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

bar, the factor setting off phytoplankton blooms in the inshore water must be
the warmth of the inshore water. In this connection it should be noted that
Rodgers (op. cit., page 371) says "Whether this change [of water color across
the bar] is due to impoundment of runoff, or whether the warmer water promoted
the growth of biological material, is a point which requires clarification."
On 14 April 1977 the thermal bar crossed the Cook Plant survey grid just
lakeward of its center. Phytoplankton densities were about 2000 cells/ml along
the 4~ isotherm, were somewhat higher at the lakeward edge of the grid, and
were greatly higher along the shore. Figure 2 shows the position of the
thermal bar in the field of contours of phytoplankton densities. Surface water
temperatures ranged from less than 20 offshore to more than 100 at the beach.
On this day the plant's thermal plume was small and lay around station DC-1,
the first station immediately off the plant. In the plume area phytoplankton
density was greater than 4000 cells/ml, although densities greater than 5000
per ml were found at station SDC-.5-2 south of the plume and at stations in the
northern and southern sides of the grid.
Figure 3 presents histograms of phytoplankton densities, and of the
concentrations of the conservative ions sulphate and chloride by one degree
intervals of surface water temperature. Phytoplankton were most abundant in
the warm water near shore. Sulphate may show some evidence of runoff being
impounded by the thermal bar but a total variation of 3.4 ppm (16.8 to 20.2) is
hardly an indication of significant runoff impoundment. Chloride showed no
evidence of impoundment by the bar.
We conclude, as we have in the cases of other thermal bar conditions in
the study area, that spring warming at the shore is the primary reason for
greater phytoplankton abundance shoreward of the bar.

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