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