Lakes across the Northern Hemisphere have experienced enhanced atmospheric deposition of anthropogenically derived Hg for over 100 years. In the present study, we quantified Hg fluxes to the sediments of ten small drainage lakes across Vermont and New Hampshire, USA, for the period ∼1800 to present. Dates were established by 210Pb. Total Hg (HgT) fluxes to sediments ranged from 5 to 17μgm-2yr-1 during pre-industrial times, and from 21 to 83μgm-2yr-1 presently. Present-day HgT fluxes are between 2.1 to 6.9 times greater than pre-1850 fluxes. Current-day direct atmospheric Hg deposition to the study region was estimated at 21μgm-2yr-1, which agrees well with measured HgT deposition, when re-evasion of Hg is accounted for. Our data suggest that Hg fluxes to lake sediments have declined in recent decades, owing to reductions in atmospheric Hg deposition to the lake surface. Watershed export of atmospherically deposited Hg remains elevated relative to present-day deposition rates, which contributes to the impression that Hg retention by watershed soils has declined.
Bibliographical noteFunding Information:
We thank Steve Couture, Bob Estabrook, and Steve Landry of the NH Department of Environmental Services for their project support; Ed Glassford, Kate Peyerl, and Kellie Merrell of the VT Department of Environmental Conservation, for analytical chemistry, coordinating both field sampling and lab processing, and for figure preparation; Kelly Thommes of the St. Croix Watershed Research Station for assistance in the 210 Pb dating; and, Dr. Ruth Mickey of the University of Vermont for assistance with statistics and Dr Mary C. Watzin, also of UVM, for her thoughtful manuscript review. We gratefully acknowledge Rochelle Araujo, Ray Thompson, and Alan VanArsdale of USEPA for their continued interest and support of this research. Finally, we thank our anonymous reviewer for informative comments to earlier manuscript drafts. This project was funded largely by USEPA, under cooperative agreement CR-82549501, and the results of this research do not necessarily reflect the views of USEPA.
- Atmospheric deposition