A Study Of Lake Water Balance And Water Vapor Using Isotopes In Fuxian Lake Basin

Stable isotopes of water(?¹⁸O and?²H)can serve as a practical tool in the understanding of the 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 lake water largest water surface 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?¹⁸O 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,which 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.Fuxian Lake basin water vapor samples were collected using a set of cryogenic cold trap method.We designed and improved this method suitable for Southwest China.The variation characteristics of water vapor isotopes in this basin,the local influence factors,the relationship with precipitation isotopes and large-scale water vapor sources were studied.Water vapor?¹⁸O shows lower during the monsoon period,and higher during non-monsoon period.Water vapor d-excess shows a large fluctuations,but with a weak seasonality.The local meteorological factors have different effects on water vapor?¹⁸O and d-excess.Water vapor?¹⁸O is mainly affected by local relative humidity,wind speed,precipitation amount and vapor pressure.While water vapor d-excess shows a negative correlation with air temperature,and positive correlation with vapor pressure.Comparing water vapor and precipitation isotopes during the same period,it is found that general equilibrium between water vapor and precipitation during the monsoon period.Water vapor and precipitation in non-equilibrium state because dynamic fractionation in isotope during the non-monsoon period.We established the local meteoric water line(LMWL)and the local meteoric vapor line(LMVL).Moisture sources,transport paths and convection process also influence the water vapor?¹⁸O.During the monsoon period,moisture mainly from the regions of Bengal,Arabian Sea,South China Sea and Western Pacific,the water vapor and precipitation relative depletion?¹⁸O.During the non-monsoon period moisture mainly from the local hydrological cycle,and also affected by the Westerly,the water vapor and precipitation relative enrichment?¹⁸O.