Water Chemistry And Its Influencing Factors Of Hot Spring In Shigatse Region,Tibet

The Shigatse region is located in the southwestern border of the Tibet Autonomous Region,where tectonic movements are vigorous,geothermal hot springs are widely exposed,and geothermal resources are abundant.According to statistics,there are a total of 120 geothermal display areas.Geothermal hot springs in the region are mainly in two states:bathing development and natural,but in recent decades,systematic research on the water chemistry characteristics of geothermal hot springs in the region is relatively lacking.In order to reveal the hydrochemical characteristics and influencing factors of geothermal hot spring water in Shigatse region of Tibet and other related information,this study selected27 geothermal hot springs(54 springs)with typical hot spring exposure in Shigatse region as the research objects.2020 dry season(December)and2021 wet season(August)to systematically sample these geothermal hot springs.By using the geothermal water chemical method to analyze the water chemistry of the hot springs in the study area,using the hydrogen and oxygen stable isotope to estimate the recharge source of the underground hot water,the elevation of the recharge area,etc.,and using the geothermal temperature scale to estimate the thermal storage temperature of the hot springs,to determine the influencing factors of the thermal storage temperature of geothermal hot springs.The main results are as follows:(1)The temperature of the hot spring water in the study area is13?87?,the p H value is between 6.55?9.27,and the acid-base degree is quite different;the variation range of TDS is 123?3143 mg/L,which belongs to fresh water or brackish water;the variation range of ROD is-425?67 m V with a turbidity range of 0.33?98.8 NTU.The dominant cation in hot spring water is Na⁺,and the dominant anion is HCO₃^-,the chemical types of water mainly include Na-HCO₃·Cl type,Na·Ca-HCO₃·Cl type,Ca-HCO₃ type,Na-Cl type,Na-HCO₃ type,Na·Ca-HCO₃ type,Na·Ca-HCO₃·SO₄ type,Na-SO₄·Cl type and Na-HCO₃·SO₄ type.The contents of 11 trace elements(Fe,Al,Mo,Zn,Cu,Ni,Mn,Ti,Ba,Be,Sb)are all low,and the five characteristic components of Si O₂,F,Li,As,B are rich in content.It is related to the strong dissolving ability of the hot spring water in this area,which makes the trace elements in the surrounding rock released into the underground hot water for enrichment.(2)In certain range,the Na⁺and Cl^-concentrations increased in the downstream sample sites of the four hot springs,and the water chemistry types in the lower reaches of the rivers near the Ru Jiao Boiling Spring,the Dagejia Geyser and the Kawu Boiling Spring have changed,indicating that these hot spring waters are closely related to the surface water cycle.(3)According to?D and?¹⁸O data,the 27 hot springs studied in the Shigatse region of Tibet are affected by the recharge of atmospheric precipitation in the wet season than in the dry season.However,except for Khambu hot spring,other geothermal hot springs have different degrees of ¹⁸O drift due to water-rock interaction.Among them,the supply elevation of the 11 springs of Khambu hot spring is 4252?4301 m,and the supply area temperature is-6.27?-5.53?.Both estimation results show that the main supply method of Khambu hot spring is the infiltration and recharge of atmospheric precipitation received by the mountains near the hot spring exposure area.(4)The deep underground temperature of the hot spring in the study area is 39.05?188.04?and the circulation depth range is 184.76?1096.88m.There are abundant geothermal resources in the region,and the most of them belong to High-temperature geothermal resources.According to the silicon-enthalpy equation,the mixing ratio of shallow groundwater is about 66?95%.These research results not only update the basic information of hot spring water chemistry in Shigatse region,but also provide a basis for in-depth understanding of hot spring hydrological cycle process and sustainable development and utilization of hot spring resources in Shigatse region of Tibet.