) into the
rainforest watersheds, and (2) low-solute local groundwater recharged within the lowland
rainforest watersheds. In bedrock groundwater, high δ13C (-4.89 o/oo), low 14C (7.98 pmC),
high R/RA for He (6.88), and low 36Cl/Cl (17x10-15) suggest that elevated DIC, He,
and Cl concentrations are derived from magmatic outgassing and/or weathering of
volcanic rock beneath nearby Volcan Barva. In local groundwater, the magmatic
signature is absent and data suggest atmospheric sources for He and Cl and a biogenic
soil-gas CO2 source for DIC. 14C dating suggests the age of bedrock groundwater is
2700-4300 years (most likely at the lower end of the range). Local groundwater has
14C>100 pmC, indicating the presence of “bomb carbon” and thus ages less than
~50 years for these samples collected in 2006. Overall, the C, He, and Cl data are
consistent with a prior conceptual hydrologic model developed with major ion and
water-balance data from this tropical rainforest: (1) the large variation in solute
concentrations can be explained by mixing of the two distinct groundwaters, (2) bedrock
groundwater is much older than local water, (3) elevated solute concentrations in bedrock
groundwater are derived from volcanic fluids and/or rock, and (4) local water has not
had significant interaction with volcanic rock. Tracers with different behaviors
and capabilities converge on the same hydrologic interpretation. Also, transport of
magmatic CO2 into the lowland rainforest (as DIC in the IGF) seems to be significant
relative to other large ecosystem-level carbon fluxes. Dissolved carbon export from
the watersheds via streamflow is dominated by DIC (DOC accounts for |
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