Geochemical Dynamics Of The Limestone Profile During CO₂ Cycle

Geochemical kinetics originated from chemical kinetics,mainly studying the dynamics of geological reactions and mass migration.Because thermodynamics can only solve the direction and extent of chemical reactions,geochemical dynamics not only studies forward modeling,but also focuses on inversion problems,often dealing with kinetics under variable temperature conditions,and more research on heterogeneous reactions.Because there are many factors affecting the CO₂ cycle in the soil air of limestone profile,and its understanding is still not clear,especially some of the impact mechanisms need to be further analyzed.The karst carbon cycle urgently needs the geochemical power of the CO₂ cycle of lime soil profile.The analysis is conducted to provide a reference for the soil carbon pool carbon cycle mechanism and the estimation of karst carbon sinks.In this study,the three sections of the Puding Ecological Station were monitored and sampled,and the main conclusions were as follows:1.From January 2018 to February 2019,this study conducted continuous sampling analysis and monitoring of CO₂ concentration and?¹³C value of soil air in three sections of the Prestation Karst Observatory,and the soil of three sections.Physical and chemical properties,soil organic carbon?¹³C value,soil particle size and pH were measured.2.On the seasonal scale,the main driving force for the change of soil CO₂ concentration is precipitation and atmospheric temperature.Precipitation and atmospheric temperature can directly affect the strength of soil respiration,directly control the change of CO₂ concentration in soil air,showing the law of summer high and low winter.3.In the vertical space,the soil air CO₂ concentration generally increases with the depth of the soil.The distribution of soil air CO₂concentration in different layers of the profile is affected by the concentration gradient of the soil.The influence of caves,followed by other factors,such as soil particle size,pH,organic carbon and nitrogen content.4.Vegetation controls the concentration of CO₂ in the limestone profile.The main sources of soil CO₂ are the decomposition of soil organic matter,plant root respiration and soil biological respiration.The amount of vegetation on the soil directly controls the CO₂ concentration of the soil profile.Different types of soil vegetation and coverage between soil profiles in the same region under the same climatic conditions will result in different CO₂ concentrations and carbon isotope values in the soil air.5.The dynamic mechanism of the limestone profile during CO₂ cycle is mainly divided into three parts:one is the decomposition of soil organic matter,the root respiration of plants and the biological respiration of soil during the process of soil respiration,which produces a large amount of CO₂ enriched in the soil;The second is the ventilation effect between the soil and the subsoil fissures or caves.The ventilation mode of the subsoil fissures or caves controls the diffusion direction of soil CO₂.The ventilation effect of the caves and fissures of the soil has a great influence on the soil CO₂ concentration.And the cracks inhale CO₂ in the soil in summer,and CO₂ in the soil in winter;the third is karstification.The occurrence of karstification has an effect on its migration and diffusion.In summer,the most intense karstification occurs.The karst consumes part of the CO₂ in the soil air,and the hydrodynamic force caused by precipitation continuously moves the soil CO₂ downward.Soil respiration and precipitation are weakened,karstification is weakened,and the impact on soil CO₂ is also reduced.