Lithium isotopes as tracers of groundwater circulation in a peat land

Abstract

8 9Water circulation in the peat bog of a maar depression in the Massif Central (France) was traced with 10 lithium isotopes on water samples collected in the area from springs, surface-and groundwaters, as 11 well as on solid samples taken from peat bogs. 18In the present study, we explain the extremely enriched 7 Li signature of the groundwaters by an -IntroductionA wetland is an area covered at least part-time by usually quite shallow water. Wetlands can 36 be natural or artificial, permanent or temporary, and the water in them can be static or 37 flowing, and fresh, brackish or salty. Wetlands form where water collects in a low-lying area 38 with poor drainage. The water filling a wetland can have many origins: precipitation is a 39 major source of water for many wetlands, but others are maintained by water that periodically 40 overflows from rivers, lakes, etc., whereas a third source of water for wetlands is 41 groundwater. All three sources generally deliver water to wetlands in regular cycles, based on 42 the natural cycle of water through the hydrosphere. It is also worth noting that understanding 43 the hydrology of a wetland is primordial for efficient flood control, paleoclimate analyses, 44 and studying its role in the overall ecology. 45The present study investigates the use of Li and its isotopes as a proxy of ground-to-surface 46 water exchanges in a peatland from a mire-lake complex in the French Massif Central, as the 47 capability of Li isotopes as hydrogeological tracers was earlier demonstrated by Hogan and 48 Blum (2003). As one aim of the work was to determine geochemical constraints on the 49 hydrological functioning of a peatland, our primary objective was to constrain hydro-reservoir 50 signatures and the exchanges of water and solutes with adjacent ground and uplands. One 51 particularly important aspect of this work was to evaluate the mechanisms of water and solute 52 transfer between the reservoirs by applying Li as a new isotopic tracer. 53Lithium has two stable isotopes of mass 6 and 7, with natural abundances of 7.5% and 92.5% 54 respectively. Lithium is a mobile element that tends preferentially to go into the fluid phase 55 during water/rock interactions. The relative mass difference between the two isotopes is 56 considerable at 17%, generating significant mass-dependant fractionation during geochemical 57 processes. The range of variation in lithium-isotope compositions is more than 50‰ in 58 geological materials (see Coplen et al., 2002;Tomascak, 2004 for data compilation). As Li is 59 3 a recently developed isotopic tracer, not all the processes that could induce and control 60 isotopic fractionation are as yet well constrained. However, in the context of water/rock 61 interactions, numerous studies (Huh et al., 1998(Huh et al., , 2001Pistiner et al., 2003; Kisakurek et al., 62 2004 Kisakurek et al., 62 , 2005 Pogge von Strandmann et al., 2006;Millot et al., 2007Millot et al., , 2010aMillot et al., , 2010b have 63 clearly shown that isotopic fractionation ...

Implications of Peat Soil Conceptualization for Groundwater Exfiltration in Numerical Modeling: A Study on a Hypothetical Peatland Hillslope

“…These techniques, applicable for peatland sites, include conventional direct hydrological measurements (use of piezometers, slug tests, boreholes, etc.) (Johansen et al, 2011; Rossi et al, 2012), thermal imaging and other remote sensing techniques (Bechtold et al, 2018; Briggs et al, 2016; Hare et al, 2015, 2017), geophysical measurements (Lowry et al, 2009; McLachlan et al, 2017), and use of natural tracers, including stable water isotopes (Isokangas et al, 2017; Levy et al, 2014, 2016; Négrel et al, 2010). These methods provide valuable information on the current state of GW‐SW connectivity but are of little use in predicting how the system will react to changing conditions, such as groundwater abstraction, changes in land use, or climate change.…”

Multivariate analysis of trace elements in shallow groundwater in Fuchu in western Tokyo Metropolis, Japan

“…Dissolved Si mainly exists in a hydrated form as H 4 SiO 4 (aq) or Si(OH) 4 , and Si neither presents as any ionic species nor extensively absorb to other mineral surfaces (Hem 1989). Both Li and B are considered as inert solutes in groundwater, thus their isotopes 6 Li and 11 B have been used as groundwater tracers in many studies (Hogan and Blum 2003;Négrel et al 2010). This suggests higher mobility of Li, B, and Si in groundwater.…”

The influence of water–rock interactions on household well water in an area of high prevalence chronic kidney disease of unknown aetiology (CKDu)

“…The δ 7 Li values in continental crust ranges from approximately −5‰ to +5‰ 38 ; however, preferential dissolution of 7 Li and preferential adsorption and incorporation of 6 Li into secondary minerals results in a higher and much broader range of values in river water (+5‰ to +43‰) 37,39-41 and groundwaters (+7‰ to +37‰) 28,42,43 . Values as high as +1225‰ have also been reported in groundwater from a peat bog influenced by agrochemicals 44 .…”