Transcript pptx

Using Chesapeake Bay Models To Evaluate Dissolved
Oxygen Sampling Strategies
Aaron J. Bever, Marjorie A.M. Friedrichs, Carl T. Friedrichs
Outline:
Models and data used.
Methods of calculating hypoxic volume from 3-dimensional model results
How does the number of stations included in the interpolations influence
hypoxic volume?
Is improved temporal resolution more important than adding stations?
The models show temporally variable (daily-weekly) DO concentrations
and hypoxic volumes. Where do the models recommend the highfrequency data be collected, and how can this high-frequency data help the
models?
[email protected]
22, February 2011: Chesapeake Bay Program office, Annapolis MD.
Models used: Two 3-D hydrodynamic models with dissolved oxygen
CH3D-ICM:
Complex, multi-component ecosystem model presently used by the CBP.
Extensively calibrate to CBP data.
Model results provided by Ping Wang.
Regional Ocean Modeling System (ROMS) with a one-equation oxygen model:
Constant respiration (no nutrients, primary production, etc.), oxygen
saturation at the surface, diffusion of DO, advection of DO with water masses.
No calibration to data.
Model results provided by Malcolm Scully (ODU).
Data used:
Chesapeake Bay Program vertical profiles of DO
Collected bay-wide monthly or bi-monthly
Takes about 7-14 days to sample all stations.
Time-frame of investigation:
Calendar year 2004.
Focusing on hypoxic volume and spatial model estimates of
dissolved oxygen.
Hypoxic Volume was calculated from the models in five ways.
Total hypoxic volume from 3D model results.
Hypoxic volume estimated by the model using the observed station locations
(snapshot in time).
Hypoxic volume using observed station locations at the exact time each was
observed. (directly comparable to the observed hypoxic volume).
Hypoxic volume estimated using all Chesapeake Bay Program stations.
Hypoxic volume estimated using a subset of Chesapeake Bay Program stations
and targeted specific locations.
Hypoxic volume was calculated using the Chesapeake Bay Program Visual Basic
volume calculator software.
Hypoxic volume calculated from station locations for three of the five methods and
the observations.
Absolute Time Match (directly comparable to observations)
Time-snapshot
All Stations
25
Absolute Time Match
Time-snapshot
All Stations
Observations
1-Eq. DO Model, Hypoxic Volume (<2 mg/L)
20
15
10
5
0
1/14/2004
25
3/4/2004
4/23/2004
6/12/2004
8/1/2004
9/20/2004
11/9/2004
12/29/2004
Absolute time Match
Time-snapshot
All Stations
Observations
ICM, Hypoxic Volume (<2 mg/L)
20
15
10
5
0
1/14/2004
3/4/2004
4/23/2004
6/12/2004
8/1/2004
9/20/2004
11/9/2004
12/29/2004
Models suggest estimates of hypoxic volume can be improved through better observing the
time-variation in low DO, or DO at strategic locations.
 Adding more stations may not improve the estimates of hypoxic volume.
Estimates using all CBP station locations is nearly identical to using the subset actually observed in
2004.
 Better resolving the time-variation in low DO will help better estimate hypoxic volume, and better
validate/calibrate the models.
25
Absolute Time Match
Time-snapshot
All Stations
Observations
1-Eq. DO Model, Hypoxic Volume (<2 mg/L)
20
15
10
5
0
1/14/2004
25
3/4/2004
4/23/2004
6/12/2004
8/1/2004
9/20/2004
11/9/2004
12/29/2004
Absolute time Match
Time-snapshot
All Stations
Observations
ICM, Hypoxic Volume (<2 mg/L)
20
15
10
5
0
1/14/2004
3/4/2004
4/23/2004
6/12/2004
8/1/2004
9/20/2004
11/9/2004
12/29/2004
Using the model estimates to investigate strategic locations where hypoxia occurs.
Fraction of Time Hypoxia Occurred
ICM Model
Chesapeake Bay Program station locations.
1-Eq. DO Model
Using the model estimates to investigate strategic locations where the variability in
DO is high.
Standard Deviation of Bottom Oxygen Concentration
ICM Model
1-Eq. DO Model
Choose station
locations based on
the frequency of
hypoxia, variability in
DO concentration,
and CBP station
locations.
Calculate the hypoxic
volume based on
station subsets to
help determine how
important different
locations are.
Start with a minimum number of stations
Selected Station Locations
1-Eq. DO Model
Start with a minimum number of stations
Selected Station Locations
ICM Model
Include all CBP stations
Selected Station Locations
1-Eq. DO Model
Include all CBP stations
Selected Station Locations
ICM Model
By simply including more stations the hypoxic volume estimated from
the stations may have improved, but not as well as hoped.
Instead
Strategic placement based on model estimates should help:
Improve the data by using the models to target locations of moderate dissolved
oxygen variability near the edge of where hypoxia occurs.
Allows for a more robust estimate of hypoxic volume through time.
•Will help examine how the “real” hypoxic volume changes over the 1-2
weeks CBP profiles are being collected.
Helps improve relationships between short-term (daily to weekly) DO forcing
factors and the observed DO concentrations.
Improve the models by strategically adding high frequency data to locations where
validation is needed.
Near the northern and southern hypoxia extent to determine spatial
dimensions through time.
In a known hypoxic region to determine the vertical DO/hypoxia extent
through time.
Minimum number of stations: Plus one near the northern hypoxic
extent
1-Eq. DO Model
ICM Model
Minimum number of stations: Plus one near the south-eastern extent
of hypoxia
1-Eq. DO Model
ICM Model
Improvements in hypoxic volume estimates from adding a station.
Hypoxic volume estimates from the 1-Eq. DO model improved when a single strategic station
was added.
Hypoxic Volume estimates from the ICM model were unchanged by adding either of these
stations.
Stations on the outer range of hypoxia, and where the variability in DO is high, have the
potential to improve estimates of hypoxic volume and significantly contribute to our
understanding of the driving forces behind DO concentration within the Chesapeake Bay.
Potential Instrument Locations Based on Model Estimates
1-Eq. model shown; ICM model shows
similar results.
Northern Bay
Middle Bay
Extra Slides
Hypoxic volume from the stations and the total estimated hypoxic volume from the
3D fields. 1-Eq. Model
Hypoxic volume from the stations and the total estimated hypoxic volume from the
3D fields. ICM
Potential Instrument Locations: ICM model
Spatial model estimated bottom DO concentration (mg/L).
1-Eq. Model
2 mg/L is contoured in black.
Spatial model estimated bottom DO concentration (mg/L).
ICM model: Much more calibrated to observed profiles, much less variable than 1-Eq.
2 mg/L is contoured in black.
X and Y axis are in UTM, per ICM output.