Historical trends in mercury deposition as recorded in lake cores near Glacier Bay National Park and Preserve, Alaska
Nagorski SA, Engstrom DR, Krabbenhoft DP, Lepak RF, Fitzgerald WF. 2019. Historical trends in mercury deposition as recorded in lake cores near Glacier Bay National Park and Preserve, Alaska. Natural Resource Report. NPS/SEAN/NRR—2019/1928. National Park Service. Fort Collins, Colorado
Sediment cores were collected from four lakes on Chichagof Island in southeast Alaska in May, 2015 for the purpose of obtaining profiles of total mercury deposition over multiple centuries. Core sections were analyzed for organic content and dry density, age dated using 210Pb isotopes and constant rate of supply dating models, and for three of the cores, analyzed for total mercury (Hg) and stable isotopes of mercury (∆199Hg and δ202Hg). The three cores with full analyses (single cores from Rectangle, Sapsucker, and Goldeneye Lakes (unofficial names)) were age dated as far back as the 11th century. Total mercury fluxes to each lake were fairly constant prior to the 18th century, followed by sharp increases in two of the lakes (Rectangle and Goldeneye) in the mid-19th centuries, at the start of the Industrial Revolution. Rectangle and Sapsucker Lakes then show their strongest deposition increases in the mid-20th centuries, with peak flux values during 1990s-2000, perhaps reflecting increased coal burning in Asia and global small scale gold mining operations. Modern fluxes of Hg to the lakes are 2-4 times higher than during preanthropogenic (pre-year 1500) times. Mercury flux profiles also track closely with those in a regional ice core that exhibits sharp increases late in the 20th century. Differences in profiles between the lakes, as well as some incongruence of profiles from the same lakes in 2003, highlight the need to obtain multiple cores per lake and multiple lakes in order to track fine-scale local changes in sediment accumulation rates and atmospheric mercury deposition. Variations among cores and lakes are likely attributable to heterogeneous timing of release and sourcing in the watershed from geogenic and atmospheric sources. Lake cores such as these, especially if augmented by larger sample sizes, are excellent archives of long term Hg wet and dry deposition to remote areas such as those in the Southeast Alaska Network of National Park units.
- Type
- Published Report
- Authors
- Nagorski, Sonia; Engstrom, Daniel; Krabbenhoft, David; Lepak, Ryan; Fitzgerald, William
- Date of Issue
- 2019-05
- Publisher
- National Park Service
- Units
- GLBA , NRSS , SEAN
- Keywords
- contamination, deposition, lake core, mercury, stable isotope
- Subjects
- Ecological Framework: Air and Climate | Air Quality | Air Contaminants , Ecological Framework: Geology and Soils | Geomorphology | Lake Features and Processes , Ecological Framework: Human Use | Non-point Source Human Effects | Non-point Source Human Effects