with contributions from: An innovative modeling approach for simulating hypoxia/anoxia in estuarine ecosystems Mark J. Brush James N. Kremer Scott W. Nixon with contributions from: John Brawley Nicole Goebel Jamie Vaudrey

USE OF MODELS IN MANAGEMENT Chesapeake Bay Model Baretta & Ruardij (1988) ERSEM I (1995) ERSEM II (1997) Odum (1983) (1994) Riley (1946, 1947) Steele (1974) Kremer & Nixon (1978) Rigler & Peters Also: Reckhow (1994 & others) Håkanson (1995, 2004) Hofmann & Lascara (1998) Pace (2001) Duarte et al. (2003) Fulton et al. (2003) NUMBER OF PUBLICATIONS USE OF MODELS IN MANAGEMENT

Trade-off between realism & predictability: Increasing complexity / realism # of parameters predictability Loss of utility at lowest complexity? Generality Precision Realism Because this is certainly one of the more challenging topics I’ve had to talk about, I’ve sketched roadmap to help us all navigate these tricky waters. R. Levins (1966, 1968)

Published Gmax Functions Phytoplankton Primary Production Published Gmax Functions 1971-1998 Brush et al. (2002) elevated Eppley Gmax , d-1 Eppley Curve TEMPERATURE, oC

Duarte et al. (2003) “The Limits to Models in Ecology”

Can we find a middle ground? Empirical “Stressor-Response” Models Can we find a middle ground? Generality Precision Question: Can a simplified eutrophication model be useful as a heuristic and management tool? R. Levins (1966, 1968) Parsimony Principle Ockam's Razor Realism Complex, Mechanistic Systems Models

Estuarine Eutrophication Model

* Need to accurately model Estuarine Eutrophication Model * Need to accurately model both states and rates Phyto Production Pelagic Respiration C flux to sediments Macro Metabolism Denitrification

Light x Biomass (“BZI”) Models … capped by available nutrients Phytoplankton Primary Production Light x Biomass (“BZI”) Models Pd = *Chl*Zp*PAR +  … capped by available nutrients Cole & Cloern (1987) MEPS v. 36 Brush et al. (2002) MEPS v. 238

Water Column Respiration Rd = *e kT*Chl10

Estuaries and Nutrients Carbon Flux to Sediments & Benthic Respiration Nixon (1981) Estuaries and Nutrients The Humana Press Csed = 0.25*Pd Rsed = *e kT

Denitrification DENIT = Nload*f(RT) Nixon et al. (1996) Biogeochemistry 35(1) DENIT = Nload*f(RT)

… a hybrid, empirical-mechanistic Empirical Functions Robust, data-driven, & apply across several systems - ideal when mechanistic formulations are insufficient or poorly constrained. Reduce model complexity by integrating multiple processes (which are often poorly constrained) into simplified, bulk functions. Produce output we can measure and test. Excellent tools for model validation. … a hybrid, empirical-mechanistic approach

Greenwich Bay Eutrophication Model Greenwich Bay, RI (Avg Z = 3 m)

Surface Phytoplankton Lower West Passage Chl-a

Surface DIN

Bottom O2

Bottom O2 with Forced Maximum Chlorophyll a original run max chl

* Need to accurately model Annual Primary Production both states and rates Rate Processes In the absence of flux measurements  model MERL fcn of T, Chl, NPP Annual Primary Production g C m-2 y-1 Observed: 281 – 326 Modeled: 306

System-Level Validation: Nutrient Reduction Scenarios Keller (1988) Nixon et al. (2001) Nixon et al. (1996)

Empirical-Mechanistic Empirical Models Complex, Mechanistic Systems Models A Simplified, Hybrid Empirical-Mechanistic Systems Model Generality Precision R. Levins (1966, 1968) Realism Multiple, parallel modeling approaches, e.g.: Latour, Brush & Bonzek (2003) Scavia et al. (2003) Borsuk et al. (2002, 2004)

Models for Hypoxia Applied in Narragansett Bay Oviatt et al. Models for Hypoxia Applied in Narragansett Bay NOAA Coastal Hypoxia Research Program Because this is certainly one of the more challenging topics I’ve had to talk about, I’ve sketched roadmap to help us all navigate these tricky waters.

Full 3D resolution in ROMS: Because this is certainly one of the more challenging topics I’ve had to talk about, I’ve sketched roadmap to help us all navigate these tricky waters.

Nutrient Reduction Scenarios Bottom O2, mg/L 0% watershed N,P 0% Narr. Bay N,P 0% Narr. Bay N,P & saturating O2

LOWER NARRAGANSETT BAY PROVIDENCE RIVER

Scope for Improvement: Pre-Colonial Inputs Bottom O2 Nixon (1997) Estuaries 20(2)

Effect of Macroalgal Decomposition Bottom O2 Bottom O2

Effect of Macroalgal Decomposition

Stochastic Simulation Kremer (1983) Bottom O2

Dr. Brush’s wardrobe provided by: Acknowledgements James N. Kremer Scott W. Nixon John Brawley Nicole Goebel Jamie Vaudrey Dr. Brush’s wardrobe provided by: Bay St. Louis Kmart