Transcript Fundamental Equation - Dept of Natural Resources

Chesapeake Bay Environmental
Model Package
• A coupled system of
watershed, hydrodynamic
and eutrophication models
• The same package used for
the 2002 load allocations
• The same package used for
the 2004 native oyster study
Regional
Atmospheric
Deposition
Model
Watershed
Model
Hydrodynamic
Model
The CBEMP circa
1999
Eutrophication
Model
SAV
Component
Benthos
Component
excretion
Filter
Feeders
feeding
Particulate
Organic
Matter
Deposit
Feeders
diagenesis
excretion
diagenesis
Dissolved
Oxygen
sediment-oxygen
demand
biodeposits
Sediments
Dissolved
Nutrients
sediment-water
exchange
Water
Column
respiration
filtration
settling
Particulate
Organic
Matter
Dissolved
Nutrients
Oxygen
Demand
respiration
Diagenesis Model
with Benthos
Key Assumptions and Properties
• The model is run for 10 years, 1985-1994,
on a grid of 3000 surface elements (~4 km2)
using time steps of 15 minutes
• Oysters are restricted to their historical
spatial distribution
• The model is parameterized for Chesapeake
Bay native oysters
Key Assumptions and Properties
• A spatially-uniform mortality rate is
specified that combines effects of predation,
disease, and harvest
• Oyster biomass is dynamically computed
based on local conditions including food
availability, salinity, dissolved oxygen, and
suspended solids
Fundamental Equation
d FF
   Fr  POC  FF  r  FF    FF 2  hm r FF
dt
FF = filter feeder biomass (mg C m-2)
α = assimilation efficiency (0 < α < 1)
Fr = filtration rate (m3 mg-1 filter feeder carbon d-1)
POC = particulate organic carbon in overlying water (mg m3)
r = specific respiration rate (d-1)
β = predation rate (m2 mg-1 filter feeder C d-1)
hmr = mortality rate due to hypoxia (d-1)
t = time (d)
Modeled Effect of Temperature on Filtration
Modeled Effect of Solids on Filtration
From Jordan
Model
Particulate Carbon Budget
Dissolved Oxygen Budget
Particulate Nitrogen Budget
Dissolved Nitrogen Budget
Particulate Phosphorus Budget
Dissolved Phosphorus Budget
Filtration Rates
Filtration Rate
m3/g oyster C/d
0.22
0.26
0.027 to 0.33
0.27
0.455
0.238
0.202
0.238
Source
Comments
Jordan's thesis
Newell&Koch
Epifanio & Ewart
Riisgard
Model, CB4
Model, Choptank Deep
Model, Choptank Shallow
Model, ET9
mean value T > 20C.
Average of measures at 20 and 25 C
For algal suspension greater than 1 mg C/L
Computed for a 2.1 g DW oyster at 27 to 29 C
Summer average
Summer average
Summer average
Summer average
Carbon Deposition
Carbon Deposition
g C/g Oyster C/d
0.099
0.03
0.002 to 0.012
0.050
0.088
0.118
0.096
Source
Comments
Jordan's thesis
Haven & Morales
Tenore & Dunstan
Model, CB4
Model, Choptank Deep
Model, Choptank Shallow
Model, ET9
mean value T > 20C.
see havens_ingestion spreadsheet
depends on C concentration, range is 0.1 to 0.7 mg/L
Summer average
Summer average
Summer average
Summer average
Respiration
Respiration
g DO/g oyster C/d
0.03 to 0.06
0.017
0.02
0.042
0.040
0.041
0.041
Source
Comments
Boucher & Boucher-Rodini
Dame, Spurrier, Zingmark
Dame (ecological efficiencies)
Model, CB4
Model, Choptank Deep
Model, Choptank Shallow
Model, ET9
spring-summer rates, N excretion includes urea
Annual average
1 g DW oyster at 20 to 30 C
Summer average
Summer average
Summer average
Summer average
Ammonium Excretion
NH4 excretion
Source
mg N/g oyster C/d
< 0.1
Hammen et al.
2.8 to 3.88
Boucher & Boucher-Rodini
0.8
Srna & Baggaley
4.8 to 7.9
Magni et al
2.20
Model, CB4
1.43
Model, Choptank Deep
1.52
Model, Choptank Shallow
2.05
Model, ET9
Comments
NH4 + urea
spring-summer rates, N excretion includes urea
NH4 only, 1 g oyster at 20 C
Ruditapes and Musculista
Summer average
Summer average
Summer average
Summer average
Seasonal Variation in Oyster Density
Annual Variation in Autumn Oyster
Density
Mg C/sq m
Conclusions
• Our results are consistent with alternate
investigations including Officer et al. 1982,
Gerritsen et al. 1994, and Newell&Koch
2004.
• The greatest ecosystem service of feasible
oyster restoration appears to be SAV
restoration.
• Other ecosystem services provided by
oysters include nitrogen removal and
dissolved oxygen enhancement.
Conclusions
• Oysters have larger impact on their local
environment than system-wide
• We recommend restoration target specific
areas with suitable environments. Look for
improvements on similar scales.
Criteria for benthic control of phytoplankton
(Officer et al. 1982)
• Shallow water depths (2 to 10m)
• A large and widespread population as
opposed to more localized regions
• Partially-enclosed regions with poor
hydrodynamic exchange with adjacent
water bodies
Suspension-feeding bivalve model … applied
to Chesapeake Bay (Gerritsen et al. 1994)
• Existing bivalves consume more than 50%
of primary production in shallow freshwater
and oligohaline reaches
• In deep mesohaline portions, bivalves
consume only 10% of primary production
• Use of bivalves to improve water quality of
large estuaries will be limited by the depth
and width of the estuary
Modeling seagrass density in response to …
bivalve filtration (Newell & Koch)
• The presence of modest levels of oysters (<
12 g C/sq m) reduced suspended sediment
concentrations by an order of magnitude