Physical Factors: Current,
Substrate, Temperature,
and Oxygen
Unit 1: Module 4, Lecture 3
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.
Developed by: Merrick, Richards
Updated: August 2003
U1-m4-s2
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.
Developed by: Merrick, Richards
Updated: August 2003
U1-m4-s3
Current
 Current influences:
 Ecological distribution
 Morphological adaptations
 An organism’s behavior
www.dec.state.ny.us/website/dow/stream/empfamilies.htm
A mayfly larva with a dorsoventrally
flattened body minimizing drag in
current.
Developed by: Merrick, Richards
www.dec.state.ny.us/website/dow/stream/orderpagetwo.htm
A collembola with a rounded body,
suiting it for areas of slow current.
Updated: August 2003
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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.
www.uga.edu/srel/Coal_Ash/sunfish.jpg
www.lambs-inn.com/new-images/ trout-sm.jpg
www.cnr.vt.edu/efish/families/ictaluridae.html
Developed by: Merrick, Richards
www.cnr.vt.edu/efish/families/ictaluridae.html
Updated: August 2003
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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.
Developed by: Merrick, Richards
Updated: August 2003
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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.
www.mountainspecs.com/creek.jpg
Developed by: Merrick, Richards
Updated: August 2003
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Longitudinal sediment distribution
 The predominant substrate size decreases as
you move downstream.
Mean gradient
Distance downstream
Bed material size
Boulders and
cobbles
Gravel
Sand
Silt
www.shorelandmanagement.org/depth/rivers/04.html
Developed by: Merrick, Richards
Updated: August 2003
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Chattahoochee River tributaries
 Percent of bottom covered by various
substrates
Developed by: Merrick, Richards
Updated: August 2003
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Particle size
Category
Dia (mm)
Boulder
Cobble
Wentworth
scale
> 256
< -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
< 0.063
>5
Silt
www.mountainspecs.com/creek.jpg
www.aquatic.uoguelph.ca/rivers/chphys.htm
www.enn.com/news/enn-stories/2000/02/02172000/alaska.jpg
Developed by: Merrick, Richards
Updated: August 2003
U1-m4-s10
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.
Developed by: Merrick, Richards
 As organic matter
increases in stream
substrates, macro
invertebrate diversity
tends to increase
www.mcmullans.org/ canal/lock_60.htm
Updated: August 2003
U1-m4-s11
Faunal selection of substrates
Group
Preferred Substrate
Lithophilous
Gravel, Cobbles, Boulders
Psammophilous
Sand
Xylophilous
Wood
Phytophilous
Plants
Developed by: Merrick, Richards
Updated: August 2003
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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.
www2.state.id.us/fishgame/fish/fishstocking/hatcheries/mccall.htm
Developed by: Merrick, Richards
 The availability and
distribution of a
particular substrate type
necessary for spawning
is often critical in
creating suitable habitat
for a particular species.
www2.state.id.us/fishgame/fish/fishstocking/hatcheries/mccall.htm
Updated: August 2003
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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.
www.centralnewyorker.com/mayflyhatchchart.htm
Developed by: Merrick, Richards
Updated: August 2003
U1-m4-s14
Maximum daily temperature range in relation to
stream order in temperate streams
www.mountainspecs.com/creek.jpg
www.fermatainc.com/wis/
www.aquatic.uoguelph.ca/rivers/chphys.htm
Developed by: Merrick, Richards
Updated: August 2003
U1-m4-s15
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.
Developed by: Merrick, Richards
Updated: August 2003
U1-m4-s16
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
www.cnr.vt.edu/efish/families/umbridae.html
ww.usask.ca/biology/skabugs/Ephem/mayfly.html
www.usask.ca/biology/skabugs/flies/chiron.html
Developed by: Merrick, Richards
Updated: August 2003
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