Abstract. This study investigates the combined hydrogen deuterium and triple oxygen
isotope hydrology of the Salar del Huasco, an endorheic salt flat with
shallow lakes at its centre that is located on the Altiplano Plateau,
N Chile. This lacustrine system is hydrologically dynamic and complex
because it receives inflow from multiple surface and groundwater sources. It
undergoes seasonal flooding, followed by rapid shrinking of the water body
at the prevailing arid climate with very high evaporation rates. At any
given point in time, ponds, lakes, and recharge sources capture a large
range of evaporation degrees. Samples taken between 2017 and 2019 show a
range of δ18O between −13.3 ‰ and 14.5 ‰,
d-excess between 7 ‰ and −100 ‰, and
17O-excess between 19 and −108 per meg. A pan evaporation
experiment conducted on-site was used to derive the turbulence coefficient
of the Craig–Gordon isotope evaporation model for the local wind regime.
This, along with sampling of atmospheric vapour at the salar
(-21.0±3.3 ‰ for δ18O,
34±6 ‰ for d-excess and 23±9 per meg for 17O-excess), enabled the accurate reproduction of
measured ponds and lake isotope data by the Craig–Gordon model. In contrast
to classic δ2H–δ18O studies, the
17O-excess data not only allow one to distinguish two different types of
evaporation – evaporation with and without recharge – but also to identify
mixing processes between evaporated lake water and fresh flood water.
Multiple generations of infiltration events can also be inferred from the
triple oxygen isotope composition of inflow water, indicating mixing of
sources with different evaporation histories. These processes cannot be
resolved using classic δ2H–δ18O data alone. Adding
triple oxygen isotope measurements to isotope hydrology studies may
therefore significantly improve the accuracy of a lake's hydrological
balance – i.e. the evaporation-to-inflow ratio (E / I) – estimated by water
isotope data and application of the Craig–Gordon isotope evaporation model.
Supplementary material to "Triple oxygen isotope systematics of evaporation and mixing processes in a dynamic desert lake system"
