Deep lake water balance by dual water isotopes in Yungui Plateau, southwest China

Abstract

Stable isotopes of water (δ18O and δ2H) serve as a practical tool in the understanding of regional hydrological cycle, in particular, where the regional water cycle is stressed by both climate change and human activities. Lake water in southwest China is believed to play an important role in the local hydrology and possible modification of local climate. Water isotopes in lake systems are influenced by both the input water isotope and surface evaporation, such that they can be used as a natural tracer to evaluate these effects. Here we present a detailed water isotope balance study in a plateau lake – Fuxian Lake, the deepest and largest water body in Yungui Plateau, southwest China, with analogues of a steady state of water isotope equilibrium. The lake water isotopes are significantly enriched in heavy isotope due to evapoconcentration during the long residence time. We simulated the dual isotopes in the lake water using the Craig and Gordon model constrained by the observed water isotopes in lake water, river water, and atmospheric vapor. Results show consistent results for both δ18O and d-excess with values of −2.6‰ and −9.0‰ at the present relative humidity and E/I ratio. The test simulations also demonstrate how potential change in climate and/or lake water E/I ratio could impact lake water isotopes, and how the dual water isotope approach can unequivocally define the climatic and hydrological controls on lake water isotopes. These findings may be relevant for anticipating and detecting hydrological response to future climate change and water source management, e. g. inter - basin diversion projects. The results from this study highlight the potential of water isotopes in regional water cycle work, paleo climate reconstruction from lacustrine record, as well as human activity on water management.