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着倾斜的河床不断晃动，形成了一个空间可变的内部冲刷带。这里的温度和溶解氧变化很快，可能会在数小时内影响鱼类栖息地。加拿大安大略湖汉密尔顿港周围温度随时间变化的巨大空间差异部分受盆地形状和水深测量的控制。相对于类似深度的陡峭、宽阔的顺风端，沿盆地轻度倾斜、狭窄、逆风端的站点的时间变化几乎是其两倍。由于温跃层和氧跃层重合，相同的物理机制导致缓坡处的溶解氧变化也是陡坡的两倍。整个内部冲刷区经常发生缺氧事件，大大减少了缺氧物种的鱼类栖息地。在动态沿海地区，每周测量会忽略温度和溶解氧的急性时间变化。在这里，我们证明了现场观察和 3 维 (3D) 流体动力学建模可以预测盆地形态测量如何影响内部冲刷区的内部塞切动力学和空间变异性。