Atmospheric Mercury Deposition from Litterfall in the Eastern USA
Martin Risch1, John Dewild2, David Gay3, Leiming Zhang4, Elizabeth Boyer5 and David Krabbenhoft6
Atmospheric mercury deposition from litterfall was found to be an important route for mercury loading to forest ecosystems in the eastern USA. Mercury (Hg) monitoring of autumn litterfall was done for six years at 27 National Atmospheric Deposition Program (NADP) sites in deciduous and mixed deciduous-coniferous forests in 16 states. Hg concentrations and the dry weight litterfall catch in samples from passive collectors were used to compute annual litterfall Hg deposition. Monitoring results from 2007–2009 and 2012–2014 indicated annual litterfall Hg deposition rates were equal to or higher than annual wet Hg deposition rates in 70 percent of the records at co-located NADP precipitation-monitoring sites. Annual littrfall Hg deposition was a median 11.7 and a maximum 23.4 micrograms per square meter per year. Annual litterfall Hg deposition measurements were closely aligned with modeled dry deposition of gaseous elemental, oxidized, and particulate-bound Hg air concentrations at co-located NADP atmospheric monitoring sites. These findings indicate atmospheric Hg loading to forest ecosystems can be measured more completely and dry Hg deposition models are improved when litterfall Hg deposition data are included. A long-term, litterfall Hg monitoring network can be a cost-effective and useful complement to precipitation Hg and atmospheric Hg monitoring networks.
1U.S. Geological Survey, email@example.com 2U.S. Geological Survey, firstname.lastname@example.org 3University of Illinois, email@example.com 4Environment Canada, firstname.lastname@example.org 5University of Pennsylvania, email@example.com 6U.S. Geological Survey, firstname.lastname@example.org