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Boundary Habitats

• Estuaries

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Interactions among physical parameters
Seasonality
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Characteristics of biological communities Marsh
habitats

• Generally, high density but low diversity
• Physiological stresses
• Low topographic substrate variability
• But very high potential for productivity due to
  nutrient input

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Components

• Macrophytes (seagrasses, sedges, rushes,
  cordgrasses)
• Epiphytic algae (macro- and micro-)
• Benthic macroalgae and microalgae
• Phytoplankton

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Estuary edge zonation in marshes
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High primary productivity

• E.g., may have gt4000 plants per meter square
• Second only to tropical rainforests in
  productivity, among natural ecosystems

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High secondary productivity

• Benthic macrofauna dense
• Clams, annelids, crustaceans
• Critical for coastal fisheries
• Used as nursery areas for many pelagic spp
• Approx 2/3 of fishery derived from nursery areas
  in estuaries
• What factors influence this productivity?

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Questions

• Why are estuaries so productive?
• How are offshore fisheries impacted by estuary
  quality?
• What limits productivity?
• How are estuaries sensitive to anthropogenic
  stress?

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Why are estuaries productive?

• Nutrient trap
• Tides provide an energy subsidy for the resident
  aquatic species
• Autotrophs are present all year
• Combination of freshwater and saltwater creates
  many different habitats

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Variety of habitats
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Physical complexity of an estuary basin
Shallow Water
Open Water
Deep Water
Deep Channel
A. Cross Section of Chesapeake Bay or Tidal
Tributary
Migratory Finfish Spawning and Nursery Habitat
B. Oblique View of the Chesapeake Bay and its
Tidal Tributaries
Shallow Water Habitat
Open Water Habitat
Deep Water
Deep Channel
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Freshwater links with estuaries
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Sediment trapping in tributaries
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What happens to stream input?

• Nutrient (sediment) trap effects due to physical
  factors
• Settling with dispersion of water flow
• Nutrients adsorbed on clays
• Flocculation
• pH salinity change
• alter electrostatic charges
• water small particles attract
• increasing particle size and
• tendency to settle

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Biotic sediment trapping plants
Spartina - cordgrass
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Plant effects in estuarine productivity

• Sediment trap effect due to reduction of flow
  velocity
• Nutrient pump effect
• Nutrients taken by roots from sediments
• Transferred to water column (for phytoplankton)
• Nutrient modulation effect
• Uptake when nutrients are abundant
• Net release back to water when nutrients are
  scarce (through decomposition)

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Biotic sediment trapping animals

• Biodeposition
• Filter feeders collect suspended matter, compact
  it
• Clearance rates can be very high 10s of
  liters per day per clam or oyster

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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 fisheries depend 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)
• Mollusks
• Oysters 1988 peak of 3 million, now lt1 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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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 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 Cheasapeake 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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Why They Are Being Destroyed

• Level of habitat loss is 80 to 95
• Many factors contribute to this destruction
• Storm sewers are difficult to regulate due to old
  infastructure

(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