Investigating the Response of a Density Field to Variable Forcing Conditions in a River-Dominated, Microtidal Estuary, Mobile Bay, AL.

Long-term time series from six water quality monitoring stations throughout Mobile Bay, AL, were used to investigate the spatial and temporal variability in the density field in response to a range of forcing conditions. Near-bottom density was measured at 3 stations along the main axis of the estuary and used to calculate horizontal density gradients in response to river flow. The observed longitudinal gradients were strongest during periods of low discharge in the summer and weaker gradients were associated with periods of high river discharge during late winter and early spring. A linear decrease in the horizontal density gradients with increasing discharge was observed in Mobile Bay. This is a different response than those observed in partial mixed meso-tidal systems (e.g. Narragansett Bay, Delaware Bay), where the density gradients follow a power law dependence with the horizontal density gradient increasing with increasing river discharge. Additional analyses on the response of the density field under varying wind and tidal ranges are currently underway. The importance of these forcing conditions on the density field has significant implications on the structure and strength of the circulation and associated water quality within estuarine systems.