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Mercury Mass Balance in Decomposing Leaf Litter

Kathleen Knight and Dr. David R. Miller
University of Connecticut, Natural Resources Department


Tree leaves accumulate large amounts of mercury (Hg), during each growing season from the atmosphere. Leaf senescence is a significant transfer of atmospheric mercury to the soil surface. Nonetheless, little is known about the disposition of the mercury in decomposing litter. This study was designed to determine the Hg transport and storage pathways in the decomposition process. Composting the litter allowed us to control the decomposition rate and monitor the Hg budget of the compost during the various stages of decomposition. Two compost piles of tree leaf litter were observed, to reveal the movement and chemical transformations mercury goes through during the leaf degradation process. One of the piles was turned manually while the other remained static to provide two different aeration conditions.

Measurements of the Hg inputs (wet and dry deposition), the Hg outputs (leaching and evasion to the atmosphere) and the Hg storage in the pile were made over a 6 month composting season. The measurements demonstrated that only a small amount of the Hg originally in the leaves was leached into the soil. The loss to the atmosphere through gaseous evasion was insignificant. Leaf decomposition released less than one percent of the total Hg in the leaf material. Thus, over 99% of the initial Hg in the leaves remained tightly held to the organic matter during decomposition.