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Combining isotopic tracers ( 222 Rn and δ 13 C) for improved modelling of groundwater discharge to small rivers
Author(s) -
Lefebvre K.,
Barbecot F.,
Larocque M.,
Gillon M.
Publication year - 2014
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.10405
Subject(s) - groundwater , aquifer , hydrology (agriculture) , groundwater discharge , tracer , environmental science , geology , stable isotope ratio , surface water , inflow , discharge , groundwater flow , drainage basin , environmental engineering , physics , geotechnical engineering , cartography , quantum mechanics , nuclear physics , geography , oceanography
In regions where aquifers sustain rivers, the location and quantification of groundwater discharge to surface water are important to prevent pollution hazards, to quantify and predict low flows and to manage water supplies. 222 Rn is commonly used to determine groundwater discharge to rivers. However, using this isotopic tracer is challenging because of the high diffusion capacity of 222 Rn in open water. This study illustrates how a combination of isotopic tracers can contribute to an enhanced understanding of groundwater discharge patterns in small rivers. The aim of this paper is to combine 222 Rn and δ 13 C DIC to better constrain the physical parameters related to the degassing process of these tracers in rivers. The Hallue River (northern France) was targeted for this study because it is sustained almost exclusively by a fractured chalk aquifer. The isotopes 222 Rn, δ 13 C DIC , δ 2 H and δ 18 O were analysed along with other natural geochemical tracers. A mass balance model was used to simulate 222 Rn and δ 13 C DIC . The results of δ 2 H and δ 18 O analyses prove that evaporation did not occur in the river. The calibration of a numerical model to reproduce 222 Rn and δ 13 C DIC provides a best‐fit diffusive layer thickness of 3.21 × 10 −5 m. This approach is particularly useful for small rivers flowing over carbonate aquifers with high groundwater DIC where the evolution of river DIC reflects the competing processes of groundwater inflow and CO 2 degassing. This approach provides a means to evaluate groundwater discharge in small ungauged rivers. Copyright © 2014 John Wiley & Sons, Ltd.