Groundwater age dating with chlorofluorocarbons

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Therefore, it provides a cost-effective tool to understand the groundwater flow system.Laboratory and field studies have consistently shown that CFCs are stable in the aerobic environments and their concentrations of groundwater can reflect atmospheric values at the time of recharge (Oster et al. Wetlands play an important role in climatic regulation, water conservation and purification, and the maintenance of biological diversity.First, the sample was introduced into a stripping chamber, and the CFCs were purged with ultrapure N and quantitatively collected in a trap (A 35 cm long, 1/8 steel use stainless (SUS) pipe, filled with Res-sil C and Porapak T) cooled at −40 °C by a refrigerant mixture of methanol and dry ice.Then the trap should be heated to 95 °C in the hot water to let the CFCs be injected into the gas chromatography through pre-column and analytical column in sequence by carrier gas.It was found that the CFC-11 apparent age was much older than that estimated by other CFC species.

Observation sites of R2, S6 and, S15 are located at the middle and at the two sides of wetland valley, respectively.

For the analysis of dissolved methane, a pre-cleaned 25 ml glass vial was filled with unfiltered water, capped under water, and preserved by adding a drop of bactericide at the sampling site and kept chilled with ice until delivered to the laboratory.

To analyze Fe in the groundwater, unfiltered fresh water was taken into a pre-clean 100 ml plastic bottle and then 1 ml o-phenanthroline solution was added before sealing the bottle at site.

Major ions were determined by ion chromatography (LC-10AS, Shimazu) Methane gas was measured by a gas chromatography (GC-14B, Shimadzu) equipped with a flame ionization detector (FID) with a reproducibility of about ±2 %.

Fe was measured by spectrophotometer (TU1810, Beijing Tuopu Instrument Co., Ltd.) according to o-phenanthroline spectrophotometric method with detection limit of 0.03 mg/l.

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