The Impacts of Volcanic Activity on Microbial Growth—A Simulation Experiment in the Qiliao Section in Shizhu County, Chongqing, China

The impact of volcanic activity on microorganisms has always been a hot topic of discussion during geological history. Further studies are needed on the effects of volcanic activity on microbial growth in shale and the differences in nutrients provided by volcanic ash and other weathered rocks. This study's results indicated that TOC contents at the bottom of the shale layer are 1.93-4.44% and 3.0% on average. The TOC contents at the top of the layer are 3.38-5.13% and 4.0% on average. It indicated that TOC contents at the bottom of the shale layer are smaller than the TOC contents at the top of the layer, suggesting that volcanic activity posed a long-term effect on biological growth. Seven different leachate concentrations were set in this experiment as follows: 1/10, 1/100, 1/500, 1/1000, 1/1500, 1/2000, and 1/2500. The results showed that the growth status of Pseudourostyla crassipes was affected by the addition of leachates with different concentrations compared to the control group. Additionally, the synthesis of chlorophyll a by <i>Anabaena pseudoichthyoides</i> was the most efficient with the 1/10 volcanic ash leachate. Through the analysis of major and trace elements in the solution before labeland after cultivation, the main elemental content of Ca²⁺, Mg²⁺, Na⁺, and K⁺ decreased by 3.8~87.24%, 75.96~92.70%, 86.56~95.67%, and 5.42~20.52% in the solution after microbial growth respectively. The trace elements B, Ba, Zn, and Fe decreased by 27.54~94.39%, 20~82.03%, 70.45~98.29%, and 99%. It was found that the B, Ba, Fe, and Zn elements decreased significantly. The nutrients from volcanic ash are the main factor promoting microbial growth. It can be indicated that the volcanic ash soaking solution has a higher content of nutrients when compared to the solubility of nutrients in volcanic ash compared to that of granite. A higher content of nutrients promotes microbial growth. The calculation results indicate that a volcanic eruption with a quantity of several 10¹⁰ m³ has a significant impact on microorganisms, lasting from tens of thousands to hundreds of thousands of years.