Increased atmospheric deposition of mercury in reference lakes near major urban areas
- U.S. Geological Survey, Austin, TX 78754, USA
- Received 28 March 2011
- Revised 27 September 2011
- Accepted 6 November 2011
- Available online 13 December 2011
1. Introduction
2. Methods
3. Results
4. Discussion
Acknowledgments
Appendix. Supplementary data
References
Abstract
Atmospheric deposition of Hg is the predominant pathway for Hg to reach sensitive ecosystems, but the importance of emissions on near-field deposition remains unclear. To better understand spatial variability in Hg deposition, mercury concentrations were analyzed in sediment cores from 12 lakes with undeveloped watersheds near to (<50 km) and remote from (>150 km) several major urban areas in the United States. Background and focusing corrected Hg fluxes and flux ratios (modern to background) in the near-urban lakes (68 ± 6.9 μg m−2 yr−1 and 9.8 ± 4.8, respectively) greatly exceed those in the remote lakes (14 ± 9.3 μg m−2 yr−1 and 3.5 ± 1.0) and the fluxes are strongly related to distance from the nearest major urban area (r2 = 0.87) and to population and Hg emissions within 50–100 km of the lakes. Comparison to monitored wet deposition suggests that dry deposition is a major contributor of Hg to lakes near major urban areas.
Graphical abstract
Highlights
► Hg deposition analyzed in cores from 6 near-urban and 6 remote reference lakes. ► Focus and background corrected Hg flux is ∼4.5 times greater near major cities. ► Strong relation (r2 = 0.87) between Hg deposition and distance from nearest city.
Keywords
- Mercury;
- Sediment;
- Urban;
- Lake;
- Core
Figures and tables from this article:
Fig. 1. Lakes where sediment cores were collected and selected major cities.
Fig. 2. Mercury mass accumulation rate and focus-corrected anthropogenic Hg accumulation rates for 12 lake-sediment cores.
Fig. 3. Relations between three explanatory variables and Hg accumulation rates to 12 lakes. Graph a: distance from major urban area and HgA,F (post-1990 anthropogenic focus-corrected Hg accumulation (gray diamond)) and HgWET (mean wet deposition from 2001 to 2008 for 18 MDN sites (black diamond)). Graph b: population within 100 km of the lake and HgA,F. Graph c: estimated reactive Hg (RGM and Hg(P)) emissions in the nine 0.5 degree cells over and around the lake and HgA,F.
Table 1. Summary of estimated Hg fluxes to 12 lakes. Lakes are sorted with increasing distance from the nearest major city. HgA,F is post-1990 anthropogenic, focus-corrected Hg flux.
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