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 NO 3 > 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), Hydrographic transects of observed salinity and suspended-sediment concentration (mg liter -1 ) in the Delaware Estuary

Temperature (color) and salinity (contours) during June 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 High chlorophyll regions occur upstream and downstream of two turbidity maxima.

Nitrogen, oxygen, chlorophyll and absorption at 4 m depth Nitrogen and oxygen concentration (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, m 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),

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),

River Q = 100 m 3 s -1 u tide = 0.7 m s -1 sand_01 initial = 0 in suspension = 0.5 m in bed w settle = 2 mm s -1 E rate = 5 x kg m -2 s -1  crit = 0.2 Pa 150 km0 km sand salt depth (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 depth (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

Concentrations of nitrogen species along estuary axis for July 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), NO 3 NH 4

Pennock, J. (1985), Chlorophyll distributions in the Delaware estuary: regulation by light-limitation, Estuarine, Coastal and Shelf Science, 21(5), 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), 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 (c p ) 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% light level suspended sediment contours salinity contours NO 3 day 40 chlorophyll day 40

PAR distribution along estuary axis (for nominal surface I o = 400 W m -2 ) Observed June 2010 ROMS model day 40 Distance along estuary axis (km) 1% light level I (z) = I o e -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 flow tides at Bay mouth Circulation forms a salt wedge km long in mid-estuary Sediment transport model (CSTM) single non-cohesive sediment parameters from Cook (2009) for Delaware ETM zone w settle = 2 mm s -1, E rate = 5 x kg m -2 s -1,  crit = 0.2 Pa Circulation forms an Estuarine Turbidity Maximum upstream of salt wedge Nitrogen cycle model (Bio_Fennel): NO 3, NH 4, plankton, zooplankton, detritus, benthic remineralization, denitrification initial/river values from Sharp NO 3 = 50, NH 4 = 5 mmol m -3 …

Summary (2) Light absorption model: Att seawater + Att chl *[chl] + Att sed *[sed] ; Att sed = 250 from Hill (OASIS) Light penetration depth scales, maximum chlorophyll, NO 3 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 landward ROMS 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-D Delaware model