An idealized model of sediments,
nutrients, phytoplankton and optics
in the Delaware Bay
John L. Wilkin
Institute of Marine and Coastal Sciences
Rutgers, the State University of New Jersey
with Jacqueline McSweeney (RIOS student, LMU),
Bob Chant, Dove Guo, Maria Aristizabal, Eli Hunter (Rutgers),
Chris Sommerfield (U. Delaware),
John Warner and Chris Sherwood (USGS)
Delaware Bay and River
Estuarine
turbidity
maximum
Highly eutrophied
NO3 > 50 mmol m-3 but no
extreme primary
productivity: phytoplankton
remain below “nuisance
levels.”
Paradigm is that suspended
sediment limits light and
suppresses growth.
Test this hypothesis using
an idealized 2-D estuary
model (ROMS) with a
nitrogen ecosystem model
(Fennel) and sediment
transport model (CSTM)
coupled through the biooptical absorption (PAR).
Hydrographic transects of observed salinity and suspended-sediment
concentration (mg liter-1) in the Delaware Estuary
Cook, T., C. Sommerfield, and K. Wong (2007), Observations of tidal and springtime sediment transport in the upper
Delaware Estuary, Estuarine, Coastal and Shelf Science, 72(1-2), 235-246.
Temperature (color) and salinity (contours) during June 2010.
McSweeney, J., J. Wilkin, and R. Chant, “Profiling the Optics, Sediment, and Phytoplankton in the Delaware
Bay,” Research Internships in Ocean Sciences (RIOS), Rutgers University, 2010
Chlorophyll (color), optical backscatter (contours), and PAR (red
profiles) during June 2010. High chlorophyll regions occur upstream
and downstream of two turbidity maxima.
Nitrogen, oxygen, chlorophyll and absorption at 4 m depth
50
2.0 m-1
40
30
100
20
50
0.5 m-1
0
10
Chlorophyll concentration (µg/L)
Nitrogen and oxygen concentration (µM)
150
0
river distance (km)
McSweeney, J., J. Wilkin, and R. Chant, “Profiling the Optics, Sediment, and Phytoplankton in the Delaware
Bay,” Research Internships in Ocean Sciences (RIOS), Rutgers University, 2010
PAR (photosynthetically active radiation) measured with profiling
radiometer. (Integration across 6 wavelengths 412 nm to 660 nm.)
McSweeney, J., J. Wilkin, and R. Chant, “Profiling the Optics, Sediment, and Phytoplankton in the Delaware
Bay,” Research Internships in Ocean Sciences (RIOS), Rutgers University, 2010
Time-series data from the New Castle mooring
Cook, T., C. Sommerfield, and K. Wong (2007), Observations of tidal and springtime sediment transport in the upper
Delaware Estuary, Estuarine, Coastal and Shelf Science, 72(1-2), 235-246.
Salinity versus distance for all Delaware Estuary surface
samples from 1978–2003.
Sharp, J., K. Yoshiyama, A. Parker, M. Schwartz, S. Curless, A. Beauregard, J. Ossolinski, and A. Davis (2009), A
Biogeochemical View of Estuarine Eutrophication: Seasonal and Spatial Trends and Correlations in the Delaware
Estuary, Estuaries and Coasts, 32(6), 1023-1043.
ROMS model: “2-D” depth/along-axis (3 grid points across)
20 s-levels, Δx = 750 m. Similar to “ESTUARY_TEST”
River Q = 100 m3 s-1
utide =
0.7 m s-1
depth (m)
salt
0 km
sand_01
initial = 0 in suspension
= 0.5 m in bed
wsettle = 2 mm s-1
Erate = 5 x 10-4 kg m-2 s-1
crit = 0.2 Pa
sand
150 km
salt wedge
depth (m)
salt at t = 40 days
Estuarine Turbidity
Maximum (ETM)
0 km
sand at t = 40 days
150 km
Control case: Run 13
Suspended noncohesive sediment in model (kg m-3)
time = 40 days
Suspended Sediment Concentration observed (mg liter-1)
Control case: Run 13
Suspended noncohesive sediment in model (mg liter-1)
time = 40 days
Suspended Sediment Concentration observed (mg liter-1)
Schematic of ROMS “Bio_Fennel”
ecosystem model
PAR absorption is modified by modeled
dI
suspended sediment
 Att concentration:
(z) * I(z)
Att(x,z) = AttSW + AttChl*Chlorophyll(x,z,t)
dz + AttSed*Sed(x,z,t)
[Chl:C]*[C:N]*Phyt
Concentrations of nitrogen species along estuary axis for July 1986.
NO3
NH4
Sharp, J., K. Yoshiyama, A. Parker, M. Schwartz, S. Curless, A. Beauregard, J. Ossolinski, and A. Davis (2009), A
Biogeochemical View of Estuarine Eutrophication: Seasonal and Spatial Trends and Correlations in the Delaware
Estuary, Estuaries and Coasts, 32(6), 1023-1043.
Chlorophyll concentrations
in Delaware Bay
Pennock, J. (1985), Chlorophyll distributions in the
Delaware estuary: regulation by light-limitation,
Estuarine, Coastal and Shelf Science, 21(5), 711-725.
Att(x,z) = AttSW + AttChl*Chlorophyll(x,z,t) + AttSed*Sed(x,z,t)
slope = 75 m-1 (kg m-3)-1
is sediment specific attenuation
coefficient (AttSed in ROMS)
Attenuation coefficient (k) vs. suspended sediment from a multiple
regression on in situ observations of PAR (from profiling radiometer),
suspended sediments (filtration), chlorophyll (fluorometer), and DOC.
Pennock, J. (1985), Chlorophyll distributions in the Delaware estuary: regulation by light-limitation, Estuarine,
Coastal and Shelf Science, 21(5), 711-725.
slope = 250 m-1 (kg m-3)-1
is sediment specific attenuation
coefficient (AttSed in ROMS)
Beam attenuation coefficient (cp) vs. suspended particulate mass (SPM)
from observations using LISST and DFC at MVCO.
Hill, Paul, E. Boss, J. Newgard, B. Law, T. Milligan: Observations of the sensitivity of beam attenuation to particle
size in a coastal bottom boundary layer, unpublished manuscript, ONR OASIS Project
1% light
level
salinity
contours
chlorophyll
day 40
NO3 day 40
suspended sediment
contours
PAR distribution along estuary axis (for nominal surface Io = 400 W m-2)
Observed June 2010
I(z) = Ioe-1
1% light
level
ROMS model day 40
Distance along estuary axis (km)
Test hypothesis on sediment/optics control on photosynthesis:
Disable sediment optics feedback by setting AttSed = 0
No sediment light limitation,
yet much less chlorophyll ?
Average primary productivity (mmol N m-3 day-1)
mean over 40 days of simulation
Average primary productivity (mmol N m-3 day-1)
mean over last 10 days of simulation
Mean denitrification mmol N m-2 day-1
Mean primary production mmol N m-2 day-1
Distance (km)
Summary (1)
2-D depth/along-axis model of idealized Delaware circulation
steady river flow
tides at Bay mouth
Circulation forms a salt wedge 10-20 km long in mid-estuary
Sediment transport model (CSTM)
single non-cohesive sediment
parameters from Cook (2009) for Delaware ETM zone
wsettle = 2 mm s-1 , Erate = 5 x 10-4 kg m-2 s-1 , crit = 0.2 Pa
Circulation forms an Estuarine Turbidity Maximum upstream of salt
wedge
Nitrogen cycle model (Bio_Fennel): NO3, NH4, plankton,
zooplankton, detritus, benthic remineralization, denitrification
initial/river values from Sharp NO3 = 50, NH4 = 5 mmol m-3
…
Summary (2)
Light absorption model:
Attseawater + Attchl*[chl] + Attsed*[sed] ; Attsed = 250 from Hill (OASIS)
Light penetration depth scales, maximum chlorophyll, NO3 and
sediment in the 2-D model are comparable to observations
Chlorophyll concentrations are low upstream of ETM, and there is
little consumption of nitrogen
Turbidity attenuates light to levels that suppress primary
productivity despite ample nutrients
Downstream from ETM, turbidity decreases, water column
stratifies and phytoplankton bloom occurs
Without AttSed, nitrogen is consumed in the upper estuary and the
Bay ecosystem becomes unrealistically nutrient limited
Mean salinity in model down estuary from canal
C&D canal
ROMS 3-D
Delaware model
Mean along-estuary velocity at cross-section
velocity
cross-section
ROMS Delaware
3D model
Observed
seaward landward