Citation:

Jarvis, B., Jim Hagy, J. Lehrter, AND M. Murrell. Modeling Diel Oxygen Dynamics and Ecosystem Metabolism in a Shallow, Eutrophic Estuary. Gulf Estuarine Research Society (GERS) Fall 2016 Meeting, Pensacola Beach, FL, November 03 - 05, 2016.

Impact/Purpose:

This project is part of SSWR 4.02B, nutrient response and recovery. This work includes field and modeling efforts performed un the subtasks ADOS and NRDA, targeting dissolved oxygen condition in Weeks Bay, Alabama and anticipated improvement with nutrient reduction implementation.

Description:

Weeks Bay is a shallow eutrophic estuary that exhibits frequent summertime diel-cycling hypoxia and periods of dissolved oxygen (DO) oversaturation during the day. Diel DO dynamics in shallow estuaries like Weeks Bay are complex, and may be influenced by wind forcing, vertical and horizontal mixing, variation in freshwater inflow, cloud cover, and temperature. This study utilized continuous DO monitoring and 3-D hydrodynamic and water quality models to examine physical and biological controls on DO dynamics in Weeks Bay. We used coupled Environmental Fluid Dynamics Code (EFDC) and Water Quality Analysis Simulation Program (WASP) models to simulate hydrodynamics and water quality for May-Oct 2015. Observed vertical DO gradients varied on a diel basis, with larger amplitude variations at depth relative to the surface, underscoring the importance of benthic production and respiration as a driver of ecosystem metabolism in Weeks Bay. Hydrodynamic and water quality models simulated seasonal and event-driven dynamics, but struggled to resolve the amplitude of daily DO fluctuations, particularly in bottom waters. These results emphasize the need for models to accurately resolve the partitioning of system metabolism between the benthos and water column to improve model predictions of dynamic ecosystem processes.

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