The role of microalgae and their carbonic anhydrase on the biological dissolution of limestone

This study aims to investigate the effect of microalgae and their carbonic anhydrase (CAex) on limestone dissolution. The dynamics of Ca 2+ and Mg 2+ release, the model for the amount of Mg 2+ released and biological cumulative effect time by the microalgae Chlamydomonas reinhardtii ( CR ) and Chlorella pyrenoedosa ( CP ), and the algal stable carbon isotopic composition (δ 13 C) in the presence and absence of the membrane-impermeable CAex inhibitor acetazolamide (AZ) were compared in a medium containing limestone. The amount of Mg 2+ released from the limestone in the treatment without AZ was more than that with AZ during the logarithmic phase. The amounts of Mg 2+ release unit algal biomass and unit time in CR and CP were 3.37 × 10 −4 and 2.44 × 10 −4 mg/μg days in the treatment without AZ, respectively, and only 1.99 × 10 −4 and 2.19 × 10 −4 mg/μg days in the treatment with AZ, respectively. The biological dissolution of the algae increased with increasing algal CAex activity. The variation of Ca 2+ was influenced by reprecipitation, and the algal limestone dissolution cannot be shown distinctly. The CAex of the microalgae may be beneficial for CaCO 3 reprecipitation, and the δ 13 C values of the algal cells with AZ were lower than those without AZ. Therefore, AZ not only can inhibit limestone dissolution by inhibiting microalgal growth, but also can reduce limestone dissolution by decreasing CAex catalysis. The results suggest the important influence of microalgae and their CAex on the biokarst process.