1 research outputs found
A Pulse of Mercury and Major Ions in Snowmelt Runoff from a Small Arctic Alaska Watershed
Atmospheric mercury (Hg) is deposited
to Polar Regions during springtime
atmospheric mercury depletion events (AMDEs) that require halogens
and snow or ice surfaces. The fate of this Hg during and following
snowmelt is largely unknown. We measured Hg, major ions, and stable
water isotopes from the snowpack through the entire spring melt runoff
period for two years. Our small (2.5 ha) watershed is near Barrow
(now Utqiaġvik), Alaska. We measured discharge, made 10 000
snow depths, and collected over 100 samples of snow and meltwater
for chemical analysis in 2008 and 2009 from the watershed snowpack
and ephemeral stream channel. Results show an “ionic pulse”
of mercury and major ions in runoff during both snowmelt seasons,
but major ion and Hg runoff concentrations were roughly 50% higher
in 2008 than in 2009. Though total discharge as a percent of total
watershed snowpack water equivalent prior to the melt was similar
in both years (36% in 2008 melt runoff and 34% in 2009), it is possible
that record low precipitation in the summer of 2007 led to the higher
major ion and Hg concentrations in 2008 melt runoff. Total dissolved
Hg meltwater runoff of 14.3 (± 0.7) mg/ha in 2008 and 8.1 (±
0.4) mg/ha in 2009 is five to seven times higher than that reported
from other arctic watersheds. We calculate 78% of snowpack Hg was
exported with snowmelt runoff in 2008 and 41% in 2009. Our results
suggest AMDE Hg complexed with Cl<sup>–</sup> or Br<sup>–</sup> may be less likely to be photochemically reduced and re-emitted
to the atmosphere prior to snowmelt, and we estimate that roughly
25% of the Hg in snowmelt is attributable to AMDEs. Projected Arctic
warming, with more open sea ice leads providing halogen sources that
promote AMDEs, may provide enhanced Hg deposition, reduced Hg emission
and, ultimately, an increase in snowpack and snowmelt runoff Hg concentrations