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Development of the Neuse Estuary Eutrophication Model: Background and Calibration By James D. Bowen UNC Charlotte Neuse River Estuary Model Pamlico Sound Applied Water Quality Modeling Research Neuse Estuary Neuse River Estuary Facts About the Neuse River

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Development of the neuse estuary eutrophication model background and calibration l.jpg

Development of the Neuse Estuary Eutrophication Model: Background and Calibration

By

James D. Bowen

UNC Charlotte


Neuse river estuary model l.jpg
Neuse River Estuary Model Background and Calibration

Pamlico

Sound

Applied Water

Quality Modeling

Research

Neuse

Estuary


Neuse river estuary l.jpg
Neuse River Estuary Background and Calibration


Facts about the neuse river l.jpg
Facts About the Neuse River Background and Calibration

  • 3rd Largest River Basin in NC (6,234 mi2)

  • 200 miles long, 3000 stream miles

  • Estuary in lower 50 miles

  • 1.5 million people in basin, mostly near headwaters

  • Nutrient loading has doubled since 70’s


Neuse river problems algal blooms l.jpg
Neuse River Problems: Algal Blooms Background and Calibration

Blue-GreenAlgae Bloom near New Bern


1997 bottom water do conc l.jpg

Neuse River Problems: Low DO Background and Calibration

1997 Bottom Water DO Conc.


Low do and fish kills 94 96 l.jpg
Low DO and Fish Kills: 94-96 Background and Calibration

Cherry Point

Streets

Ferry


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Water Quality Research Project Background and Calibration

MODMON = MODeling and MONitoring

  • Interdisciplinary Applied Research

    • Water Quality and Biological Monitoring

    • Water Quality Modeling to predict w.q. improvement (30% nutr. red.)


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Physical Background and Calibration

Processes

Neuse EstuaryEutrophicationModel


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Neuse Estuary Background and CalibrationEutrophicationModel

Water Column

Biological Processes


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Benthic/Water- Background and Calibration

Column Interactions

Neuse EstuaryEutrophicationModel


Neuse estuary eutrophication model12 l.jpg
Neuse Estuary Eutrophication Background and CalibrationModel


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Special Features of Modeling Background and Calibration

Unusually challenging system to model

  • intermittent, weak stratification (wind driven)

  • no strong tidal forcing

  • sediments have important effects on nutrient and DO dynamics

  • blooms of several different phytoplankton groups @ different times and places


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Neuse Estuary Eutrophication Model Background and Calibration

  • based upon 2-d laterally averaged model CE-Qual-W2

  • Nutrient, phytoplankton, organic matter, DO model

  • 3 phytoplankton groups (V.3)

    • summer assemblage, diatoms, dinoflagellates


W2 phytoplankton growth model l.jpg

1 Background and Calibration

m /mmax

0

Light,

Nutrients

W2 Phytoplankton Growth Model

1

T.R.M.

0

Topt

Temperature

m = mmax * min(m / mmax) * T.R.M.


W2 x section representation l.jpg

S1 Background and Calibration

S1

S2

S2

S3

S3

S4

W2 X-section Representation

  • trapezoidal cross-sections for each segment

Layer 1

Layer 4

Sediment

Compartments

  • quasi-3d sediment/water-column interaction model


W2 sediment submodel l.jpg
W2 Sediment Submodel Background and Calibration

  • simple sediment diagenesis model

    • 1 constituent: Sediment organic carbon (SOC)

    • SOC fate processes:

      • redistribution, decomposition

    • SOD decomposition rate determines fluxes:

      • O2 demand, PO4 release, NH3 release

    • N, P, S, Fe redox reactions not considered

      • e.g. NH3/NO3, NO3/N2, SO4/H2S

    • can simulate sediment “clean-up”


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1991 Simulation Description Background and Calibration

  • Time Period:

    • March 1 - September 27, 1991

  • Boundary Data Frequency

    • Daily Flow and NO3, monthly WQ

  • Hydrodynamic Calibration Data

    • hrly. water elevations, salinities, velocities @ 3 estuary stations

  • WQ Calibration Data

    • monthly mid-water nutrients, DO, chl-a @ 4 estuary stations


H 2 o n inflows 1991 l.jpg
H Background and Calibration2O & N Inflows - 1991


Inflow n p molar ratio 1991 l.jpg
Inflow N/P molar ratio - 1991 Background and Calibration

Redfield Ratio


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Other Model Characteristics Background and Calibration

  • 62 horizontal segments, 18 layers

  • execution time step = 10 min.

  • 2 branches: Neuse & Trent Rivers

  • 12 tributaries: 9 creeks, 3 WWTP’s

  • 16 state variables

  • Boundary Conditions: Flow @ Streets Ferry, Elevation @ Oriental


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Neuse Estuary Model Results Background and Calibration Transport Model

  • Water elevations

    • time histories

    • spectral analysis

  • Salinity distributions

    • time histories @ one segment

    • animations


Elevations @ cherry point l.jpg
Elevations @ Cherry Point Background and Calibration

Observed

Model

March

April

May


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Water Level @ New Bern Background and Calibration

MAE = 0.1 m

Julian Day


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Elev. Fluctuations - Power Spectrum Background and Calibration

Observed

@ Cherry Point

n = 0.020

Amplitude (m)

Model

Frequency (Cycles/day)


Salinities @ cherry point l.jpg

0 Background and Calibration

4

8

12

16

Salinities @ Cherry Point

Model: Surface

Observed: Top

Bottom

Salinity (ppth)

Model: Bottom

May

Sep

Mar

July


Modeled salinities september 1991 l.jpg
Modeled Salinities - September 1991 Background and Calibration


1991 predicted salinities may sept animation l.jpg
1991 Predicted Salinities: Background and Calibration May - Sept. animation


Neuse estuary 1991 nitrogen l.jpg
Neuse Estuary - 1991 Nitrogen Background and Calibration


Neuse estuary 1991 chl a conc s l.jpg
Neuse Estuary - 1991 Chl-a Conc.’s Background and Calibration


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WQ Conditions: Summary Background and Calibration

  • Seasonal/Spatial Trends

  • nutrients decreasing downstream

  • April mid-estuary phytoplankton bloom

  • June upper-estuary phytoplankton bloom

  • several pulses of high NOx conc. @ New Bern

  • August high-flow event

    • high nutrients, low chl-a @ New Bern

    • high Sept. chl-a @ New Bern


1991 wq simulations l.jpg
1991 WQ Simulations Background and Calibration

  • Single parameter displays

    • Nitrate

    • Phytoplankton

    • Cumulative chl-a

  • Multi-parameter display

    • New Bern time history


Modeled nitrate september 1991 l.jpg
Modeled Nitrate - September 1991 Background and Calibration


1991 predicted nitrates may sept animation l.jpg
1991 Predicted Nitrates: Background and Calibration May - Sept. animation


Modeled do september 1991 l.jpg
Modeled DO - September 1991 Background and Calibration


1991 predicted do may sept animation l.jpg
1991 Predicted DO: Background and Calibration May - Sept. animation


Modeled chl a september 1991 l.jpg
Modeled chl-a - September 1991 Background and Calibration


1991 predicted chl a may sept animation l.jpg
1991 Predicted chl-a: Background and Calibration May - Sept. animation


Water quality prediction new bern l.jpg

Sal. Background and Calibration

NOx

DO

Chl

Water Quality Prediction - New Bern

0

Surface

Middle

6

.5

0

Surface

10

Middle

4

50

0

May

Sep

Mar

July


Calibration summary l.jpg
Calibration Summary Background and Calibration

  • Transport Model

    • elevation variations predicted within 0.1 m

    • salinity variations within 2 ppth

    • dynamics nicely represented

  • Water Quality Model

    • blooms of phytoplankton well represented

    • seasonal variations also represented

    • New Bern chl-a shows influence of physical processes


Summary continued l.jpg
Summary, continued Background and Calibration

  • Water Quality Model

    • DO dynamics fit expectations based on 1997 monitoring

  • Overall model performance

    • consistent with previous modeling efforts

    • sufficient for water quality improvement predictions