58
GORDON A. RILEY
have been due to sampling errors, for the particulate matter sinks to
the bottom of the carboy and may not be thoroughly detached during
the mixing process prior t o sampling. Nevertheless, there was an
indication of the maintenance of general level, if not a true steady
state, for a considerable period.
The second carboy was subjected to overnight bubbling to create
an initial substrate. Pseudomonas was then added as before, and
carbon was again determined at weekly intervals. During the first 1 2
weeks the average was 98 f 37 pg C/litre. At the end of the 13th
week there was an anomalously high value of 1.29 mg C/litre. Probably
the filter was grossly contaminated. The possibility of a second cycle
of bacterial growth seemed unlikely; there was no evidence of it in
plate counts made concurrently. During the remaining four weeks the
organic carbon was somewhat higher than it had been in the early part
of the experiment (140-170 pg C/litre).
The third experiment was inoculated with 10ml of unfiltered
surface water. The first sample taken a week later had a concentration
of 191 pg Cjl. Subsequently the level declined, and there was a more
or less steady state of 106 34 pg C/litre until the end of the 15th
week. During the last two weeks there was an increase in organic
matter (270-300 pg C/litre).
The experiments described thus far indicated that newly formed
aggregates in filtered sea water are subject to a rapid increase initially,
followed by rapid bacterial utilization, so that by the time the stable
phase has been reached the concentration of particulate organic carbon
will be roughly half the earlier maximum. At this point the remaining
organic matter would appear to be resistant to further attack, although
persistence of living bacteria implies either further utilization at a
very slow rate or some slight degree of further aggregation of filterable
materials or direct utilization of dissolved organic matter by bacteria.
Some variability has been noted in the so-called stable phase in
some experiments, and the level varies somewhat from one experiment
to another. However, the variation is not large, and the general level
of the experimental product is more or less the same as that of naturally
occurring particulate matter in the sea and is also similar to that
attained in bubbling experiments. The bubbling experiments and in
situ production appear to be somewhat analogous in that the rapid
rate of initial particle production quickly gives way to a situation in
which further formation appears t o be inhibited. This might be a
physical inhibition of the sort postulated for bubbling experiments, or
it might be caused by exhaustion of substances suitable for aggregation.
If this is simply a matter of physical inhibition by the standing
GORDON A. RILEY
have been due to sampling errors, for the particulate matter sinks to
the bottom of the carboy and may not be thoroughly detached during
the mixing process prior t o sampling. Nevertheless, there was an
indication of the maintenance of general level, if not a true steady
state, for a considerable period.
The second carboy was subjected to overnight bubbling to create
an initial substrate. Pseudomonas was then added as before, and
carbon was again determined at weekly intervals. During the first 1 2
weeks the average was 98 f 37 pg C/litre. At the end of the 13th
week there was an anomalously high value of 1.29 mg C/litre. Probably
the filter was grossly contaminated. The possibility of a second cycle
of bacterial growth seemed unlikely; there was no evidence of it in
plate counts made concurrently. During the remaining four weeks the
organic carbon was somewhat higher than it had been in the early part
of the experiment (140-170 pg C/litre).
The third experiment was inoculated with 10ml of unfiltered
surface water. The first sample taken a week later had a concentration
of 191 pg Cjl. Subsequently the level declined, and there was a more
or less steady state of 106 34 pg C/litre until the end of the 15th
week. During the last two weeks there was an increase in organic
matter (270-300 pg C/litre).
The experiments described thus far indicated that newly formed
aggregates in filtered sea water are subject to a rapid increase initially,
followed by rapid bacterial utilization, so that by the time the stable
phase has been reached the concentration of particulate organic carbon
will be roughly half the earlier maximum. At this point the remaining
organic matter would appear to be resistant to further attack, although
persistence of living bacteria implies either further utilization at a
very slow rate or some slight degree of further aggregation of filterable
materials or direct utilization of dissolved organic matter by bacteria.
Some variability has been noted in the so-called stable phase in
some experiments, and the level varies somewhat from one experiment
to another. However, the variation is not large, and the general level
of the experimental product is more or less the same as that of naturally
occurring particulate matter in the sea and is also similar to that
attained in bubbling experiments. The bubbling experiments and in
situ production appear to be somewhat analogous in that the rapid
rate of initial particle production quickly gives way to a situation in
which further formation appears t o be inhibited. This might be a
physical inhibition of the sort postulated for bubbling experiments, or
it might be caused by exhaustion of substances suitable for aggregation.
If this is simply a matter of physical inhibition by the standing