Ground Water. 2021 Mar 21. doi: 10.1111/gwat.13096. Online ahead of print.
ABSTRACT
Mass balance calculations and hydrodynamics of groundwater flow suggest that the solutes in brines of the coastal sabkha aquifer from the Emirate of Abu Dhabi are derived largely from ascending geologic brines into the sabkha from the underlying formations. Solute interpretation for the ascending brine model was based on two independent but secondary lines of evidence (solute ratios and solute fluxes). In the current study, direct primary evidence for this ascending brine model was provided through analyses of δ81 Br, δ37 Cl, and 87 Sr/86 Sr. Different solute histories of geologic brine and seawater provide an “isotopic fingerprint” that can uniquely distinguish between the two possible sources. Samples from the coastal sabkha aquifer of Abu Dhabi were determined to have a mean δ81 Br of 1.17‰ that is statistically equal, at the 95% confidence level, to the mean of 1.11‰ observed in the underlying geologic brine and statistically different than seawater. Similarly, the δ37 Cl in sabkha brine has a mean of 0.25‰ and is statistically equal to a mean of 0.21‰ in the underlying geologic brines at the 95 % confidence level and statistically different from seawater. Also, dissolved strontium isotope data are consistent with the ascending brine model and even with the complex set of processes in the sabkha the variance in strontium isotope results is similar to the geologic brine. These observations provide primary direct evidence consistent that the major source of these solutes (and presumably others in the aquifer) is from discharging geologic brines, not from adjacent seawater.
PMID:33745130 | DOI:10.1111/gwat.13096
