Dynamics of total culturable bacteria and its relationship with methylmercury in the soils of the water level fluctuation zone of the Three Gorges Reservoir

Field investigations were conducted to study the temporal and spatial distribution characteristics of total culturable bacteria (TCB) and its relationship with methylmercury (MeHg) in the soils of the water level fluctuation zone of the Three Gorges Reservoir. Different altitudes (170–180, 170–175, 165–170 and 160–165 m) in Zhenxi (Site 1), Shibaozhai (Site 2) and Tujing (Site 3), Chongqing, China were chosen as sampling sites. Results indicated that TCB did not have significant difference in the top (0–10 cm) and sub (10–20 cm) soil of the non-inundated area (175–180 m), but showing a significant difference in the water level fluctuation zone (<175 m, suggesting that water level fluctuation had an important effect on TCB. Moreover, TCB in soils of various altitudes of Site 1 and 2 had significant difference, while for Site 3, this difference was not significant. And the difference of TCB in Site 2 was much greater than that in Site 1. These results suggested that there were significant differences for TCB in soils of mainstream and tributaries. In addition, TCB in soils of 10–20 cm had significant or highly significant positive correlations with MeHg level (r ≥ 0.762, P ≤ 0.048), thus we assumed that there may be some aerobic microorganisms playing dominant roles in mercury methylation.