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Ecological Modeling: Algae

Ecological Modeling: Algae

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Ecological Modeling: Algae

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  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, • John’s Model, • Don’s 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)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?

  18. 7 7 6 6 5 5 max max 4 4 m m 3 3 2 2 1 1 0 0 0 0 10 10 20 20 30 30 40 40 o o 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

  19. 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)

  20. 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.

  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)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….

  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, LD50’s) 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 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

  29. Other Approaches… • More Empirical Relationships • e.g. TP vs. Chlorophyll a • Quantum Yield Approach • Eo*A* = 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