Abstract
A shallow site in the western arm of Lake Superior near Duluth, Minnesota was sampled bimonthly from May to October during 1989 and 1990 to identify seasonal and annual changes in bacterioplankton communities. The greatest change in bacterioplankton abundance was between 1989 (1.48 × 109/L ± 0.06 SE) and 1990 (1.14 × 109/L ± 0.06 E). The majority of bacterial cells (65%) were cocci. Individual cells were larger during 1989 (0.067 μm3 ± 0.007 SE) than 1990 (0.025 μm3 ± 0.002 SE). Although the rate of thymidine incorporation varied from 0.2 to 47.0 pmol/L/h over both years (mean = 12.1 pmol/L/h ± 1.3 SE), no consistent temporal or spatial changes were detected. Bacteria were more abundant (∼2x) and productive (∼10x) at the mouth of the Lester River than offshore of this site. During July and August, a benthic nepheloid layer (BNL) formed at shallow offshore sites but bacterioplankton abundance and production in this BNL were usually similar to values measured in the hypolimnion. Three additional sites from the Duluth basin northeast to the Chefswet basin were sampled during late summer (Aug-Sept) 1990 to identify spatial differences in bacterioplankton communities. Although the number of bacteria was often greater at shallower sites compared to deeper sites further offshore, a strong gradient was not found and bacterial production was similar at all sites. These results may be due in part to the lake basin morphology in this region of Lake Superior, as well as the time when these additional offshore sites were investigated.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 196-213 |
| Number of pages | 18 |
| Journal | Journal of Great Lakes Research |
| Volume | 30 |
| Issue number | SUPPL. 1 |
| DOIs | |
| State | Published - 2004 |
Bibliographical note
Funding Information:We thank the captain and crew of the R/V Seward Johnson and pilots and crew of the research submersible Johnson-Sea-Link II from the Harbor Branch Oceanographic Institution. R. Axler, C. Lar-son, and C. Owen helped with sampling from the R/V Noodin. K. Saxrud helped measure bacterial cells. We are also grateful to D. Anderson for guidance on cell volume formulas. This research was supported by grants from the Legislative Commission on Minnesota Resources and the National Undersea Research Center (NOAA) at the University of Connecticut-Avery Point. Part of this work is also the result of research sponsored by the Minnesota Sea Grant College Program (Project number R/CL-21) supported by the NOAA Office of Sea Grant, United States Department of Commerce, under Grant No. US DOC/NA86AA-D-SG112. This paper is journal reprint number JR492. The U.S. Government is authorized to reproduce and distribute reprints for government purposes, not withstanding any copyright notation that may appear hereon.
Keywords
- Bacterioplankton
- Benthic nepheloid layer
- Biovolume
- Cell morphology
- Lake Superior
- Offshore gradients
- Production
- Thymidine incorporation