2015 Delaware Estuary Science and Environmental Summit

Aboozar Tabatabai and John Wilkin

بسم هللا الرحمن الرحيم

Ocean Modeling Group

Department of Marine and Coastal Sciences Rutgers University

January 27, 2015

Estimation of Nitrogen Removal in Delaware Estuary as a Function of Spatial Residence Time

aboozar@rutgers.edu

Shelf

INTRODUCTION

Modeling Fresh Water Age

2

Details at Zhang et al. (2009) and Spatial Residence Time

Hydrodynamical Model

• ROMS (BGC Fennel with DOM)

• 98x386 horizontal grid (~ 0.2x2 km resolution)

• 20 terrain-following vertical layers (~ 0.03-6.2 m resolution)

• Realistic forcing: Six rivers (USGS), wind and ambient physical climatology (NARR), tides (ADCIRC), BGC parameters (DLEM, USGS and Sharp)

3

Biogeochemical Model De

tails

at D

ruon

et a

l. (2

010)

4

SDet

Burial

Denitrification

Remineralization

DON

NH4

Phy

Phy SDet LDet

Resuspension

Bottom PON

N2

Bottom Cell

Bottom Stress

Solubilization

Solubilization

Remineralization

Uptake

Velocity

Modeling Nitrogen Loss; Benthic Processes

Model Evaluation (Hydrodynamical)

Deta

ils a

t Mun

roe

et a

l. (2

013)

7

Model Evaluation (Biogeochemical)

Nitrogen Loss Estimation

8

9

10

Spatial RT vs. N Loss

11

12

Proposed Relationship

N Loss= a.(RT)b

Conclusion

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A 3D coupled hydro-biogeochemical model was employed to study N cycling in Delaware Estuary, with satisfactory results in the main Bay. We modified a classic RT estimation technique to be incorporated in the model. This is a powerful tool for other biogeochemical applications (including observational studies). Denitrification and N burial rates are highly variable spatially, as well as temporally, and using different methods of averaging yields very different total N loss estimates in the model. In order to improve previous N loss estimates based on very few observations, we introduced a log-log relationship between N loss and RT with a statistically significant correlation. These site and time-specific relationships are products of a simplified N-cycle model and may be applied, with consideration, to fill the gaps in data or improve N Loss estimations and balancing a N budget.

Thank you for your attention

Dettmann, E. H., 2001; Effect of Water Residence Time on Annual Export and Denitrification of Nitrogen in Estuaries: A Model Analysis. Estuaries 24(4): 481–490. Druon, J. N. et al., 2010: Modeling the Dynamics and Export of Dissolved Organic Matter in the Northeastern U.S. Continental Shelf. Estuarine, Coastal and Shelf Science 88(4): 488–507. Munroe, D., et al., 2013; Oyster Mortality in Delaware Bay: Impacts and Recovery from Hurricane Irene and Tropical Storm Lee. Estuarine, Coastal and Shelf Science. Nixon, S. W. et al., 1996; The Fate of Nitrogen and Phosphorus at the Land-Sea Margin of the North Atlantic Ocean. In Nitrogen Cycling in the North Atlantic Ocean and Its Watersheds. Robert W. Howarth, ed. Pp. 141–180. Springer Netherlands. Seitzinger, S. P. 1988; Denitrification in Freshwater and Coastal Marine Ecosystems: Ecological and Geochemical Significance. Limnology and Oceanography 33(4): 702–724. Zhang G.W. et al., 2010: Simulation of Water Age and Residence Time in New York Bight. Journal of Physical Oceanography 40(5): 965–982.

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References