however, groundwater was found to be an important source of MeHg to the lake, with
concentrations as high as 12 ng/L in a hyporheic-zone sample (Stoor et al., 2006).
At a lake in glacial outwash (Wisconsin, USA), groundwater (sampled by piezometers and
dug wells) both discharges to the lake and receives recharge from lake waters. Mercury enters
from atmospheric
deposition to the lake, and, apparently, through soils to groundwater.
Mercury concentrations in groundwater discharge (mean 12 ng/L) to the lake was higher than
that of water from nearby wells (mean 2.8 ng/L), showing the importance of reactions near and
at the sediment/water interface (Krabbenhoft & Babiarz, 1992). In a New Jersey, USA, Coastal
Plain watershed, groundwater discharging to a major river contained concentrations of THg
in urban areas (some mainly in particulate form) that were higher than those in forested
wetlands areas. Concentrations of THg in unfiltered water were 36 and 177 ng/L in discharge
to the river at two sites in an urban area (Barringer et al., 2010a) and were not representative
of background concentrations for that aquifer, which typically are < 10 ng/L (Barringer & Szabo,
2006). Bradley et al. (2012) also found Hg in groundwater discharge
to be an important input
to a southern USA Coastal Plain stream, although the THg concentrations in the groundwater
were an order of magnitude lower than the concentrations in urban groundwater discharge
in the study of Barringer et al. (2010a).
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