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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 -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