The Ecology of Interfaces: Riparian Zones

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The Ecology of InterfacesRiparian Zones

• Your Guide Today
• Alisa

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The Riparian Zone

• The forested land along rivers, streams, and
  lakes is known as the "riparian zone". 
• Riparian comes from the Latin word ripa, meaning
  bank.
• Riparian zones are areas of transition between
  aquatic and upland ecosystems.

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Ecology of Interfaces

• The Riparian Zone
• Defining and delineating
• Life-history strategies
• Morphological and physiological adaptations
• Reproductive adaptations
• Successional and Vegetative Patterns
• Physical controls
• Biotic patterns

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Defining Riparian Zones

• Difficult to determine extent.
• Encompasses stream channel between low and high
  water marks.
• Uplands from high water line to areas that may be
  influenced by elevated water tables or flooding.
• Availability of soils to hold water.

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Landform Definition

• Landform definitions are based on some idealized
  cross-sectional shape of a river channel.
• The riparian zone is defined as that area between
  the low-flow level of the watercourse and the
  highest point of transition between the channel
  and its floodplain.
• Does not include important areas such as adjacent
  wetlands or billabongs, which may influence
  streams or lakes.
• This definition does provide an easy, helpful and
  rough guide.

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Three Zone System
Welsch (1991) describes riparian forests as
ecosystems that can be depicted in three zones
adjacent to stream systems consisting of
undisturbed forest, managed forest, and runoff
control.
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Vegetation Definition

• Based on the idea that vegetation in riparian
  zones is different to the surrounding terrestrial
  ecosystem.
• This has not been of wide practical use, as the
  riparian zone itself contains a wide range of
  vegetation types, from mature trees to emergent
  macrophytes.
• Vegetation change may reflect periodic events
  with a long return time, for example, fire, flood
  or severe drought.

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Functional Definition

• Defines the riparian zone in terms of its
  function and effects.
• The riparian zone is usually defined as the part
  of the landscape, which exerts a direct influence
  on stream channels or lake margins, and on the
  water and aquatic ecosystems contained within
  them.
• Features that can be affected directly by the
  riparian zone, include
• channel morphology and bank stability
• the physical and chemical
• properties of the water
• the aquatic ecosystem
• water quality
• conservation-wildlife-recreational-aesthetic
  values.

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Size of Riparian Zone

• Related to
• Size of stream
• Position of stream within drainage network
• Hydrologic regime
• Geomorphology

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• Longitudinal continuity of the vegetation
• The existence of continuous vegetated strips
  along the channel contributes to the control of
  the flow or movement of water, nutrients,
  sediment and species
• Lateral dimension of the channel and floodplain
• defines the size of the area where hydrological
  and ecological processes and functions take
  place.
• Composition and structure of the riparian
  vegetation
• reflects the ecological quality of riparian
  elements.

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Vegetation and Water Table Depth
Small changes in depth to water make large
differences in size of vegetation.
From Verry
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Function of Vegetation in Riparian Zone
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Life-History Strategies

• Riparian plants subjected to floods, erosion,
  abrasion drought, freezing and toxic
  concentrations of ammonia
• Life-history strategies allow plants to endure,
  resist or avoid extreme conditions

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Life-History Strategies

• Classification of plants into four categories
• Invader
• Produces large numbers of propagules (both wind
  and water borne) that colonize alluvial
  substrates
• Endurer
• Resprouts after breakage or burial of the stem or
  roots from floods or after being eaten
• Resister
• Withstands flooding for weeks during the growing
  season, moderate fires or epidemics
• Avoiders
• Lacks adaptations to specific disturbances
  individuals germinating in unfavorable habitats
  do not survive

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Adaptations

• Morphological adaptations in response to anoxia
  or unstable conditions
• Adventitous roots
• Grow above anaerobic zone to enable oxygen
  absorption.
• Stem buttressing
• Root and stem flexibility
• Allows for shear stress resistance due to
  flooding
• Air spaces in roots and stems to diffuse oxygen

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Reproductive Adaptations

• Primary reproductive characteristics are
• Trade-off between sexual and asexual reproduction
• Seed size
• Timing of dormancy
• Timing of seed dispersal
• Dispersal mechanisms
• longevity

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Example

• Dispersal of seeds at retreat of floodwaters
• Ensures moist seedbeds for successful germination
• Seed transport by flowing waters
• Seeds float better
• Dispersal by animals and wind.

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Successional and Vegetative Patterns

• Physical controls
• Complex interactions between hydrology,
  geomorphology, light, temperature and fire.
• Hydrology most important
• Power and frequency of floods inversely
  proportional
• High-power, low frequency to Low-power,
  high-frequency.
• High-power, low frequency affects whole
  floodplain and creates large geographic features
• Medium power medium frequency determines patterns
  of ecosystem structure
• Low power, high frequency occur annually and
  determine short-term patterns such as seedling
  survival.

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Physical Controls in Determining Vegetative
Distribution

• Ability of soils and sediments to hold water
• Existence of tributary and groundwater flows
• How long the substrate remains saturated
• Soil deposition rates
• Aggrading
• Soil being deposited
• Degrading
• Soil being eroded
• Maintaining steady-state
• Erosion keeping up with deposition
• Physical features constantly changing

From Tabacchi, 1998)
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Phsyical Controls

• Lateral channel migration speed
• Sediment supply depends on
• Land use
• Climate
• Tectonic activity (high in Amazon)
• light and temperature effects
• Understory light tends to be highest at forest
  edge and declines towards interior.
• Seedling densities have not been correlated with
  light intensity
• Fire effects
• In humid regions, plants can not withstand fire
• In arid regions, 40 of plants burned within 12
  years.

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Plant Succession (from Tabacchi, 1998)
Note An autogenic succession describes a
succession where the stimulus for change is an
internal one. For example gradual soil
improvement could allow a new species to
develop. An autogenic succession can be
contrasted by an allogenic succession. This
describes a change in succession where the
stimulus for change is an external one. For
example a flood could bring about a change in
species.
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Biotic Patterns

• Longitudinal corridors affect movement of
• Water
• Nutrients
• Sediments
• Species

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Riparian Corridorsfrom Forman (Landscape Mosaics)
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Ecological influences

• Competition
• Small due to disturbance
• Herbivory
• Strong influence on vegetation
• Soils
• Degree of saturation
• Affects plant distribution from river uplands
• Disease
• Some pests spread rapidly in riparian corridors
• Basal area is greater than uplands forest
• Note Basal area is a measure of tree density. 
  It is determined by estimating the
  cross-sectional area of all trees at 4.5 feet
  above the ground.  Basal area is expressed as
  square feet per acre.

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Primary Production
Per Area
Total

• Generally, higher production in riparian forests
  than in upland forests.

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Spatial Zonation

• Transverse gradient perpindicular to stream
  channel
• Cyclical succession in floodplain due to
  disturbance, erosion and deposition
• More stable in upper terraces
• Mostly primary succession in riparian zones,
  although some successional patterns begin with
  plant fragments.
• Disturbance allows for invasion

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Primary succession vs. secondary succession

• Primary succession - occurs on an area of newly
  exposed rock or sand or lava or any area that has
  not been occupied previously by a living (biotic)
  community.
• Secondary succession - takes place where a
  community has been disturbed, e.g., in a plowed
  field or a clearcut forest or fire.

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Physical Functions of Riparian Zones

• Mass movement of materials and channel morphology
• Wood in streams and riparian zones
• Microclimate
• Ecological corridors

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Mass Movement

• Material comes from
• Erosion of stream banks (root strength and
  resilience) and uplands
• Uplands
• If no vegetation, banks are unstable and channels
  widen by large amounts annually
• Bank erosion 30 times more prevalent on
  non-vegetated banks.
• Vegetation modifies sediment transport
• Trapping material
• Material sticks to vegetation
• Altering hydraulics
• Physical structures slow water, decrease power
  and hold material in place.

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Wood in Streams and Riparian Zones

• Woody debris
• Accumulates during floods in piles
• Each pile has one big piece that traps other
  smaller pieces, increasing pile size
• Can find 160 piles per km of stream
• Piles affect streams
• Dissipate energy
• Trap moving materials
• Form habitats
• Redirect water currents to create erosional and
  depositional environments
• Redirected currents can widen channels and
  capture eroded material

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Woody debris

• Woody debris results in longer residence times
  and storage of water
• Experiments show that leaves and other organic
  matter added to streams with woody debris move
  much slower and not as far and streams with no
  woody debris.
• 80 of salmon carcasses travel only 200 m from
  their release site.
• Provides habitat for fish and macroinvertebrates.
• Retains plant seeds and fragments and protects
  them from erosion, abrasion and herbivory.
• Most seedling germination is associated with
  woody debris on an exposed cobble bar.
• Offers protection for small mammals and birds
• Diversity and abundance of small mammals is
  greater in areas with woody debris.

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Microclimate

• Riparian zones control microclimate of streams
• Temperature of streams highly correlated with
  riparian soil temperature

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Climate
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During the day, temp is lower in stream and rises
the most to 15 m out for both During the night,
the temp after cutting is more constant and
higher in the stream than before cutting
Both day and night similar. Before cutting, temp
relatively constant After cutting, temp rises
significantly
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Stream Temp vs. Soil Temp.
Stream water temperatures highly correlated with
soil temperatures
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Microclimate
Air temperature above the streams increased
exponentially with decreasing buffer width
Relative humidity was inversely proportional to
air temperature
Tyler Ledwith, Six Rivers National Forest,
Eureka, CA , http//www.watershed.org/news/sum_96/
buffer.html
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Microclimates

• Forests affect discharge through ET
• Reduced streamflow causes physiological problems
  among some organisms.

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Ecological Corridors

• Corridors maintain biological connections
• Invasions
• Plants move up and down riparian corridors rather
  than overland routes.
• In a study in two watersheds in WA, exotic
  species richness was approximately 33 greater in
  riparian zones than in uplands, and mean number
  and cover of exotic species were gt 50 greater
  in riparian zones than in uplands. (DeFerrari,
  C.M. Naiman, R.J., 1994)

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Ecological Functions of Riparian Zones

• First, a quick definition
• allochthonous sources of carbon come from outside
  the aquatic system (such as plant and soil
  material).
• Carbon sources from within the system, such as
  algae and the microbial breakdown of particulate
  organic carbon, are autochthonous.
• In streams and small lakes, allochthonous sources
  of carbon are dominant while in large lakes and
  the ocean, autochthonous sources dominate. (Eby,
  2004)

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Sources of Nourishment

• Allochthonous inputs and herbivory
• Organic matter from riparian vegetation nourishes
  aquatic organisms in stream.
• Organic matter is higher in small to medium
  streams and decreases as stream order increases.
• Riparian zones also all a lot of DOM (dissolved
  organic matter) to rivers

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Inputs of material in a first order (Grady) and
second order (Hugh White) stream. CBOM(coarse
benthic organic matter) gt0.04 inches and FBOM
lt0.04 inches Small wood between 0.4 and 2 inches
and large wood gt2 inches From Verry
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Transfer Pathways

• Five transfer pathways of organic material to
  streams
• Direct litterfall
• Blow-in from soil surface
• Groundwater baseflow
• Stormflow
• Seepage from wetlands

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Transfer Pathways
Terre Firme-upland forest with closed canopy,
sandy organic soils Campina-low and open forest
with sandy soil. Savanna-flat plains, shallow
watertable, often poorly drained Montane-high,
mountainous region (Andes). High erosion and
deposition rates
Litterfall contributions similar in all
terrains Groundwater contributions highest in
soils of low organic content (Campina) Wetland
contributions are lowest in Montane region due to
topography and lack of wetlands adjacent to
stream, although stormflows are highest.
From McClain and Richey, 1996
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Transfer Pathways
Types of OM transported via major pathways. Dark
indicates greater proportion.
From McClain and Richey, 1996
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Animal Influences

• Insects
• Defoliation alters water yield and nutrient
  cycling
• Beaver
• Changing river flows and flood dynamics
• Moose
• Selective browsing shift plant community from
  decidous to coniferous

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Beaver Impacts in Minnesota (Naiman, 1988)
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Insect Defoliation
Insect defoliation in 1974-1975 shows increased
nitrogen exports from stream. From Swank et al,
1981
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Riparian Zones as Nutrient Filters

• Physical
• Biological
• Variability
• Patterns of diversity
• Natural disturbances
• Invasion of exotics
• Regional diversity
• Macroinvertebrate communities

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Physical Buffers

• Sediments and pollutants are deposited in
  riparian forests and streamside grasses (Daniels
  and Gilliam)
• 80-90 of sediments removed in under 20 meters of
  riparian areas.
• Coarse sediments deposited first, then fine
  sediments deposited further into the forest and
  near stream.

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Biological Buffers

• Nutrient removal by plant uptake
• High transpiration in riparian forests
• Short term accumulation of nutrients
• Non-woody biomass
• Long term accumulation of nutrients
• Woody biomass
• Nitrogen saturation phosphorus limiting
• May be restricted by limited access to water.

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Buffer Variability

• High variability in buffer zone potentials for
  nutrient removal
• Subsurface flow paths (rooted vs. non-rooted
  soils)
• Plant cover (trees vs. grass)
• Soil characteristics (sandy vs. loamy)

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Patterns of Diversity

• Biodiversity patterns show intermediate
  disturbance hypothesis.
• The Intermediate Disturbance Hypothesis (IDH)
  proposes that biodiversity is highest when
  disturbance is neither too rare nor too frequent.
  
• With low disturbance, competitive exclusion by
  the dominant species arises.
• With high disturbance, only species tolerant of
  the stress can persist.
• Main channels generally have higher biodiversity
  than tributaries

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Species Richness

• Species richness higher in transitional zones in
  mid-river due to IDH

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Natural Disturbances-Floods

• Facilitates the coexistence of congeneric species
• Congeneric-relative belonging to the same genus
• Dominant species on mid-range of soils grains and
  non-dominant on extremes (gravel and silt)
• Maintains dominant tree species by reducing
  competition
• Causes erosion and deposition of silt and litter,
  increased organic matter accumulations
• Increased diversity at upper edges of floodplain

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Invasion by Exotics

• In areas of moderate floods, more invasions
  possible (IDH)
• Control through
• Landscape characteristics (river connectivity)
• Patch structure (availability of habitat)
• Natural environmental features

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Other Factors

• Refuges for Regional Diversity
• Act as safe site during droughts
• Macroinvertebrate Communities

Sweeney, 1993
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Habitat

• Nesting and perching for birds
• Corridors for migration
• Protection from predation
• Breeding areas
• Feeding areas

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Environmental Alterations

• Human Alterations
• Management and Restoration
• Tools for the Future

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Human Alterations

• In Europe
• Land clearing and deforestation during Greek and
  Roman times
• 19th century and 20th century construction and
  hydroelectric projects accelerated alterations.
• In North America
• Similar to Europe on a shorter time scale

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Human Alterations

• Flow variability and channel width decreased due
  to
• River impoundments
• Reduce depth and duration of flooding
• Allow invasive species to take over
• Water management
• Increase competition for moisture
• Displace native species
• Lowering water table
• Desiccate floodplain
• Loss of cottonwood
• Changes in riparian vegetation very susceptible
  to minimum and maximum flows.

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Human Alterations

• Some increases in other species.
• Poplar willow (from WC Johnson)

Dam constructed in 1935
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Human Alterations
Species richness and percent vegetative cover
lower on a regulated river than on a natural river
From Nilsson, 1991
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Management and Restoration

• Role of riparian zones to control pollution
  through good BMPs
• Use of multi-species buffer strips to protect
  streams.
• Three active zones (up-slope order)
• Permanent forest (10 m wide)
• Influence stream environment (temp, light,
  habitat diversity)
• Shrubs and trees (4 meters wide)
• Control pollutants in subsurface flow and surface
  runoff
• Maximize infiltration, deposition of sediments,
  biological and chemical transformations
• Herbaceous vegetation (7 meters wide)
• Spreads overland flow facilitating coarse
  sediment deposition
• Adaptable to different stream orders
• Managed system should act as a natural one for
  long-term sustainability

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Tools for the Future

• Riparian system functions (a review)
• Biodiversity
• Habitat
• Biogeochemical cycles
• Microclimate
• Resistance and resilience to disturbance
• Recreation, aesthetics

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Tools for the Future

• Management approaches
• Restore and revegetate disturbed areas
• Select appropriate species to maintain genetic
  integrity and biodiversity of area
• Conduct vegetation survey in a representative
  remnant stand
• Review historical records such as photographs and
  land descriptions
• Analyze pollen from preserved bottom sediments to
  reconstruct pre-disturbance vegetative
  communities
• Conduct field trials
• Factors to consider when revegetating (from Webb
  and Erskine, 2003)
• Flood disturbance
• Vegetation zone along riparian corridor
• Species succession
• Substrate composition
• Corridor planting width
• Planting methods
• Native plant regeneration
• Large woody debris recruitment
• Cost

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Tools for the Future

• Site specific approaches integrate
• Research
• Demonstration
• Application of buffers
• To help determine
• Effects of vegetation type and management
  approach of long-term control of pollution
• Response of riparian zones to stresses such as
  storms and temperature extremes
• Processes controlling groundwater microbial
  dynamics

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Tools for the Future

• REMM (Riparian Ecosystem Management Model) (From
  Hubbard and Lowrance, 1994)
• Three zoned buffer system
• Interactive modules to track water movement,
  nutrient cycling and vegetative growth on a daily
  basis
• Soil characterized in three layers to simulate
  vertical and horizontal movement of water and
  nutrients
• Can simulate growth of upper and lower canopies
  concurrently
• N and P demand is determined as a function of
  biomass.
• Water depths determined based on vegetation and
  hydrology.

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Tools for the Future

• Need to develop flexible, adaptive schemes.
• Discontinuities may occur that change zone from
  sink to source
• Interactions between two stresses
• Two chronic (Nutrient loading and global warming)
• One chronic and one acute (large storm)
• Unforeseen issues that may develop

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About the Author

• Professor College of Ocean and Fishery Sciences,
  University of Washington
• Education
• B.S. 1969 California State Polytechnic University
  (Zoology) M.A. 1971 University of California,
  Los Angeles (Zoology, Ichthyology)Ph.D. 1974 Ariz
  ona State University (Zoology, Ecosystem Science)
• Professional Appointments
• 1988-present Professor, College of Ocean
  Fishery Sciences and College of Forest Resources,
  University of Washington
• 1988-1996 Director, Center for Streamside
  Studies, University of Washington
• 1985-1988 Director, Center for Water and the
  Environment, Natural Resources Research
  Institute, University of Minnesota
• 1978-1985 Director, Matamek Research Program,
  Woods Hole Oceanographic Institution
• 1977-1978 Assistant Curator, Academy of Natural
  Sciences of Philadelphia
• 1974-1976 Postdoctoral Fellow, Fisheries Research
  Board of Canada, Pacific Biological Station
• This article has been cited 556 times

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About the Author

• PROFESSIONAL ACTIVITIES AND AWARDS
• National Research Council (Canada) Postdoctoral
  FellowshipArizona State University
  FellowshipsBeta Beta Beta Biological Honor
  Society and Sigma Xi
• Kaiser Professor - University of Wisconsin
  (1995)Associate Editor, Aquatic Conservation
  Marine and Freshwater Ecosystems
• Associate Editor, Landscape Ecology
• Associate Editor, Ecosystems
• Associate Editor, Frontiers in Ecology and the
  Environment
• Distinguished Professor of Ecology - Colorado
  State University (1997)
• Aldo Leopold Leadership Program (1999)
• Distinguished Faculty Research Award University
  of Washington (2000)
• H.B.N. Hynes Lecturer, Canadian River Institute,
  University of New Brunswick (2004)
• PROFESSIONAL SOCIETIES
• American Institute of Biological Sciences
• Ecological Society of America
• RESEARCH INTERESTS
• Biophysical processes associated with lotic and
  riparian ecosystems, watershed management, and
  the role of animals in shaping ecosystem
  processes.