The Hyporheic Zone: Example of a field study

Matt Miller

Matthew.P.Miller-1@Colroado.edu

Contributions from D. McKnight and N. Mladenov

““Hypo” – Greek, meaning underHypo” – Greek, meaning under

““Rheo” – meaning current or flowRheo” – meaning current or flow

What is the Hyporheic Zone?What is the Hyporheic Zone?

The Hyporheic Zone

*An area where stream water mixes with groundwater and eventually returns to the stream.

Hyporheic exchangeHyporheic exchange In the bed and banks of streams, water and solutes In the bed and banks of streams, water and solutes

can exchange in can exchange in both directionsboth directions across the across the streambed. streambed.

HHyporheic exchangeyporheic exchange mixes water & solutes from mixes water & solutes from surface and subsurface environments. surface and subsurface environments.

Figure from Winter et al. 2000

SomeSome important conceptsimportant concepts Hyporheic flowpaths leave and return to the stream Hyporheic flowpaths leave and return to the stream

many times within a reach many times within a reach ExchangeExchange of surface water back and forth b/w active of surface water back and forth b/w active

channel and subsurface is rapid. channel and subsurface is rapid. Within several km, stream water often completely Within several km, stream water often completely

exchanged with the porewater of the hyporheic zoneexchanged with the porewater of the hyporheic zone This repeatedly brings stream water into close contact This repeatedly brings stream water into close contact

with geochemically- and microbially-active sediment. with geochemically- and microbially-active sediment.

Figure from Harvey & Wagner

2000

Mixing of chemically-different waters and chemical transformations

Chemical gradients at the Chemical gradients at the interfaceinterface

How extensive How extensive can a hyporheic zone be?can a hyporheic zone be?

Depends on:Depends on: the type of the type of sedimentsediment in the streambed and banks in the streambed and banks the variability in the variability in slopeslope of the streambed of the streambed the the hydraulic gradientshydraulic gradients in the adjacent ground- in the adjacent ground-

water system water system The HZ can be as much as several feet in depth The HZ can be as much as several feet in depth

and hundreds of feet in width. and hundreds of feet in width. HZ dimensions increase with increasing width of HZ dimensions increase with increasing width of

stream and permeability of streambed stream and permeability of streambed sediments.sediments.

What are some common methods What are some common methods usedused

to quantify hyporheic flowpaths? to quantify hyporheic flowpaths?

Injection & transport of Injection & transport of a solute tracer in the a solute tracer in the

streamstream A tracer is released, A tracer is released,

and measurements and measurements of its passage are of its passage are made at a location made at a location downstream. downstream.

What will a graph of What will a graph of tracer concentration tracer concentration over time look like over time look like at the downstream at the downstream monitoring point?monitoring point?

Injection & transport of Injection & transport of a solute tracer in the a solute tracer in the

streamstream

Dye tracer illustrates water Dye tracer illustrates water storage at channel marginsstorage at channel margins:: 1) sides are initially dye-free 1) sides are initially dye-free

Photo courtesy of Jud Harvey, USGS, Reston, VA

Dye tracer illustrates water Dye tracer illustrates water storage at channel marginsstorage at channel margins::2) all parts of channel have dye2) all parts of channel have dye

Photo courtesy of Jud Harvey, USGS, Reston, VA

Dye tracer illustrates water Dye tracer illustrates water storage at channel marginsstorage at channel margins::

3) sides retain dye longer than center 3) sides retain dye longer than center channel channel

Photo courtesy of Jud Harvey, USGS, Reston, VA

Modeling the transport of a Modeling the transport of a conservative soluteconservative solute

Main Channel:

Storage Zone:

Advection

Dispersion

Lateral inflow

Transient storage

Transient storage

Decay

Decay

Modeling Hyporheic Exchange: OTISModeling Hyporheic Exchange: OTIS

Example of a field study: Green Example of a field study: Green Lakes Valley Lakes Valley

Site DescriptionSite Description

ALBION TOWNSITE

LAKE ALBION

GL4

GL5

NAVAJO STREAM

NIWOT RIDGE

Atmospheric N DepositionAtmospheric N Deposition

Sources: GroundwaterSources: Groundwater

Sources: SnowmeltSources: Snowmelt

Where does the water end up?Where does the water end up?

Question 1:Question 1: How is hyporheic exchange in the upper reaches How is hyporheic exchange in the upper reaches of the Green Lakes Valley impacting transport of Carbon and of the Green Lakes Valley impacting transport of Carbon and

Nitrogen to downstream surface waters?Nitrogen to downstream surface waters?

Research QuestionResearch Question

Hypothesis:Hypothesis: Given the presence of a porous wetland in the Given the presence of a porous wetland in the upper reaches of the catchment there will be substantial upper reaches of the catchment there will be substantial

hyporheic exchange and subsequently high rates of processing hyporheic exchange and subsequently high rates of processing of both C and N.of both C and N.

*Tracer Injection w/ LiBr*Tracer Injection w/ LiBr

*Modeled with OTIS*Modeled with OTIS

*Sampled for:*Sampled for:-DOC-DOC

-N species-N species-Li and Br-Li and Br

Tracer Injection ExperimentTracer Injection Experiment

Solute Transport Modeling ResultsSolute Transport Modeling Results

Reactive Transport ResultsReactive Transport Results

Water samples are collected Water samples are collected and analyzed at and analyzed at downstream sitesdownstream sites

What will a graph of What will a graph of measured concentrations measured concentrations compared with compared with concentrations predicted concentrations predicted with and without in-with and without in-stream and storage zone stream and storage zone reactions look like?reactions look like?

Stream Decay Stream Decay (λ)(λ) Storage Zone DecayStorage Zone Decay (λ(λss))

NONO33-- -1.0 x 10-1.0 x 10-3-3 1.0 x 101.0 x 10-4-4

NHNH44++ 1.2 x 101.2 x 10-3-3 -7.9 x 10-7.9 x 10-5-5

DOCDOC 1.6 x 101.6 x 10-2-2 -1.3 x 10-1.3 x 10-4-4

Redox IndexRedox Index 6.5 x 106.5 x 10-3-3 -8.4 x 10-8.4 x 10-5-5

λC

λsC

Reactive Transport ResultsReactive Transport Results

Measured EEM at S3Measured EEM at S3

PARAFAC modeled EEM at S3PARAFAC modeled EEM at S3

Conservative Transport EEM at S3Conservative Transport EEM at S3

Reactive Transport ResultsReactive Transport Results