sediment flux calculation in the shallow water environment -- lynnhaven inlet experiment
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Sediment Flux Calculation in the Shallow Water Environment --
Lynnhaven Inlet Experiment
Harry Wang, Yuepeng Li, and Mark Brush
July 10, 2006
Virginia Institute of Marine Science /
School of Marine Science
College of William and Mary
Outline
- Hydrodynamic model in Lynnhaven
- Laboratory sediment flux experiment
- Numerical model simulation of laboratory-scale experiment
- Sediment flux calculation applied to field scale simulation
(1) Hydrodynamic Model
- Unstructured grid finite difference/finite volume model
- Conserving mass locally as well as globally
- Capable of simulating wetting-and-drying
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LYNN0006
Va Pilots St
WB-DM23
EB-DM13
BB-DM13BB
WNC
N
EW
S
1 0 1 2 Kilometers
Model Grid and Observation Stations
WNC
0
0.2
0.4
0.6
0.8
1
240 242 244 246 248 250 252 254 256 258 260
Days from 1/1/2005
Wate
r ele
vati
on
(m)
Modeled Observed
Va. Pilot St.
-0.5
-0.25
0
0.25
0.5
0.75
1
305 310 315 320 325 330 335
Days from 1/1/2005
Wat
er e
leva
tio
n(m
)
Modeled Observed
Comparison of Tides
E-W (middle)
-1
-0.5
0
0.5
1
305 310 315 320 325 330 335
Velo
cit
y(m
/s)
Modeled Observed
N-S (middle)
-1
-0.5
0
0.5
1
305 310 315 320 325 330 335
Velo
cit
y(m
/s)
Modeled Observed
E-W (bottom)
-1
-0.5
0
0.5
1
305 310 315 320 325 330 335
Velo
cit
y(m
/s)
Modeled Observed
N-S (bottom)
-1
-0.5
0
0.5
1
305 310 315 320 325 330 335
Velo
cit
y(m
/s)
Modeled Observed
N-S (surface)
-1
-0.5
0
0.5
1
305 310 315 320 325 330 335
Velo
cit
y(m
/s)
Modeled Observed
E-W (surface)
-1
-0.5
0
0.5
1
305 310 315 320 325 330 335
Velo
cit
y(m
/s)
Modeled Observed
What is unique about shallow water sediment ?
The usual case:
Bacterial respirationin the sediments consumes oxygen
& releases nutrients
However, in shallow systems
during the day:
Photosynthesis by benthic microalgae (BMA) can reverse
these fluxes
2005 Sediment Chlorophyll-a
0
5
10
15
20
25
J F M A M J J A S O N D
ug c
m-2
Eastern Branch
0
10
20
30
40
50
J F M A M J J A S O N D
ug c
m-2
Inlet
0
5
10
15
20
25
J F M A M J J A S O N D
ug c
m-2
Western Branch
0
10
20
30
40
50
J F M A M J J A S O N D
ug c
m-2
Broad Bay
Benthic Chl A spatial distribution in three tributaries
(2) Sediment flux laboratory experiment
- Seasonal measurements at several locations throughout the Lynnhaven
- Fluxes are: dissolved oxygen, ammonia, nitrite + nitrate, and phosphate
- These fluxes are critical to the calibration of the sediment model
Sediment Flux Lab Methods
• 4 cores per site with overlying water
• 2 water blanks
Incubation chambers at VIMS:• stirred• maintained at field temperatures
Western Branch:mud-sand mix
Shallow oxic layer(~ 2-3 cm)
Anoxic layerclose tosurface
Inlet:sandy sediments,
well flushed, lower impact?
Thick oxic layer(severalcentimeters)
Anoxic layer isdeeper
DO Flux
-4.0
-2.0
0.0
2.0
4.0
6.0
WB EB I N BB
mm
ol/m
2/h
Dark
Light
DO Flux
-4.0
-2.0
0.0
2.0
4.0
6.0
WB EB I N BB
mm
ol/m
2/h
DO Flux
-4.0
-2.0
0.0
2.0
4.0
6.0
WB EB I N BB
mm
ol/m
2/h
NH4 Flux
-200
-100
0
100
200
300
400
500
WB EB I N BB
umol
/m2/h
Dark
Light
NH4 Flux
-200
-100
0
100
200
300
400
500
WB EB I N BB
umol
/m2/h
NH4 Flux
-200
-100
0
100
200
300
400
500
WB EB I N BB
umol
/m2/h
O2 flux
NH4+ flux
APRIL
JULY
NOVEMBER
APRIL
JULY
NOVEMBER
NOx Flux
-30
-20
-10
0
10
20
30
WB EB I N BB
umol
/m2/h
Dark
Light
NOx Flux
-30
-20
-10
0
10
20
30
WB EB I N BB
umol
/m2/h
NOx Flux
-30
-20
-10
0
10
20
30
WB EB I N BB
umol
/m2/h
PO4 Flux
-10
0
10
20
30
WB EB I N BB
umol
/m2/h
Dark
Light
PO4 Flux
-10
0
10
20
30
WB EB I N BB
umol
/m2/h
PO4 Flux
-10
0
10
20
30
WB EB I N BB
umol
/m2/h
APRIL
JULY
NOVEMBER
APRIL
JULY
NOVEMBER
NOx flux
PO43- flux
Model Formulation
1) Oxygen formulation
Where:
BMAO2: net oxygen produced by benthic microalgae (gm O2 m-2)
w1: coefficient of oxygen produced by benthic microalgae into water column (0.7)
w2: coefficient of oxygen produced by benthic microalgae into sediment (0.3)
L: depth water column bottom box (m)
LBMAOwO
BMAOwSODs
/*)]0([
*
212
22
Model Formulation (con’t)
2) Light field in the sediment
Where
Imean: mean light in benthic microalgae matIs: irradiance at the surface of sedimentKsed: Attenuation due to sediment solidKalgae: Attenuation due to benthic microalgae self shading (m2g-1C)BMA: benthic microalgae biomass (g C m-2)
BMAaeKa
BMAaeKaKsed
smean
eeII
*lg
*lg1
Model Formulation (con’t)
• Important spatial varying parameters obtained:
For sandy sediment: (Inlet and Broad Bay)Ksed: 0.35Kalgae: 0.16 (m2g-1C)
For muddy sediment: (Western Branch and Eastern Branch)Ksed: 0.6Kalgae: 0.27 (m2g-1C)
**These parameter are then used for spatial interpolation in the field scale numerical model simulation
July simulation in Eastern Branch
Without sediment
July simulation in Eastern Branch
With sediment
November simulation in Eastern Branch
Without sediment
November simulation in Eastern Branch
With sediment
November simulation in Inlet
Without sediment
November simulation in Inlet
With sediment
July DO Fluxes
-4.00-2.000.002.004.006.00
WB EB IN BB
mm
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
July NOx Fluxes
-5.00
0.00
5.00
10.00
15.00
WB EB IN BB
um
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
Nutrient Flux simulation in July
July NH4 Fluxes
-200.00
0.00
200.00
400.00
600.00
WB EB IN BB
um
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
July PO4 Fluxes
-10.00
0.00
10.00
20.00
30.00
WB EB IN BB
um
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
November NH4 Fluxes
-100.00
0.00
100.00
200.00
WB EB IN BB
um
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
November PO4 Fluxes
-2.00
-1.00
0.00
1.00
2.00
3.00
WB EB IN BB
um
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
Nutrient Flux simulation in November
November DO Fluxes
-2.00
0.00
2.00
4.00
WB EB IN BB
mm
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
November NOx Fluxes
-40.00
-30.00
-20.00
-10.00
0.00
10.00
WB EB IN BB
um
ol/m
2/h
Measured Dark Modeled Dark Measured Light Modeled Light
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