An idealized model of sediments, nutrients, phytoplankton and optics
in the Delaware Bay
John L. WilkinInstitute 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
Estuarineturbiditymaximum
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 bio-optical absorption (PAR).
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.
Hydrographic transects of observed salinity and suspended-sediment concentration (mg liter-1) in the Delaware Estuary
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 N
itrog
en a
nd o
xyge
n co
ncen
trati
on (
µM)
Chlorophyll concentration (µg/L)
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
50
40
30
20
10
0
50
0
150
100
2.0 m-1
0.5 m-1
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.)
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.
River Q = 100 m3 s-1
utide = 0.7 m s-1
sand_01initial = 0 in suspension = 0.5 m in bed wsettle = 2 mm s-1
Erate = 5 x 10-4 kg m-2 s-1 τcrit = 0.2 Pa 150 km0 km
sand
salt
dept
h (m
)ROMS model: “2-D” depth/along-axis (3 grid points across)20 s-levels, Δx = 750 m. Similar to “ESTUARY_TEST”
150 km0 km
salt at t = 40 days
dept
h (m
)
salt wedge
sand at t = 40 days
Estuarine Turbidity Maximum (ETM)
Control case: Run 13
Suspended noncohesive sediment in model (kg m-3)
Suspended Sediment Concentration observed (mg liter-1)
time = 40 days
Control case: Run 13
Suspended noncohesive sediment in model (mg liter-1)
Suspended Sediment Concentration observed (mg liter-1)
time = 40 days
Schematic of ROMS “Bio_Fennel” ecosystem model
PAR absorption is modified by modeled suspended sediment concentration:
Att(x,z) = AttSW + AttChl*Chlorophyll(x,z,t) + AttSed*Sed(x,z,t)
[Chl:C]*[C:N]*Phyt
dIdz
=Aττ(z)* I(z)
Concentrations of nitrogen species along estuary axis for July 1986.
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.
NO3
NH4
Pennock, J. (1985), Chlorophyll distributions in the Delaware estuary: regulation by light-limitation, Estuarine, Coastal and Shelf Science, 21(5), 711-725.
Chlorophyll concentrations in Delaware Bay
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 = 75 m-1 (kg m-3)-1
is sediment specific attenuation coefficient (AttSed in ROMS)
Att(x,z) = AttSW + AttChl*Chlorophyll(x,z,t) + AttSed*Sed(x,z,t)
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
slope = 250 m-1 (kg m-3)-1
is sediment specific attenuation coefficient (AttSed in ROMS)
1% lightlevel
suspended sedimentcontours
salinitycontours
NO3 day 40
chlorophyll day 40
PAR distribution along estuary axis (for nominal surface Io = 400 W m-2)
Observed June 2010
ROMS model day 40
Distance along estuary axis (km)
1% lightlevel
I(z) = Ioe-1
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 primary production mmol N m-2 day-1
Mean denitrification mmol N m-2 day-1
Distance (km)
Summary (1)2-D depth/along-axis model of idealized Delaware circulation
steady river flowtides at Bay mouth
Circulation forms a salt wedge 10-20 km long in mid-estuary
Sediment transport model (CSTM)single non-cohesive sedimentparameters from Cook (2009) for Delaware ETM zonewsettle = 2 mm s-1 , Erate = 5 x 10-4 kg m-2 s-1 , τcrit = 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,
denitrificationinitial/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
seaward landwardROMS Delaware 3D model
Observed
Mean along-estuary velocity at cross-section
C&D canal
velocity cross-section
Mean salinity in model down estuary from canal
ROMS 3-DDelaware model