Bioadvection of mercury from the Great Salt Lake to surrounding terrestrial ecosystems and sublethal toxic effects on a terrestrial songbird
Mercury (Hg) is a neurotoxin and global pollutant that in aquatic ecosystems is converted into methylmercury (MeHg), which readily biomagnifies. The Great Salt Lake (GSL) in Utah contains some of the highest MeHg concentrations ever measured in natural waters. While terrestrial organisms typically have very low concentrations of Hg because MeHg is produced almost exclusively in aquatic environments, the Hg concentrations we have measured in spiders along the shoreline of GSL are 60 fold higher than in spiders along nearby Utah Lake. We hypothesized that brine flies with their larval stage in the GSL act as vectors that transfer Hg from the lake to surrounding terrestrial ecosystems where they are eaten by spiders and other organisms. We also hypothesized that songbirds that consume spiders would be exposed to high levels of Hg with possible adverse effects. To test these ideas we characterized spatial and temporal variation in total mercury (HgT) and MeHg concentrations in surface water, brine flies, and spiders at GSL in 2012-2013. We also quantified spatial distribution of HgT concentrations during the 2012-2014 in blood of adult and nestling Loggerhead Shrikes, Lanius ludovicianus, a terrestrial songbird of conservation concern, and investigated sublethal effects due to Hg exposure.
Concentrations of HgT were roughly 100-700 ppb (dw) in brine flies and 400-3000 ppb (dw) in spiders. Seasonal maxima in concentrations of HgT and MeHg in brine flies and spiders occurred in spring and fall, periods of peak migratory bird numbers at the GSL. These seasonal trends mirrored HgT concentrations in surface waters of the GSL, suggesting the lake was the source of mercury. HgT concentrations in nestling shrike blood averaged 91 ppb (ww) and ranged from 7-354 ppb. Average HgT concentrations in adults/juveniles was 912 ppb and ranged from 127-4003 ppb. Approximately 20% of adults/juveniles had blood HgT concentrations above thresholds previously shown to reduce breeding success in other songbirds. HgT concentrations of shrikes decreased with increasing distance from the shoreline, again suggesting the GSL is the ultimate source of HgT in these organisms. Preliminary data from a subset of videos do not show a correlation between nestling Hg levels and nestling feeding rates. Ongoing research will attempt to correlate HgT concentrations and additional parental care behaviors.