The National Atmospheric Deposition Program (NADP) approved the Mercury Litterfall Network (MLN) in 2021 to complement the Mercury Deposition Network (MDN) that monitors mercury in precipitation and the Atmospheric Mercury Network (AMNet) that monitor mercury in air.
The Mercury Litterfall Network offers a means by which an NADP site sponsor can obtain measurements that provide an estimate of an important source of mercury dry deposition to a forested landscape. A site sponsor can subscribe to the Mercury Litterfall Network for a fee and receive:
- supplies for collecting annual samples of litterfall from a forested study plot near their site,
- sample mercury analysis,
- data on mercury concentrations and litterfall mercury deposition.
The transitional Mercury Litterfall Network data is currently hosted on the USGS ScienceBase Catalogue public website. In combination with data from the MDN and AMNet networks, the litterfall data can be used to examine ranges of mercury dry deposition, to estimate combined wet and dry mercury deposition, and to evaluate mercury models.
The importance of litterfall mercury data for quantifying atmospheric mercury deposition to forests was demonstrated with studies at NADP sites in the eastern USA from 2007-2009 and 2007 to 2014. Maps on this web page show the NADP study sites and mean annual atmospheric mercury deposition from litterfall and precipitation at the sites. Litterfall mercury deposition was compared with estimated mercury dry deposition based on NADP data in another study
Information on joining the network is available here.
There are two requirements for an NADP site to participate in the Mercury Litterfall Network:
- forest near the NADP site that is suitable for establishing a representative study plot for collecting annual litterfall samples; and
- joining the NADP as a subscriber.
The Mercury Litterfall Network starts sample collection prior to the onset of autumn leaf fall, a date that varies with latitude, altitude, and forest type (approximately August through September). Sites can join the Mercury Litterfall Network during any year, but will need to deploy sample collectors before leaf fall begins. NADP has litterfall sampling kits available and ready to ship to site operators.
The protocols for the litterfall mercury monitoring initiative explain the forest study plot and sample collection. Passive collectors are systematically deployed and emptied to obtain an annual sample of ambient litterfall during the entire autumn leaf drop season in deciduous and mixed deciduous-coniferous forests. Contact NADP to start litterfall monitoring in other forest types.