Ecological Modeling: Algae -Why? - Who? - What? - How?

Ecological Ecological Modeling: AlgaeModeling: Algae-Why?-Why?

-Who?Who?

-What?What?

-How?How?

• Who?Who?

• What?What?

Examples of Models with Algal Examples of Models with Algal Modeling IncludedModeling Included• CIAO- Coupled Ice Atmosphere Ocean Model CIAO- Coupled Ice Atmosphere Ocean Model • ERSEM- European Regional Seas Ecosystem ModelERSEM- European Regional Seas Ecosystem Model• CE QUALCE QUAL• DSSAMtDSSAMt• HSPFHSPF• WASPWASP• AquatoxAquatox• EcosimEcosim• FFFMSIPaAG,FFFMSIPaAG,• John’s Model,John’s Model,• Don’s modelDon’s model• ……………………..Yada, Yada, Yada, ..Yada, Yada, Yada,

What is typically What is typically modeled?modeled?- Phytoplankton- Phytoplankton- Periphyton- Periphyton

Pennate DiatomsPennate Diatoms

Centric DiatomsCentric Diatoms

Filamentous Green AlgaeFilamentous Green Algae

ChrysophyteChrysophyte

CryptophyteCryptophyte

DinoflagellatesDinoflagellates

Filamentous CyanobacteriaFilamentous Cyanobacteria

Coccoid CyanobacteriaCoccoid Cyanobacteria

Red AlgaeRed Algae

Brown AlgaeBrown 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: The How: Algal Population Growth Algal Population Growth

FormulaFormula

dA/dt = max(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?

uMaxuMax

• Usually set by Usually set by Temperature:Temperature:– Eppley 1972 (most Eppley 1972 (most

common*)common*)

• Other approachesOther approaches– species-genera specific species-genera specific

temperature temperature relationshipsrelationships

– Multiple TMultiple Toptopt, T, Tmaxmax T Tmin, min, fxnsfxns

0

1

2

3

4

5

6

7

0 10 20 30 40

Temperature (oC)

m

ax

0

1

2

3

4

5

6

7

0 10 20 30 40

Temperature (oC)

m

ax

Nutrient LimitationNutrient Limitation

• Monod kineticsMonod kinetics• Usually applied Usually applied

as the single as the single most limiting most limiting nutrient nutrient (Leibig’s (Leibig’s “Law of The Minimum” “Law of The Minimum” improperly invoked).improperly invoked).– Half saturation Half saturation

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

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60

Nutrient Concentration

/

max

= max*(N/(Ks+N)

0

5

10

15

20

25

30

35

0 0.04 0.08 0.12

Phosphorus (mg/L)

P U

pta

ke

(u

g/m

2/s) v=0.5 m/s

0.1 m/s

v=0.05 m/s

(B)

Challenges:Challenges:

– How to set the KHow to set the Kss..

– What nutrient What nutrient concentration to concentration to use: bulk or use: bulk or microscale?microscale?

Half Saturation Constants

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

0

0.2

0.4

0.6

0.8

1

FV

0 1 2 3 4Velocity (m/s)

FV=0.25 FV=0.5 FV=0.75 FV=0.1

Velocity Enhancement of PeriphytonProductivity - Model Formulation

Figure 2. Predictions from biofilm theory using hypothetical model parameters.

LightLight• Photosynthesis versus Photosynthesis versus

Irradiance Curves (PE Irradiance Curves (PE curves)curves)– EEkk is needed. is needed.

• Challenges:Challenges:– How to calculate effective How to calculate effective

E.E.

– How to set EHow to set Ekk (remember….. (remember….. plants/algae plants/algae physiologically adapt). physiologically adapt).

0 20 40 60 80 100

P

0.0

0.1

0.2

0.3

0.4

0.5

0.6

EEkk

PPmaxmax

• Effective E:Effective E:– Typically Calculated Typically Calculated

by 1by 1stst order order attenuation attenuation accounting for accounting for water+ constituentswater+ constituents

– EEdd or E or Eodod, or E, or Eoo??

– PAR, PUR, or PHAR?PAR, PUR, or PHAR?

• Integrate over Integrate over depth and time for depth and time for applicable Dt. applicable Dt.

WASP 6 manual

Note:Note:

•dA/dt = max(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….

GrazingGrazing

• Zero Order loss term/ConstantZero Order loss term/Constant

• First order loss termFirst order loss term

• Kinetics based on constant Kinetics based on constant grazer biomass/abundance but grazer biomass/abundance but accounts for monod kineticsaccounts for monod kinetics

• Kinetics with grazer abundance Kinetics with grazer abundance predicted as well (Lotkka-predicted as well (Lotkka-Volterra, NPZ models)Volterra, NPZ models)

Other losses….Other losses….

• Settling?Settling?

• Mortality- Mortality- – Viral, fungal, Ecotox pollutants (e.g. Viral, fungal, Ecotox pollutants (e.g.

phototoxins, LDphototoxins, LD5050’s) other..?’s) other..?

• Drift/scour (fxn velocity and biomass)Drift/scour (fxn velocity and biomass)

• Algal Algorithms Algal Algorithms embedded in embedded in spatial modelsspatial models

Still Not Very Satisfying....Still Not Very Satisfying....

• Uncertainties in Temperature and Uncertainties in Temperature and maxmax

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

• Treatment of KTreatment of Kss’s and E’s and Ekk’s as constants’s as constants• Transient luxury uptake of nutrients rarely Transient luxury uptake of nutrients rarely

accounted for (e.g. Carbon storage and accounted for (e.g. Carbon storage and growth at night, i.e. “unbalanced” growth).growth at night, i.e. “unbalanced” growth).

• Minimal Constraints on loss termsMinimal Constraints on loss terms• Stability issuesStability issues

Other Approaches…Other Approaches…

• More Empirical RelationshipsMore Empirical Relationships– e.g. TP vs. Chlorophyll e.g. TP vs. Chlorophyll aa

• Quantum Yield ApproachQuantum Yield Approach– EEoo*A**A* = Primary Production = Primary Production

Free stuffFree stuff

• I (Heather/Laurel) will post Stella I (Heather/Laurel) will post Stella modelsmodels

• http://www.hps-inc.comhttp://www.hps-inc.com//

• Download isee Player (its free)Download isee Player (its free)

Background ReadingsBackground Readings

• Eppley 1972Eppley 1972

• Chapra pages 603-615 Chapra pages 603-615

• Brush et al. 2002Brush et al. 2002

• Chapra  742-747 (Solar Radiation and light Chapra  742-747 (Solar Radiation and light extinction sections) extinction sections)

• WASP ManualWASP Manual

• Kirk: Light and Photosynthesis in the seaKirk: Light and Photosynthesis in the sea

• Sverdrup: Conditions for phytoplankton Sverdrup: Conditions for phytoplankton bloomsblooms