Phytoplankton of the seasonal surveys of 1977, and further pre- vs. post-operational comparisons at Cook Nuclear Plant / John C. Ayers, Susan J. Wiley.

CONCLUSIONS

During the thermal bar condition of 14 April 1977 surface water
temperatures ranged from less than 2~C offshore to more than 10~ at the beach
and phytoplankton were more than twice as abundant near shore than offshore.
Average concentrations of the conservative ions, sulphate and chloride, were
not significantly higher inshore of the bar than offshore. It is concluded
that spring warming of the water, not impoundment of shore runoff, triggered
the higher abundances of phytoplankton on the shoreward side of the thermal bar.
In the dominant and codominant taxa of the Cook Plant phytoplankton
collections, green algae and diatoms have continued to occur with
preoperational frequencies. Since 1972 flagellates appear to be slightly less
frequent as dominants than before, and blue-green algae appear to have
increased in their frequency of dominance since 1973. Increased dominance of
blue-greens in summer and fall in recent years has been found in other studies
and is an accepted fact; the degree of dominance of these algae in the Cook
Plant collections, however, is in part an artifact due to the counting of
individual cells in most of the forms which was begun with the collections of
1974. The trends in dominants are consistent with known changes in the lake;
there is no evidence that operation of Cook Plant has produced the changes.
The centric diatom Cvclotella comensis, previously collected in others of
the Great Lakes and from other parts of Lake Michigan, appeared for the first
time in the Cook Plant collections in October 1975 and has been taken with
increasing regularity in the seasonal surveys since then. It occurred for the
first times in 100% of the station samples in October 1976 and in July and
October 1977. It attained dominant or codominant status in five cases in
October 1976 and 15 cases in July 1977. Its failure to achieve dominance in

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