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## Ecological Modeling: Algae

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**Ecological Modeling: Algae**-Why? Who? What? How?**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,**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**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**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)**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