Research On Composite Deposition Of Huanglong Typical Diatom And Travertine In Plateau Cold Water Environment

The specific karst landform has aroused tremendous attention which was formed by calcium carbonate and travertine deposition.Especially,the travertine deposition can greatly change the contour of riverbed.Huanglong is unique alpine travertine sedimentary landscape with great scientific and cultural value,which is included in the"World Cultural and Natural Heritage List"by UNESCO in 1992.Besides,Huanglong not only has singificant tourism value,but also is worth to determine the law of travertine deposition,and investigate the local ecological and geological evolution,especially focus on the effect and contribution of environmental organisms in the same period.This study take the complex depositional systems of travertine and Huanglong typical diatom as the research content,based on analysising of hydrochemical characteristics,combine with the depositional feature of supergene travertine,exploring the effect of diatom in travertine deposition behaviors.This research could provide a theoretical basis for conservation of travertine landscape and microbiological effects on travertine deposition in Huanglong.Water is the lifeblood of the travertinelandscape.Using comparative analysis of hydrochemical variations of surface water in the wet season in 2015 and 2016,the results showed that the basic physicochemical properties of surface water is keep stable,the precipitation decreasing and increase of surface runoff infiltration may become the reason for surface water change.Ca²⁺and CO₃^2-are regular changes with altitude,the concentration of Ca²⁺and HCO₃^-has decreased from 206 mg/L to 87.7 mg/L,780 mg/L to 317 mg/L,respectively.Analyzing of organic content of surface water in august2016 showed that total phosphorus content was less than 0.02 mg/L,the maximal value of chemical oxygen demand?COD?is 6.02 mg/L,ammonia nitrogen content is less than 0.15 mg/L?except Wucai ponds?.Overall,the surface water environment quality in Huanglong is meet a criterion.Due to the decrease of precipitation and the influence of tourism activities,the Huanglong scenic has been obviously degradation in recent years,which is mainly manifested that dry up of travertine ponds,algae growth with large areas,color variations of travertine.In this study,the chemical composition and organic content of black,yellow and white travertine are characterized,the total carbon,silicon,sulfur,magnesium,aluminum and other elements were decreased with the travertine color from black to white.The specific fluorescent staining of travertine polysaccharide shows that there are a lot of fluorescent markers on the surface of the black travertine,and the signal is strong.The yellow travertine surface fluorescent staining area is small,and the white travertine is basically not stained,reflecting the three travertine colors from black to white,the polysaccharide content gradually decreased,and the degree of biological participation weakened.In addition,the quantitative test results of three travertine organic carbons shows that the black travertine organic carbon content averaged up to0.63%and the white travertine is 0.20%.Taking into account that silicon,sulfur,iron and other elements are the main elements of the typical psychrophilic microbes diatom and filamentous algae in Huanglong,therefor,the black color of travertine in Huanglong is caused by biological factors.In order to investigate the interaction between organisms and travertine,we collected the algae mats and separated the psychrophilic diatoms in the Zhengyan ponds.The microscopic morphology of the algae mats shows that filamentous algae,diatoms and travertine particles are the basic units that make up the algae mats.During the dry season,the deposition of travertine is slow.The diatom,filamentous algae and calcite crystals are mainly based on etching.During the wet season,the deposition rate of travertine is faster,and the algae can provide a template for travertine the deposition.Studies on the growth and metabolism of diatoms in fresh water environment and Huanglong water shows that the high concentration of calcium ion?110mg/L?could inhibit the growth of diatom and affected the chlorophyll synthesis of diatoms.The Energy dispersive spectrdmeter?EDS?scanning analysis of diatom in different environments along the direction of raphe shows that the changes of phosphorus and sulfur were synergistic.The results of diatom EDS shows that the Ca/Si is 0.12 in freshwater environment,and in high calcium environment is 0.10.The proportion of travertine in situ is up to 0.88%.The composite deposition of diatom and travertine in cold water environment was simulated in laboratory.The results shows that the whole process of travertine deposition is in accordance with the exponential decay equation,and the correlation coefficient R²is more than 0.80.The microscopic morphology of travertine shows that Ca CO₃is crystallized better calcite in pure calcium carbonate system,and calcite crystal in diatom group is longer irregular,so diatom could control the growth of calcite crystal,and the calcite could be etched to a certain extent.