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

Ecological restoration defined

Evolutionary strategies Population dynamics Community structure 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

• • • Structural Focal species Species diversity Functional groups • • • Restoration actions Channel configuration Instream habitat restoration Stocking • • • • • • • • • Functional Food web interactions Production (1 o or 2 o ) 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

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 Particle Substrate, hydraulics & food resources 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.

Narrow focus on physical structure

Fitness Survival Reproduction 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 % pools during late growing season, low-water Rubble Gravel Fines Dominant substrate <10 C >10 C Dissolved oxygen (mg/l) Restoration often only address physical factors, which may or may not be limiting % cover during late growing season, low water Reach-scale physical Spawning areas Riffle-run areas Fines Site-scale physical Fry Adults and juveniles Max water temperature during summer (degrees C) Water quality 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 Construct or provide structures to create pools, but beware unintended negative effects (e.g., Donner und Blitzen River) Spawning areas Riffle-run areas 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 Relate discharge to pool depth and pool depth to maximum water temperatures % cover during late growing season, low water Quantify sources of cover throughout the year Example 3: Is bed composition suitable and heterogeneous to accommodate different life stages?

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

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

Structural restoration can be ecologically successful, but only if: 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 Structures can increase physical heterogeneity… …and still have non-significant effects on fish populations From Pretty et al. 2003 Structures None Structures None

Functional approaches to restoration

Restoration of processes that sustain lotic ecosystems Food webs Nutrient cycling Dynamic properties of natural systems contribute to proper function Resource transfer Processes often operate at large spatiotemporal scales

Functional approaches to restoration: Strategies

Processes Strategies Population dynamics Resource transfer OM matter processing Nutrient transformation Restore connectivity Longitudinal, vertical, and lateral Increase channel complexity/retentiveness Resource production Food web dynamics Habitat maintenance Biotic interactions Restore energy inputs: sunlight & OM 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 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: 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 3.0

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DAY 0 DAY 1 ARUNDO NATIVES DAY 3 WEEK 1 WEEK 2 WEEK 4 MONTH 2 From Dudley and Neargarder, unpublished data Contribution to secondary production 2.0

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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 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: Examples

Restore natural disturbance regime Townsend et al. 1997 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

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 Natural flow regime Timing, frequency, magnitude, duration, predictability Goal should be to recreate processes that sustain natural chemical, physical and biological functions and patterns Chemical •Dissolved Solids •Nutrient Cycling Physical •Sediment Transport •Channel Morphology •Thermal Regime Use channel design to best replicate natural disturbance regime, given the current governing conditions 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 Interactions: Slope and primary production Kiffney & Roni 2007 Wallace 1999

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 (~10 2 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) (~10 4 m) Why: Food resources, temperature, stream size

Natural flow regime Timing, 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 mayfly Species adaptations (disturbance regimes, habitat requirements, spatial/temporal scales of habitat use) Adapted from Lake 2007 fluvial trout

Restoration

Instream habitat restoration: Does it work? Sometimes.

Evolutionary processes Historical events Disturbance regime Anthropogenic activities Regional Species Pool Physiological constraints Abiotic filters: Habitat / Dispersal Hierarchy of interacting variables that influences reach scale conditions Biotic filters: Competition / Predation Local community composition