Simulation of Methylmercury Content and SRB Methylation in Phragmites australis Soil Under Different Salinity Conditions

The MeHg content in the reed wetland soil of Liaohe was studied by the indoor-simulated constant temperature culture method. Under different aerobic and anaerobic conditions, the flooding salinity (CK, 0.5%, 1.0%, 1.5%, 2.0%) changes relationship whether SRB plays a leading role in the formation of MeHg. The results showed that under aerobic conditions, the content of MeHg in the surface layer and the bottom layer showed a trend of decreasing first and then increasing with the increase of culture time. Both of them have a lower MeHg content when the flooding salinity is 2.0%. The number of SRB bacteria showed a trend of “upgrading-depleting” with the increase of flooding salinity. Under anaerobic conditions, the MeHg content of surface and bottom soil changed slowly in the early stage of culture (the first 10 days), and the MeHg content increased rapidly after 15 days of culture, and decreased significantly on the 25th day. The number of SRB bacteria showed a trend of “depleting-upgrading” as the flooding salinity increased. Linear fitting showed that there was no obvious linear relationship between the change of MeHg content in soil and the number of SRB bacteria, and other microorganisms may play a role in methylation of mercury. Under anaerobic conditions, MeHg content in surface soil was significantly positively correlated with organic matter ( p < 0.01), but negatively correlated with total mercury ( p < 0.05). The mercury methylation process is affected by many environmental factors, and the mechanism of mercury methylation in different environments is different.