Nira Salant Department of Geography University of British Columbia Effects of Streambed Periphyton...
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![Page 1: Nira Salant Department of Geography University of British Columbia Effects of Streambed Periphyton on Hydraulics and Sediment Deposition in Streams.](https://reader037.fdocuments.in/reader037/viewer/2022103101/56649f2a5503460f94c44d7b/html5/thumbnails/1.jpg)
Nira SalantDepartment of Geography
University of British Columbia
Effects of Streambed Periphyton on Hydraulics and Sediment
Deposition in Streams
![Page 2: Nira Salant Department of Geography University of British Columbia Effects of Streambed Periphyton on Hydraulics and Sediment Deposition in Streams.](https://reader037.fdocuments.in/reader037/viewer/2022103101/56649f2a5503460f94c44d7b/html5/thumbnails/2.jpg)
What is periphyton?
![Page 3: Nira Salant Department of Geography University of British Columbia Effects of Streambed Periphyton on Hydraulics and Sediment Deposition in Streams.](https://reader037.fdocuments.in/reader037/viewer/2022103101/56649f2a5503460f94c44d7b/html5/thumbnails/3.jpg)
What does periphyton do?
Food and habitat
Physical effects?
I. Hydraulics
II. Sediment deposition
![Page 4: Nira Salant Department of Geography University of British Columbia Effects of Streambed Periphyton on Hydraulics and Sediment Deposition in Streams.](https://reader037.fdocuments.in/reader037/viewer/2022103101/56649f2a5503460f94c44d7b/html5/thumbnails/4.jpg)
Sediment deposition
Trapping,Adhesion,Clogging
Turbulence
Algae: High profile Diatoms: ‘Sticky’
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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
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Deposition from water column: Diatoms
Diatoms: ‘Sticky’
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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
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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
![Page 9: Nira Salant Department of Geography University of British Columbia Effects of Streambed Periphyton on Hydraulics and Sediment Deposition in Streams.](https://reader037.fdocuments.in/reader037/viewer/2022103101/56649f2a5503460f94c44d7b/html5/thumbnails/9.jpg)
Deposition from water column: Algae
Algae: High profile
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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…
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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
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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
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Implications
Streambed patchiness and complexity
Flow conditions, sediment accumulation, interstitial infiltration Habitat
condition
Organism behavior
…a function of periphyton structure
and distribution
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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)
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I. Hydraulics
‘Closed’ ‘Open’
Filamentous periphyton ‘patches’
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'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
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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)
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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
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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
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Diatoms 24 WeeksDiatoms 4 Weeks
None
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