PARTICULATE ORGANIC MATTER I N SEA WATER
61
At the end of the fourth week 1 ml of raw sea water was added to
each bottle to find out if a fresh and active supply of bacteria could
alter the trend. It did not do so. When the experiment was terminated
at the end of the fifth week the concentrations in the three bottles were
0.14, 0.1 I , and 0.05 mg C/litre, respectively.
I n summary, the maximum sustained concentration of particulate
organic carbon, either in long term bubbling experiments or in situ
aggregation, is seldom much more than 0.2 mg C/litre. This concentration tends to be maintained for a considerable period even when
part of the product is removed. However, a downward trend has been
noted, particularly in cases of heavy cropping, and deep sea samples
frequently have a lower steady state concentration than surface
samples. A hypothesis has been proposed that particle formation
inhibits further formation and that this is responsible for the upper
limit of concentration, but there are further indications that the supply
of filterable organic matter can be reduced to a point where a maximum
concentration of particles cannot be attained or maintained.
2. Bacteria
Most of the experiments were accompanied by plate counts of
bacteria. Aliquots of water from experimental bottles were diluted
serially in autoclaved water and the series was plated on enriched sea
water agar. The plates were then incubated for 3-5 days at 1 5 O C .
The dilutions ranged through several orders of magnitude. Ideally
the investigator can discard plates which have too few colonies for a
good count, or are so heavily overgrown that there is danger of fusion
of colonies, and can base his judgement on one or two plates in the
middle of the range. There are subjective elements in this procedure,
and replication is not as precise as might be desired. Moreover, as
everyone who has dealt with this problem is well aware, plate counts
commonly give much lower values than direct visual examination.
These and certain other difficulties will have to be taken into account
in evaluating the results that are to be described.
The early series of experiments, for which carbon values are given
in Table 11, were mostly of short duration. Some involved an initial
inoculation with Pseudomonas sp., and in other cases a natural flora
was allowed to develop. In the former case the method was simply
to introduce a small quantity of an actively growing culture of bacteria
in the proportion of 0.1 ml of culture per litre of filtered sea water. The
actual number of bacteria was not determined in each case, but on two
occasions when samples of sea water were plated immediately after
inoculation, the count was of the order of lo3 cells/ml.
61
At the end of the fourth week 1 ml of raw sea water was added to
each bottle to find out if a fresh and active supply of bacteria could
alter the trend. It did not do so. When the experiment was terminated
at the end of the fifth week the concentrations in the three bottles were
0.14, 0.1 I , and 0.05 mg C/litre, respectively.
I n summary, the maximum sustained concentration of particulate
organic carbon, either in long term bubbling experiments or in situ
aggregation, is seldom much more than 0.2 mg C/litre. This concentration tends to be maintained for a considerable period even when
part of the product is removed. However, a downward trend has been
noted, particularly in cases of heavy cropping, and deep sea samples
frequently have a lower steady state concentration than surface
samples. A hypothesis has been proposed that particle formation
inhibits further formation and that this is responsible for the upper
limit of concentration, but there are further indications that the supply
of filterable organic matter can be reduced to a point where a maximum
concentration of particles cannot be attained or maintained.
2. Bacteria
Most of the experiments were accompanied by plate counts of
bacteria. Aliquots of water from experimental bottles were diluted
serially in autoclaved water and the series was plated on enriched sea
water agar. The plates were then incubated for 3-5 days at 1 5 O C .
The dilutions ranged through several orders of magnitude. Ideally
the investigator can discard plates which have too few colonies for a
good count, or are so heavily overgrown that there is danger of fusion
of colonies, and can base his judgement on one or two plates in the
middle of the range. There are subjective elements in this procedure,
and replication is not as precise as might be desired. Moreover, as
everyone who has dealt with this problem is well aware, plate counts
commonly give much lower values than direct visual examination.
These and certain other difficulties will have to be taken into account
in evaluating the results that are to be described.
The early series of experiments, for which carbon values are given
in Table 11, were mostly of short duration. Some involved an initial
inoculation with Pseudomonas sp., and in other cases a natural flora
was allowed to develop. In the former case the method was simply
to introduce a small quantity of an actively growing culture of bacteria
in the proportion of 0.1 ml of culture per litre of filtered sea water. The
actual number of bacteria was not determined in each case, but on two
occasions when samples of sea water were plated immediately after
inoculation, the count was of the order of lo3 cells/ml.