Factors enhancing productivity: Tidal mixing

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Factors enhancing productivity Tidal mixing

• Ebb flow of tides enhances settling of
  sediments/nutrients
• Resuspension of materials can enhance
  phytoplankton productivity

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Factors affecting light productivity
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Links between estuaries and fisheries

• Fisheries classifications
• Economic
• Commercial
• Recreational
• Subsistence
• What is being harvested
• Arthropods (crabs, shrimp)
• Molluscs (clams, oysters)
• Fish

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Offshore fishery dependence on estuaries

• 70 90 of commercial catch from east coast of
  USA is estuarine dependent
• Fishery productivity is correlated with area of
  marsh and vegetated habitat

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Example of fisheries in North Carolina estuaries

• Arthropods
• Blue crabs (40 million)
• Shrimp (20 million)
• Molluscs
• Oysters 1988 peak of 3 million, now 1 million)
• Clams also declining, from 1980 8 million
• Fish
• Menhaden, flounder, croaker, weakfish gt 24
  million
• Recreations catch can exceed commercial

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Estuaries and fisheries, an example
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Estuary Productivity Complexity

• Evaluating Human Impacts

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Questions

• How do people influence estuary productivity?
• What regulates dynamic processes?
• Which of complex processes are most critical?
• How do we answer these questions?

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Estuaries are especially sensitive to human
impacts

• Sediment trapping can be problematic
• Tradeoff between adding nutrients and increasing
  turbidity
• High sediment loads clog filtering systems of
  animals
• Sediments carry pollutants (dredge spoils of Cape
  Cod harbors are toxic wastes)
• Filter feeders tend to concentrate toxins
• Estuaries are the First stop for poor
  agriculture and waste management

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Other reasons for estuarine sensitivity

• Vulnerability of estuarine organisms
• Many already at the limit of physiological
  tolerances
• Added stress of chemicals, hypoxia may reduce
  reproduction below critical limits
• Food web structure is based on few species
• Low diversity is high risk

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SedimentSources to the Ch. Bay and Tribs

• Watershed Inputs (1,2 and 3)
• Shoreline erosion (4)
• Ocean (5)
• Biogenic production
• Relative contribution varies in proportion
  different areas of the Bay and tribs

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Sediment transport in Chesapeake Bay
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Sediment Budget Choptank Estuary 1979-80
(Yarbro et. al, 1983)
12 Upland
8 From estuary
80 Shoreline

81 Deposited
19 Transfer down estuary
Total Sediment input 0.43 x 106 metric tonnes
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Challenges to estuaries

• Level of habitat loss is 80 to 95
• Many factors contribute to this destruction in
  Chesapeake Bay

(EPA study)
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Information about Stormwater

• More oil than was released in the Exxon Valdez
  spill flows into Galveston Bay per yr
• One quart of spilled motor oil covers three
  football fields
• Takes 20 years for an aquatic system to recover
  from oil contamination
• In the Chesapeake Bay, 15 P, 14 N, and 9 of
  sediment loads come from storm water

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Stormwater Pollutants

• Suspended soilds from steet dust and eroded
  sediments
• Heavy metals from motor vehicleswear of plating,
  bearings and brake linings
• Chlorides from salt application
• Oils, grease and other hydrocarbons from vehicle
  exhaust and lubricants

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Potential PoliciesVegetated Shoreline Buffer
Zones

• Improve water quality, create new habitat
• Difficulties waterfront land values are
  expensive, need to remove existing buildings,
  political opposition, reluctant governments

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Potential PoliciesBest management practices
(BMPs)

• Advanced
• Detention ponds
• Vegetated filter strips
• Catch basin filters
• Baseline
• Preventive maintenance
• Education.

Detention pond
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How do we evaluate impacts of pollution or
management practices?

• e.g., submerged aquatic vegetation (SAV) is
  disappearing why and what other parts of the
  estuary are affected?
• What do we need to know?
• How do we integrate mountains of detailed data?

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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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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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Recent applications
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Symbols in model

• Stressors sea level rise, societal-driven
• Responses SAV, Oysters, Benthic Diversity, Fish,
  Manatees, Mangroves
• Concerns population declines, loss of habitat,
  altered hydrology

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