Detailed monitoring of changing mercury and methylmercury concentration in a creek during baseflow and flood events indicates MeHg is produced within the stream and further suggests that algal biofilms, also called periphyton, are major sources of MeHg generation.
These findings may explain why past improvements in overall stream water quality have not resulted in concomitant improvements in MeHg concentration in water and in fish. Additionally, future alterations to stream management practices or climate that alter the abundance, activity, or composition of periphyton may have unintended negative consequences as they have the potential to influence MeHg production within the creek.
Sediments and floodplain soils in the East Fork Poplar Creek (EFPC) watershed in Oak Ridge, Tennessee, are contaminated with high levels of mercury from an industrial source at the headwaters. While baseflow conditions have been monitored, concentrations of Hg and MeHg during high-flow storm events—when the stream is more hydrologically connected to the floodplain—have yet to be assessed. The present study evaluates baseflow and event-driven Hg and MeHg dynamics in EFPC, five kilometers upstream of the confluence with Poplar Creek to determine the importance of hydrology to in-stream concentrations and downstream loads and ascertain if dynamics are comparable to systems without an industrial Hg source. Particulate Hg and MeHg were positively correlated with discharge (r2=0.64 and 0.58, respectively) and total suspended sediment (r2=0.97 and 0.89, respectively). Dissolved Hg (HgD) also increased with increasing flow (r2=0.18) and was associated with increases in dissolved organic carbon (DOC) (r2=0.65) similar to dynamics observed in uncontaminated systems. Dissolved MeHg (MeHgD) decreased with increases in discharge (r2=0.23) and was not related to dissolved organic carbon concentrations (p=0.56), dynamics comparable to relatively uncontaminated watersheds with a small percentage of wetlands (<10%). While stormflows exert a dominant control on HgP, MeHgP, and HgD concentrations and loads, baseflows were associated with the highest MeHgD concentration (0.38 ng/L) and represented the majority of the annual MeHgD load.
Riscassi, A., C. Miller, and S.Brooks. 2016. “Seasonal and Flow-driven Dynamics of Particulate and Dissolved Mercury and Methylmercury in a Stream Impacted by an Industrial Mercury Source.” Environmental Toxicology and Chemistry 35(6): 1386–1400. DOI: 10.1002/etc.3310
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