Discussion on the formulas used to calculate the dissolution rate by the rock tablet method
The dissolution rate of carbonate rocks is an important parameter for investigating the karst carbon cycle and evaluating the carbon sink effect;as well as a key indicator for studying karst development and karst hydrogeological problems.The rock tablet method is currently one of the main methods for quantitatively evaluating karstification and its carbon sink intensity,and has been widely recognized and used.The rock tablet method can not only analyze the factors affecting the dissolution rate of carbonate rocks(e.g.,climate,lithology,soil properties),but also further explore the temporal and spatial variation characteristics of subsurface karstification by burying carbonate rock tablets at different depths.However,in current studies related to the calculation of carbonate dissolution rates using the rock tablet method,there are different versions of the dissolution rate calculation formula,and there are still some problems in its application,resulting in significant differences in the dissolution rate values calculated using different formulas for the same monitoring data,which adversely affects the accurate determination of the regional dissolution process and assessment of the karst carbon sink effect.This study firstly reviewed the origin,operational procedure,and basic principles of the carbonate rock tablet method and clarified the key links such as the preparation of the rock tablets(the standard rock tablets were uniformly made of limestone in the same stratum,usually the Rongxian formation of the upper Devonian collected from Guilin in Guangxi,or the upper Cretaceous collected from Slovenia,with a diameter of 4 cm and a thickness of 3mm to5 mm),burial layers(in the air,on the surface,and at the soil depths of 20 cm and 50 cm),burial duration(typically corresponding to one hydrological year),and weighing(using a balance with one-millionth precision).The advantages and limitations of commonly used carbonate dissolution rate calculation methods are summarized.Then,the paper analyzed some of the published formulas for calculating the carbonate dissolution rate using the rock tablet method and discovered that some of the formulas have the following issues,(1)The coefficient(method)from the daily dissolution rate to the annual dissolution rate is incorrect,further intensifying the uncertainty of the results;(2)The short-term test results were extrapolated over a long time scale,disregarding the influence of the dynamic changes in environmental conditions on the carbonate dissolution rate;(3)Unit conversion errors.These problems can result in significant calculation errors in the carbonate dissolution rate and make it difficult to conduct comparisons among regions.Finally,based on the fundamental principle of the rock tablet method,this study proposes a suggested formula for calculating the carbonate dissolution rate using the rock tablet method.The suggested formula can further enhance the standardization of the carbonate dissolution rate using the rock tablet method,providing data support for conducting global analysis and comparative research,revealing the laws of karst development,and improving the accuracy of karst carbon sink estimation.This study also proposes that methods should be selected based on the characteristics of the study area and research purpose.At the same time,it is of great necessity to strengthen the correlations between various test methods.
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