Collections > UNC Chapel Hill Undergraduate Honors Theses Collection > Modeling oxygen dynamics and predicting hypoxic conditions in the Neuse River Estuary, North Carolina
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Modeling oxygen dynamics and predicting hypoxic conditions in the Neuse River Estuary, North Carolina

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  • | Filesize: 5.8 MB
  • Date Deposited: 2018-12-05
  • Date Created: 2018-12-01

Path:  Collections > UNC Chapel Hill Undergraduate Honors Theses Collection > Modeling oxygen dynamics and predicting hypoxic conditions in the Neuse River Estuary, North Carolina

Dissolved oxygen (DO) is essential for marine organisms to maintain basic metabolic processes. Conditions of low DO concentrations, hypoxia, can stress and kill organisms. Hypoxia often occurs in bottom water in estuaries as a result of increased DO consumption and water column density stratification. Previous DO modeling studies have taken into account physical and biogeochemical processes in forecasting hypoxic events. However, these studies have typically focused on variations over timescales of weeks to months. In many estuaries, oxygen levels can vary over much shorter timescales due to changes in mixing associated with tides or wind. We analyzed temperature, salinity, and DO profiles measured every 30 minutes in the Neuse River Estuary (NRE) of North Carolina from June to July of 2016 to understand the factors that drive hypoxia in a shallow, intermittently mixed estuary. Bottom DO varied between well-oxygenated and hypoxic over hours to days. Bottom DO concentration correlated strongly with salinity differences between the top and bottom water. We assessed the ability of a two-layer box model, developed to predict seasonal variations in DO in the same system, to predict DO variations on the order of hours to days. The model was unable to capture the DO variations in both the top and bottom water layers that were observed as the water column mixed and as it stratified. Sensitivity analyses suggested that changes in bottom DO as the water column stratified were not well represented by a consumption term with a constant rate coefficient, and the parameter values for the term that describes vertical mixing are not reasonable for this system over these timescales. This simple model could be improved and used to forecast hypoxic events in the NRE, which could help inform nutrient management policies and the management of fisheries and recreation within the estuary and other similar ecosystems.

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