A Simple, Direct Method to Measure Dissolved Co2 Using Soda Lime

A method for the direct assessment of the dissolved CO2 concentration in supersaturated water is presented that is based on changes to the physical chemistry of soda lime due to uptake of CO2. The approach is an adaptation of a standard method used for the quantifi cation of soil respiration, and was found to agree with pCO2 measurements made using infrared gas analysis. In this method, the soda lime is deployed in a CO2 bucket chamber, and a water sample is allowed to outgas for 48 hours. The initial dissolved CO2 concentration is then determined from changes in the dry mass of soda lime, which is blank-corrected and adjusted based on differences in molecular weights of soda lime before and after the chemical adsorption of CO2. The method is applicable to highly-supersaturated surface water and emergent groundwater.