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Sediment Flux Calculation in the Shallow Water Environment -- Lynnhaven Inlet Experiment

Sediment Flux Calculation in the Shallow Water Environment -- Lynnhaven Inlet Experiment. Harry Wang, Yuepeng Li, and Mark Brush. July 10, 2006 Virginia Institute of Marine Science / School of Marine Science College of William and Mary. Outline. - Hydrodynamic model in Lynnhaven

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Sediment Flux Calculation in the Shallow Water Environment -- Lynnhaven Inlet Experiment

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  1. Sediment Flux Calculation in the Shallow Water Environment -- Lynnhaven Inlet Experiment Harry Wang, Yuepeng Li, and Mark Brush July 10, 2006 Virginia Institute of Marine Science / School of Marine Science College of William and Mary

  2. Outline - Hydrodynamic model in Lynnhaven - Laboratory sediment flux experiment - Numerical model simulation of laboratory-scale experiment - Sediment flux calculation applied to field scale simulation

  3. (1) Hydrodynamic Model Unstructured grid finite difference/finite volume model - Conserving mass locally as well as globally - Capable of simulating wetting-and-drying

  4. Model Grid and Observation Stations

  5. Comparison of Tides

  6. However, in shallow systems during the day: Photosynthesis by benthic microalgae (BMA) can reverse these fluxes What is unique about shallow water sediment ? The usual case: Bacterial respiration in the sediments consumes oxygen & releases nutrients

  7. 2005 Sediment Chlorophyll-a

  8. Benthic Chl A spatial distribution in three tributaries

  9. (2) Sediment flux laboratory experiment Seasonal measurements at several locations throughout the Lynnhaven Fluxes are: dissolved oxygen, ammonia, nitrite + nitrate, and phosphate - These fluxes are critical to the calibration of the sediment model

  10. Sediment Flux Lab Methods Incubation chambers at VIMS: • stirred • maintained at field temperatures • 4 cores per • site with • overlying • water • 2 water • blanks

  11. Western Branch: mud-sand mix Shallow oxic layer (~ 2-3 cm) Anoxic layer close to surface

  12. Inlet: sandy sediments, well flushed, lower impact? Thick oxic layer (several centimeters) Anoxic layer is deeper

  13. APRIL APRIL O2 flux NH4+ flux JULY JULY NOVEMBER NOVEMBER

  14. APRIL APRIL NOx flux PO43- flux JULY JULY NOVEMBER NOVEMBER

  15. Model Formulation Oxygen formulation Where: BMAO2: net oxygen produced by benthic microalgae (gm O2 m-2) w1: coefficient of oxygen produced by benthic microalgae into water column (0.7) w2: coefficient of oxygen produced by benthic microalgae into sediment (0.3) L: depth water column bottom box (m)

  16. Model Formulation (con’t) 2) Light field in the sediment Where Imean: mean light in benthic microalgae mat Is: irradiance at the surface of sediment Ksed: Attenuation due to sediment solid Kalgae: Attenuation due to benthic microalgae self shading (m2g-1C) BMA: benthic microalgae biomass (g C m-2)

  17. Model Formulation (con’t) • Important spatial varying parametersobtained: For sandy sediment: (Inlet and Broad Bay) Ksed: 0.35 Kalgae: 0.16 (m2g-1C) For muddy sediment: (Western Branch and Eastern Branch) Ksed: 0.6 Kalgae: 0.27 (m2g-1C) **These parameter are then used for spatial interpolation in the field scale numerical model simulation

  18. July simulation in Eastern Branch Without sediment

  19. July simulation in Eastern Branch With sediment

  20. November simulation in Eastern Branch Without sediment

  21. November simulation in Eastern Branch With sediment

  22. November simulation in Inlet Without sediment

  23. November simulation in Inlet With sediment

  24. Nutrient Flux simulation in July

  25. Nutrient Flux simulation in November

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