Examining temporal trends in the production and bioaccumulation of methylmercury in a restored wetland habitat on Brier Island, Nova Scotia

Mercury (Hg) is a contaminant of global concern due to its ability to undergo long-range transport from distant sources to sensitive ecosystems. In wetlands, Hg is readily methylated to methylmercury (MeHg) by sulfate-reducing bacteria. MeHg, a neurotoxin, then bioaccumulates and biomagnifies through aquatic food webs. Our study site, Big Meadow Bog (BMB) on Brier Island, Nova Scotia, underwent a water table restoration in 2018 which flooded the bog, altering Hg cycling. To determine the effects of this flooding on the biogeochemical cycling of Hg, outflow surface water was collected over five years (2018-2023) and invertebrate samples were taken over three summers (2021, 2022, and 2023). The filtered water samples were analyzed for MeHg, total mercury (THg), dissolved organic carbon (DOC), and nutrients (PO43-, NO3-, and SO42-), while THg and MeHg were quantified from invertebrate samples. MeHg, DOC, PO43-, and NO3- concentrations were significantly higher in the first year post-flooding and decreased through subsequent years. MeHg, DOC, and NO3- concentrations were all strongly correlated and significantly higher in the summer months than the winter months, indicating that biotic MeHg production was considerably affected by these factors. MeHg concentrations in water were correlated with those in invertebrate tissues, suggesting that this environment is conducive to invertebrate MeHg uptake. Further investigations into the composition of DOC and its role in MeHg cycling as well as the role of nutrients in the bioaccumulation of MeHg is warranted to complete our understanding of the biogeochemical cycling of Hg in altered wetlands.