Incorporating ecological concepts into
channel design: structural and functional
approaches to restoration
Nira Salant
Intermountain Center for River Rehabilitation and Restoration
Principles of Stream Restoration and Design: Part II
August 2011
Ecological restoration defined
Theory
Evolutionary strategies
Population dynamics
Community structure
Science
Structure and components
Function and process
Practice
Passive
Active
Ecological considerations for restoration
Assuming goal is ecologically successful restoration…
Natural drivers
Function and process
Dynamic systems
Part of a watershed
Typical restoration
Habitat
Structure and components
Biological success
Survival, growth, reproduction
…we need to ensure that the habitat characteristics preferred and required by biota
are present and persistent at the relevant scale
Ecological approaches to restoration: Structural
versus functional
Functional
Structural
• Focal species
• Species diversity
• Functional groups
Restoration actions
• Channel configuration
• Instream habitat restoration
• Stocking
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Food web interactions
Production (1o or 2o)
Nut. cycling, OM processing
Population dynamics
Disturbance regime
Restoration actions
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Connectivity
Flow and sediment regimes
Channel complexity
Riparian processes
Structural approaches to restoration
• Channel configuration
• Instream habitat restoration
• Stocking
Follstad Shah et al. 2007
One of the most common river
restoration practices
Habitat degradation considered
most serious threat to
biodiversity
Only 2% of U.S. rivers of high
natural quality (Benke 1990)
Instream habitat restoration
Basic assumption:
Species richness and abundance are limited by degree of physical
habitat heterogeneity
“If you build it, they will come”
Kerr et al. 2001
Basic approach:
Restoration of resources or
environmental conditions necessary to
sustain an individual population or group
of populations
Instream habitat restoration:
Focus on creating habitat heterogeneity
Niche theory: diversification/specialization
Environmental conditions favorable for a larger number of species
Range of conditions available for different life history requirements
Reduces competitive dominance
Provides refugia from predators and disturbance
Relevant at a range of spatial scales
Food resources,
hydraulics &
competition
Food resources,
temperature, &
stream size
Substrate, hydraulics & food resources
Particle
Habitat unit or reach
Channel
Instream habitat restoration: Common approaches
Actions
Boulder additions
LWD additions
Add pool-riffle sequences
Channel reconfiguration
Goals
Increase habitat quality/quantity
Increase hydraulic heterogeneity
Increase substrate heterogeneity
Increase food resource quality/quantity
Ultimate objective: Increase fish density and biomass
Native or sport fish? Fish diversity?
Instream habitat restoration:
Does it work? Sometimes.
Fitness
Narrow focus on
physical structure
Reproduction
Survival
Growth
Other factors may be limiting
to growth, survival, etc.
Habitat
Physical
• Substrate
• Flow depth, velocity, etc.
• Temperature
• Connectivity
Chemical
• DO
• Nutrients
• pH
• Salinity
• Conductivity
Biotic
• Primary production
• CPOM & FPOM
• Predators/competitors
• Disease
• Connectivity
Limiting factors
Variation among life stages
Schlosser 1991
Instream habitat restoration: Limiting factors
Select habitat suitability indices for brown trout
Any one habitat factor could be limiting; depends upon conditions and life stage
<10 C
>10 C
% pools during late growing
season, low-water
Rubble
Gravel
Fines
Dominant substrate
Dissolved oxygen (mg/l)
Fry
Spawning
areas
% cover during late growing
season, low water
Reach-scale physical
Riffle-run
areas
Fines
Site-scale physical
Adults and
juveniles
Max water temperature
during summer (degrees C)
Water quality
Restoration
often only
address
physical
factors, which
may or may
not be
limiting
Altered
physical
conditions
may not
persist over
time
Instream habitat restoration
Using suitability indices to guide design
Example 1: Does the percentage of pools remain suitable as flow changes?
> 20% pools, ideally between 50-70%
But recognize that too many pools can
create problems for other life stages if
substrate changes
% pools during late growing
season, low-water
Spawning
areas
Riffle-run
areas
Construct or provide structures to create
pools, but beware unintended negative
effects (e.g., Donner und Blitzen River)
Fines
Instream habitat restoration
Unintended negative effects: Donner und Blitzen River, Oregon
2001 (before weirs installed)
2009 (5 years after weirs installed)
Pools 71%
Riffles 13%
Loss of riffles and pools,
increase in fines
Pools 63%
Riffles 10%
Instream habitat restoration
Using suitability indices to guide design
Example 2: Do pools remain deep enough to provide thermal refugia
and/or cover at low flow? Is there enough overhead cover at low flow?
Fry
Adults and
juveniles
% cover during late growing season,
low water
Relate
discharge to
pool depth
and pool
depth to
maximum
water
temperatures
Quantify sources of cover throughout the year
Example 3: Is bed composition suitable and heterogeneous to
accommodate different life stages?
Suitability Indices: Ecohydraulic Models
1.0
Suitability indices for depth and velocity
(based on spawning habitat preference)
Spawning Habitat Preference
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0.1
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0.0
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1.0
1.2
Depth (m)
Spatial distribution of depth and velocity
1.0
Spawning Habitat Preference
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Spatial distribution of suitability
0.1
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Velocity (m/s)
1.2
1.4
1.6
Instream habitat restoration:
Does it work? Sometimes.
Discordance between spatial scale of
restoration relative to the perturbation
Larson et al. 2001
Instream habitat restoration: Bottom line
1.
2.
3.
4.
Structural restoration can be ecologically successful, but only if:
Habitat quality, quantity, or heterogeneity are limiting factors
Larger-scale processes do not override reach-scale responses
Targeted biota should be there, can get there, and will stay there
Constructed habitat persists under imposed flow and sediment regimes
Structures can increase
physical heterogeneity…
Structures
None
From Pretty et al. 2003
…and still have non-significant
effects on fish populations
Structures
None
Functional approaches to restoration
Restoration of processes that sustain lotic ecosystems
Food webs
Nutrient cycling
Resource transfer
Dynamic properties of natural systems
contribute to proper function
Processes often operate at large
spatiotemporal scales
Functional approaches to restoration: Strategies
Processes
Strategies
Population dynamics
Resource transfer
Restore connectivity
Longitudinal, vertical, and lateral
OM matter processing
Nutrient transformation
Increase channel complexity/retentiveness
Resource production
Food web dynamics
Restore energy inputs: sunlight & OM
Habitat maintenance
Biotic interactions
Restore natural flow and sediment regime
Disturbance regime
Functional approaches to restoration: Examples
Restore energy inputs: autotrophic and heterotrophic production
Two basic energy sources:
Allochthonous and autochthonous
Productivity potential of a system is generally driven by the amount of basal resources
(bottom-up control)
Type of basal resource can determine trophic structure and function
Terrestrial organic matter
Sunlight
Allan 1995
Functional approaches to restoration: Examples
Restore energy inputs: allochthonous energy sources
Supported by breakdown of organic matter by microorganisms
(heterotrophic)
Coarse particulate organic matter (CPOM)
Leaves, needles, woody debris, dead algae > 1 mm
Fine particulate organic matter (FPOM)
Soil, feces, reduced CPOM; 1 mm – 0.5 µm
Dissolved organic matter (DOM)
Carbs, fatty acids, humic acids; <0.5 µm
Controls on breakdown:
-Microorganisms (bacteria, fungi)
-Macroinvertebrates (shredders, collectors)
-Mechanical abrasion
-Leaf chemistry
-Temperature
Functional approaches to restoration: Examples
Restore energy inputs: autochthonous energy sources
Photosynthesis (primary production)
Vascular plants
Mosses
Algae
Bacteria
Diatoms
Phytoplankton
Controls on production:
-Light
-Nutrients
-Substrate
-Temperature
Functional approaches to restoration: Examples
Restore energy inputs: autotrophic and heterotrophic production
Dominant type of energy source
varies with stream size, substrate,
riparian vegetation, and location in the
watershed
Allochthonous: narrow, coarse
substrate, forested, low-order
Autochthonous: wide, fine substrate,
high-order
River Continuum Concept
Longitudinal variation in energy production
and trophic structure
Functional approaches to restoration: Examples
Restore energy inputs: tools for heterotrophic systems
1. Replace non-native riparian vegetation with native species
Speed of breakdown (refractory vs. labile)
Nutritional value
Contribution to secondary production
2.5
2.0
1.5
1.0
ARUNDO
0.5
CADDISFLY LARVAL MASS (GRAMS)
NITROGEN CONTENT DURING DECOMPOSITION (%)
2.0
3.0
1.5
1.0
0.5
NATIVES
0.0
DAY 0
DAY 1
DAY 3
WEEK 1
WEEK 2
From Dudley and Neargarder, unpublished data
WEEK 4 MONTH 2
0.0
ARUNDO
WILLOW
ALDER
Functional approaches to restoration: Examples
Restore energy inputs: tools for heterotrophic systems
2. Increase channel complexity and OM retention with natural structures
Consider type of structure and disturbance effects
From Muotka and Laasonen, 2002
Loss of mosses during
restoration shifted
resource base from
detritus to algal
production, resulting in
altered benthic
community
Mosses and woody
debris contribute to
habitat, hydraulic refugia,
and retention (esp. at
high discharges)
Functional approaches to restoration: Examples
Restore natural disturbance regime
Intermediate disturbance hypothesis
Greatest biodiversity at intermediate
levels of disturbance frequency and
intensity
Evolutionary adaptations to a
disturbance regime
- Life history
- Behavioral
- Morphological
E.g., disturbance-vulnerable
caddisflies downstream of dam
Townsend et al. 1997
Functional approaches to restoration: Examples
Restore natural disturbance regime: evolutionary adaptations
Life-history
Synchronization of life-cycle event (e.g., reproduction, growth,
emergence) with occurrence of disturbance (long-term average)
Type of disturbance: high predictability and frequency
Examples:
– Cottonwood seed release
– Salmonid egg hatching
Functional approaches to restoration: Examples
Restore natural disturbance regime: evolutionary adaptations
Behavioral
• Direct responses to an individual event; based on environmental cues
• Type of disturbance: low predictability, high frequency, high magnitude
Morphological
• Growth forms and biomass allocation; tradeoff with reproduction
• Type of disturbance: large magnitude and high frequency
Functional approaches to restoration: Examples
Restore natural disturbance regime: tools for restoration
Ideally, return or replicate natural flow regime and sediment supply
Job becomes much more difficult when this is not possible
Goal should be to
recreate processes that
sustain natural chemical,
physical and biological
functions and patterns
Use channel design to
best replicate natural
disturbance regime,
given the current
governing conditions
Natural flow regime
Timing, frequency, magnitude, duration, predictability
Chemical
Physical
•Dissolved Solids
•Sediment Transport
•Nutrient Cycling
•Channel Morphology
•Thermal Regime
Biological
•Community Composition
•Life History Strategies
•Biotic Interactions
Functional approaches to restoration: Examples
Potential ways channel design can recreate natural disturbance regime
Design channel for frequent (~2 year) overbank flooding
Seed germination,
riparian growth (OM,
sediments, water)
Design channel with lateral and vertical high-flow refugia
Lateral pools
Large woody debris,
aquatic vegetation
Side channels
Off-channel ponds
connected at high flow
In general, create conditions for regular bed mobilization (flood flows), moderate levels
of bank erosion, and some instream deposition  Dynamic, self-maintaining channel
But remember, each system is unique
Functional approaches to restoration:
Challenges
1. Difficult to identify relevant processes, spatiotemporal
scales and limiting factors
2. Assessments can require high level of expertise and be
costly and time-consuming
3. Lack of standardized methods
Benefits
1. Ecological goals are more likely to be achieved
2. System will require less long-term maintenance
3. Whole-system recovery rather than single feature response
Implications for practice
1. Prioritize restoration efforts by assessing the source and scale of
degradation processes, the condition of the regional species pool and
identifying limiting factors
2. Assess whether a structural approach will be adequate or whether a
functional approach to restoration is needed, but also recognize that
structural changes may help restore process and function
3. Realize that temporal variability can be as important as spatial variability
(some natural systems are dynamic); realize that each system is unique
4. Biotic variables may be as important to restore as physical variables; physical
improvements may not illicit positive biological responses
5. Monitor both abiotic and biotic variables at concordant and relevant
spatiotemporal scales to quantify links between restoration actions and
desired ecological responses
Extra slides
Instream habitat restoration:
Limitations of structural approach (1)
Additional abiotic and biotic drivers
Heterotrophic or allocthonous
energy sources
Wallace 1999
Interactions:
Slope and primary production
Kiffney & Roni 2007
Spatial scales of variability: Macroinvertebrates
Top and bottom of individual particles (~10-3 m)
Why: food resources, hydraulics & competition
Spatial scales of variability: Macroinvertebrates
Habitat unit: pool versus riffle (~102 m)
Why: Substrate, hydraulics, food resources
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Collector gatherers
Shredders
Depositional
Fine sediment
Scrapers
Filterers
Current loving
Erosional
Coarse sediment
Spatial scales of variability: Macroinvertebrates
Longitudinal (RCC) (~104 m)
Why: Food resources,
temperature, stream size
Natural flow regime
Timing, frequency, magnitude, duration, predictability
Chemical
Physical
•Dissolved Solids
•Sediment Transport
•Nutrient Cycling
•Channel Morphology
•Thermal Regime
Biological
•Community Composition
•Life History Strategies
•Biotic Interactions
From Ebersole et al. 1997
From Ebersole et al. 1997
Limiting factors
Connectivity (lateral and longitudinal)
Competition,
predation,
non-native species
Disease
mayfly
Species adaptations
(disturbance regimes, habitat
requirements, spatial/temporal scales
of habitat use)
Adapted from Lake 2007
fluvial trout
Instream habitat restoration:
Does it work? Sometimes.
Evolutionary
processes
Historical events
Disturbance
regime
Regional Species Pool
Anthropogenic
activities
Restoration
Physiological
constraints
Abiotic filters:
Habitat / Dispersal
Biotic filters:
Competition / Predation
Hierarchy of interacting
variables that influences
reach scale conditions
Local community
composition