Analyses Of Regional Differences Of Hydrogen And Oxcegen Isotopes In Precipitation And Vapor Sources In Shiyang River Basin

Stable isotopes are very sensitive to environmental change and have been widely used in the studies about climatology,ecology,physical geography,hydrology and other fields.Atmospheric precipitation is an important part in the water cycle process on the earth.The study of hydrogen and oxygen isotopes in precipitation is helpful to understand the water cycle process.The natural environment of the upstream and the downstream of Shiyang River Basin are quite different,so there are also differences in their precipitation isotope changes.Based on three sampling points in the upstream and four sampling points in the downstream of the Shiyang River Basin from June 2017 to May 2019,a total of 547 precipitation samples and corresponding meteorological data were collected in order to make clear the difference of hydrogen and oxygen isotopic composition of precipitation in different regions of Shiyang River Basin.A comparative analysis of the hydrogen and oxygen isotopic composition of precipitation between upstream with downstream was made,combining with the HYSPLIT model to explore the sources of water vapor.There are following main conclusions.?1?The?¹⁸O values of precipitation in the Shiyang River Basin show obvious seasonal change characteristics,that higher in summer and autumn and lower in winter and spring.The overall change trend of d-excess is opposite to the seasonal change trend of?¹⁸O.The weighted average?¹⁸O value of annual precipitation in the downstream is higher than that in the upstream.The local meteoric water line?LMWL?in the Shiyang River Basin is:?D=7.6?¹⁸O+7.3;The LMWL in upstream is:?D=7.8?¹⁸O+9.9;The LMWL in downstream is:?D=7.2?¹⁸O+2.6.The slope and intercept of the LMWL in the downstream are lower than those in the upstream.?2?Hydrogen and oxygen isotopes of precipitation in Shiyang River Basin show obvious“temperature effect”,and?¹⁸O values of each sampling point is positively correlated with temperature?T?.The“temperature effect”of precipitation isotopes in the upstream is more significant than that under T>8?,while that in the downstream is more significant under T>0?,and the“temperature effect”is more significant under T<8?,but not shown under T<0?.?3?There is no“precipitation effection”in the downstream of Shiyang River Basin at the annual scale,but there is a certain“precipitation effection”in the upstream.At the seasonal scale,the upstream show significant“precipitation effect”in the summer and winter,while the downstream show obvious“precipitation effect”in the summer.The“precipitation effect”is significant in the upstream under the condition of snowfall and rainfall intensity of light rain.The“precipitation effect”is significant in the downstream under moderate rain.Continuous precipitation events of the basin also show“precipitation effect”.?4?The“elevation effect”of isotope in precipitation exists in Shiyang River Basin.When the elevations increase by every 100 meters,?¹⁸O values decrease by 0.22‰.The“elevation effection”during the cold season is more obvious than that during the warm season.In the upstream,the“elevation effection”excists during the warm season and shows less obvious.The“elevation effection”exists in the downstream.When the elevations increase by every 100 meters,?¹⁸O values decrease by 0.38‰.The“elevation effection”is more obvious during the cold season than during the warm season.?5?The vapor of the basin mainly comes from the westerly circulation.The contribution of vapor from the north and southeast to precipitation in the basin is small,and that from the southwest can almost be ignored.The water vapor entering the basin from the northwest mainly comes from the North Atlantic sea area,the high latitude area of the European continent or the Central Asia area.The water vapor from the north direction mainly comes from the evaporation of Siberian continent.The water vapor from the southwest direction may come from the Indian Ocean or the water vapor from the West which turns against the terrain obstruction.The water vapor from the southeast direction comes from the Pacific Ocean,that it is mainly transported inland from southeast monsoon in summer and autumn.