Explicit Modeling of Radon-222 in HydroGeoSphere During Steady State and Dynamic Transient Storage |
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| Authors: | BS Gilfedder I Cartwright H Hofmann S Frei |
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| Institution: | 1. Limnological Research Station University of Bayreuth, Department of Hydrology, Bayreuth Center of Ecology and Environmental Research (Bayceer) Universitätsstrasse 30, 95447, Bayreuth, Germany;2. School of Geosciences Building 28, Monash University, Clayton, Victoria, Australia 3800;3. School of Earth Sciences, The University of Queensland, St. Lucia, QLD, 4072, Australia;4. Department of Hydrology, Bayreuth Center of Ecology and Environmental Research (Bayceer) University of Bayreuth, Universitätsstrasse 30, 95447, Bayreuth, Germany |
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| Abstract: | Transient storage zones (TSZs) are located at the interface of rivers and their abutting aquifers and play an important role in hydrological and biogeochemical functioning of rivers. The natural radioactive tracer 222Rn is a particularly well-suited tracer for studying TSZ water exchange and age. Although 222Rn measurement techniques have developed rapidly, there has been less progress in modeling 222Rn activities. Here, we combine field measurements with the numerical model HydroGeoSphere (HGS) to simulate 222Rn emanation, decay and transport during steady state (riffle-pool sequence) and transient (bank storage) conditions. Comparing the HGS mean water ages with the conventional 222Rn apparent ages during steady state showed a systemic underestimation of apparent age with increasing dispersion and especially where large concentration gradients exist within the subsurface. A large underestimation of apparent water age was also observed at the advective front during bank storage where regional high 222Rn groundwater mixes with newly infiltrated surface water. The explicit modeling of radiogenic tracers such as 222Rn offers a physical interpretation of this data as well as a useful way to test simplified apparent age models. |
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