Fluoride as an (eco)hydrological tracer in semiarid mountainous streams: insights from comparing F/Cl ratio and water stable isotopes (δ18O and δ2H)

MACCHIOLI GRANDE, MARCOS; POCA, MARÍA; LARROVERE, MARIANO; URAN, GIMENA; JOBBÁGY, ESTEBAN

San Luis

Workshop; I Regional Workshop on Isotope Ecohydrology; 2020

GEA (IMASL)

Mountainous semiarid streams are the main source of water for most of northwestern Argentina. The composition of these natural surface waters in this region is controlled by weathering of the crystalline basement. Some of these rivers contain high levels of fluoride, because of dissolution of F-bearing minerals from granitic rocks. Semiarid conditions would favor evaporative concentration of fluoride, similar to what occurs to its sister halogenide chloride, despite the former is mostly retained in minerals, and therefore has a different hydrochemical behavior.Additionally, little is known about F bio-accumulation, and whether F can be a good tracer of different sources of water uptake by plants. Therefore, the concentration of F in plants of different use of water (riverine vs crops irrigated with groundwater) could also help understanding the dynamic of this element in the plant-soil system, and assess a possible use as an ecohydrological tracer. We tested whether fluoride can be a natural hydrological tracer in semiarid mountainous streams draining a uniform lithology, comparing its spatial distribution with other natural traces such as chloride (F/Cl ratio) and water stable isotopes (δ18O and δ2H). Furthermore we evaluated the role of evaporative concentration in further accumulation/retention of fluoride in vegetation, in an ecohydrological approach comparing with water stable isotope composition in the water-plant-soil system.