Physical Factors: Current, Substrate, Temperature, and Oxygen

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Physical Factors Current, Substrate,
Temperature, and Oxygen

• Unit 1 Module 4, Lecture 3

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Objectives

• Students will be able to
• explain how current influences and effects the
  type of organisms in a stream.
• predict and describe longitudinal sediment
  distribution in a stream.
• classify sediment particles by size.
• describe how particle size influences aquatic
  organisms.
• describe how temperature and oxygen levels affect
  aquatic organisms in a stream.

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Physical factors Current, substrate,
temperature, and oxygen

• Module 4 Lecture 3 consists of three parts which
  you can do in whatever order suits your class
• Physical factors
• Organic Matter
• Stream Chemistry.

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Current

• Current influences
• Ecological distribution
• Morphological adaptations
• An organisms behavior

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Current and body shape

• Sunfish and bullheads with broad body forms are
  adapted to slow current.

• Stonecats and trout with streamlined body forms
  are adapted to fast current.

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Current

• The distribution of diatoms, algae, and rooted
  macrophytes are influenced by current.
• Diatoms species can by sorted into taxa that are
  adapted to slow and fast moving water.
• Attached algae appear to increase in abundance in
  conditions with fast current and hard substrates.
• Rooted macrophytes thrive in slow water with soft
  sediments.

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The effect of substrate on organisms

• The diversity of materials making up the
  substrate of a stream make it complex and
  dynamic.
• The composition of the substrate plays an
  important role in shaping what organisms inhabit
  a particular stream reach.
• Due to other factors such as current,
  temperature, and oxygen levels it is important
  not to attribute the presence or absence of a
  specific species solely to the substrate type
  encountered at particular site.

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Longitudinal sediment distribution

• The predominant substrate size decreases as you
  move downstream.

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Chattahoochee River tributaries

• Percent of bottom covered by various substrates

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Particle size
Category Category Dia (mm) Wentworth scale
Boulder Cobble Boulder Cobble gt 256 lt -8
Large Small 128 - 256 64 - 128 -7 -6
Pebble Large Small 32 - 64 16 - 32 -5 -4
Gravel Coarse Medium Small 8 - 16 4 - 8 2 - 4 -3 -2 -1
Sand Very Coarse Coarse Medium Fine Very Fine 1 - 2 0.5 - 1 0.25 - 0.5 0.125 - 0.25 0.063 - 0.125 0 1 2 3 4
Silt lt 0.063 gt 5
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Organic matter as a substrate component

• Organic materials ranging from plants stems to
  logs tend to function as substrates for
  organisms, while particles less than 1 mm in size
  may serve as food for macro invertebrates.
• Diversity and density of invertebrates often
  increases with the presence of organic matter as
  part of the substrate.

• As organic matter increases in stream substrates,
  macro invertebrate diversity tends to increase

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Faunal selection of substrates
Group Preferred Substrate
Lithophilous Gravel, Cobbles, Boulders
Psammophilous Sand
Xylophilous Wood
Phytophilous Plants
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Fish spawning habitat

• Most stream dwelling fish select a hard
  substrate, ranging from large stones to mixed
  gravel on which to spawn.

• The availability and distribution of a particular
  substrate type necessary for spawning is often
  critical in creating suitable habitat for a
  particular species.

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The effect of temperature on organisms

• This figure illustrates seasonal differences in
  the emergence of mayfly species that would in
  part be cued by temperature.

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Maximum daily temperature range in relation to
stream order in temperate streams
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Oxygen

• In most unpolluted streams dissolved oxygen is
  near saturation and is, therefore, of minor
  biological concern.
• Current serves to deliver oxygen rich water to
  respiratory structures.
• Fish can actively move water over gills, however,
  most invertebrates cannot and are dependent on
  current to deliver oxygen.
• These organisms are referred to as respiratory
  conformers their respiratory rate closely
  follows the ambient oxygen concentration.

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Oxygen related adaptations

• Fish actively swim and draw water over their
  gills
• Macroinvertebrate larvae with conspicuous gills
  are respiratory conformers
• Midge larvae with hemoglobin are adapted to live
  in poorly oxygenated stream sediments