A Study Of Partitioning Evapotranspiration Of The Alpine Meadow Eco-system In The Upper Reaches Of The Shule River Basin

Partitioning evapotranspiration is an important research content of agriculture,hydrology,agrology,meteorology and so on.It has very important application value in the study of eco-system management,crop yield simulation,water resources planning and management,environmental protection and so on.Based on the changes of stable isotopic composition(?represent?D and?¹⁸O)of atmospheric water vapor,evaporation,transpiration and evapotranspiration and meteorological factors in alpine meadow ecosystem.To partitioning the alpine meadow eco-system evapotranspiration in the upper reaches of the Shule River Basin into evaporation and transpiration,and to quantify the contribution of transpiration and soil evaporation to the evapotranspiration of the alpine meadow eco-system in the upper reaches of the Shule River Basin,clarify the characteristics of water vapor exchange in the upper reaches of the Shule River Basin,and providing basic data for the study of plant water use and regional water recycling in alpine meadow eco-system.The main results are as follows:?1?Meteorological factors directly or indirectly affect the composition of stable hydrogen and oxygen isotopes in the evapotranspiration of alpine meadow eco-system.the temperature varies little from 0:00 to 8:00 at night,and increases gradually from8:00 to 17:00,and then decreases gradually after 17:00.The relative humidity decreased at first and then increased during the day,and the minimum value appeared near 16:00.The variation of daily wind speed is very small,which is basically maintained at 1⁵m/s.The variation of solar net radiation is consistent with the process of temperature change.?2?The seasonal variations of stable isotopic composition of evaporation??_E?,transpiration??_T?,and evapotranspiration(?_ET)are generally like a"V"shape,the values of?_E,?_T and?_ETT were higher in July and September,and the lowest values appeared on August 8.The results were-20.6‰,-13.9‰and-15.8‰,respectively.And their diurnal variation characteristics are as follows:the values of?_E,?_T and?_ETT gradually increase during the period of 10:00-14:00.The maximum value was reached at 14:00-15:00,and then decreased gradually after 15:00.?_ETT is affected by environmental conditions and leaf water isotope enrichment degree.The turbulent air mass developed and gradually expanded in the morning,the lower hydrogen and oxygen stable isotopic composition of the upper layer enters the boundary layer,affected the stable isotopic composition of mixed water vapor in the chamber.Therefore,?_ETT is lower in the morning.Around14:00-15:00,the relative humidity is lower,the net solar radiation is higher,the temperature is higher,strong transpiration rate to promote plant transpiration to isotope stable state,leaf water isotope enrichment,and at the same time make the boundary layer rich in atmospheric heavy isotopes,so?_ETT increases rapidly.?3?Using isotope analyzer and specific chamber to calculate the stable isotopic composition of evaporation??_E?,transpiration??_T?and evapotranspiration(?_ET)separately can effectively partitioning the alpine meadow eco-system evapotranspiration.The partitioning results show that transpiration contributed 62%to the total ET,and even reached above 90%around 12:00 at high transpiration rate.And evaporation just contributed 38%to the total ET.So transpiration is the main form of water consumption in the growing season of alpine meadow ecosystem.At the same time,it provides scientific support for the study of water vapor exchange characteristics and regional water recycling in alpine meadow ecosystem.