Litterfall Mercury Monitoring Initiative


The National Atmospheric Deposition Program (NADP) has a new litterfall mercury monitoring initiative to complement the Mercury Deposition Network (MDN) monitoring for mercury in precipitation and the Atmospheric Mercury Network (AMNet) monitoring for mercury in air.

The litterfall monitoring initiative offers a way for a NADP site sponsor to get measurements to approximate a large part of the mercury dry deposition in a forest landscape. A site sponsor subscribes to the litterfall monitoring initiative for a fee and receives:

  • supplies for collecting annual samples of litterfall from a forest study plot near their site,
  • analysis of the samples for mercury and methylmercury,
  • data on mercury and methylmercury concentrations and litterfall mercury deposition of total mercury and methyl mercury.

Like other NADP network data, the litterfall mercury monitoring data will be hosted on the NADP 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 to total mercury deposition was shown in 3-year study at 23 MDN sites in 15 states. Study results were published in a scientific journal and presented at two NADP science symposiums. An indication of the importance of litterfall deposition is shown in these maps from the study.

Siting Requirements/Start Up

There are two requirements for an NADP site to participate in the litterfall mercury monitoring initiative as part of the transition program:

  1. forest near the NADP site that is suitable for establishing a representative study plot for collecting annual litterfall samples; and
  2. joining the NADP as a cooperator.

The litterfall mercury monitoring initiative began sample collection with onset of autumn leaf fall in 2012, which varies by latitude, altitude, and forest type (approximately August through September). Sites can join the litterfall monitoring initiative during any year, but will need to be operating before leaf fall begins. NADP has litterfall sampling kits ready to go.

The protocols for the litterfall mercury monitoring initiative explain the forest study plot and sample collection. One of the litterfall collectors from the 3-year study is shown here.


The NADP litterfall mercury monitoring fee is $2,600 per site. This fee pays for sampling supplies, sample analysis, shipping to the site, and site support. Like other NADP networks, the site pays to ship the monthly litterfall samples to NADP (2 to 6 shipments, depending on location and forest type). Also, the site operator will spend approximately 1 hour each month, first to deploy 8 sample collectors and then to retrieve and ship the 8 monthly litterfall samples. The samples can be collected at the same time as the MDN sample is collected (about 1 hour per month). No extra equipment or supplies are needed.

For More Information

Additional details about the new initiative for litterfall mercury monitoring are in the 12-Point Plan, including protocols for site selection, sample collection, and data management. For more information about starting litterfall sample collection, contact the U.S. Geological Survey transition program site liaison, Martin Risch at 317-600-2763,, or David Gay at the NADP Program Office (217.244.0462,

The 12-Point Plan (the official NADP proposal) is available here, as is a printable announcement of the network.

Forest-cover types in the eastern USA with Mercury Deposition Network sites in litterfall study, showing mean annual litterfall Hg dry deposition, 2007–2009. (Click to enlarge)

Mean annual litterfall mercury dry and mercury wet deposition at litterfall mercury study sites, 2007–2009 (Click to enlarge)

Litterfall sample collector.
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Litterfall Monitoring Sites.
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