The hydrodynamics of the upper Neuse River Estuary, North Carolina and their influence on dissolved oxygen distribution

Four years of hydrographic data along the main channel of the Neuse River Estuary (NRE) were used to determine mean distributions of salinity, temperature and dissolved oxygen (DO). These distributions varied seasonally and direct relationships between salinity, salinity stratification and bottom DO concentrations were determined. A seasonal DO budget confirms that vertical mixing and biological demand primarily control DO concentrations.; On shorter timescales, lateral variability was noted through the deployment of two bottom-mounted Acoustic Doppler Current Profilers (ADCPs), two bottom-mounted Conductivity-Temperature and Depth (CTD) sensors, and two autonomous vertically profiling CTD/DO systems. The profiling systems were novel instrumentation developed specifically for this application to achieve high vertical and temporal resolution of salinity and DO data. Additionally, several data collection periods using a boom-mounted ADCP and a winch-driven CTD were used to increase the spatial coverage of the upper NRE. Data analysis techniques such as spectral and wavelet analysis were used to identify several physical phenomena, including barotropic and baroclinic seiches, lateral upwelling of high salinity/low DO water and wind-driven, low frequency lateral salinity variability.; The three-dimensional finite difference model, Environmental Fluid Dynamics Code (EFDC), was calibrated for the NRE and was used to simulate flow and transport conditions during the summers of 1999 and 2000. Model data were independently validated with observed data and were statistically shown to adequately reproduce conditions in the NRE. Experimentation with boundary conditions documented the sensitive nature of the upper NRE to both freshwater discharge and wind.; A linear, two layer theoretical model was applied to the upper NRE to quantify the vertical variability in the pycnocline caused by across channel wind. Wind speeds greater than 10 m s−1 can force the pycnocline to surface of the windward shore. This motion also causes the low DO water below the pycnocline into the upper regions of the water column.; Previous studies of the NRE had noted lateral variability, but had never tried to quantify this variability or to determine the cause. The development of novel profiling instruments provided data that linked physical phenomena to biological events and provided insight into the mechanisms behind a fish kill.