How realistic can we be?

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Estuary Productivity Complexity

• Evaluating Human Impacts

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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

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Most general level of model
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2nd level of abstraction components

• Materials to be measured
• Processes that define the system
• Influences on those processes
• Simplify by aggregating functional groups

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Hierarchy, state variables and forces
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Vocabulary of systems symbology
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3rd level Connect the flows, quantify
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Add spatial realism
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Secure accurate baseline data
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4th level run and evaluate the model
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5th level refine the model
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6th level make predictions

• What if . . .
• Sensitivity analysis

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Predicting community structural change

• Ecological Modelling 158233-240
• Alternate stable states Enteromorpha vs.
  Zostera

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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

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Model parameters from long-term studies
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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