Intense variability of dissolved oxygen and temperature in the internal swash zone of Hamilton Harbour, Lake Ontario

The thermocline of large, stratified lakes is constantly sloshing along the sloping bed, creating a spatially variable internal swash zone. Temperature and dissolved oxygen vary rapidly here, potentially impacting fish habitat on timescales hours. Large spatial differences in time-dependent variance temperature around Hamilton Harbour, Lake Ontario, Canada, were partly controlled by basin shape bathymetry. temporal variability was nearly twice as large at sites mildly sloping, narrow, upwind end relative to those similar depth steeper, broad, downwind end. Because oxycline coincident, same physical mechanisms resulted also great mild slope compared steeper slope. Frequent hypoxic events occurred throughout zone, drastically reducing availability for anoxia-intolerant species. In dynamic littoral weekly measurements would overlook acute oxygen. Here, we demonstrate that field observations 3-dimensional (3D) hydrodynamic modelling can predict how morphometry affects seiche dynamics zones.