ABSTRACT

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

摘要

大型，分层湖泊的温跃层沿倾斜的床层不断晃动，形成一个空间变化的内部斜流带。温度和溶解氧变化很快，可能在数小时的时间内影响鱼类的栖息地。加拿大安大略湖汉密尔顿港附近温度随时间的变化具有较大的空间差异，部分受盆地形状和测深法控制。与盆地较陡峭，宽阔，顺风端的深度相似的地区相比，沿盆地中度倾斜，狭窄，上风端的站点的时间变异性几乎是其两倍。因为温跃层和奥西兰是重合的，所以相同的物理机制导致在温和的坡度处的溶解氧变化也比在陡峭的坡度处大两倍。整个内部冲刷区都发生了频繁的缺氧事件，大大降低了缺氧耐性物种的鱼类栖息地。在动态沿海区域，每周测量将忽略温度和溶解氧的急性时间变化。在这里，我们证明了野外观测和3维（3D）流体动力学建模可以预测盆地形态如何影响内部斜切动力学和内部斜流带的空间变异性。