56
GORDON A. RILEY
The question of bacterial effects was reopened a t a later time with
somewhat more conclusive results. The work by Batoosingh et al.
(1969), involving comparison of bubbling tests with water that was
refiltered immediately, provided the necessary material, for it was
found that two filtrations in rapid succession were a fairly effective
means of sterilizing the water. Two sets of experiments were performed
in which this was held for 5 days and for 12 days and then was filtered
a third time, and the 12-day set was plated t o determine the degree of
sterility. A duplicate set was given an immediate third filtration to
serve as a control to gauge the amount of additional formation during
the 5-12 day periods, and a fourth set had 1 ml of raw sea water added
to the doubly filtered water to examine the question of whether double
filtration would in itself affect the normal process of aggregation.
Plate counts indicated that the filtration procedure was reasonably
effective. Some plates were completely negative and none had more
than a few bacteria per ml. The observed increase in organic carbon
averaged 19 pg C/litre in five-day experiments and 6 pgllitre in the
twelve-day set. The general range in values was such that these
averages were not significantly different from each other nor from the
controls. If one chooses to believe that the increase is real, it is no
more than might be expected from incipient aggregation of the type
described by Sheldon et al. (1967), which may be entirely a physical
phenomenon, although this is not as yet definitely established. I n
contrast, inoculated 12-day experiments showed a mean increase of
155 pg C/litre, which was significantly higher than controls or the
accompanying experiments, although it is somewhat lower than is
commonly obtained in water that has been filtered only once.
A cruise on the Canadian oceanographic ship “ Hudson ” in JuneJuly 1967 provided an opportunity for experiments with samples taken
from a variety of water masses off the eastern Canadian seaboard.
Complete time series were difficult under shipboard conditions, for it
was desirable to process as many different samples as possible within
the limited time available. Most of the experiments were of 6-8 days’
duration, which should be long enough to determine whether particle
formation was occurring but probably not long enough to establish a
maximum concentration. Samples were filtered by gravity through
silver filters (0.45 or 1.2 p ) into four-litre polyethylene bags. Approximately one week later the water was removed through filters of the
same pore size used initially, and these were frozen for later analysis
ashore. Results are summarized by area and depth range in Table 111.
The area listed as coastal and bank waters includes the Scotian
Shelf, one station each on the Grand Banks and Flemish Cap, and one
GORDON A. RILEY
The question of bacterial effects was reopened a t a later time with
somewhat more conclusive results. The work by Batoosingh et al.
(1969), involving comparison of bubbling tests with water that was
refiltered immediately, provided the necessary material, for it was
found that two filtrations in rapid succession were a fairly effective
means of sterilizing the water. Two sets of experiments were performed
in which this was held for 5 days and for 12 days and then was filtered
a third time, and the 12-day set was plated t o determine the degree of
sterility. A duplicate set was given an immediate third filtration to
serve as a control to gauge the amount of additional formation during
the 5-12 day periods, and a fourth set had 1 ml of raw sea water added
to the doubly filtered water to examine the question of whether double
filtration would in itself affect the normal process of aggregation.
Plate counts indicated that the filtration procedure was reasonably
effective. Some plates were completely negative and none had more
than a few bacteria per ml. The observed increase in organic carbon
averaged 19 pg C/litre in five-day experiments and 6 pgllitre in the
twelve-day set. The general range in values was such that these
averages were not significantly different from each other nor from the
controls. If one chooses to believe that the increase is real, it is no
more than might be expected from incipient aggregation of the type
described by Sheldon et al. (1967), which may be entirely a physical
phenomenon, although this is not as yet definitely established. I n
contrast, inoculated 12-day experiments showed a mean increase of
155 pg C/litre, which was significantly higher than controls or the
accompanying experiments, although it is somewhat lower than is
commonly obtained in water that has been filtered only once.
A cruise on the Canadian oceanographic ship “ Hudson ” in JuneJuly 1967 provided an opportunity for experiments with samples taken
from a variety of water masses off the eastern Canadian seaboard.
Complete time series were difficult under shipboard conditions, for it
was desirable to process as many different samples as possible within
the limited time available. Most of the experiments were of 6-8 days’
duration, which should be long enough to determine whether particle
formation was occurring but probably not long enough to establish a
maximum concentration. Samples were filtered by gravity through
silver filters (0.45 or 1.2 p ) into four-litre polyethylene bags. Approximately one week later the water was removed through filters of the
same pore size used initially, and these were frozen for later analysis
ashore. Results are summarized by area and depth range in Table 111.
The area listed as coastal and bank waters includes the Scotian
Shelf, one station each on the Grand Banks and Flemish Cap, and one