Stream Solute Dynamics: Hyporheic Processes

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Stream Solute DynamicsHyporheic Processes

• Lecture 18

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Outline for the week

• Slug vs constant rate additions
• Estimates of discharge
• Estimates of lateral inflow
• Hyporheic dynamics
• In-stream storage and transport
• Conservative vs Non-Conservative solutes
• Spiraling length and uptake
• Relationships to stream ecology

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Hyporheic Zonehypo beneath, rheic flow

• ? Residence Time
• Microbial Biofilms
• Heterotrophic
• Organic Matter Decomposition
• Nutrient Regeneration

Surface Water
Groundwater
Hyporheic Zone
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Why does hyporheic flow occur?
A response to local hydraulic gradients from
riffles to pools.
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Manometer setup to measure vertical hydraulic
gradient
VHG ?H/ ?L
from Cox et al. (2005)
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VHG DistributionSycamore Creek, AZ
from Dahm et al. (2006)
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Geomorphology Matters!

• Streambed complexity, head gradients (Harvey
  Bencala 1993)
• Stream size (DAngelo et al. 1993)
• Channel sinuosity (Wroblicky et al. 1998)
• Channel confinement, secondary or abandoned
  channels, channel splits, bars (Kasahara
  Wondzell 2003)
• Sediment size, hydraulic conductivity (Morrice et
  al. 1997, Storey et al. 2003)

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What is transient storage?(Note the dye
shadow behind the rock)
Flow direction
How much of the total in-stream storage is made
up of this in-channel vs true hyporheic storage?
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Lateral vs Hyporheic storage
True hyporheic
Lateral eddies
From Runkel (1998)
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Effects of transient storage on advective
transport of a solute
DAngelo et al. (1993)
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The OTIS Model Equation
Dispersion f(stream area, dispersion
coefficient solute gradient)
Advection f(velocity, solute gradient)
Change in stream concentration over time
Transient storage exchange f(exchange
coefficient, concentration difference,
transient storage fraction) Not necessarily
hyporheic!!
Lateral input f(lateral velocity,
concentration difference) This is groundwater
dilution
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Effects of transient storage on OTIS simulation

• D dispersion
• Q/A velocity
• QL lateral inflow
• AS transient storage area
• a exchange coefficient

DAngelo et al. (1993)
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Transient storage matters
Ball Cr., Coweeta, July 1991
H.J. Andrews Forest, September 1987
The OTIS model fit is better when transient
storage is included.
From DAngelo et al. (1993)
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Non-parametric comparison of residence time
distributions derived from constant-rate and
instantaneousstream tracer experiments
Payn, R.A. M.N. Gooseff, D.A. Benson, O.A.
Cirpka,J.P. Zarnetske, W.B. Bowden, J.P.
McNamara, and J.H. BradfordGSA 2007 Paper No.
129-7
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Constant vs Slug AdditionsForm of the Results
PDF
CDF
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Residence Time Distribution (RTD) Comparisons
Coarse-bedded
Fine-bedded
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Geomorphology
Hyporheic Exchange
Subsurface Biogeochemistry
Stream Ecosystem Functioning
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Hyporheic Solute Injections

• Pre-addition sampling for water chemistry
• 10 minute injections of a NaBr solution
• Conductivity measurements to monitor for solute
  movement
• Calculation of velocity

Injection Well
Monitoring Wells
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Fit Measured
Surface Flow
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Conductivity (mS)
Hyporheic Flow
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32
0
2
4
6
8
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Time (hours)