PHYSICAL-MECHANISMS LEADING TO HYPOXIA AND ANOXIA IN WESTERN LONG-ISLAND SOUND

Increased thermal and haline stratification during the summer exacerba te low dissolved oxygen (DO) concentrations in western Long Island Sou nd (WLIS). Occasionally, as in the summer of 1987, DO is depleted from the water column. In this study, the interaction of thermal and halin e stratification and their influence on vertical mixing and DO concent rations in WLIS is elucidated. Diagnostic calculations involving a spe cified longitudinal density gradient are performed using a simple one dimensional (vertical) mixed layer model. Numerical experiments are ca rried out under typical hydrographic, hydrodynamic, and atmospheric su mmer conditions in WLIS. Results illustrate intratidal and fortnightly variations of the vertical structure of density and DO subject to bio logical consumption. Modifications to the summer longitudinal density gradient in WLIS produce important changes to its hydrodynamic field a nd its water quality. Therefore, proposed water withdrawal from the Hu dson River should be considered carefully.