John Wiley & Sons, Ltd.

Seasonal and flow‐driven dynamics of particulate and dissolved mercury and methylmercury in a stream impacted by an industrial mercury source

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Sediments and floodplain soils in the East Fork Poplar Creek (EFPC) watershed in Oak Ridge, TN, are contaminated with high levels of mercury (Hg) from an industrial source at the headwaters. While baseflow conditions have been monitored, concentrations of Hg and methylmercury (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, 5‐km 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) and dissolved Hg (HgD) also increased with increasing flow (r2=0.18), and was associated with increases in dissolved organic carbon (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 DOC 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. This article is protected by copyright. All rights reserved

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