A Shallow-water Coastal Habitat Model for Regional Scale Evaluation of Management

Decisions in the Chesapeake RegionC. L. Gallegos, D. E. Weller, X. Li, H-C. Kim,

T. E. Jordan, P. J. Neale, J. P. Megonigal

RD-8308701-0

Overview• Study Systems• Objectives and Tasks• Modeling Approach• Model Structure• Preliminary Results• Progress and Next Steps

Importance of Shallow-water Tributary Embayments (STE) in Chesapeake Bay

Formation of estuaries as drowned river mouths has resulted in highly articulated shorelines for east coast estuaries.

Shallow-water Tributary Embayments are Critical to Two of the Designated Use

Categories

Susceptible to Large Phytoplankton Blooms due to Shallow Water and Proximity to

Nutrient Sources

106 108 110 112 114 116 118 120

0

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Day of Year, 2004

Chl

orop

hyll

(mg

m-3)

Rhode River, MD Continuous Monitor

April 16-30, 2004

High Phytoplankton Productivity Results in Low A.M. D.O. and Large

Diurnal Swings

MD Department of Natural Resources, “Eyes on the Bay”, Shallow Water Monitoring Program, Rhode River 2004.http://mddnr.chesapeakebay.net/newmontech/contmon/eotb_results_graphs.cfm?station=SERC

Catastrophic Losses of SAV in Chesapeake Bay Occurred First in Western Shore STE

July 1966

Distribution of Water Milfoil in the Rhode River, MD

July 1967

Bayley, S., H. Rabin and C. H. Southwick, 1968. Recent decline in the distribution and abundance of Eurasian milfoil in Chesapeake Bay. Chesapeake Science 9: 173-181.

Areas Slated for Restoration of SAV are Concentrated in Shallow Tributary

Embayments and Tidal Creeks

Chesapeake Bay Program Tier-II Restoration Goal: Restore SAV to the 1-m contour in areas in which it historically occurred.

Main CB Model Segmentation Scheme Treats Most STE as 1 to 3 Cells

West R.

Rhode R.

South R.

Severn R.

Magothy R.

Premise: The ecological importance of shallow-water tributary embayments far exceeds their volumetric contribution to the Bay, and the main-stem concentrations of water quality constituents.

Objectives and Tasks: Estuarine Modeling End Points

Objective: To provide a tool to predict the magnitude and trends of existing and emerging indicators of the ecological condition of critical shallow water habitats.

Important Stressors:Suspended SedimentsNutrientsUV Irradiance

Model Output:Phytoplankton ChlorophyllWater Clarity (diffuse attenuation coefficient)Dissolved Oxygen

Objectives and Tasks: Watershed Inputs to STE

• Use spatial analysis to describe the “population”of STE around the shore of Chesapeake Bay and its major tributaries

• Apply previously developed statistical models relating land cover and physiographic province to nutrient discharges to quantify the distributions of local watershed inputs of water and nutrients across the population of STE

Modeling Approach• STE exhibit a wide range of

sizes, shapes, influence by local watershed, and exchange with main stem estuary

• STE are far too numerous to model individually, on a creek-by-creek basis

Modeling Approach• We are employing an approach that uses a large

number of simple, generic models of subestuaries and tidal creeks, incorporating inputs from local watersheds, internal processing, and exchange at the seaward boundaries

• Our approach will make extensive use of Monte Carlo simulation and generalized sensitivity analysis to determine a range of outcomes, under different management scenarios, for the diversity of shallow-water systems encountered around Chesapeake Bay.

Model Structure: Conceptual

Riparian ZonesFresh Oligo- Meso- Poly-halineTidal Marshes

TidalNon-Tidal

Streams, Rivers Well-mixed Estuarine Waters

Watershed

Groundwater and Non-channelized Surface Water Flow

Stratified Waters

Shallow sub-estuaries: Where we will modelbiotic responses to multiple stressors

The watershed and its drainage systems: Sources and filtersof multiple stressors

• We conceive of STE as part of a continuum of aquatic ecosystems linking watersheds with coastal marine waters

• Focus on well-mixed estuarine tidal waters, which contain a mixture of freshwater from their local watershed, and more saline water from adjacent estuarine or coastal waters

Shallow Subestuaries and Subwatersheds of the Chesapeake Bay ³

0 25 50 75 10012.5Kilometers

Subestuaries

Subwatersheds

Shorelines

Subestuary and Watershed Delineation

128 shallow subestuaries and their local watersheds were delineated around the Chesapeake Bay.

18 subestuary metrics were developed: subestuary area, volume, depth range, percentage of shallow water (0-1m, 1-2m, 0-2m),

mouth width, etc.

Subestuary Subestuary Subestuary Subestuary Subestuary ……ID Name Area(km2) Perimeter(km) Volume(km3)

ELK01 Elk River 9.36 59.05 0.0097

NOR01 Northeast River 15.84 40.63 0.0249

CB101 Spesuit Narrows 5.50 84.39 0.0039

CB201 Romney Creek 4.36 41.19 0.0032

BSH01 Bush River 31.30 107.95 0.0513

GUN01 Gunpowder River 49.46 192.16 0.0769

MID01 Middle River 9.86 67.50 0.0142

PAT01 Old Road Bay 3.43 18.05 0.0063

PAT02 Bear Creek 4.70 48.83 0.0101

BAC01 Back River 17.58 68.57 0.0256

PAT03 Northwest Harbor 3.32 33.12 0.0244

PAT04 Middle Branch 6.75 41.97 0.0254

PAT05 Curtis Creek 5.93 52.13 0.0258

PAT06 Stony Creek 2.64 25.84 0.0052

……

Analysis of Subestuary Metrics

Will provide input for parameter distributions in Generalized Sensitivity Analysis

Some Characteristic Metrics

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Subestuary Area (km2)

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e Fr

eque

ncy

Subestuary Area

0 50 100 150 200 250 3800 4000

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Subwatershed Area:Subestuary Area ratio

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Watershed:Estuary ratio

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Subwatershed Area (km2)

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e Fr

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Subwatershed Area

0 2 4 6 8 100.0

0.1

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Mean Depth (m)

Rel

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Mean Depth

Potential SAV habitat and actual SAV presence in five subestuaries near Baltimore.

Percentage of SAV presence and coverage abundance (1971-2003) were calculated from VIMS SAV dataset.

Pa t ap s c o R iv er

G u n p o w d e r R iv e r

B ac kR

i ve r

B i r d R i v e r

M i d d le R i ver

Practical Application of Watershed/Subestuary

Delineation

A g r ic u l t u r a l D e v e lo p e d F o r e s t e d M ix e d0 . 0

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1 . 0

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1 . 4

SA

V C

over

age

(%)

A

B

AA

S A V c o v e r a g e a b u n d a n c e u n d e r d i f f e r e n t la n d u s e s f o r a l l s e le c t e d s u b e s t u a r y - w a t e r s h e d s w i t h d i f f e r e n t p h y s io g r a p h ic p r o v in c e s o f p ie d m o n t , c o a s t a l lo w la n d a n d c o s t a l u p la n d .

A g r ic u l t u r a l D e v e lo p e d F o r e s t e d M ix e d0 . 0

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1 . 0

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1 . 8

SA

V C

over

age

(%)

A B

C

B

A

S A V c o v e r a g e a b u n d a n c e u n d e r d i f f e r e n t la n d u s e s f o r a l l s e le c t e d s u b e s t u a r y - w a t e r s h e d s w i t h p h y s io g r a p h ic p r o v in c e o f c o a s t a l lo w la n d a n d c o s t a l u p la n d .

Land use impact on SAV coverage abundance shows different pattern in different physiographic provinces.

See poster by Yong Li and Don Weller

Water Column Model Structure

predation

sinking

BAC_N BAC_P

SQN

MQN

LQN

SPHY_P

MPHY_P

LPHY_P

MQP

SQP

LQP

Benthic System

Pelagic System

sedimentfrominput

uptakecell lysis

sediment ?frominput

assimilated

DOPDON

labile organic uptake remineralization

NeighboredBox

DIPDIN

bact

ivor

y

SPHY_N

MPHY_N

LPHY_N

cell lysis

SZOO_P

MZOO_P

LZOO_P

SZOO_N

MZOO_N

LZOO_Ngrazing

excreted

sinking

DET_PDET_Nremineralization

egested

mortality

• N vs. P limitation

• 3 Phyto & zoo size-fractions

• Sedimentation & remineralization

• Physical exchange with neighboring segments

Model Testing

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Unknown sinks

Timing

Day of Year

Chl

orop

hyll

(mg

m-3)

Model Data

50 100 150 200 250 30002468

1012141618202224

Unobserved sources

Drawdown

Timing

Day of Year

DIN

(µM

)

Model Data

Nitrogen Chlorophyll

*See poster by Hae-Cheol Kim

Progress

Scheduled Activity Year 2 ActualMeasure CDOM export from wetlands & watersheds * * * * Measurements commenced spring

2004, nearing completionGIS analysis of subestuaries * * CompleteGIS analysis of coastal plain watersheds * * Complete

Statistical analysis of nutrient discharge data * * Limited progress

Coding of subestuary componene models * Draft 1 complete

Validate subestuary model predictions * * * * Underway

Link Subestuary and watershed models * * * To commence

Model flow-alteration/land-use change scenarios * * Pending completion of

watershed/subestuary linkage

Next Steps

• Link watershed and subestuary models• Iron out remaining issues in water column

model• Analyze nutrient discharge data• Explore model parameter space

(preliminary to generalized sensitivity analysis)