Influence of Geomorphic Complexity on Hyporheic Flow and Nutrient Processing Prepared by Dan Baker for CE 413

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 $$$ is paying for form -- not functionRestoration $$$ is paying for form -- not function

General Hypothesis Stream geomorphic complexity enhances hyporheic exchange increasing the potential for nutrient uptake Stream Geomorphic Complexity Hyporheic Exchange Nutrient Uptake

Collective influence of physical and hydraulic variation within a stream –Bedforms –Planform –Substrate texture –Woody debris –Hydraulics –Vegetation Stream Geomorphic Complexity Hyporheic Exchange Nutrient Uptake

Mosaic of Complexity Substrate Hydraulics Topography

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

Multiscale Complexity Frissell (1986)

Textural Composition and spatial distribution of patches of grain sizes –Bed patches with differing grain size distributions and permeability (Buffington and Montgomery 1999)

Downstream variation Bedform spacing Variation of thalweg elevation Water surface concavity Longitudinal roughness

Measures (cont.) Planform Variation –Sinuosity –Width variability Amplitude & wavelength Wavelength ( ) Q Stream Bank Amplitude (  )

Measures (cont.) Flow obstructions –Woody debris Instream transient storage –Vegetation –Eddies/backwater Hyporheic flow –Area of storage & exchange coefficients Hydraulic conditions –Velocity & depth

Hyporheic is a Greek word meaning “under river.” Exchange of stream water between surface water / flow through stream bed Stream Geomorphic Complexity Hyporheic Exchange Nutrient Uptake

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

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 moderationTemperature moderation Contaminant removalContaminant removal

How do we measure hyporheic flow? Well method Tracer method

OTIS Model Developed by USGS Numerical model to fit parameters to actual flow conditions

Increased exchange across microbially rich stream bed –Provides sufficient exposure and ideal conditions for nutrient uptake Stream Geomorphic Complexity Hyporheic Exchange Nutrient Uptake

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

Nitrogen & Global Population

What is Eutrophication?

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

Headwater streams encompass up to 80% the stream network

“The physical, chemical, and biotic integrity of our nation’s 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

Experimentally Added NO 3 Stream Nitrogen Cycle

Our Current Study Follows general hypothesis of this talk Uptake in agricultural vs urban stream Incorporate flow variability

Summary Many measures of complexity Water doesn’t just go downstream Small streams are important Restore not just physical form but ecological functionRestore not just physical form but ecological function