Mercury transport in an alpine watershed in the Rocky Mountains

Campbell, D; Mast; Clow

Atmospheric wet deposition of mercury (Hg) is moderately high (7-10 mg m-2 y-1) at high elevations of the Rocky Mountains, but little research has been done on the fate of Hg in these systems. In the alpine watershed of Andrews Creek in Rocky Mountain National Park, Colorado, seasonal patterns and interannual variability in total Hg (THg) transport were investigated during water years 2003-2005. Most of the annual flux of THg was transported in dissolved form during snowmelt runoff, with both THg and discharge peaking during late June. Peak THg concentrations were associated with peak dissolved organic carbon (DOC), especially hydrophobic acids, being flushed from soils and other shallow groundwater matrices such as talus deposits. DOC and Hg accumulated in soils during the 2002 drought, and were flushed out when snowmelt runoff returned to near average in 2003. Over the 3 year study period, the highest streamwater THg concentrations were ~ 3 ng L-1 during snowmelt runoff in 2003. After the snowmelt peak, concentrations declined to less than 1 ng L-1 in late summer of 2003. In 2004, peak THg was somewhat less at 2.4 ng L-1, but remained above 1.5 ng L-1 through autumn. Heavier than normal summer precipitation that contained high Hg levels fed runoff through late summer. Rainfall runoff during 2004 had the opposite effect of the drought, flushing much of the THg that normally accumulates in the watershed during those seasons, and leaving a smaller supply available for transport during the 2005 runoff season. In 2005, snowmelt THg peaked briefly around 2.4 ng L-1, then declined to less than 0.5 ng L-1, producing an annual THg flux about 25% lower than in the previous years. Despite thin and sparse soil cover in the Andrews Creek watershed, Hg export is controlled by the supply of DOC and Hg in soils, and by hydrologic flushing from those soils. Precipitation amount and its seasonal distribution affect Hg transport over multiple years. Ongoing studies are contributing to better understanding of current and future ecosystem effects of Hg deposition, and the interaction of potential changes in mercury deposition, nutrient deposition, and climate in mountain environments.

Mercury transport in an alpine watershed in the Rocky Mountains

Collections