Influence of Geomorphic Complexity on Hyporheic Flow and Nutrient Processing

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Influence of Geomorphic Complexity on Hyporheic
Flow and Nutrient Processing

• Prepared by Dan Baker for
• CE 413

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Why do we care?

• Vast areas of ocean
  fed by the worlds
  rivers are dying
• Continuing population growth demands more
  fertilized crops and fossil fuel usage
• Restoration is paying for form -- not
  function

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General Hypothesis
Hyporheic Exchange
Nutrient Uptake
Stream Geomorphic Complexity

• Stream geomorphic complexity enhances hyporheic
  exchange increasing the potential for nutrient
  uptake

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• Collective influence of physical and hydraulic
  variation within a stream
• Bedforms
• Planform
• Substrate texture
• Woody debris
• Hydraulics
• Vegetation

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Mosaic of Complexity
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Geomorphic Complexity

• Why does it matter?
• Biological
• Fish and aquatic insect habitat
• Organic matter retention
• Physical
• Promotes hyporheic exchange
• Evidence of natural flow regime
• Chemical
• Nutrient processing

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Multiscale Complexity
Frissell (1986)
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Textural

• Composition and spatial distribution of patches
  of grain sizes
• Bed patches with differing grain size
  distributions and permeability

(Buffington and Montgomery 1999)
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Downstream variation

• Bedform spacing
• Variation of thalweg elevation
• Water surface concavity
• Longitudinal roughness

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Measures (cont.)

• Planform Variation
• Sinuosity
• Width variability
• Amplitude wavelength

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Measures (cont.)

• Flow obstructions
• Woody debris
• Instream transient storage
• Vegetation
• Eddies/backwater
• Hyporheic flow
• Area of storage exchange coefficients
• Hydraulic conditions
• Velocity depth

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• Hyporheic is a Greek word meaning under river.
• Exchange of stream water between surface water /
  flow through stream bed

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Hyporheic Flow

• Multi scale phenomena
• Spatial centimeters to kilometers
• Geology Channel Morphology
• Temporal minutes to months
• Flow path length Sediment hydraulic
  conductivity

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Benefits of Hyporheic Flow

• Connectivity between aquatic and terrestrial
  systems
• Temporal storage of stream
  water and nutrient processing
• Increased exposure to
  microbially rich sediments
• Increased stream habitat
• Invertebrates
• Salmonid spawning redds
• Temperature moderation
• Contaminant removal

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How do we measure hyporheic flow?

• Well method
• Tracer method

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OTIS Model

• Developed by USGS
• Numerical model to fit parameters to actual flow
  conditions

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Hyporheic Exchange
Nutrient Uptake
Stream Geomorphic Complexity

• Increased exchange across microbially rich stream
  bed
• Provides sufficient exposure and ideal conditions
  for nutrient uptake

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History of Nitrogen Fertilizer

• Naturally occurring nitrogen sources
• Microbes lightning
• Lightning
• Before fertilizer, crop production limited by
  naturally available nitrogen
• Fritz Haber discovered an energy hungry process
  to free nitrogen in 1909
• Post World War II, the US government had a
  surplus of bomb building ammonium nitrate
• Used to boost agricultural production ?
  population was free to increase

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Nitrogen Global Population
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What is Eutrophication?
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Understanding the Transport of Nitrogen

• Originally rivers were thought of as conveyor
  belts
• Then scientists thought all rivers removed
  nitrogen proportional to their size
• Now we believe that small streams remove the more
  nitrogen than large streams

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Headwater streams encompass up to 80 the stream
network
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The physical, chemical, and biotic integrity of
our nations waters is sustained by services
provided by wetlands and headwater
streams.-Where Rivers are Born

• Flood control
• Extensive wetlands
• Trap sediment
• Transform carbon from inorganic ? organic
• Maintain biological diversity

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Stream Nitrogen Cycle
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Our Current Study

• Follows general hypothesis of this talk
• Uptake in agricultural vs urban stream
• Incorporate flow variability

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Summary

• Many measures of complexity
• Water doesnt just go downstream
• Small streams are important
• Restore not just physical form but ecological
  function