Lake Ihotry is a closed lake where evaporation constitute 99% of water outputs, and where the seasonal isotopic evaporative enrichment is important (from δ18O = − 3‰ to + 6‰ and from δ2H = − 20‰ to + 30‰). For a two-year measurement period, a dynamic model of lake water level leads to an accurate determination of the water balance at a daily time step. An isotopic balance model (δ18O and δ2H), including the Craig and Gordon evaporation model, has been coupled with the water balance model in order to simulate the evolution of the lake water isotopic composition. We propose that the moisture buildup over the lake surface affects the isotopic balance during the seasonal isotopic enrichment. A mixture between a vapour in isotopic equilibrium with rainfall (75%) and the locally evaporated moisture (25%) provides a good simulation of the lake water isotopic composition.
