Positive Ion Characteristics Of Cave Drips And Responds To Environment In Karst Rocky Desertification Area

The external environmental information of karst cave usuallyreflects the changes of cave drips’geochemical characteristics,drips’positive ion is as the important hydro-chemical indicator,its characteristics’ variations and environmental responsecharacteristics is of great significance in the process of buildingindex system of cave. For establishing the index system for cave,interpreting the environment in surroundings area, and thenexploring the evolution law of rocky desertification, this papercombined the National Natural Science Foundation of China “Usingthe Cave Sediments System Research of Carbon Isotope in Guizhou,the Midwest Rocky Desertification Evolution History (41001367)”and Key Projects in the National Science and Technology PillarProgram during the Twelfth Five-Year Plan Period(2011BAC09B01)”,we monitored the chemical characteristics ofpositive ions (Ca2+, Mg2+and Sr2+) for cave drips in four caves(Shijiangjun Cave, Benzhai Cave, Daxiao Cave and Rongfa Cave) fromdifferent grades rocky desertification area in Guizhou Province andthe surrounding environment for two hydrologic year from January2011to December2012. Study has shown that the positive ion of cavedrips responded significantly to the surrounding environment, andit was sensitive to reflect the variation of the climate information such as precipitation and temperature. We summarized its variationcharacteristics and environmental response, and the conclusionsare following:(1) We according to the content variation of drips’Ca2+, Mg2+in two hydrological years of2011and2012in different grades rockydesertification, and found they respond sensitively toprecipitation. The rainfall es less and its variable ratio is smallfrom January to May in each year, and the Ca2+and Mg2+are stableand low; the rainfall is large and the heavy rains are frequent fromJune to August, and the rainfall variability is large, Ca2+and Mg2+fluctuates greatly. The rainfall is large and its variation rateis small from September to December, and the Ca2+and Mg2+of dripsis stable and and high. According to its characteristics, it canbe divided into three seasonal partitions: Seasonal Low Zone(fromJanuary to May), Seasonal Fluctuation Zone (from June to August),Seasonal High Zone (from September to December). In differentgrades rocky desertification area, the drips’response to rainfallare at different levels, among which, the response in mild rockydesertification area lags than the intense rocky desertification,and the content of Ca2+and Mg2+are more stable. It providesinformation on indicators to the research of rocky desertification,and is quite meaningful to the evaluation mechanism of rocky desertification by the establishment of index system for the cave.(2) The same water point has the same migration path, whichrestrict the main factor of residence time is rainfall dripping.Dripping migration is slow in dry season with a long residence timeand CaCO3deposite priority. Mg/Ca ratios has higher value; Instead,dripping migration is fast in wet season with long residence timeand Mg/Ca ratio has lower value. Low Seasonal Zone (from Januaryto May), Fluctuation Seasonal Zone (from June to August) and HighSeasonal Zone (from September to December), the relationship of themean of Mg/Ca and rainfall show that most drip points Mg/Ca valuesand rainfall has a better negative correlation that the higher(lower) Mg/Ca ratio, the less (and more)rainfall has. However, eachof the four caves dripping obvious correlation between the Mg/Cavalues and monthly rainfall due to the lagged effects of raindripping caves response. Therefore, future studies should payspecial attention to this phenomenon and monitor it further inlong-term.(3) The partition mean of different drip point Mg/Ca andrainfall in Benzhai Cave have shown different positive or negativecorrelation, which presented better negative correlation that donot match with other caves. We have to analyze the causes: TheBenzhai Cave is slightly rocky, and the roof with arable land and better vegetation, Ca2+and Mg2+affected by rainfall and moderateintensity rocky vary. The Benzhai Cave has thinner bedrock that makerainfall has less residence time in the roof. And two years ofmonitoring of hydrology, the Benzhai Cave has dry conditionsfrequently, which led to our relative error in the monitoringprocess. In order to reflect the information accurately, we shouldanalyze the reasons fully, monitor indicators for a long time, andreduce monitoring errors as large as possible. Founding Mg/Ca ratioand rainfall in different rocky caves show different correlations,which provides another layer of information for analysis of variousfactors on the occurrence of rocky generated further.(4) The study found the Shijiangjun Cave and the Benzhai cavedrip point Ca2+,Mg2+content formed a January centric seasonal troughperiod, due in January temperature, soil CO2concentrations havereached the lowest value from the dissolution of soluble force andforce double impact, causing cave drip Ca2+,Mg2+abnormally low inJanuary, becoming the seasonal trough period, and drawing Ca2+,Mg2+influenced by the temperature. We further statistics and Mg/Caratio relationship of drip points and the corresponding monthlyaverage temperature of the study area, founding that most drippoints Mg/Ca ratio was negatively correlated with temperature,which can be a preliminary analysis of cave drip in Mg/Ca ratios to a certain extent reflect changes in temperature. The higher Mg/Caratio is, the lower temperature does. Currently, Mg/Ca ratio isoften used to indicate rainfall information to reflect changes inwet and dry areas, the correlation between the temperature needsto be further explored in future studies which may be analysed andconfirmed deeper.