Controls on Primary Production and
Phytoplankton Biomass
Puget Sound Oceanography
Jan. 21, 2009
Main Controls on Primary Production
• Light
• Nutrients
• Temperature
Extinction of light in water follows a negative exponential:
Depth of the euphotic zone is defined by the 1% light depth (z1%)
0
% of surface irradiance
100
Beers-Lambert law:
Depth
I z = I 0e −kz
•Iz is irradiance at depth
•I0 is surface irradiance
•kz is the extinction coefficient
•z is depth
Attenuators:
•Water
•CDOM
•Particles (sediments, phytoplankton, etc.)
Calculating the attenuation coefficient:
I z = I 0e
−kz
ln( I z ) = −kz + I 0
z = depth
Iz = irradiance at depth z
Io = irradiance at the surface
k = attenuation coefficient
Take the natural log of irradiance
Perform linear regression
x = depth (m)
y = ln(light)
•the negative slope of the regression
will be k
Example:
Depth (m)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Irradiance at
depth
1424.0
649.0
272.4
122.3
64.7
28.6
13.8
7.5
4.1
Regression Output:
Constant
Std Err of Y Est
R Squared
No. of Observations
Degrees of Freedom
7.139
0.110
0.997
9.000
7.000
X Coefficient(s)
Std Err of Coef.
-0.737
0.014
= -k
So, k = 0.74
Relationship between photosynthesis and available light:
P = Pmax(1-e-αI/Pmax)e-βI/Pmax
Photosynthesis rate
β
Maximum
Photosynthesis
Pmax
Light
Saturated
α
Light
Limited
Ic
Photo-inhibited
Compensation point
P=R
IOpt
Available light (irradiance)
α = initial slope of curve. β = irradiance at onset of photo-inhibition.
Platt et al. 1980
Species differences in P-I curves:
Diatoms
Dinoflagellates
Light penetration into water
Depth (m)
Light intensity at depth (W m-2)
Clarke and Denton, 1962
Phytoplankton nutrient uptake:
Michaelis-Menten Equation
Vmax ·S
V=
Ks + S
Rate of nutrient uptake
or Growth
Vmax
Ks
Nutrient concentration (S)
V is rate of nutrient uptake
Vmax is maximum potential uptake rate
S is the concentration of the limiting nutrient
Ks is the half-saturation constant (nutrient concentration where V=½ Vmax)
Different limiting nutrients - different competitive success
Rate of nutrient uptake
or Growth
Sp 2, Nut 2
Sp 2, Nut 1
Sp 1, Nut 2
Sp 1, Nut 1
Nutrient concentration (S)
Interacting control on photosynthesis:
(Light and Temperature)
Growth
Cyanobacteria growth
Light exposure
Nicklisch et al., JPR 2007
Harald Sverdrup (1888-1957)
The proper Sverdrup
Developed theories of ocean circulation
“The Sverdrup balance”
Critical Depth hypothesis
1 Sv = flux of 1 x 106 m3 sec-1
Sverdrup in Paris after 3 years on the Arctic Ice
Sverdrup’s Critical Depth Hypothesis:
Well-mixed conditions:
Stratified conditions:
Sampling conducted in the Norwegian Sea
Classic illustration of critical depth theory from observations (from Sverdrup, 1953)
River
discharge
Tidal
Current
Stratifi-cation
Chlorophyll
Hydrodynamic processes that effect primary production
and distribution of biomass:
Approximate Working Definitions
(applicable to aquatic and marine systems)
Primary production (PP):
Primary productivity:
Gross primary production:
Net primary production:
New community production:
Production of organic matter (either dissolved or particulate)
from inorganic substrates by living organisms.
The rate of primary production (usually expressed as either an
instantaneous rate or a daily rate, per unit volume of water or
ocean surface.)
PP before any losses are subtracted (equivalent to carbon
fixation when carbon is the only element considered.)
PP in excess of the cell’s own respiratory consumption of
organic matter.
PP in excess of the total respiratory consumption of organic
matter (by autotrophs and heterotrophs when considering
populations rather than individuals).
Each production term also has a corresponding productivity, i.e. the rate of that (gross, net, or
community) production.
By definition: Gross>Net>Community