600
T
500
>o
"0 400
' :' e
u 300
E 200
100
Primary Productivity of Phytoplankton
219
-
SEf'
APR. MAY
JUN .
JUl. AUG.
SEf'
OCT
NOV
DEC
Figure 14.3. Integrated primary productivity per square meter of the pelagial zone of Lawrence Lake, MI,
1967-68. Bars indicate periods of ice cover [From Wetzel (1983).J
24oor - --.-- --r- ---,r--"T"""---r----r--r---r---r-""""""T-- r --"T""--, 24o
2000
I
-,.. 1600
' "
"' "
~
E 1200
200
I
I
160 -' ..
'>,
' "
120 ;"
u
.,
oX
'"
E 800
400
!?
80 "'2
.
40 U
0>
oX
O ~--~--~--~--~----~~~ __ ~--~--~--~~~~--~--~ O
JUN
JUL
AUG
SEP
OCT
JAN
FEB
MAR
APR
MAY
JUN
Figure 14.4. Integrated primary productivity of the phytoplankton of hypereutrophic
Wintergreen Lake, MI, 1971-72, per square meter of the trophogenic zone ( -- ) and for the
lake (-----) compensating for volumetric differences with depth. [From Wetzel (I983).J
It should be emphasized that estimates of the primary productivity of a lake
ecosystem based only on the metabolic activity of phytoplankton can be grossly in
error. The productivity of littoral macrophytes and algae attached to various
substrates, as well inputs of organic matter from the drainage basin, often can exceed
greatly the organic matter synthesized by the phytoplankton. In shallow lakes, the
phytoplanktonic productivity usually is quite subordinate to that of the rooted plants
and associated sessile algae [cf., Wetzel (1983)].
Extracellular Release of Dissolved Organic Carbon
An estimate of extracellular release of dissolved organic carbon can be determined
by obtaining a sample of filtrate, removing the labeled inorganic carbon, and then
assaying the radioactivity in dissolved organic compounds. The filtrate from each
sample can be collected in test tubes placed under the effiuent tube of the filter support
apparatus within the filtration flask. A 20-ml subsample of the filtrate is acidified to
pH 3 with 3% H 3 P0 4 in scintillation vials in an efficient hood and sparged with
pure CO 2 for a time sufficient to remove the inorganic CO 2 [usually 4 min per 10 ml
is adequate; see Hough and Filbin (1978)]. The vials then can be frozen immediately
and freeze-dried to concentrate the radioactivity of the organic compounds (McKinley
T
500
>o
"0 400
' :' e
u 300
E 200
100
Primary Productivity of Phytoplankton
219
-
SEf'
APR. MAY
JUN .
JUl. AUG.
SEf'
OCT
NOV
DEC
Figure 14.3. Integrated primary productivity per square meter of the pelagial zone of Lawrence Lake, MI,
1967-68. Bars indicate periods of ice cover [From Wetzel (1983).J
24oor - --.-- --r- ---,r--"T"""---r----r--r---r---r-""""""T-- r --"T""--, 24o
2000
I
-,.. 1600
' "
"' "
~
E 1200
200
I
I
160 -' ..
'>,
' "
120 ;"
u
.,
oX
'"
E 800
400
!?
80 "'2
.
40 U
0>
oX
O ~--~--~--~--~----~~~ __ ~--~--~--~~~~--~--~ O
JUN
JUL
AUG
SEP
OCT
JAN
FEB
MAR
APR
MAY
JUN
Figure 14.4. Integrated primary productivity of the phytoplankton of hypereutrophic
Wintergreen Lake, MI, 1971-72, per square meter of the trophogenic zone ( -- ) and for the
lake (-----) compensating for volumetric differences with depth. [From Wetzel (I983).J
It should be emphasized that estimates of the primary productivity of a lake
ecosystem based only on the metabolic activity of phytoplankton can be grossly in
error. The productivity of littoral macrophytes and algae attached to various
substrates, as well inputs of organic matter from the drainage basin, often can exceed
greatly the organic matter synthesized by the phytoplankton. In shallow lakes, the
phytoplanktonic productivity usually is quite subordinate to that of the rooted plants
and associated sessile algae [cf., Wetzel (1983)].
Extracellular Release of Dissolved Organic Carbon
An estimate of extracellular release of dissolved organic carbon can be determined
by obtaining a sample of filtrate, removing the labeled inorganic carbon, and then
assaying the radioactivity in dissolved organic compounds. The filtrate from each
sample can be collected in test tubes placed under the effiuent tube of the filter support
apparatus within the filtration flask. A 20-ml subsample of the filtrate is acidified to
pH 3 with 3% H 3 P0 4 in scintillation vials in an efficient hood and sparged with
pure CO 2 for a time sufficient to remove the inorganic CO 2 [usually 4 min per 10 ml
is adequate; see Hough and Filbin (1978)]. The vials then can be frozen immediately
and freeze-dried to concentrate the radioactivity of the organic compounds (McKinley