Ecological modeling algae
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Ecological Modeling: Algae. -Why? Who? What? How?. Who?. What?. 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, John’s Model, Don’s model

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Ecological Modeling: Algae

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Ecological Modeling: Algae

-Why?

Who?

What?

How?


  • Who?


  • What?


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,

  • John’s Model,

  • Don’s model

  • …………..Yada, Yada, Yada,


What is typically modeled?- Phytoplankton- Periphyton


Pennate Diatoms


Centric Diatoms


Filamentous Green Algae


Chrysophyte


Cryptophyte


Dinoflagellates


Filamentous Cyanobacteria


Coccoid Cyanobacteria


Red Algae


Brown Algae


The point is that is…. it is a Diverse “Group”

  • Size (pico, nano,micro)

  • Physiologically

  • Biochemically

  • Life Histories

  • And Therefore, Ecosystem Function!!


The How: Algal Population Growth Formula

  • dA/dt = mmax(T)A*MIN(NLIM)* LightLIM

  • - grazing

    • +/- advection/dispersion

    • +/- settling

Be a bit skeptical: ask can the equations capture “algal” physiologies and community dynamics that you are after?


7

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max

max

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m

m

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1

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10

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o

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Temperature (

Temperature (

C)

C)

uMax

  • Usually set by Temperature:

    • Eppley 1972 (most common*)

  • Other approaches

    • species-genera specific temperature relationships

    • Multiple Topt, Tmax Tmin, fxns


Nutrient Limitation

  • Monod kinetics

  • Usually applied as the single most limiting nutrient (Leibig’s “Law of The Minimum” improperly invoked).

    • Half saturation coefficients (ks) and nutrient concentrations are all that are needed.

m= mmax*(N/(Ks+N)


Figure 1. Model formulation for velocity enhancement in DSSAMt (Caupp et al 1998).

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.


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


  • Effective E:

    • Typically Calculated by 1st order attenuation accounting for water+ constituents

    • Ed or Eod, or Eo?

    • PAR, PUR, or PHAR?


Integrate over depth and time for applicable Dt.

WASP 6 manual


Note:

  • dA/dt = mmax(T)A*MIN(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….


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)


Other losses….

  • Settling?

  • Mortality-

    • Viral, fungal, Ecotox pollutants (e.g. phototoxins, LD50’s) other..?

  • Drift/scour (fxn velocity and biomass)


  • Algal Algorithms embedded in spatial models


Still Not Very Satisfying....

  • Uncertainties in Temperature and mmax

    • can lead to large variations in accumulation rates and biomass.. (exponentially compounding uncertainty)

  • Treatment of Ks’s and Ek’s 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


Other Approaches…

  • More Empirical Relationships

    • e.g. TP vs. Chlorophyll a

  • Quantum Yield Approach

    • Eo*A* = Primary Production


Free stuff

  • I (Heather/Laurel) will post Stella models

  • http://www.hps-inc.com/

  • Download isee Player (its free)


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


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