PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
185
November to zero in May. The reason for this was not discussed but it
may indicate a tendency for ice to accumulate the nutrient, which is
returned to the water upon melting. Phosphate concentrations below
the ice did not alter significantly during the same period, however, SO
that, in this case at least, phosphate uptake by the ice did not occur.
Bursa (1961), working at the same location as Grainger (1959),
found that the phytoplankton bloom which began in May at the time
of the spring melt reached its maximum in mid-August when phosphate
levels had been reduced to their pre-melt values (Fig. 14). The bloom
consisted very largely of the diatom Achnantes taeniata Grunow. By
the end of September, the herbivorous zooplankton had almost completely removed the phytoplankton, and by late October, the ice cover
had returned.
A similar pattern of variation in the plant population (as measured
by chlorophyll a) was described by Apollonio for the water below the
ice island, though the return of the snow cover at mid-August could
also have helped to diminish the phytoplankton.
D. Partially enclosed sea area8
In partially enclosed sea areas such as embayments or estuaries,
nutrient levels often undergo cycles which are different, especially in
timing, from those found in more open waters. In Narragansett Bay,
for example, nutrient concentrations are maximal during the summer
months and are reduced to their minimal levels in the winter (Ferrara,
1953; Smayda, 1957; Pratt, 1965). Pratt (1965) made a detailed study
of nutrient changes and plankton production during the period
November 1959 to June 1963. The main phytoplankton flowering
began in December or January and was followed by a succession of
minor blooms which finished by early summer, the plant population
consisting predominantly of Skeletonema costatum. While phosphate
concentrations never fell below 0.3 pg-atoms PO;--P/l and were normally greater than this, nitrate concentrations became undetectable
well before the peak of the phytoplankton bloom was reached, growth
continuing for up to five weeks after nitrate had been depleted. The
data obtained from a station at the mouth of the bay is illustrated in
Fig. 15.
In the open sea, the stability of the water column is a necessary
prerequisite to the inception of a phytoplankton bloom (Sverdrup,
1953); otherwise turbulence would cause the dispersal of the plant
population. In Narragansett Bay, however, the physical features are
such that, in spite of tidal turbulence, the phytoplankton are effectively
contained together (Smayda, 1957). Firstly, there is little interchange
185
November to zero in May. The reason for this was not discussed but it
may indicate a tendency for ice to accumulate the nutrient, which is
returned to the water upon melting. Phosphate concentrations below
the ice did not alter significantly during the same period, however, SO
that, in this case at least, phosphate uptake by the ice did not occur.
Bursa (1961), working at the same location as Grainger (1959),
found that the phytoplankton bloom which began in May at the time
of the spring melt reached its maximum in mid-August when phosphate
levels had been reduced to their pre-melt values (Fig. 14). The bloom
consisted very largely of the diatom Achnantes taeniata Grunow. By
the end of September, the herbivorous zooplankton had almost completely removed the phytoplankton, and by late October, the ice cover
had returned.
A similar pattern of variation in the plant population (as measured
by chlorophyll a) was described by Apollonio for the water below the
ice island, though the return of the snow cover at mid-August could
also have helped to diminish the phytoplankton.
D. Partially enclosed sea area8
In partially enclosed sea areas such as embayments or estuaries,
nutrient levels often undergo cycles which are different, especially in
timing, from those found in more open waters. In Narragansett Bay,
for example, nutrient concentrations are maximal during the summer
months and are reduced to their minimal levels in the winter (Ferrara,
1953; Smayda, 1957; Pratt, 1965). Pratt (1965) made a detailed study
of nutrient changes and plankton production during the period
November 1959 to June 1963. The main phytoplankton flowering
began in December or January and was followed by a succession of
minor blooms which finished by early summer, the plant population
consisting predominantly of Skeletonema costatum. While phosphate
concentrations never fell below 0.3 pg-atoms PO;--P/l and were normally greater than this, nitrate concentrations became undetectable
well before the peak of the phytoplankton bloom was reached, growth
continuing for up to five weeks after nitrate had been depleted. The
data obtained from a station at the mouth of the bay is illustrated in
Fig. 15.
In the open sea, the stability of the water column is a necessary
prerequisite to the inception of a phytoplankton bloom (Sverdrup,
1953); otherwise turbulence would cause the dispersal of the plant
population. In Narragansett Bay, however, the physical features are
such that, in spite of tidal turbulence, the phytoplankton are effectively
contained together (Smayda, 1957). Firstly, there is little interchange