Chemical and isotopic signature of old groundwater and magmatic solutes in a Costa Rican rain forest: Evidence from carbon, helium, and chlorine

摘要: [1] C, He, and Cl concentrations isotopes in groundwater surface water a lowland Costa Rican rain forest are consistent with the mixing of two distinct groundwaters: (1) high-solute bedrock representing interbasin flow (IGF) into (2) low-solute local recharged lowlands. In groundwater, high δ13C (−4.89‰), low 14C (7.98 pM), R/RA for He (6.88), 36Cl/Cl (17 × 10−15) suggest that elevated tracer derived from magmatic outgassing and/or weathering volcanic rock beneath nearby Volcan Barva. signature is absent, data atmospheric sources biogenic soil gas CO2 source dissolved inorganic carbon. Dating suggests age 2400–4000 years (most likely at lower end range). Local has > 100 pM, indicating presence “bomb carbon” thus ages less than ∼55 years. Overall, conceptual hydrologic model originally proposed on basis budget major ion data: large variation solute can be explained by groundwaters, much older (3) fluids rock, (4) not interacted rock. Tracers different capabilities converge same interpretation. Also, transport via IGF seems to significant relative other ecosystem-level carbon fluxes.