A method for groundwater 14C age correction accounting for mixing with young and old groundwaters: application to an alluvial aquifer in the Jianghan Plain, ChinaUne méthode de correction de l’âge des eaux souterraines déterminée à l’aide du 14C tenant compte du mélange entre eaux souterraines jeunes et anciennes dans les aquifères alluviaux de la Plaine de Jianghan, ChineMétodo de corrección de la edad del agua subterránea mediante 14C en función de la mezcla con aguas subterráneas jóvenes y antiguas en los acuíferos aluviales de la llanura de Jianghan, China中国江汉平原冲积含水层中混合了年轻和古地下水的地下水 14C 年龄校正方法Método para correção de idade 14C das águas subterrâneas, contabilizando a mistura com águas subterrâneas jovens e velhas nos aquíferos aluviais da planície de Jianghan, China

The distribution of groundwater 14C ages can indicate the direction of groundwater flow. Groundwater 14C age is based on 14C radioactive decay and the 14C activity (a14C) of dissolved atmospheric carbon, but hydrochemical processes can change the groundwater a14C. A series of 14C correction models have been proposed to eliminate the influence of a14C change on 14C dating. However, mixing in the groundwater flow path and in the groundwater discharge area can also change the groundwater a14C. The classical 14C correction models do not clearly identify groundwater mixing, and their results provide mixed 14C ages. Hydrochemical components that have gradually accumulated along a groundwater flow path can be used to identify mixing and to correct a14C values. The relationship between SO42− concentrations and a14C values is used to identify groundwater mixing in the Jianghan Plain, central China. The plotted 14C vs. δ13C relationship indicates that the classical IAEA model is suitable for most samples taken from a confined aquifer. The a14C values of some samples are corrected by projecting them onto a mixing line between young groundwater and old groundwater. Having been corrected by the Mixing-IAEA model, the 14C ages of groundwater mixed with young groundwater are found to have been underestimated and were recalculated to be 3.41–12.11 ka, and the 14C ages of groundwater mixed with old groundwater are found to have been overestimated and were recalculated to be 4.97–10.78 ka. Comparison of 14C ages corrected by the Mixing-IAEA model with the IAEA model allows improved interpretation of groundwater flow directions.