NITROGEN REMOVAL FROM OAKLAND BAY AND PUGET SOUND THROUGH SHELLFISH HARVEST

Transcription

1 NITROGEN REMOVAL FROM OAKLAND BAY AND PUGET SOUND THROUGH SHELLFISH HARVEST Peter Steinberg (Herrera Environmental Consultants) Julie Hampden (Herrera Environmental Consultants) Jonathan Davis (Baywater Inc.) Daniel Cheney (Pacific Shellfish Institute) Washington Shellfish Environmental and Economic Costs and Benefits

2 Washington Shellfish Environmental and Economic Costs and Benefits An interdisciplinary study of the costs and benefits of shellfish harvest in Washington state Environmental Social Economic This talk focuses on one aspect of the study Nitrogen removal through shellfish harvest Oakland Bay (in Puget Sound) Puget Sound Comparison of this nitrogen removal to nitrogen loads

3 Washington Shellfish Environmental and Economic Costs and Benefits NOAA National Marine Aquaculture Initiative Award #NA08OAR Pacific Shellfish Institute Dan Cheney, Bobbi Hudson Northern Economics Trina Wellman, Bill Schenken Baywater, Inc. Joth Davis Herrera Environmental Consultants Peter Steinberg, Julie Hampden Puget Sound Restoration Fund Betsy Peabody, Geoff Menzies Entrix Susan Burke

4 Study Area Puget Sound Oakland Bay

5 Shellfish and Nitrogen Cycle (Simplifed) Phytoplankton, Other Microbiota, and Detritus Filter Feeding Excretion and Resuspension Shellfish Removal through Harvest Excretion and Burial in Sediments

6 Shellfish Nitrogen Cycle Shellfish remove nitrogen from the water column How much becomes resuspended or buried is difficult to measure Deterministic modeling suggests nitrogen burial in sediments under shellfish beds may be a flux twice as large as nitrogen removal through harvest (Brigolin et al 2009) Nitrogen removal through shellfish harvest is more easily quantified This study focuses on nitrogen removal through harvest Looking at other nitrogen sequestration would require more input assumptions and data (e.g. growth kinetics, mesocosm experiments)

7 Nitrogen Removal in Shellfish Harvest Variables that need to be known Mass of shellfish harvested each year Mean nitrogen concentration in shellfish A study in Henderson Inlet is being conducted to look at shellfish nitrogen concentrations by species and season In the meantime, a shellfish nitrogen concentration of 1 percent was assumed based on the literature (Rice 2001; Ojea et al. 2004; Linehan et al. 1999).

8 Shellfish Nitrogen Removal: Comparison to Nitrogen Loads Nitrogen removal in harvest should be compared to nitrogen loading rates from: Estuarine circulation Watershed inputs (rivers and groundwater) Direct wastewater inputs Atmospheric input (wet and dry) Estimation of nitrogen loading rates Oakland Bay original calculations Puget Sound literature review

9 Oakland Bay Nitrogen Loading Combined River and Groundwater Loads Estimated total flows from basin mean annual precipitation (USGS Streamstats) with 20% evaporation Estimated nitrogen concentrations from 32 nearby streams (Hood Canal lowland) Point Sources Shelton Wastewater Treatment Plant Permitted Maximum Discharges and Average Concentrations Atmospheric Loads Average wet and dry fallout rates from four regional NADP stations Marine Loads (Circulation) Salinity balance salinity data from Ecology OAK004 monitoring station

10 Oakland Bay Salinity Balance Qrain Precipitation Input Qriver River and Groundwater Input Surface Mixed Layer Qout Surface Outflow (with Salinity Ssurface) Waters Below Pycnocline Qup Upwelling Estuarine Circulation (with Salinity Sdeep) 1. Water Balance Equation (Steady State) Inflow = Outflow Qriver + Qrain + Qup = Qout 2. Salinity Balance Equation (Steady State) Upwelling Flow * Salinity at Depth = Outflow * Salinity at Surface Qup * Sdeep = Qout * Ssurface 3. Solving for Upwelling Flow Based on Known Salinity Profile and Water and Salinity Balance Equations Qup = Ssurface / Sdeep * (Qup + Qriver + Qrain)

11 Oakland Bay Nitrogen Budget Precipitation Flow: km 3 /year DIN Conc.: 104 µg/l DIN Load: 3.39 MT/year Rivers and Groundwater Flow: 0.59 km 3 /year TDN Conc.: 283 µg/l TDN Load: 168 MT/year Shelton Wastewater Flow: <.0055 km 3 /year DIN Conc.: 11,000 µg/l DIN Load: 61.1 MT/year Oakland Bay Surface Mixed Layer Salinity: 24.9 psu Oakland Bay Waters Below Pycnocline Surface Outflow to Puget Sound Flow: 17 km 3 /year DIN Conc.: 75 µg/l DIN Load: 1,270 MT/year Shellfish Harvest N removal: 11.7 MT/year Upwelling Estuarine Circulation Flow: 16.4 km 3 /year DIN Conc.: 68 µg/l DIN Load: 1,120 MT/year Salinity: 25.8 psu

12 Oakland Bay Nitrogen Budget 0.86% of Total Input

13 Puget Sound Nitrogen Budget 0.04% of Total Input

14 Discussion Shellfish harvest is a small (<1 %) component of the nitrogen balance for Oakland Bay and Puget Sound Marine loads are large Shellfish harvest nitrogen removal relatively more important in smaller, shallower portions of Puget Sound Uncertainty remains because of Unknown shellfish N concentrations (to be improved) Higher order effects (e.g. increased nitrogen burial) are not considered

15 Questions? References Brigolin, D., G.D. Maschio, F. Rampazzo, M. Giani, R. Pastres An individual-based population dynamic model for estiamting biomass yield and nutrient fluxes through an offshore mussel (Mytilus galloprovincialis) farm. Estuarine, Coastal, and Shelf Science 82: Embrey, S.S. and E.L. Inkpen Nutrient transport in rivers of the Puget Sound Basin, Washington U.S. Geological Survey Water-Resources Investigation Report , 30 p. Linehan, L.G., T.P. O Connor, and G. Burnell Seasonal variation in the chemical composition and fatty acid profile of Pacific oysters (Crassostrea gigas). Food Chemistry 64: Mackas, D.L. and P.J. Harrison Nitrogenous nutrient sources and sinks in the Juan de Fuca Strait/Strait of Georgia/Puget Sound estuarine system: Assessing the potential for eutrophication. Estuarine, Coast, and Shelf Science 44:1-21. Ojea, J., A.J. Pazos, D. Martinez, S. Novoa, J.L. Sanchez, and M. Abad Seasonal variation in weight and biochemical composition of the tissues of Ruditapes decussates in relation to the gametogenic cycle. Aquaculture 238: Rice, M.A Environmental Impacts of Shellfish Aquaculture: Filter Feeding to Control Eutrophication. pp in: M. Tlusty, D. Bengtson, H.O. Halvorson, S. Oktay, J. Pearce, and R. Rheualt, (eds.), Marine Aquaculture and the Marine Environment: A Meeting for the Stakeholders in the Northeast. Held January 11-13, 2001, at the University of Massachusetts Boston. Cape Cod Press, Falmouth, Massachusetts.