Experimental study on the utilization efficiency of Chlorella to Ca2+ and HCO3- in karst water

Chlorella was collected from Dalongdong cave in Shanglin county of Guangxi to study its utilization efficiency of Ca2+and HCO3- in three water bodies with different concentrations of DIC (4.6 mmol·L-1, 2.5 mmol·L-1and 0.5 mmol·L-1) in the closed system. The results show that: (1)After 7 days of cultivation in three different DIC solution of 4.6 mmol·L-1、2.5 mmol·L-1and 0.5 mmol·L-1, Chlorella biomass increased from 0.04 Abs，to 0.56 Abs,0.50 Abs and 0.44 Abs, respectively. In the environment with high HCO3-and Ca2+ concentration, Chlorella absorbed 54.95% of HCO3- in group A and 48.00% of HCO3- in group B, it also absorbed 28.26% of Ca2+ in group A and 24.14% of Ca2+in group B. In the environment with low HCO3- concentration, it was difficult for Chlorella to absorb HCO3- in group C (0.5 mmol·L-1). These findings indicate that the high concentration of HCO3- in karst reservoirs plays a role of "fertilization" on the growth of Chlorella,which is significant to the karst process-related carbon sink;(2)The amount of Ca2+ deposition caused by Chlorella photosynthesis using HCO3- was higher than the amount of Ca2+ absorbed by Chlorella photosynthesis;(3)Photosynthesis from Chlorella make δ13CDIC positive, while the respiration make δ13CDIC negative in the culture medium.