Development of climatic and vegetation conditions and the geochemical and isotopic composition in the Franconian Albvorland aquifer system

The impact of climatic and vegetation conditions over the past 15 Ka on the chemical composition and C-14 dating of ground water from the Franconian A lbvorland aquifer system is discussed. Seven groundwaters over a flow dista nce of 25.5 km are investigated. Groundwater dating is made by C-14 Of diss olved inorganic carbon (DIC) and aqueous fulvic acid as well as O-18. C-14 dating via fulvic acid gives groundwater ages consistent with climatic and vegetation records and variations in the groundwater composition. No correc tion for geochemical processes is required, since under these geochemical c onditions fulvic acid remains stable over this time period and how-distance . On the other hand,C-14 dating via DIC requires correction of the C-14 val ue due to perturbation by different geochemical processes. Up to a groundwa ter how distance of approximately 17 km and an age of about 10 Ka, the C-14 dating by DIC shows considerable dependence on the C-14-correction model a pplied. Beyond this groundwater age,C-14-DIC dating results in an overestim ation by two to three C-14 half-lives (T-1/2=5730 a). This deviation may re sult from different groundwater recharge conditions at the end of the past glaciation and geochemical processes acting on DIC that cannot be adequatel y characterized. The present study has implications for humic substance med iated transport of pollutants in natural aquatic systems over long time per iods. (C) 2000 Elsevier Science Ltd. All rights reserved.