Hydrochemical Characteristics And Influencing Factors Of Drip Water In The Jiutian Cave Of Shandong Peninsula

Isotope and trace elements of stalagmite are of great significance in the field of paleoclimate reconstruction.The drip water is the main source of isotope and trace elements of stalagmite.The monitoring of drip water can provide reference for the uncertainty in the interpretation of stalagmite paleoclimate.The data of this study are:cave environment data from December 2011 to December 2014,including cave air temperature,relative humidity,CO₂ concentration of the cave,drip rate.Isotope data of drip water from March 2013 to December 2014,mainly including Drip water carbon and oxygen isotope.Trace element data of drip from December 2011 to December 2014,including Ca²⁺,Mg²⁺,Sr²⁺,Ba²⁺.Temperature and rainfall data of Yiyuan meteorological station are from 2012 to 2014.The data were analyzed by time series analysis method to investigate the seasonal and interannual regular changes of carbon and oxygen isotope and trace elements in drip water,and analyzed the influencing factors.The main conclusions are as follows:?1?The average annual temperature of Jiutian cave is:15.9°C,15.5°C,17°C,the seasonal variation is not significant;the cave humidity is relatively large,the annual average humidity is about 90%,and the seasonal variation of humidity in the cave is characterized by low summer and high winter.The farther away from the structural opening,the less affected by the ventilation of the cave,and the higher CO₂concentration.There is a correlation between drip rate and precipitation,but there is a lag effect between them.The seasonal and inter-annual changes of precipitation affect the seasonal and inter-annual changes of drip rate.There are some spatial differences in monitoring drip rate,which are mainly related to factors such as overlying soil layer,and rock layer thickness and migration channel at each drip point.?2?There is no significant seasonal change in drip water DIC-?¹³C at the monitoring point in the cave.When the change of CO₂ concentration is small,the change of drip water DIC-?¹³C is small,and when the change of CO₂ concentration is large,the influence on the concentration of drip water DIC-?¹³C is significant.but there is also hysteresis between them.The DIC-?¹³C of the peak value of temperature and precipitation is light,and there is also hysteresis between them,which is mainly related to the hysteresis effect of drip rate caused by overlying soil thickness,drip point migration path and other factors.?3?There is no seasonal variation law of drip?¹⁸O.The correlation between external precipitation,temperature inside the cave and?¹⁸O of monitoring point is not significant.The drip?¹⁸O is related to the thickness of the overburden,the migration path of the drip point,and the development of the drip point.The height of the drip point and the distance between the structural opening and the ventilation condition also affect the variation of?¹⁸O.?4?Dripping Ca²⁺and Mg²⁺showed significant seasonal and interannual variations.The seasonal variation characteristics are related to the dissolution of soil and rock on the drip point under the condition of climate change,which is characterized as high in summer and autumn,low in winter and spring.In terms of interannual variation,the concentration of Ca²⁺and Mg²⁺ions in each monitoring point in 2012 was higher than that in 2013,which was higher than that in 2014.And the interannual characteristics of precipitation affected the interannual variation of Ca²⁺and Mg²⁺concentrations.The precipitation of pre-calcite?PCP?and piston effect have a great influence on the concentration of Ca²⁺in the drip water.?5?The changes of Sr²⁺and Ba²⁺in drip water are similar,and Sr²⁺and Ba²⁺may have similar effects.The summer is hot and rainy,the dissolution of soil and carbonate is strengthened,and the Sr²⁺and Ba²⁺ions are increased.The seasonal variation is higher in summer and autumn and lower in winter and spring.In 2014,the drought was less,the precipitation was less,and the high values of Sr²⁺and Ba²⁺ions showed hysteresis.In addition to precipitation,the factors affecting the concentration of Sr²⁺and Ba²⁺in drip water are related to soil thickness,water-rock interaction time and karst water migration path.The complexity of the influencing factors leads to significant spatial differences in Sr²⁺and Ba²⁺concentrations.?6?The drip water Mg/Ca,Sr/Ca,Ba/Ca responded significantly to the external drought events.In 2014,the drought,Mg/Ca,Sr/Ca,Ba/Ca fluctuated significantly,and the drought year ratio increased.The precipitation of precalcin?PCP?is related to the piston effect.There is a correlation between the change of trace element ratio and the dry and wet conditions of the outside.