Using terrigenic ⁴He to identify and quantify regional groundwater discharge to streams

Abstract

[1] We present a new technique for identifying and quantifying the discharge of long residence time, regional groundwater to rivers using naturally occurring tracers measured within the river. Terrigenic 4 He and 222

Are we missing the tail (and the tale) of residence time distributions in watersheds?

“…This problem is compounded by the finding that methods commonly used in small watersheds such as the CIM, tritium, or 3 H/ 3 He will not capture similar components of old groundwater in other watersheds [Frisbee et al, 2011;Gardner et al, 2011;Smerdon et al, 2012]. Continued progress in our fundamental understanding on residence times in watersheds then depends on our ability to find and test alternative age-dating techniques that are more physically realistic, capable of detecting a broader range of residence times, capable of being employed across multiple scales, and capable of being employed in surface water systems in different climatic regimes, geographical locations, and geological settings.…”

“…The notion that groundwater plays an important role in streamflow generation is not new [Pinder and Jones, 1969;Sklash and Farvolden, 1979]. However, the role of old groundwater in streamflow processes has largely been ignored until very recently [Frisbee et al, 2011;Gardner et al, 2011;Smerdon et al, 2012]. Are the watershed processes in some of these studies properly characterized, while others are missing important process information because their residence times are biased short?…”

Using <sup>14</sup>C and <sup>3</sup>H to understand groundwater flow and recharge in an aquifer window

“…The residence time of water within an aquifer is a key parameter in describing catchment storage and may be used to estimate historical recharge rates (Le Gal La Salle et al, 2001;Cook and Robinson, 2002;Cartwright and Morgenstern, 2012;Zhai et al, 2013), elucidate groundwater flow paths (Gardner et al, 2011;Smerdon et al, 2012), calibrate hydraulic models (Mazor and Nativ, 1992;Reilly et al, 1994;Post et al, 2013) and characterize the rate of contaminant Published by Copernicus Publications on behalf of the European Geosciences Union. (Böhlke and Denver 1995;Tesoriero et al, 2005).…”

“…Additionally, during high flow, water from rivers is likely stored temporarily in the banks (McCallum et al, 2010;Unland et al, 2014); however, the depth and lateral extent to which bank exchange water infiltrates the aquifer is not well documented. Lastly, knowledge of residence times of groundwater in close proximity to the river can provide important information on groundwater-river interactions (Gardner et al, 2011). Local groundwater flow paths in connection with rivers are often underlain by deeper regional flow paths (Tóth, 1963), but the role these flow paths play in contributing to river baseflow remains unclear (Sklash and Farvolden, 1979;McDonnell et al, 2010;Frisbee et al, 2013;Goderniaux et al, 2013).…”

Use of Hydrochemistry, Stable Isotope, Radiocarbon, 222Rn and Terrigenic 4He to Study the Geochemical Processes and the Mode of Vertical Leakage to the Gambier Basin Tertiary Confined Sand Aquifer, South Australia

“…Following the procedure described by Gardner and Solomon [30], samples were retrieved after 24 h of equilibrium in the well. 222 Rn was measured at the CSIRO Environmental Isotope Laboratory in Adelaide, using low-level liquid scintillation counting [31], and dissolved 4 He was analysed with a Stanford Research Systems RGA 220 quadrupole mass spectrometer with cryogenic separation (Poole et al [32], cited in Gardner et al [5]). The integrity of the samples was checked for terrigenic 4 He lost during the sampling (which has already been 'excess air corrected' [33,34]) and is based on the ratio of measured neon-20 ( 20 Ne m ) to neon-20 equilibrium with the atmosphere ( 20 Ne eq ).…”