Characterizing a Major Episodic Event: a Recurrent Winter-Spring Plume in Southern Lake Michigan

B.J. Eadie1, D.J. Schwab1, T.H. Johengen2, P.J. Lavrentyev2, P.L. Van Hoof1, G.S. Miller1, R.E. Holland3, G.A. Leshkevich1, N.R. Morehead1, M.B. Lansing1, J.A. Robbins1, N. Hawley1, L. Lefkawitz4 and D.N. Edgington5.

1NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 48105
2Cooperative Institute for Limnology and Ecosystem Research
3University of Michigan Atmospheric, Oceanic and Space Sciences, Ann Arbor, MI, 48109
4Battelle Northwest, Seattle, Washington
5Center for Great Lakes Studies, University of Wisconsin-Milwaukee

American Geophysical Union, San Diego, CA, Feb, 1997

Abstract:We report observations of the initiation and subsequent development of an extensive coastal turbidity plume in southern Lake Michigan. The onset of this feature appeared to coincide with the melting of shore ice in late March, and with the occurrence of a major storm. Within a few days, the plume was approximately 10 km wide and over 300 km in length, implying that the source of the reflective materials was widely distributed. The high turbidity plume persisted for over a month, progressing northward along the eastern shore with a major offshore transport feature. Sediment traps within this feature recorded only one major mass flux event for the year. The plume was sampled on two occasions and found to contain 5-10 times as much suspended matter as open-lake locations outside the visible plume. Although particulate phosphorus, PAH and 137Cs content were lower (on a weight basis) on plume than open-lake particles, the high suspended matter concentrations within the plume resulted in very high concentrations on a volume basis; total particulate P was 3 times open lake concentration and 'extractable-available P' was nearly 10 times as high within the plume. Extrapolating from one plume sample, approximately 75kg of PCB were resuspended in this event. The diatom community structure within the plume was significantly different from outside the plume and was characteristic of more eutrophic waters. The abundance of non-diatom phytoplankton and microbial food web organisms were elevated at the plume edge. These results formed the basis for a new, 5 year, NSF-NOAA program in Lake Michigan assessing the impacts of episodic events on sediment resuspension, transport and subsequent ecological effects.