Estuary Productivity & Complexity Evaluating Human Impacts

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

Most general level of “model”

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

Hierarchy, state variables and forces

Vocabulary of systems symbology

3rd level: Connect the flows, quantify

Add spatial realism

Secure accurate baseline data

4th level: run and evaluate the model

5th level: refine the model

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

Predicting community structural change Ecological Modelling 158:233-240 Alternate “stable” states: Enteromorpha vs. Zostera

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

Model parameters from long-term studies

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