Physical Stream Habitat

What is Habitat?Broad Definition (EPA):The spatial structure of the environment which allows species to live, reproduce, feed and move

In Relation to Streams (USGS):The physical and chemical characteristics of a stream that determine suitability for habitation and reproduction of stream organisms

What is Physical Habitat?The template of water depth, water velocity, substrate, cover and temperature that supports the stream ecosystem USGS

Stream MorphologyAquatic CommunityPhysical HabitatChemical HabitatInterspecies InteractionsLand UseVegetationHydrologicConditionsGeologyTopography

Measurable Characteristics of Physical HabitatChannel morphology / typeFlow regimeSediment texture / mobilityBank structural features / stabilityRiparian condition and connectivityPhysiochemical temperature, DO, metals, nutrients, turbidity, etc.

Mill Creek

Salmon and trout habitat requirements include: adequate but not excessive stream flows cool well-oxygenated unpolluted water streambed gravels that are relatively free of fine-sediments adequate food supply instream structural diversity (interposed pools, riffles, hiding and resting cover)

Washington State Dept of Fish Wildlife

Physical stream characteristics affect stream organisms by defining: Habitat volume Habitat quality Disturbance magnitude Disturbance frequency

Habitat varies over spatial & temporal scalesStream CorridorRestoration, 199x

LargeScaleFineScaleHeirarchical Classification System

Scalar UnitDefinitionRole in Habitat CharacterizationWatershed BasinArea defined by topography that contributes water and sediment to the stream networkDetermines boundary conditions within which river operatesSegment Physiographically defined unit, based on relief, morphology and landscape positionDetermines boundary conditions within which river operatesReach TypeLength of channel with uniform constraints resulting in a specific assemblage of geomorphic unitsDescribes channel planform and geometryGeomorphic UnitFluvial channel forms representing distinct form-process associationsDetermines channel character and behaviorHabitat TypePatches of relatively uniform flow and substrate characteristics Describes ecologically relevant hydraulic and substrate conditions

103 m102 m101 m100 m10-1 mWatershedSegmentReach TypeGeomorphicUnitMicrohabitatTypeHow is each scale important to the species of interest?

Temporal Variability incorporates predictable and unpredictable cyclesMacroinvertsSalmon

Physical habitat a function of processes operating at multiple spatial and temporal scalesHow do we objectively assess it?

Define Stream Habitat Types (Classification)Bisson et al, 1982McCain et al, 1990 (USFS) Hawkins et al, 1993 (USFS)Thomson et al, 2001 (UK, AUS)Fish -Centric

McCain et al, 1990

McCain et al, 1990Bisson et al, 1982

Hawkins et al, 1993

Hawkins et al, 1993

McCain et al, 1990

Hydraulic HabitatFlow types can be distinguished by velocity and depth using Froude Number F =vgd

Panfil & Jacobson, 2000

Thomson et al, 2001

Stream Habitat types are created and maintained by erosion and deposition of sediments.Hjulstroms Diagram

Mechanics of Habitat FormationShear Stress/Velocity Reversal HypothesisHelical FlowContraction/Expansion of Flow

t = rghsv ~ f(Rs)Knighton, 1998

Helical flow in meander bendsKnighton, 1998

Flow contraction and expansionWohl, 1998

Increased roughness reduces shear, promoting deposition of finer materialMcBain & Trush, 2004

Diversity is a function of fluctuations in erosion and deposition processes over varying scalesWhat promotes Habitat Diversity?Disturbance

Natural flow regime Varying sediment inputs

Structural diversity - LWDNatural stream systems are subject to the full spectrum of spatial & temporal disturbancesEpisodic Sediment Transport

Natural Flow Regime5 characteristics:FrequencyMagnitudeDurationTimingRate of ChangeKey factor = extremes included

Disturbance acts to reset processesMount, 1995

Large Woody DebrisIncreases local scour and depositionProvides structural habitatTransient nature (moves, breaks, clumps, decays)All add to habitat diversity and complexity

Buffington & Montgomery 1999Plane BedWood-poorPool-riffle

Buffington & Montgomery 1999Wood-richPool-riffle

Stream habitat diversity maintained over time

Species adaptSalmon spawning and run timingFoothill Yellow-legged Frog oviposition timing Cottonwood regeneration accidental forest

Redrawn by Bledsoe from Schlosser (1995)Diversity in Trout Habitat

Alterations to flow regime & sediment supply alter habitat diversity & biodiversityStream Corridor Restoration, 1998

Alterations to Stream SystemsFlow extraction diversions groundwater withdrawalFlow augmentationag runoffhydropowerSedimentation development loggingminingSediment Lossdamsmining

Channel Bed Coarsening Loss of Fines/Gravels Vegetation Encroachment Low bed mobilityDegradation Channel Bed Fining Excess Fines/Gravels Lack of vegetation High bed mobilityAggradation

Effect of DamsBlock Sediment

Flatline Hydrograph

Disrupt ConnectivityChannel Degradation bed coarsening, loss of fines/gravelsLoss of extreme flows (loss of disturbance) low bed mobility, vegetation encroachment, low habitat diversityBlock habitat access, alter water chemistry, shift from lentic to lotic system

What can we do to improve spawning habitat conditions downstream of dams?

Broad Definition incorporates all physical and chemical constituents along with biotic interactions

Specific Def incorporates the quality of instream and riparian characteristics that influence aquatic community structureHave to think big picture, but in terms of or specific to the species of interestAlthough physical habitat varies over space and time, for practicality, we focus on an accessible habitat of importance to the species of interest.

For fish, the most limiting habitats are generally spawning and summer low flow. In spring habitat quality is low (lack of adequate substrate) and disturbance could be high. In summer, both habitat volume and habitat quality are low, even though disturbance is low.Fluctuations in Sediment Transport (the real disturbance) is a result of fluctuations in flow regimeIf Physical habitat forms the template for aquatic communities, biological potential is limited by the quality of physical habitat

Thus Habitat Diversity and Biodiversity are linked