Transcript Lect4-Habitat_Processes

Physical Stream Habitat
What is “Habitat”?
Broad Definition (EPA):
“The spatial structure of the environment which
allows species to live, reproduce, feed and move”
In Relation to Streams (USGS):
“The physical and chemical characteristics of a
stream that determine suitability for habitation and
reproduction of stream organisms”
What is “Physical Habitat”?
“The template of water depth, water velocity,
substrate, cover and temperature that
supports the stream ecosystem” – USGS
Hydrologic
Conditions
Geology
Topography
Land Use
Vegetation
Stream Morphology
Physical Habitat
Chemical Habitat
Aquatic Community
Interspecies
Interactions
Measurable Characteristics of
Physical Habitat
•
•
•
•
•
•
Channel morphology / type
Flow regime
Sediment texture / mobility
Bank structural features / stability
Riparian condition and connectivity
Physiochemical – temperature, DO, metals,
nutrients, turbidity, etc.
Mill Creek
Salmon and trout habitat requirements
include:
• adequate but not excessive stream flows
• cool well-oxygenated unpolluted water
• streambed gravels that are relatively free of finesediments
• adequate food supply
• instream structural diversity (interposed pools, riffles,
hiding and resting cover)
Washington State Dept of Fish Wildlife
Physical stream characteristics
affect stream organisms by defining:
• Habitat volume
• Habitat quality
• Disturbance magnitude
• Disturbance frequency
Habitat varies over spatial & temporal scales
Stream Corridor
Restoration, 199x
Heirarchical Classification System
Large
Scale
Scalar Unit
Definition
Role in Habitat
Characterization
Watershed
Basin
Area defined by topography that
contributes water and sediment to
the stream network
Determines boundary
conditions within which
river operates
Segment
Physiographically defined unit,
based on relief, morphology and
landscape position
Determines boundary
conditions within which
river operates
Reach Type
Length of channel with uniform
constraints resulting in a specific
assemblage of geomorphic units
Describes channel
planform and geometry
Geomorphic
Unit
Fluvial channel forms
representing distinct form-process
associations
Determines channel
character and behavior
Habitat Type Patches of relatively uniform flow Describes ecologically
and substrate characteristics
Fine
Scale
relevant hydraulic and
substrate conditions
Watershed
Segment
Reach Type
Geomorphic
Unit
Microhabitat
Type
103 m
102 m
101 m
100 m
10-1 m
How is each scale important to the species of interest?
Salmon
Macroinverts
Temporal Variability incorporates
‘predictable’ and ‘unpredictable’ cycles
Physical habitat a function of
processes operating at multiple
spatial and temporal scales
How do we objectively assess it?
Define Stream Habitat Types
(Classification)
• Bisson et al, 1982
• McCain et al, 1990 (USFS)
• Hawkins et al, 1993 (USFS)
• Thomson et al, 2001 (UK, AUS)
Fish Centric
McCain et al, 1990
McCain et al, 1990
Bisson et al, 1982
Hawkins et al, 1993
Hawkins et al, 1993
McCain et al, 1990
Hydraulic Habitat
Flow types can be
distinguished by
velocity and depth
using
Froude Number
v
F=
gd
Panfil & Jacobson, 2000
Thomson et al, 2001
Stream Habitat types are created and maintained
by erosion and deposition of sediments.
Hjulstrom’s Diagram
Mechanics of Habitat Formation
• Shear Stress/Velocity Reversal
Hypothesis
• Helical Flow
• Contraction/Expansion of Flow
t = rghs
v ~ f(Rs)
Knighton, 1998
Helical flow in meander bends
Knighton, 1998
Flow contraction and expansion
Wohl, 1998
Increased roughness
reduces shear,
promoting deposition of
finer material
McBain & Trush, 2004
What promotes Habitat Diversity?
Diversity is a function of fluctuations in erosion
and deposition processes over varying scales
Disturbance
Natural stream systems are subject to the full
spectrum of spatial & temporal disturbances
• Natural flow regime
• Varying sediment inputs
Episodic Sediment Transport
• Structural diversity - LWD
Natural Flow Regime
• 5 characteristics:
 Frequency
 Magnitude
 Duration
 Timing
 Rate of Change
• Key factor = extremes included
Disturbance acts to ‘reset’ processes
Mount, 1995
Large Woody Debris
• Increases local scour and deposition
• Provides structural habitat
• Transient nature (moves, breaks, clumps,
decays)
All add to habitat diversity and complexity
Plane Bed
Wood-poor
Pool-riffle
Buffington & Montgomery 1999
Wood-rich
Pool-riffle
Buffington & Montgomery 1999
Stream habitat diversity maintained over time
 Species adapt
• Salmon – spawning and run timing
• Foothill Yellow-legged Frog – oviposition
timing
• Cottonwood regeneration – accidental forest
Spawning
habitat with
incubation
of eggs
Movement to
Spawn
Movement to Feed
Movement
to Spawn
Refugia from
harsh environmental
conditions (e.g.,
extreme temperatures
or flows) with
unfavorable growth
conditions
Movement to Refuge
Mosaic of
feeding habitat(s)
with favorable
growth conditions
Movement to Feed
Habitat
1
Habitat
3
Habitat
2
Diversity in Trout Habitat
Redrawn by Bledsoe from
Schlosser (1995)
Alterations to flow regime & sediment supply
alter habitat diversity & biodiversity
Stream
Corridor
Restoration,
1998
Alterations to Stream Systems
• Flow extraction
• Sedimentation
– diversions
– groundwater
withdrawal
– development
– logging
– mining
• Flow augmentation
– ag runoff
– hydropower
• Sediment Loss
– dams
– mining
Degradation
• Channel Bed Coarsening
• Loss of Fines/Gravels
• Vegetation Encroachment
• Low bed mobility
Aggradation
• Channel Bed Fining
• Excess Fines/Gravels
• Lack of vegetation
• High bed mobility
Effect of Dams
• Block Sediment
• Channel Degradation –
bed coarsening, loss of
fines/gravels
• “Flatline”
Hydrograph
• Loss of extreme flows
(loss of disturbance) –
low bed mobility, vegetation
encroachment, low habitat
diversity
• Disrupt
Connectivity
• Block habitat access, alter
water chemistry, shift from
lentic to lotic system
What can we do to improve
spawning habitat conditions
downstream of dams?