Long-term trends (1998-2022) of total mercury in mosquitofish (Gambusia holbrooki) from the Everglades Protection Area, Florida, USA.

Mercury bioaccumulation has been a serious environmental concern in Florida's Everglades. Mosquitofish (Gambusia holbrooki) composite samples were collected from 12 stations within the Everglades Protection Area and Everglades National Park from 1998 to 2022 and were analyzed for total mercury (THg). Annual average mosquitofish THg concentrations observed at the 12 stations differed significantly and varied from 11 ng g-1 at an inflow station to 86 ng g-1 at an interior station. Four stations displayed significant declines in mosquitofish THg concentrations, whereas six stations showed weak declines. No stations had a significantly increasing trend over the monitoring period. Additionally, the relationship between key environmental variables that may influence mercury methylation and bioaccumulation, and mosquitofish THg concentrations was evaluated. Results indicate that mosquitofish THg concentration increased as conductivity, alkalinity, and water color content increased from low to mid-levels, and then decreased when these variables reached their respective high ranges. Mosquitofish THg concentration increased as dissolved oxygen and total iron increased from low to mid-levels, but did not show significant changes when the concentrations of these variables further increased. Furthermore, mosquitofish THg increased as TP concentration increased from an oligotrophic to eutrophic state. Mosquitofish THg concentration did not differ significantly at sulfate concentration below 20 mg L-1, but decreased when sulfate concentration further increased beyond 20 mg L-1. Data for mosquitofish THg concentrations pooled from all stations for the period of record did not show significant changes across level of atmospheric mercury loading and annual total rainfall. These findings suggest that complex biogeochemical processes control spatial and temporal variations of mosquitofish THg concentrations in this subtropical wetland.