Phytoplankton Processes

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Phytoplankton Processes

• Processes and Equations Implemented in WASP7
  Eutrophication Module

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atmosphere
DO
Reaeration
Phytoplankton(3)
Photosynthesis
Periphyton
Respiration
Death Grazing
Detritus DW
P
N
C
Si
Dissolved OM
NH3
PO4
SiO2
CBOD1
Nitrification
Mineralization
Adsorption
CBOD2
NO3
SSinorg
CBOD3
N2
Settling
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Phytoplankton

• The growth rate of a population of phytoplankton
  in a natural environment
• is a complicated function of the species of
  phytoplankton present
• involves differing reactions to solar radiation,
  temperature, and the balance between nutrient
  availability and phytoplankton requirements
• Due to the lack of information to specify the
  growth kinetics for individual algal species in a
  natural environment,
• this model characterizes the population as a
  whole by the total biomass of the phytoplankton
  present

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Phytoplankton Kinetics
PO4
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Phytoplankton Growth
NO3
SiO2
Light
Phyt
NH3
OM DWCNPSi
PO4
Gmax maximum specific growth rate
constant at 20 C, 0.5 4.0 day-1 XT
temperature growth multiplier , dimensionless XL
light growth multiplier, dimensionless XN
nutrient growth multiplier, dimensionless
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Standard Temperature Function for Phytoplankton
Growth
Temperature multiplier
where ?G temperature correction factor for
growth (1.05 1.1) T water temperature,
C
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Additional Temperature Functions for
Phytoplankton Growth
Temperature multiplier
where Topt optimum temperature for growth,
C T water temperature, C ?1
temperature coefficient below opt, 1/C2 ?2
temperature coefficient above opt, 1/C2
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Comparison of Temperature Functions
TF1 exponential temperature function, ?G
1.08 TF2 Topt temperature
functions a ?1, ?2 0.02 b ?1, ?2 0.002
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Light Effects on Phytoplankton
Steele Light Limitation Function
It,z light intensity at time t and depth z,
langleys/day Is saturating
light intensity of phytoplankton, langleys/day
(300 600)
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Seasonal and Diel Light Variation
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Incident Light Flux to Surface
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Input Light Option 1 model uses input light
functions directly

• Instantaneous light
• User inputs instantaneous light flux as time
  function, ly/day
• User does not input daylight fraction (or sets it
  to 1.0)

• Seasonal light
• User inputs total daily light Itot as time
  function, ly/day
• User inputs daylight fraction as time function
• Model uses average light during daylight hours
• Iave Itot / fday

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Input Light Option 2 model calculates diel light
each day using input seasonal light functions

• Seasonal light
• User inputs total daily light as time function,
  ly/day
• User inputs daylight fraction as time function
• Model fits diel light as half sine curve between
  sunrise and sunset using total daily light

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Light Variation with Depth
Surface reflectance loss
Beer-Lambert light attenuation with depth
I0 light just beneath surface, ly/day Ke
light extinction coefficient, m-1 (0.5-5) z
depth, m
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Total Light Extinction

• Ke back background light extinction due to
  ligands, color, etc.
• Ke shd algal self shading,
• Ke solid solids light extinction
• Ke DOC DOC light extinction,

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Light Extinction Components
Background
Solids
DOC
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Light Extinction Components
Algal Self Shading

• Options
• Model Calculates (Default)
• Mult 0.0587, Exp 0.778
• User Specifies Mult Exp
• Switch Off Self Shading

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Integrated Light Effects on Phytoplankton
Steele function integrated over depth and
averaged over day
H average depth of segment,
m Ke total light extinction coefficient ,
per meter I0 incident light intensity just
below the surface, langleys/day
(assumes 10 reflectance) Is saturating
light intensity of phytoplankton,
langleys/day fday fraction of day that is
daylight
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Phytoplankton Growth, reprise
Gmax maximum specific growth rate
constant at 20 C, 0.5 4.0 day-1 XT
temperature growth multiplier , dimensionless XL
light growth multiplier, dimensionless XN
nutrient growth multiplier, dimensionless
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Nutrient Limitation of Phytoplankton Growth
KMN half-saturation constant for N, mg/L
KMP half-saturation constant for P, mg/L
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Half-Saturation Nutrient Kinetics
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Phytoplankton Kinetics, reprise
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Phytoplankton Death
Death rate constant
k1R endogenous respiration rate constant,
day-1 ?1R temperature correction factor,
dimensionless k1D mortality rate constant,
day-1 k1G grazing rate constant, day-1, or
m3/gZ-day if Z(t) specified Z(t) zooplankton
biomass time function, gZ/m3 (defaults to 1.0)
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Phytoplankton Settling
Settling rate constant
vS settling velocity, m/day (0 0.5) AS
surface area, m2 V segment volume, m3
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Phytoplankton Constants
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Phytoplankton Spatial Parameters

• Temperature multiplier and time function
• Light extinction multiplier and time function
• Solar radiation multiplier
• Zooplankton density
• Canopy light interception

• Initial chlorophyll a concentrations

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Phytoplankton Time Functions

• Water temperature
• Solar radiation
• Fraction daylight
• Light extinction

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Typical Rate Coefficients

• Maximum growth rate ? 2 day-1 (0.5 4)
• Respiration rate ? 0.1 day-1 (0.05 0.2)
• Death rate ? 0.05 day-1 (0.01 0.5)
• Settling rate ? 0.2 m/day (0 0.5)
• Optimum light intensity ? 350 Ly/d (300 600)
• Nutrient half-saturation constants
• Nitrogen 0.01 0.03 mg/L
• Phosphorus 0.001 0.005 mg/L

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Phytoplankton Output
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Light Output