Oysters, reef restoration and water quality: A Chesapeake Bay perspective

M. Lisa KelloggVirginia Institute of Marine Science

Increasing Interest in Oysters and WQWhy?• 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

The Promise of Oyster Reef Restoration

Source: Tom Toles (2013) The Washington Post.

Oysters and Nitrogen CyclingOysters 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

sediments3) Denitrification

- For purposes of this talk, “denitrification” = net flux of di-nitrogen gas to atmosphere

* Timescale of removal varies widely

Oysters and N Cycling: What We Know…NCBO – Sponsored Workshop

Jan. 10 – 11, 2013Wachapreague, 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) Wally Fulweiller (U. Mass) Mike Piehler (UNC)Iris Anderson (VIMS) Boze Hancock (TNC) B.K. Song (VIMS)Suzy Avvasian (EPA) Troy Hartley (VA Sea Grant) Angie Sowers (ACOE)Peter Bergstrom (NCBO) Lisa Kellogg (VIMS) Howard Townsend (NCBO)Bonnie Brown (VCU) Doug Lipton (MD Sea Grant) Bruce Vogt (NCBO)Steve Brown (TNC) Mark Luckenbach (VIMS) Eric Weissberger (MD DNR) Mark Brush (VIMS) Fredrika Moser (MD Sea Grant) Jim Wesson (VMRC)Ruth Carmichael (USA) Annie Murphy (VIMS) Stephanie Westby (NCBO) Susan Connor (ACOE) Mike Owens (UMCES) Line zu ErmgassenJeff Cornwell (UMCES) Ken Paynter (UMD) (Cambridge)

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

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

Source: Kellogg et al. (2013) Quantifying Nitrogen Removal by Oysters: Workshop Report, NOAA Chesapeake Bay Program Office.

• 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

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

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Enha

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Oyster Biomass (g DW m-2)

Piehler and Smyth (2011)Sisson et al. (2011)Smyth et al. (2013)Kellogg et al. (2013)Kellogg et al. (In prep)Kellogg et al. (Ongoing)

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Organic Matter

Buried Nitrogen

Ammonium(NH4

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NitrogenGas (N2)

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Nitrous Oxide (N2O)

Organic Nitrogen

Biodeposits/Organic Nitrogen

Atmospheric/Upstream Nitrogen

Inputs

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5

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7 7 79B

C* D*

Nitrogen RemovalA. AssimilationB. Deep burialC. Return of N2O to atmosphereD. Return of N2 to atmosphere

1. Uptake2. Filtration3. Biodeposition4. Burial5. Mineralization

Legend

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Oyster Shell

* Nitrogen cycling pathways resulting in removal assumed to be similar to those shown for sediments

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6. Nitrification7. Denitrification8. Anammox9. DNRA10. Diffusion

Nitrogen Cycling

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Microphytobenthos

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(NO3-)

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O2

Oxygen Production

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Dissolved Organic Nitrogen 10

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Oysters and N Cycling: What We Know…Denitrification• Many factors interact

to influence rates • Reefs (NC, VA & MD)

- 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

Source: Kellogg et al. (2013) Quantifying Nitrogen Removal by Oysters: Workshop Report, NOAA Chesapeake Bay Program Office.

Oysters and N Cycling: What We Know…Denitrification• Aquaculture (MD and VA)

- 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

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Holyoke (2008)Higgins et al. (2013)

Source: Kellogg et al. (2013) Quantifying Nitrogen Removal by Oysters: Workshop Report, NOAA Chesapeake Bay Program Office.

Impacts on WQ: Choptank River, MD ExampleMeasured 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

Impacts on WQ: Choptank River, MD ExampleLocation vs. goals

Harris Creek restoration: ~$31 million over 5 years

Impacts on WQ: Lynnhaven River, VA ExampleTN reduction needed to meet TMDLs:

1,409,078 lbs. y-1

Maximum enhancement of denitrification via reef restoration:

~465 acres of oyster reef in 1894x 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

Impacts on WQ: Lynnhaven River, VA ExampleTN 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

40:271-277b Murray and Hudson (2013) Virginia Shellfish

Aquaculture Situation and Outlook Report

Impacts on WQ: Lynnhaven River, VA ExampleA few words of caution and a request:

Source:http://www.vbgov.com/government/offices/eso/Documents/tmdl-local-strategy.pdf, Accessed 11/14/2013

Oysters and Water QualityA few summary points:1) Oyster reef restoration and/or oyster aquaculture can be

part of the solution to water quality problems2) Need to consider nitrogen removal in terms of

enhancement above existing conditions3) Location of reefs/aquaculture relative to goals is important4) Need to take into account the scale of the problem to

assess feasibility of the proposed solution5) Need to consider options in context of other costs and

benefits6) We are happy to help you translate our numbers, just ask

lkellogg@vims.edu