Physical mechanisms leading to hypoxia and anoxia in Western Long Island Sound

Abstract

Increased thermal and haline stratification during the summer exacerbate low dissolved oxygen (DO) concentrations in western Long Island Sound (WLIS). Occasionally, as in the summer of 1987, DO is depleted from the water column. In this study, the interaction of thermal and haline stratification and their influence on vertical mixing and DO concentrations in WLIS is elucidated. Diagnostic calculations involving a specified longitudinal density gradient are performed using a simple one dimensional (vertical) mixed layer model. Numerical experiments are carried out under typical hydrographic, hydrodynamic, and atmospheric summer conditions in WLIS. Results illustrate intratidal and fortnightly variations of the vertical structure of density and DO subject to biological consumption. Modifications to the summer longitudinal density gradient in WLIS produce important changes to its hydrodynamic field and its water quality. Therefore, proposed water withdrawal from the Hudson River should be considered carefully.