ICMGP 2022 – On-Demand / Poster Presentation

Abstract Information :

As surface waters of lakes warm, their depths are losing dissolved oxygen (DO), thereby increasing the extent of seasonal anoxia. Methylation of mercury becomes more likely under these conditions, in both the water column and benthos. To understand whether these ecosystem shifts lead to enhanced mercury bioaccumulation in lake fishes, we compared mercury concentrations in brook trout to the temperature and chemistry of four lakes in New York across a 17-year period. Preliminary results indicate that dissolved organic matter and pH were important predictors of spatial and temporal variation in fish mercury. In addition, mercury levels in fish rose when the proportion of the water column that went anoxic during the summer exceeded ~ 20% of the water column. To better assess this relationship, we used high-frequency sensors to continuously monitor oxygen in 15 lakes through one growing season. These lakes varied in the degree and duration of oxygen depletion, ranging from normoxia throughout the water column to anoxia in > 50% of the water column through the entire monitoring period (June-October). Trout mercury concentrations were also highly variable. The influence of anoxia and other chemical factors was evident in our spatial comparisons, including high mercury concentrations being associated with anoxia. Given that the world?s temperate lakes show a strong long-term trend toward deep-water oxygen depletion, our results suggest the potential for concomitant increases in fish mercury. Warming driven enhancement of the bioavailability and transfer of mercury pollution into lacustrine food webs could necessitate expansions of mercury monitoring efforts and fish consumption advisories. Importantly, this causal chain acts on existing mercury pools, in addition to new inputs that are a common focus of mercury control efforts.