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

Theory

Science

Practice

Evolutionary strategiesPopulation dynamicsCommunity structureStructure and componentsFunction and process

PassiveActive

Ecological restoration defined

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

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

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

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

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

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?

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.

Limiting factorsVariation among life stages

Schlosser 1991

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

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)

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%

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

Suitability Indices: Ecohydraulic Models

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Suitability indices for depth and velocity (based on spawning habitat preference)

Spatial distribution of depth and velocity

Spatial distribution of suitability

Discordance between spatial scale of restoration relative to the perturbation

Larson et al. 2001

Instream habitat restoration: Does it work? Sometimes.

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

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

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

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

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

Functional approaches to restoration: ExamplesRestore energy inputs: autochthonous energy sourcesPhotosynthesis (primary production)

Vascular plantsMossesAlgaeBacteriaDiatomsPhytoplankton

Controls on production:-Light-Nutrients-Substrate-Temperature

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

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

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From Dudley and Neargarder, unpublished data

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

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

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

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

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

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

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

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 driversHeterotrophic or

allocthonous energy sources

Interactions:Slope and primary production

Wallace 1999 Kiffney & Roni 2007

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

• 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

Spatial scales of variability: Macroinvertebrates

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

From Ebersole et al. 1997

From Ebersole et al. 1997

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

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