Pond ecosysæm
247
Booth
(1946)
estimated that the half—time for the
hydrolysis
of
carbon
dioxide
at 20° C is 750 seconds.
It appears that removal of the dissolved
gas
by converting to bicarbonate does not significantly increase the
flux
of carbon dioxide in the 100 micron boundary layer at the pond surface… For
the conditions in a typical grow—out pond,
flux of carbon dioxide into the
pond appears limited by diffusion in the laminar surface layer.
The relation for diffusion—driven flux expressed in Eqn. 2, can now be
used to calculate the amount of carbon dioxide that can diffuse from a well
mixed
atmosphere
(with a carbon dioxide concentration of
0.03%)
into
a
weakly stirred pond,
i.e.,
a
pond with a 100 micron thick laminar surface
boundary layer. The value of D for the diffusion of carbon dioxide in water
is similar to the D of oxygen.
Assume that below 100 microns,
the concen—
tration
of
dissolved carbon dioxide is small compared with its
potential
solubility
(at this depth part of the free gas will have reacted
to
fonn
carbonates).
Based
on
these conditions,
the theoretical flux is 0.7
gm
carbon dioxide diffusing from the atuosphere into the pond/ sq
m/day.
Yet
the
photosynthetic
demand
for carbon dioxide at 5 gm C/sq m/day
is
>20
times this flux.
Pruder (1983) has discussed this anomaly in the supply of
and the demand for carbon dioxide.
II — ËŒ_ POND WATER COLUMN
A.— Carbon cycling
As previously discussed, the water of a l m deep carp polyculture pond
will have sufficient suspended bottom matter to keep the primary production
well below the theoretical maxinwnu If we assume primary production (PP) at
5 gn1C/sq m/day and a water alkalinity of 100 mg/liter as Ca—carbonate, the
carbon in the carbonate system can account for about 2.5 days' PP. However,
the steady—state of the water alka1inity, excluding diurnal cycles, implies
a
rapid recycling of reduced carbon back into the bicarbonate
system,
and
not
a
long
tern1
depletion of the
water
carbonates.
Boyd
(1982)
and
Schroeder
(1975)
discuss
several
carbon sources
for
the
carbonate—PP
balance. In summary, as gm C/sq m/day, the sources are:
plankton respiration (based on 30% of PP)
1.5
bottom aerobic heterotrophs (based on an average 3 gm BDD/sg m/day)
l.l
fish respiration (based on 500 gm fish/sq m)
1.5
flux from the atmosphere (assume calm to light winds)
0.7
bottom anaerobic fermentation (based on rates of cellulose digestion
in the upper sedinent layers)
0.4
Considering the positive effect that added carbonate can have on_ pond
water quality with soft water and
carbonate—poor soils, carbonate initial—
ly in the bottom soils may also be a contributor to the PP carbon balance.
Decay
of
added
organic matter is a potential source .Of- carbonate—
carbon,
especially
when.nethane production is Significant in
the anox1c
fermentation
of precipitated organic matter or when added manure is
in
the
fluid flocculent form. A change in the algae 6C would be expected in accord
with
changes in the SC of the added organic matter.
A clear
change
has
only been observed when flocculent, fluid goose manure was the added carbon
source
(Table 1).
247
Booth
(1946)
estimated that the half—time for the
hydrolysis
of
carbon
dioxide
at 20° C is 750 seconds.
It appears that removal of the dissolved
gas
by converting to bicarbonate does not significantly increase the
flux
of carbon dioxide in the 100 micron boundary layer at the pond surface… For
the conditions in a typical grow—out pond,
flux of carbon dioxide into the
pond appears limited by diffusion in the laminar surface layer.
The relation for diffusion—driven flux expressed in Eqn. 2, can now be
used to calculate the amount of carbon dioxide that can diffuse from a well
mixed
atmosphere
(with a carbon dioxide concentration of
0.03%)
into
a
weakly stirred pond,
i.e.,
a
pond with a 100 micron thick laminar surface
boundary layer. The value of D for the diffusion of carbon dioxide in water
is similar to the D of oxygen.
Assume that below 100 microns,
the concen—
tration
of
dissolved carbon dioxide is small compared with its
potential
solubility
(at this depth part of the free gas will have reacted
to
fonn
carbonates).
Based
on
these conditions,
the theoretical flux is 0.7
gm
carbon dioxide diffusing from the atuosphere into the pond/ sq
m/day.
Yet
the
photosynthetic
demand
for carbon dioxide at 5 gm C/sq m/day
is
>20
times this flux.
Pruder (1983) has discussed this anomaly in the supply of
and the demand for carbon dioxide.
II — ËŒ_ POND WATER COLUMN
A.— Carbon cycling
As previously discussed, the water of a l m deep carp polyculture pond
will have sufficient suspended bottom matter to keep the primary production
well below the theoretical maxinwnu If we assume primary production (PP) at
5 gn1C/sq m/day and a water alkalinity of 100 mg/liter as Ca—carbonate, the
carbon in the carbonate system can account for about 2.5 days' PP. However,
the steady—state of the water alka1inity, excluding diurnal cycles, implies
a
rapid recycling of reduced carbon back into the bicarbonate
system,
and
not
a
long
tern1
depletion of the
water
carbonates.
Boyd
(1982)
and
Schroeder
(1975)
discuss
several
carbon sources
for
the
carbonate—PP
balance. In summary, as gm C/sq m/day, the sources are:
plankton respiration (based on 30% of PP)
1.5
bottom aerobic heterotrophs (based on an average 3 gm BDD/sg m/day)
l.l
fish respiration (based on 500 gm fish/sq m)
1.5
flux from the atmosphere (assume calm to light winds)
0.7
bottom anaerobic fermentation (based on rates of cellulose digestion
in the upper sedinent layers)
0.4
Considering the positive effect that added carbonate can have on_ pond
water quality with soft water and
carbonate—poor soils, carbonate initial—
ly in the bottom soils may also be a contributor to the PP carbon balance.
Decay
of
added
organic matter is a potential source .Of- carbonate—
carbon,
especially
when.nethane production is Significant in
the anox1c
fermentation
of precipitated organic matter or when added manure is
in
the
fluid flocculent form. A change in the algae 6C would be expected in accord
with
changes in the SC of the added organic matter.
A clear
change
has
only been observed when flocculent, fluid goose manure was the added carbon
source
(Table 1).