156
8. Impact of Dynamic Light and Nutrient Environments
In addition to the N concentration affecting variability in the phytoplankton populations, changes the half-saturation constant (Ks) regulate the ability of cells to take up nutrients . Higher Ks values require higher ambient nutrient concentrations to maintain maximum nutrient uptake rates. With N
concentrations replete (0.003 moles/rn") , the Ks value of diatoms is increased. Figure 8.14 shows the ratio of diatoms to dinoflagellates equals 1
over the year when the Ks values are identical (0.0005 moles/rn ') for both
groups. As the Ks for diatoms is increased incrementally to 0.001 moles/m"
(run 4), the ability of dinoflagellates to utilize N is higher than that of the diatoms and the dinoflagellate population dramatically increases relative to
diatoms.
Until now , we have not considered the influence of a second nutrient on
the two populations. If the Ks for Si uptake is set to 0.00005 moles/m", diatom abundance is dependant on two nutrients, and dinoflagellate populations increase over time relative to diatoms (Figure 8.15). Unless both N
and Si are replete in the environment, the maximum growth rate for the diatoms cannot be realized. For diatoms, either N or Si will limit growth, depending on the physiological demand and the population size in the parcel
of water. This demonstrates Liebig's "Law of the Minimum"-at any
given time, if one nutrient is below the minimum requirement, the maximum growth potential of phytoplankton cannot be reached.
The model can be used to test responses in phytoplankton growth to
varying Si to N ratios. As a consequence, we can explore different scenarios, ranging from replete to limiting concentrations for both nutrients . Such
exploration is particularly useful, for example , to illuminate implications of
nutrient loading in a coastal ocean. Figure 8.16 shows the results of three
1: RATIO
1.00
- -
2: RATIO
- - - .,- , 1!
- -
3: RATIO
4: RATIO
- - -,- - - -- - - - , . - - - - -----,
,
...{.. '"
.
.
{
..... .
0 .50
0 .00
0.00
182.50
i
I
.
i
..J
i
=
365.00
DAYS
2
547 .50
FIGURE 8.14
8. Impact of Dynamic Light and Nutrient Environments
In addition to the N concentration affecting variability in the phytoplankton populations, changes the half-saturation constant (Ks) regulate the ability of cells to take up nutrients . Higher Ks values require higher ambient nutrient concentrations to maintain maximum nutrient uptake rates. With N
concentrations replete (0.003 moles/rn") , the Ks value of diatoms is increased. Figure 8.14 shows the ratio of diatoms to dinoflagellates equals 1
over the year when the Ks values are identical (0.0005 moles/rn ') for both
groups. As the Ks for diatoms is increased incrementally to 0.001 moles/m"
(run 4), the ability of dinoflagellates to utilize N is higher than that of the diatoms and the dinoflagellate population dramatically increases relative to
diatoms.
Until now , we have not considered the influence of a second nutrient on
the two populations. If the Ks for Si uptake is set to 0.00005 moles/m", diatom abundance is dependant on two nutrients, and dinoflagellate populations increase over time relative to diatoms (Figure 8.15). Unless both N
and Si are replete in the environment, the maximum growth rate for the diatoms cannot be realized. For diatoms, either N or Si will limit growth, depending on the physiological demand and the population size in the parcel
of water. This demonstrates Liebig's "Law of the Minimum"-at any
given time, if one nutrient is below the minimum requirement, the maximum growth potential of phytoplankton cannot be reached.
The model can be used to test responses in phytoplankton growth to
varying Si to N ratios. As a consequence, we can explore different scenarios, ranging from replete to limiting concentrations for both nutrients . Such
exploration is particularly useful, for example , to illuminate implications of
nutrient loading in a coastal ocean. Figure 8.16 shows the results of three
1: RATIO
1.00
- -
2: RATIO
- - - .,- , 1!
- -
3: RATIO
4: RATIO
- - -,- - - -- - - - , . - - - - -----,
,
...{.. '"
.
.
{
..... .
0 .50
0 .00
0.00
182.50
i
I
.
i
..J
i
=
365.00
DAYS
2
547 .50
FIGURE 8.14