incorporating ecological concepts into channel design: structural and functional approaches to...
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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
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Theory
Science
Practice
Evolutionary strategiesPopulation dynamicsCommunity structureStructure and componentsFunction and process
PassiveActive
Ecological restoration defined
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Ecological considerations for restorationAssuming goal is ecologically successful restoration…
HabitatStructure and components
Typical restoration
Function and processNatural drivers
Biological successSurvival, growth, reproduction
…we need to ensure that the habitat characteristics preferred and required by biota are present and persistent at the
relevant scale
Dynamic systemsPart of a watershed
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Ecological approaches to restoration: Structural versus functional
Structural• Focal species• Species diversity• Functional groups
Restoration actions• Channel
configuration• Instream habitat
restoration• Stocking
Functional• Food web interactions• Production (1o or 2o)• Nut. cycling, OM
processing• Population dynamics• Disturbance regime
Restoration actions• Connectivity• Flow and sediment
regimes• Channel complexity• Riparian processes
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Structural approaches to restoration
• Channel configuration• Instream habitat
restoration• Stocking
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)
Follstad Shah et al. 2007
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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
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Niche theory: diversification/specialization Environmental conditions favorable for a larger number of speciesRange of conditions available for different life history requirements
Reduces competitive dominance Provides refugia from predators and disturbance
Instream habitat restoration: Focus on creating habitat
heterogeneity
Relevant at a range of spatial scales
Particle Habitat unit or reachChannel
Food resources, hydraulics & competition
Substrate, hydraulics & food resources
Food resources, temperature, & stream size
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Instream habitat restoration: Common approaches
ActionsBoulder additions
LWD additionsAdd pool-riffle
sequencesChannel
reconfiguration
GoalsIncrease habitat quality/quantityIncrease hydraulic heterogeneityIncrease substrate heterogeneity
Increase food resource quality/quantityUltimate objective: Increase fish density and biomass
Native or sport fish? Fish diversity?
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Narrow focus on physical structure
Fitness
Survival
Reproduction
Growth
Habitat
Physical Chemical Biotic
• Substrate• Flow depth, velocity, etc.• Temperature• Connectivity
• DO • Nutrients • pH• Salinity• Conductivity
• Primary production• CPOM & FPOM• Predators/competitors• Disease• Connectivity
Instream habitat restoration: Does it work? Sometimes.
Other factors may be limiting to growth, survival, etc.
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Limiting factorsVariation among life stages
Schlosser 1991
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Instream habitat restoration: Limiting factorsSelect habitat suitability indices for brown trout
Any one habitat factor could be limiting; depends upon conditions and life stage
Reach-scale physical Site-scale physical Water quality
Restoration often only address physical factors, which may or may not be limiting
Altered physical conditions may not persist over time
Dominant substrateRubble Gravel Fines
Dissolved oxygen (mg/l)
Spawning areas
Riffle-run areas
Fines
% pools during late growing season, low-water
% cover during late growing season, low water
Max water temperature during summer (degrees C)
Fry Adults and juveniles
<10 C>10 C
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Instream habitat restorationUsing suitability indices to guide design
Example 1: Does the percentage of pools remain suitable as flow changes?
% pools during late growing season, low-water
> 20% pools, ideally between 50-70%
But recognize that too many pools can create problems for other life stages if substrate changes
Spawning areas
Riffle-run areas
Fines
Construct or provide structures to create pools, but beware unintended negative effects (e.g., Donner und Blitzen River)
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Instream habitat restorationUnintended negative effects: Donner und Blitzen
River, Oregon2001 (before weirs installed)
2009 (5 years after weirs installed)
Loss of riffles and pools, increase in fines
Pools 71%Riffles 13%
Pools 63%Riffles 10%
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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?
Instream habitat restorationUsing suitability indices to guide design
% cover during late growing season, low water
Adults and juveniles
Fry
Example 3: Is bed composition suitable and heterogeneous to accommodate different life stages?
Relate discharge to pool depth and pool depth to maximum water temperaturesQuantify sources of cover throughout the year
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Suitability Indices: Ecohydraulic Models
0.0
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Spaw
ning
Hab
itat P
refe
renc
e
Velocity (m/s)
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Spaw
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Hab
itat P
refe
renc
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Depth (m)
Suitability indices for depth and velocity (based on spawning habitat preference)
Spatial distribution of depth and velocity
Spatial distribution of suitability
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Discordance between spatial scale of restoration relative to the perturbation
Larson et al. 2001
Instream habitat restoration: Does it work? Sometimes.
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Instream habitat restoration: Bottom line
1. Habitat quality, quantity, or heterogeneity are limiting factors
2. Larger-scale processes do not override reach-scale responses
3. Targeted biota should be there, can get there, and will stay there
4. Constructed habitat persists under imposed flow and sediment regimes
From Pretty et al. 2003
Structures
None
Structures
None
Structures can increase physical heterogeneity…
Structural restoration can be ecologically successful, but only if:
…and still have non-significant effects on fish populations
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Functional approaches to restoration
Restoration of processes that sustain lotic ecosystems
Dynamic properties of natural systems contribute to proper function
Processes often operate at large spatiotemporal scales
Food webs
Nutrient cycling
Resource transfer
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Functional approaches to restoration: Strategies
Processes Strategies
Population dynamics Restore connectivity Resource transfer Longitudinal, vertical, and lateralOM matter processing Increase channel complexity/retentivenessNutrient transformation
Resource production Restore energy inputs: sunlight & OMFood web dynamics
Habitat maintenance Restore natural flow and sediment regimeBiotic interactions Disturbance regime
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Functional approaches to restoration: ExamplesRestore energy inputs: autotrophic and heterotrophic production
Allan 1995
SunlightTerrestrial organic matter
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
Two basic energy sources: Allochthonous and autochthonous
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Functional approaches to restoration: ExamplesRestore 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
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
> 1 mm
Controls on breakdown:-Microorganisms (bacteria, fungi)-Macroinvertebrates (shredders, collectors)-Mechanical abrasion-Leaf chemistry-Temperature
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Functional approaches to restoration: ExamplesRestore energy inputs: autochthonous energy sourcesPhotosynthesis (primary production)
Vascular plantsMossesAlgaeBacteriaDiatomsPhytoplankton
Controls on production:-Light-Nutrients-Substrate-Temperature
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Functional approaches to restoration: ExamplesRestore 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-orderRiver Continuum Concept
Longitudinal variation in energy production and trophic structure
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Functional approaches to restoration: ExamplesRestore energy inputs: tools for heterotrophic systems
1. Replace non-native riparian vegetation with native species
Nutritional valueSpeed of breakdown (refractory vs. labile)
Contribution to secondary production
0.0
0.5
1.0
1.5
2.0
2.5
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DAY 0 DAY 1 DAY 3 WEEK 1 WEEK 2 WEEK 4 MONTH 2
NIT
ROG
EN C
ON
TEN
T DU
RIN
G D
ECO
MPO
SITI
ON
(%)
ARUNDO
NATIVES
0.0
0.5
1.0
1.5
2.0
ARUNDO WILLOW ALDER
CADD
ISFL
Y LA
RVAL
MAS
S (G
RAM
S)
From Dudley and Neargarder, unpublished data
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Functional approaches to restoration: ExamplesRestore energy inputs: tools for heterotrophic systems
2. Increase channel complexity and OM retention with natural structuresConsider type of structure and disturbance effects 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)
From Muotka and Laasonen, 2002
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Functional approaches to restoration: ExamplesRestore natural disturbance regime
Townsend et al. 1997
Intermediate disturbance hypothesis
Greatest biodiversity at intermediate levels of
disturbance frequency and intensityEvolutionary adaptations to
a disturbance regime- Life history- Behavioral- Morphological
E.g., disturbance-vulnerable caddisflies downstream of dam
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Life-historySynchronization 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: ExamplesRestore natural disturbance regime: evolutionary adaptations
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Functional approaches to restoration: ExamplesRestore 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
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Functional approaches to restoration: ExamplesRestore natural disturbance regime: tools for restoration
Ideally, return or replicate natural flow regime and sediment supplyJob becomes much more difficult when this is not possibleGoal 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 regimeTiming, frequency, magnitude, duration, predictability
Chemical
•Dissolved Solids
•Nutrient Cycling
Physical
•Sediment Transport
•Channel Morphology
•Thermal Regime
Biological•Community Composition•Life History Strategies
•Biotic Interactions
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Functional approaches to restoration: ExamplesPotential ways channel design can recreate natural disturbance regime
Design channel with lateral and vertical high-flow refugia
Seed germination, riparian growth (OM, sediments, water)
Design channel for frequent (~2 year) overbank flooding
Side channelsOff-channel ponds connected at high flow
Lateral pools
Large woody debris, aquatic vegetation
In general, create conditions for regular bed mobilization (flood flows), moderate levels of bank erosion, and some instream
deposition Dynamic, self-maintaining channelBut remember, each system is unique
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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
Benefits1. Ecological goals are more likely to be
achieved2. System will require less long-term
maintenance3. Whole-system recovery rather than single
feature response
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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
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Extra slides
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Instream habitat restoration: Limitations of structural approach
(1)Additional abiotic and biotic driversHeterotrophic or
allocthonous energy sources
Interactions:Slope and primary production
Wallace 1999 Kiffney & Roni 2007
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Top and bottom of individual particles (~10-3 m)Why: food resources, hydraulics & competition
Spatial scales of variability: Macroinvertebrates
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Habitat unit: pool versus riffle (~102 m)Why: Substrate, hydraulics, food resources
• Collector gatherers
• Shredders• Depositional• Fine sediment
• Scrapers• Filterers• Current
loving• Erosional• Coarse
sediment
Spatial scales of variability: Macroinvertebrates
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Longitudinal (RCC) (~104 m)Why: Food resources,
temperature, stream size
Spatial scales of variability: Macroinvertebrates
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Natural flow regimeTiming, frequency, magnitude, duration, predictability
Chemical•Dissolved Solids
•Nutrient Cycling
Physical•Sediment Transport
•Channel Morphology
•Thermal Regime
Biological•Community Composition•Life History Strategies
•Biotic Interactions
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From Ebersole et al. 1997
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From Ebersole et al. 1997
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Limiting factors
Connectivity (lateral and longitudinal)
Competition, predation, non-native species
Disease
Species adaptations (disturbance regimes, habitatrequirements, spatial/temporal scales of habitat use)
mayfly fluvial trout
Adapted from Lake 2007
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Historical events
Disturbanceregime
Evolutionaryprocesses
Physiological constraints
Anthropogenicactivities
Local community composition
Biotic filters:Competition / Predation
Abiotic filters:Habitat / Dispersal
Regional Species Pool
Instream habitat restoration: Does it work? Sometimes.
Hierarchy of interacting variables that influences reach scale conditions
Restoration