Investigating Lateral Salinity Variability
at a Geomorphic Transition Zone,
Mobile Bay, Alabama.

Abstract

Bathymetry modifications, particularly shipping channels, are causing alterations in estuarine circulation and salinity intrusion into estuarine systems. This study sought to investigate the lateral salinity variability at a geomorphic transition zone in Mobile Bay, Alabama. Mobile Bay serves as an excellent location to investigate these issues as the narrow and deep shipping channel alters the relatively shallow, river dominated estuary and ultimately is suspected to be a conduit for salt intrusion to the head of Mobile Bay.

Two locations at the head of Mobile Bay, Battleship Park (BSP) located closer to the shipping channel, and Meaher Park (MP) located further from the shipping channel, were investigated over a 35-month observational period. Daily average time series at BSP and MP displayed seasonal salinity variability, with higher variability at the site closest to the shipping channel (BSP). River discharge appeared to be the primary driver of salinity variation at both locations, controlling the seasonal variation. Dry season salinities showed the strongest lateral variability between sites and differing drivers of intraseasonal variability. At the BSP site, the tropic-equatorial tidal oscillations modulated salinities and served as a first order driven intraseasonal variability. By contrast, the MP site showed no impacts associated with this fort-nightly cycle.  The ship channel appeared to be the main conduit for salt intrusion to the head of the Bay with the upper portions of the water column in the shipping channel demonstrating the largest changes in salinity across the wet and dry seasons. These findings improved understanding of the complexity of salinity dynamics in relation to bathymetry modifications. 

For more information: cloxford@eckerd.edu

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