Description of a simple hydrochemical indicator to estimate groundwater residence time in carbonate aquifers
Lalbat Frederic, F., Blavoux, B., Banton, O. 2007 Geophysical Research Letters 34 (19), art. no. L19403 0
Some chemical and/or isotope indicators are required to interpret radiocarbon data in terms of groundwater residence time. Among the simplest indicators, the Mg:Ca ratio is commonly used in carbonate aquifers. However, this ratio only accounts for the dissolution/ precipitation reaction of calcite and dolomite, whereas other dissolution reactions and ion exchanges can greatly influence the chemistry of groundwater. The aim of this study was thus to describe how the Mg:Ca ratio can be modified by the hydrogeochemical setting to define a new indicator based on the major, elements in a molasse basin in southeastern France. The new indicator was computed and the results were compared with radiocarbon activity. The study showed the new indicator correlated well with radiocarbon activity. The new indicator is more useful than the Mg:Ca ratio for long residence times and in the sectors where gypsum dissolution occurs. Copyright 2007 by the American Geophysical Union.