Ecological Modeling: Algae

1
Ecological Modeling Algae

• -Why?
• Who?
• What?
• How?

2

• Who?

3

• What?

4
Examples of Models with Algal Modeling Included

• CIAO- Coupled Ice Atmosphere Ocean Model
• ERSEM- European Regional Seas Ecosystem Model
• CE QUAL
• DSSAMt
• HSPF
• WASP
• Aquatox
• Ecosim
• FFFMSIPaAG,
• Johns Model,
• Dons model
• ..Yada, Yada, Yada,

5
What is typically modeled?- Phytoplankton-
Periphyton
6
Pennate Diatoms
7
Centric Diatoms
8
Filamentous Green Algae
9
Chrysophyte
10
Cryptophyte
11
Dinoflagellates
12
Filamentous Cyanobacteria
13
Coccoid Cyanobacteria
14
Red Algae
15
Brown Algae
16
The point is that is. it is a Diverse Group

• Size (pico, nano,micro)
• Physiologically
• Biochemically
• Life Histories
• And Therefore, Ecosystem Function!!

17
The How Algal Population Growth Formula
dA/dt mmax(T)AMIN(NLIM) LightLIM -
grazing /- advection/dispersion /-
settling
Be a bit skeptical ask can the equations capture
algal physiologies and community dynamics that
you are after?
18
uMax

• Usually set by Temperature
• Eppley 1972 (most common)
• Other approaches
• species-genera specific temperature relationships
• Multiple Topt, Tmax Tmin, fxns

19
Nutrient Limitation

• Monod kinetics
• Usually applied as the single most limiting
  nutrient (Leibigs Law of The Minimum
  improperly invoked).
• Half saturation coefficients (ks) and nutrient
  concentrations are all that are needed.

m mmax(N/(KsN)
20
Challenges

• How to set the Ks.
• What nutrient concentration to use bulk or
  microscale?

Half Saturation Constants
Figure 2. Predictions from biofilm theory using
hypothetical model parameters.
21
Light

• Photosynthesis versus Irradiance Curves (PE
  curves)
• Ek is needed.
• Challenges
• How to calculate effective E.
• How to set Ek (remember.. plants/algae
  physiologically adapt).

Pmax
Ek
22

• Effective E
• Typically Calculated by 1st order attenuation
  accounting for water constituents
• Ed or Eod, or Eo?
• PAR, PUR, or PHAR?

23

• Integrate over depth and time for applicable Dt.

WASP 6 manual
24
Note

• dA/dt mmax(T)AMIN(NLIM) LightLIM
• This is net primary production
• Also, this is the net cellular growth rate
• Equation readily allows addition of other
  environmental constraints such as salinity, pH,
  etc.

25
Grazing

• Zero Order loss term/Constant
• First order loss term
• Kinetics based on constant grazer
  biomass/abundance but accounts for monod kinetics
• Kinetics with grazer abundance predicted as well
  (Lotkka-Volterra, NPZ models)

26
Other losses.

• Settling?
• Mortality-
• Viral, fungal, Ecotox pollutants (e.g.
  phototoxins, LD50s) other..?
• Drift/scour (fxn velocity and biomass)

27

• Algal Algorithms embedded in spatial models

28
Still Not Very Satisfying....

• Uncertainties in Temperature and mmax
• can lead to large variations in accumulation
  rates and biomass.. (exponentially compounding
  uncertainty)
• Treatment of Kss and Eks as constants
• Transient luxury uptake of nutrients rarely
  accounted for (e.g. Carbon storage and growth at
  night, i.e. unbalanced growth).
• Minimal Constraints on loss terms
• Stability issues

29
Other Approaches

• More Empirical Relationships
• e.g. TP vs. Chlorophyll a
• Quantum Yield Approach
• EoA? Primary Production

30
Free stuff

• I (Heather/Laurel) will post Stella models
• http//www.hps-inc.com/
• Download isee Player (its free)

31
Background Readings

• Eppley 1972
• Chapra pages 603-615
• Brush et al. 2002
• Chapra  742-747 (Solar Radiation and light
  extinction sections)
• WASP Manual
• Kirk Light and Photosynthesis in the sea
• Sverdrup Conditions for phytoplankton blooms