2. Estuary Productivity & Complexity
Evaluating Human Impacts

3. Systems model approach
Start with general, conceptual model
Add specificity and ability to measure
Evaluate quality and degrees of influence
Aggregate groups that are very similar; add more specificity where necessary

4. Most general level of “model”

5. 2nd level of abstraction: components
Materials to be measured
Processes that define the system
Influences on those processes
Simplify by aggregating functional groups

7. Hierarchy, state variables and forces

8. Vocabulary of systems symbology

9. 3rd level: Connect the flows, quantify

10. Add spatial realism

11. Secure accurate baseline data

12. 4th level: run and evaluate the model

13. 5th level: refine the model

14. 6th level: make predictions
“What if” . . .
Sensitivity analysis

15. Predicting community structural change
Ecological Modelling 158:
Alternate “stable” states: Enteromorpha vs. Zostera

16. Prediction: community with highest exergy index should dominate
Exergy: “the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir.”
Algal: high nutrient, high salinity
Seagrass: low nutrient, low salinity

17. Model parameters from long-term studies

18. Conclusions
Adding high nutrient loads from rivers at the end of the growing season favors Enteromorpha
This leads to high production and algal turnover, causing anoxia
Adding nutrients at the beginning of the season (or reducing nutrients) favors Zostera