1. Oysters, reef restoration and water quality:
A Chesapeake Bay perspective
M. Lisa Kellogg
Virginia Institute of Marine Science

2. Increasing Interest in Oysters and WQ
Why?
• Population decline
- < 1% historic levels
• Failure to meet WQ goals
• EPA-mandated WQ
improvements (TMDLs)
increasingly expensive
- MD and VA
- Local governments will
pay bulk of costs
• Enhancing oyster
populations may cost less
than other options
- Additional benefits
Source: US EPA 2003. Economic analysis of nutrient
and sediment reduction actions to restore
Chesapeake Bay. Annapolis, MD

3. The Promise of Oyster Reef Restoration
Source: Tom Toles (2013) The Washington Post.

4. Oysters and Nitrogen Cycling
Oysters don’t filter nitrogen, they consume phytoplankton
Three primary
pathways oysters can
lower N levels in the
water column:
1)
Assimilation*
- Tissue and shell
contain N and P
2) Burial*
- Also bury P and
sediments
3) Denitrification
- For purposes of this talk,
“denitrification” = net flux
of di-nitrogen gas to
atmosphere
* Timescale of removal
varies widely

5. Oysters and N Cycling: What We Know…
NCBO – Sponsored Workshop
Jan. 10 – 11, 2013
Wachapreague, VA
Purpose: To gather experts to determine: (1) the best available values for
nitrogen removal by oysters; (2) the uncertainty associated with these
estimates; and, (3) the data gaps necessary to reduce the uncertainty
Moderated by Kevin Sellner (CRC)
Participants:
Steve Allen (ORP)
Iris Anderson (VIMS)
Suzy Avvasian (EPA)
Peter Bergstrom (NCBO)
Bonnie Brown (VCU)
Steve Brown (TNC)
Mark Brush (VIMS)
Ruth Carmichael (USA)
Susan Connor (ACOE)
Jeff Cornwell (UMCES)
Wally Fulweiller (U. Mass)
Boze Hancock (TNC)
Troy Hartley (VA Sea Grant)
Lisa Kellogg (VIMS)
Doug Lipton (MD Sea Grant)
Mark Luckenbach (VIMS)
Fredrika Moser (MD Sea Grant)
Annie Murphy (VIMS)
Mike Owens (UMCES)
Ken Paynter (UMD)
Mike Piehler (UNC)
B.K. Song (VIMS)
Angie Sowers (ACOE)
Howard Townsend (NCBO)
Bruce Vogt (NCBO)
Eric Weissberger (MD DNR)
Jim Wesson (VMRC)
Stephanie Westby (NCBO)
Line zu Ermgassen
(Cambridge)

6. Oysters and N Cycling: What We Know…
Long-term burial
• No published rates
- Ongoing analyses of data from
reefs in North Carolina by Mike
Piehler, Joel Fodrie, John
Grabowski and colleagues

7. Oysters and N Cycling: What We Know…
Assimilation
• Tissue N = 8.22 ± 0.89% of dry wt. for mid- and NE-Atlantic
- 4 studies; 14 tributaries or subestuaries; MD, VA, MA and NH
- But Mobile Bay, AL Tissue N = 11.8% N
• Shell N = 0.19-0.21% of dry wt.
- 2 studies from Chesapeake Bay
• Reefs vs. aquaculture
- 2 studies from Chesapeake Bay
- Enhancement of standing-stock
assimilation on reefs can be high
•
•
•
95 g N m-2 (848 lbs. acre-1)
Non-oyster macrofauna can enhance
assimilation by ~50%
47% of total N found in shells of oysters
and mussels
•
Likely results in sequestration for decades,
centuries or more
Source: Kellogg et al. (2013) Quantifying Nitrogen
Removal by Oysters: Workshop Report, NOAA
Chesapeake Bay Program Office.

8. Oysters and N Cycling: What We Know…
Assimilation
• Reefs vs. aquaculture
- Aquaculture harvest removes N from aquatic environment
•
•
Greater proportion of total N in tissue
N in shell may be fully or partially removed depending on shell fate
Source: Kellogg et al. (2013) Quantifying Nitrogen
Removal by Oysters: Workshop Report, NOAA
Chesapeake Bay Program Office.
Photo credit: Tom Pelton

9. - Net annual
enhancement of
2.7-55.6 g m-2 y-1
(24-496 lbs. acre-1 y-1)
- Rates within a single
site can vary by ≥2
orders of magnitude
- Intertidal rates
generally lower than
subtidal
- Increases non-linearly
with oyster biomass
- Ongoing studies in RI
by Jo Carey and
colleagues from EPA,
TNC and BU
Aerobic
Sediments
• Many factors interact
to influence rates
• Reefs (NC, VA & MD)
Anaerobic
Sediments
Denitrification
Water
Atmosphere
Enhancement of N2Column
-N Flux (µmol m-2 h-1)
Oysters and N Cycling: What We Know…
1800Nitrogen Cycling
1.
2.
3.
4.
5.
Uptake
Filtration
Biodeposition
Burial
Mineralization
1600
Atmospheric/
Upstream Nitrogen
Inputs
Legend
Nitrogen
Piehler and Assimilation Removal
A. Smyth (2011)
B. Deep burial
Sisson et al. (2011) to atmosphere
C. Return of N O
D. Return of N to atmosphere
Smyth et al. (2013)
Oxygen Production
Kellogg et al. (2013)
Phytoplankton/
Kellogg et al. (In prep)
Particulate
Kellogg et al. (Ongoing)Matter
Organic
6. Nitrification
7. Denitrification
8. Anammox
9. DNRA
10. Diffusion
1400
1200
2
2
1
C*
1000
O2
2
Dissolved
Organic
Nitrogen
400
200
3
Organic Nitrogen
B
0
Buried Nitrogen
Microphytobenthos
1
5
Ammonium
(NH4+)
6
Nitrite
(NO2-)
5
100
Ammonium
(NH4+)
200
6
1
Nitrate
(NO3-)
O2
10
10
9
Nitrate
(NO3-)
300
7
Nitrite
(NO2-)
400
Oyster Biomass (g DW m-2)
* Nitrogen cycling pathways resulting in removal assumed to be similar to those shown for sediments
Source: Kellogg et al. (2013) Quantifying Nitrogen
Removal by Oysters: Workshop Report, NOAA
Chesapeake Bay Program Office.
O2
Live Oysters
Oyster Shell
4
Organic Nitrogen
-400
D
C
1
10
A
3
0
Biodeposits/
10
10
A
10
10
-200
10
2
D*
Dissolved Inorganic
Nitrogen
1
800
600
Nitrogen
Gas (N2)
Nitrous
Oxide (N2O)
7
Nitrous
Oxide (N2O)
500
8
7
Nitrogen
Gas (N2)
600

10. Oysters and N Cycling: What We Know…
Denitrification
- No evidence yet for net
annual enhancement
- All data from floating
aquaculture
- Ongoing studies in RI by
Jo Carey, Suzy Ayvazian
and colleagues at EPA,
TNC and BU
Enhancement of N2-N Flux (µmol m-2 h-1)
• Aquaculture (MD and VA)
1800
1600
Holyoke (2008)
Higgins et al. (2013)
1400
1200
1000
800
600
400
200
0
-200
-400
May
Jun
Jul
Aug
Month
Source: Kellogg et al. (2013) Quantifying Nitrogen
Removal by Oysters: Workshop Report, NOAA
Chesapeake Bay Program Office.
Sep
Oct

11. Impacts on WQ: Choptank River, MD Example
Measured denitrification rates for a
successfully restored oyster reef
• Subtidal reef
• Oysters 3-7 years old
• High oyster biomass m-2
Estimated annual enhancement:
• 55.6 g N2-N m-2 y-1
(496 lbs. N acre-1 y-1)
Restoring all suitable bottom:
• “Suitable bottom” based on sonar
surveys and fine-scale sampling of
substratum
• 48% of total external N removed
Restoration needed to meet TMDL
requirements:
• 23% of suitable bottom

12. Impacts on WQ: Choptank River, MD Example
Location vs. goals
Harris Creek restoration:
~$31 million over 5 years

13. Impacts on WQ: Lynnhaven River, VA Example
TN reduction needed to meet TMDLs:
1,409,078 lbs. y-1
Maximum enhancement of denitrification
via reef restoration:
~465 acres of oyster reef in 1894
x 496 lbs. N acre-1 y-1 (Choptank rate)
230,789 lbs. y-1 = 16% of total
Actual potential reduction likely 1-2 orders
of magnitude lower
- Measured nitrogen flux rates in the
Lynnhaven River in October suggest rates are
~1/5 of those observed in the Choptank
- Actual amount of substratum suitable and
available for restoration likely to be
significantly lower

14. Impacts on WQ: Lynnhaven River, VA Example
TN reduction needed to meet TMDLs:
1,409,078 lbs. y-1
Removal via aquaculture harvest:
~132 kg N per 1 million
harvest-sized oystersa
=291 lbs N
Scale of aquaculture needed to meet
100% of required reduction:
4.8 billion oysters harvested y-1
X 2 years to reach harvestable size
> 9.6 billion oysters in aquaculture
28 million oysters harvested from
aquaculture in VA in 2012b
Much of Lynnhaven River closed to
shellfish harvest
Sources:
a Higgins et al. (2011) Journal of Environmental Quality
40:271-277
b Murray and Hudson (2013) Virginia Shellfish
Aquaculture Situation and Outlook Report

15. Impacts on WQ: Lynnhaven River, VA Example
A few words of caution and a request:
Source:
http://www.vbgov.com/government/offices/eso/Docu
ments/tmdl-local-strategy.pdf, Accessed 11/14/2013

16. Oysters and Water Quality
A few summary points:
1) Oyster reef restoration and/or oyster aquaculture can be
part of the solution to water quality problems
2) Need to consider nitrogen removal in terms of
enhancement above existing conditions
3) Location of reefs/aquaculture relative to goals is important
4) Need to take into account the scale of the problem to
assess feasibility of the proposed solution
5) Need to consider options in context of other costs and
benefits
6) We are happy to help you translate our numbers, just ask
lkellogg@vims.edu