The mercury production in forest ecosystems can be characterized by dynamic changes in forest lakes or reservoirs. Moreover, changes in the downstream mercury concentrations can also reflect the mercury output from forest ecosystems. Based on the analysis of distribution patterns and sediment profiles of mercury in DH1, DH2, DH3, and DH4 during the wet and dry seasons in the Dahong Lake Reservoir, the total mercury concentration of the Dahong Lake Reservoir increases significantly during the wet season (the average of the wet season is 4.33 ng·L-1, the average of the dry season is 1.85 ng·L-1), especially in the downstream. The content of total mercury and methylmercury in the water column of the Dahong Lake Reservoir is significantly higher than that of background lake levels, but it is much lower than that of contaminated lakes, indicating that evergreen broad-leaved forest in the Simian Mountains has characteristics of Hg sources and the sediments are also sources of methylmercury and inorganic mercury in the water column of the Dahong Lake Reservoir. The methylation process mainly occurs in the surface layer of sediments and the methylation process is more active during the wet season. During the wet season, it is more favorable for mercury and methylmercury to enter the sediment liquid phase from the sediment solid phase and thus the water column.
Keywords: Dahong Lake Reservoir; dry season; mercury; sediment-water interface; wet season.