The summertime subpycnocline dissolved oxygen budget in the western Long Island Sound. Grant McCardell and James O Donnell

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1 The summertime subpycnocline dissolved oxygen budget in the western Long Island Sound Grant McCardell and James O Donnell MAPBOM 2013

2 Overview WLIS hypoxia SWEM model Data-based transport estimates WLIS near-bottom DO budget

3 Overview WLIS hypoxia SWEM model Data-based transport estimates WLIS near-bottom DO budget

4 Why we care: western Long Island Sound hypoxia NYC GMA 18.9M (2010 Census)

5 Why we care Ward s Island WPCP, East River Just in NYC: 14 treatment plants 6,000 miles of pipes 135,000 catch basins 93 pump stations Staff of 2,000 $2B PA M. Hay, Capital New York

6 NYC WQ has improved NY Harbor dissolved oxygen (NYCDEP)

7 What about western Long Island Sound (WLIS)? LIS hypoxia area (blue bars) and duration (grey line) (CTDEP, 2011)

8 Overview WLIS hypoxia SWEM model Data-based transport estimates WLIS near-bottom DO budget

9 SWEM Overview System Wide Eutrophication Model Coupled biology / physics 3D model developed by Hydroqual, Inc. for EPA Circulation and mixing from ECOM (Estuarine, Coastal and Ocean Model) Biology and water quality based on RCA (Row Column Advanced Ecological Systems Operating Program) 25 state variables 125 parameter values Two phytoplankton pools (diatoms, dinoflagelletes) Hard-wired zooplankton grazing (NP) Used to simulate WQ responses to waste water management decisions

10 SWEM compensating errors Measurements (unavailable at the time of SWEM s design) indicate that: Oxygen demand (respiration) in SWEM is too low Oxygen resupply (mixing) in SWEM is too low 4 3 = 1 but so does 2 1 = 1 Just because you get the right answer doesn t mean the individual terms are correct Two wrongs don t make a right my grandmother

11 Offsetting budget terms When budget terms are almost offsetting, a small change in one term can result in a large change in the net bottom line : XYZ, Inc. makes widgets that cost $9 to make and sell for $10 What if production costs per widget decrease from $9 to $8? Concept is the same for DO: Physical resupply nearly offsets biological demand Small change in DO resupply = large change in net decline Relatively small terms with large variance may drive variability in the net

12 SWEM summary Existing respiration and production were too low Necessitated elimination of vertical mixing Just because the net result is right doesn t mean the individual terms are right Raises need for data-based estimates of physical transport (e.g. vertical mixing, horizontal advection)

13 Overview WLIS hypoxia SWEM model Data-based transport estimates WLIS near-bottom DO budget

A novel method for estimating K Concept V H. Lamb (1932): (, ω) S z = e ( 1+ i) β z where Periodic signal subject to diffusion attenuates in strength, lags in phase Examples: inside vs.

14 A novel method for estimating K Concept V H. Lamb (1932): (, ω) S z = e ( 1+ i) β z where Periodic signal subject to diffusion attenuates in strength, lags in phase Examples: inside vs. outside temperature variation, opening and closing a vial of H 2 S Two periodic signals: O 2 and temperature β ω 2K v Premise: In turbid waters with weak diurnal tides, the diel O 2 and temperature signals are only generated near the surface Hypothesis: if this frequency signal is detected at depth, it got there diffusively and will show both amplitude attenuation and a phase lag K V = i 2 ln ωδz U U 2 surface depth

15 Results: seasonal evolution of effective 2-day eddy diffusivities for O 2 (top) and heat (bottom) McCardell and O Donnell, A novel method for estimating vertical eddy diffusivities using diurnal signals with application to western Long Island Sound. J. Mar. Syst., doi: /j.jmarsys

Vertical O 2 fluxes from vertical gradients and K V estimates (vertical bars) Inferred fluxes from respiration estimates and subtidal / t (horizontal lines) Fluxes Mean June / July eddy diffusivity:

16 Vertical O 2 fluxes from vertical gradients and K V estimates (vertical bars) Inferred fluxes from respiration estimates and subtidal / t (horizontal lines) Fluxes Mean June / July eddy diffusivity: m 2 s 1 Mean June / July downward O 2 flux: mmoles m -2 day -1 Depth averaged downward O 2 flux: 14 ± 10 µ M day -1 Mean June / July downward heat flux: W m -2 Depth averaged downward heat flux: 17 ± 10 W m -3

Along-Sound flux estimates Centered finite difference Velocities from ADCP at FB02 Fluxes Along-Sound gradients from EXRK, FB02, and WS) 2005 & 2006 data, also applied to

17 Along-Sound flux estimates Centered finite difference Velocities from ADCP at FB02 Fluxes Along-Sound gradients from EXRK, FB02, and WS) 2005 & 2006 data, also applied to SWEM EXRK FB02 WS Subtidal advection dominated over tidal dispersion McCardell and O Donnell, Estimates of Horizontal Fluxes in the Western Long Island Sound. In prep.

18 Transport summary Mean vertical mixing supply is 14 ± 10 µ M day -1 Mean along-channel supply is 4 ± 6 µ M day -1

19 Transport summary Mean vertical mixing supply is 14 ± 10 µ M day -1 Mean along-channel supply is 4 ± 6 µ M day -1 Vertical transport forms bulk of the DO resupply

20 Transport summary Mean vertical mixing supply is 14 ± 10 µ M day -1 Mean along-channel supply is 4 ± 6 µ M day -1 Vertical transport forms bulk of the DO resupply Note, however, that the variance in horizontal transport is similar to that of the vertical transport Both terms are candidate controls for variability in hypoxia

21 Overview WLIS hypoxia SWEM model Data-based transport estimates WLIS near-bottom DO budget

22 Subtidal WLIS bottom O 2 budget (DA) Net Change = Sources Sinks Vertical transport: 14 ± 10 µm day 1 McCardell & O Donnell, 2008 Respiration: 20 ± 20 µm day 1 Goebel and Kremer, 2007 Along-Sound transport: 4 ± 6 µm day 1 McCardell & O Donnell, 2013 Net decline: 2 ± 2 µm day 1 O Donnell et al., 2008 Benthic demand: 5 µm day 1 Aller, 1994; Fitzgerald, 2006

23 Subtidal WLIS bottom O 2 budget (DA) Net Change = Sources Sinks Vertical transport: 14 ± 10 µm day 1 McCardell & O Donnell, 2008 Respiration: 20 ± 20 µm day 1 Goebel and Kremer, 2007 Along-Sound transport: 4 ± 6 µm day 1 McCardell & O Donnell, 2013 Net decline: 2 ± 2 µm day 1 O Donnell et al., 2008 Variability in individual terms large change in net Benthic demand: 5 µm day 1 Aller, 1994; Fitzgerald, 2006

24 WLIS summertime subpycnocline O 2 budget (DA) Net Decline Residual Upwelling? Vertical Mixing Cross- Sound? Along- Sound Benthic Demand Respiration Gains Losses

25 Acknowledgments: This work was supported by the EPA, the NOAA Coastal Services Center through the Long Island Sound Integrated Coastal Observing System (LISICOS) and the New England Regional Association of Coastal Ocean Observing Systems (NERACOOS), and the University of Connecticut. This work would not have been possible without the superior operational assistance of the technical support groups at the University of Connecticut, and Captain D. Nelson and the crew of the R/V Connecticut.

26 Questions?

LISS Hypoxia Models. James O Donnell University of Connecticut

LISS Hypoxia Models. James O Donnell University of Connecticut LISS Hypoxia Models James O Donnell University of Connecticut With the support of NOAA IOOS (NERACOOS & MARACOOS), EPA LIS Program, CT Sea Grant, CTDEEP, and UConn and in collaboration with Jim Fitzpatrick,