Nira SalantDepartment of Geography

University of British Columbia

Effects of Streambed Periphyton on Hydraulics and Sediment

Deposition in Streams

What is periphyton?

What does periphyton do?

Food and habitat

Physical effects?

I. Hydraulics

II. Sediment deposition

Sediment deposition

Trapping,Adhesion,Clogging

Turbulence

Algae: High profile Diatoms: ‘Sticky’

Sediment content of surface samples

0.01

0.10

1.00

10.00

100.00

1000.00

10000.00

0.1 1 10 100AFDM (g/m2)

AM

(g/

m2)

Graham 1990 vanDijk1993Yamada2002 Collier2002Kiffney2003 Runck2007Jowett1997 Hope RiverFlume-Diatoms Flume-Algae

Deposition from water column: Diatoms

Diatoms: ‘Sticky’

0.00

0.50

1.00

1.50

2.00

2.50

0 1000 2000 3000 4000 5000

Time (Seconds)

C/C

0

0 g/m25 g/m210 g/m2

Deposition from water column: Diatoms

Highest deposition velocity when near-bed and upper flow

shear stresses are lowand biomass is moderate

(moderate adhesion, low clogging)

Biomass increases:

Near-bed shear stress increases (structural roughening)

Deposition velocity decreases(high upward stresses and infiltration decreases = ‘clogging’)

0

1

2

3

4

5

6

0.0 2.0 4.0 6.0 8.0 10.0 12.0AFDM(g/m2)

Dep

soiti

onal

vel

ocity

wd

(cm

/h)

0

1

2

3

4

5

6

7

TK

E s

hear

str

ess

(Pa)

Depositional velocity

Max shear stress

Near-bed shear stress

Deposition from water column: DiatomsEvidence for clogging?

-6

-5

-4

-3

-2

-1

0

0.01 0.10 1.00% <125um

Dep

th (

cm)

0 g/m2

0 g/m2

3 g/m2

5 g/m2

8 g/m2

10 g/m2

Deposition from water column: Algae

Algae: High profile

Deposition from water column: Algae

0.00

0.50

1.00

1.50

2.00

2.50

0 1000 2000 3000 4000 5000

Time(S)

C/C

0

0 g/m2

15 g/m2

24 g/m2

Unclear relation between biomass, shear stress, and

depositional velocity

0

1

2

3

4

5

6

0 5 10 15 20 25 30AFDM(g/m2)

Dep

osit

iona

l vel

ocit

y w

d (c

m/h

)

0

1

2

3

4

5

6

7

TK

E s

hear

str

ess

(Pa) Deposition

decrease with biomass? Clogging?

But…

Deposition from water column: Algae

Shear stress increases with

growth stage

Surface deposition decreases with

growth stage

Later growth stage Increase in shear stress

0

5

10

15

20

25

0 5 10 15 20 25Growth stage (Weeks)

AM

(g/m

2)

0

1

2

3

4

5

6

7

TK

E s

hear

str

ess

(Pa)

0

1

2

3

4

5

6

0 5 10 15 20 25Growth stage (Weeks)

Dep

osit

iona

l vel

ocit

y w

d (c

m/h

)

0

1

2

3

4

5

6

7

Less surface deposition

BUTHigher advection and infiltration

(subsurface deposition)

Total deposition = balance of surface and subsurface deposition

High biomass reduces infiltration

Depositional velocity

Max shear stress

Near-bed shear stress

Surface samples AM

Deposition from water column: Algae

Turbulence Less surface deposition, deeper infiltration (A8 A20)

Biomass Reduced infiltration despite high advection (A16)

-6

-5

-4

-3

-2

-1

0

0.01 0.10 1.00% <125um

Dep

th (

cm)

00A8A16A20

Implications

Streambed patchiness and complexity

Flow conditions, sediment accumulation, interstitial infiltration Habitat

condition

Organism behavior

…a function of periphyton structure

and distribution

Decrease in concentration over timeExponential model

kteCtC 0)(C0 = peak concentration at time t = 0

k = decay (or deposition) rate (T-1)

h

wk

s

ws = settling velocity (D/T) = depositional velocity wd when fit to

exponential model

h = flow depth (D)

I. Hydraulics

‘Closed’ ‘Open’

Filamentous periphyton ‘patches’

'Closed'

BEp

BEeff

ADV Probe

'Open'

BEpBE

eff

ADV Probe

BEp > BE

eff = Open BE

p = BE

eff = Closed

Height measured by ADV above BE

eff

(plus 5 cm)

WSE

Flow

a)

~10 cm

~2.5 cm

Flume wall

~2.5 cm

Velocity distribution

u0

Ux

umax

0.6

0.5

0.4

0.3

0.2

0.1

PeriphytonNone

0.0 10.0 20.0 30.0 40.0 50.0

u (cm/s)

0.0

0.5

0.4

0.3

0.2

0.1

0.0 10.0 20.0 30.0 40.0

z/H

50.0

0.6

u (cm/s)

Shear stress distributionTwo-layered flow

0.0 0.01-0.01 0.02 0.03

0.1

0.2

0.3

0.4

0.5

0.6

z/H

0.1

0.2

0.3

0.4

0.5

0.6

z/H

τRe/ρUx2

Closed

Open

Logarithmic layer

Peak shear = top of Roughness layerPeriphyton

No periphyton

Shift in height of roughness layer topSame thickness

0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.005 0.01 0.015 0.02 0.025Re/ρUx

2 (

z/H

Near-bed turbulence reduction

PeriphytonNone

2) Hydrodynamic smoothing(Closed mats)

1) Shift in location of peak shear (Open mats)

Higher upper flow stress

Reduced turbulent transfer

Diatoms 24 WeeksDiatoms 4 Weeks

None