Hydrologic Cycle On The Typical Permafrost By Using Environmental Isotope In The Headwaters Of The Yangtze River

Permafrost has significantly affected on the various elements of the hydrological cycle and hydrological cycle of the mechanism in the alpine region. Due to the Yangtze River in the hinterland of the Qinghai-Tibet Plateau, the study of hydrological processes relatively weak at home and abroad in this area. Environmental isotope is widely present in natural water, the isotope fractionation lead to different water with different isotopes as mutual transformation of precipitation, surface water, groundwater, soil water and plants water in the water cycle process. This paper took Fenghuoshan watershed, located in the northern foot of Qinghai-Tibet Plateau permafrost region, with the hydrological cycle of rainfall, surface water and groundwater for the study, discussed different water bodies of water chemistry and temporal and spatial variation characteristics of hydrogen and oxygen isotopes, and the different cross-section of runoff components. The main conclusions are as follows:1. Hydrogen and oxygen isotope characteristics precipitationTheδD andδ18O compositions in precipitation have seriously seasonal fluctuations, even within the same day. Pairs ofδD andδ18O regression analysis, obtained a relationshipδD=8.2δ18O+17.3, called as Local Meteoric Water Line (LMWL).The deuterium excess (d) has the fluctuation range of-10.09‰-30.22‰, the arithmetic mean of 15.67%o in the precipitation events. Compared with the global deuterium excess (d) 10%o, the local water vapor is the main source of precipitation in the study area.Temperature is the primarly control factors ofδD andδ18O in precipitation, the correlation regression equation were:δ18O=1.22T-12.44,δD= 9.12T-79.38 (r=0.43 p<0.04);When T≥4℃,δD andδ18O show a certain " precipitation volume" effect:δ18O and T at 0.01 are significantly related;δD and T at 0.05 is significantly related. 2. Hydrogen and oxygen isotope characteristics of the riverIn the day scale, theδD andδ18O rose from June to the end of June to the highest value in early July and then began to decline to bottom around July 10, the remaining time slots are fluctuated in a narrow range. In the month scale, theδD andδ18O in all sections were similar characteristics, that June>July>August. The spring flood runoffδ18O compositions were the highest, the summer and autumn flood come second, and the freeze season were minimum.The magnitude ofδ18O and 8D were roughly equal in 1,2,3 river basins in the spring flood season, while theδ18O andδD were larger than the others due to evaporation. Theδ18O andδD decreased with the increased area, and then gradually increased.3. Chemical characteristics of river waterThe result of analysis shows that the dominating chemical compositions of river water is Na+, Ca2+, SO42-, Ca2+and Na+accounting for 75.7%, SO42- accounting for 50.2%-87.3%.The variation of soil freezing and thawing was the controlling factor in the seasonal pattern of stream chemistry, and total ion contents of river water increased in the order summer flood, spring flood, autumn recession flow, winter dry season. Spring flood had a obviously feature of ionic pulse phenomenon, summer flood was mainly diluted by precipitation, however autumn recession flow was completely dominated by interflow, frozen of streamflow and soil water were main features for witer dry season. The total ion contents of river water increased in the order summer flood>spring flood> autumn recession flow> winter dry season.The total ion contents of river water had the law of cubic polynomial curve increased with catchment area. For four periods, the concentration of NO; is not a linear function which is highest at summer flood and decreased with swamp wetland percentage, especially for spring flood and summer flood. Fenghuoshan watershed are influenced strongly by carbonates, at the same time, evaporates is responsible for 27.214%of total ion equivalent concentration.4. Runoff components June:The river is mainly supplied by groundwater, from 1 to 5 sections the ratio were 77.6%,82.1%,77.5%,55.7%,58.2%, respectively. The proportion of precipitation is relatively small. August:From 1 to 5 sections, groundwater contributed 50.5%,47.5%,47.2%,81.7%,78.3%, respectively.