Concentrations of soluble reactive phosphorus, ammonium-nitrogen, nitrate-nitrogen, silica, and chloride have all increased since the establishment of the zebra mussel (Dreissena polymorpha) in Hatchery Bay, western Lake Erie, in 1988. Total phosphorus concentrations have changed little. These results are from 188 samples collected weekly and year round before the establishment of Dreissena (1984–1987) and 192 samples post-Dreissena (1990–1993). The mean annual total phosphorus concentration for the three complete post-Dreissena years was 35 μg∙L−1 strikingly similar to the concentration of 36 μg∙L−1, which in 1959 helped to define the waters of Lake Erie as eutrophic. The relative steadiness in total phosphorus may reflect sediment reflux, because Hatchery Bay is a polymictic system. The slight increase in the biologically conservative ion, chloride, in the 1990s, is probably due to the increased precipitation and runoff in the western Lake Erie watershed. Decreased phytoplankton and associated increased water clarity caused by efficient filtering by D. polymorpha, have lessened symptoms of eutrophication and produced a situation where nutrients are not fully utilized, i.e., biological oligotrophy.
NOAA CoastWatch satellite imagery from early 1996 captured the initiation, development, and decay of a recurrent coastal plume in southern Lake Michigan (Figure 1). For the past 4 years intermittent satellite coverage has revealed a late winter‐early spring plume in the lake, a feature also observed by Mortimer [1988]. In 1996, clear weather conditions allowed researchers to observe the plume's development for the first time and they also collected water samples from helicopter and a small boat.
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