Hlevca Bogdan, Howell Edward Todd, Valipour Reza, Madani Mohammad
Ministry of the Environment, Conservation and Parks, Toronto, Canada.
Environment and Climate Change Canada, Burlington, Canada.
PLoS One. 2025 Jan 8;20(1):e0298702. doi: 10.1371/journal.pone.0298702. eCollection 2025.
The water quality and resources of Lake Ontario's nearshore ecosystem undergo heightened stress, particularly along the northwest shoreline. Hydrodynamic processes linking the distinct nearshore and offshore trophic structures play a crucial role in transporting nutrient-loaded water along and across the shore. Despite the pivotal connection between algae growth and the development of nuisance proportions, the scales over which these processes operate remain poorly understood. This study delves into the exchange dynamics between nearshore and offshore areas of Lake Ontario throughout 2018, employing a validated three-dimensional numerical model. A virtual passive age tracer is utilized to discern horizontal mixing time scales between nearshore regions of the lake (water depth < 30 m) and offshore locations. The dispersal pattern, as revealed by a passive tracer released from eight points around the model lake's perimeter, indicates more extensive diffusion in late summer when lake-wide stratification is established, compared to the mixed period. Coastal upwelling events, leading to intrusions of hypolimnetic waters, significantly contribute to net cross-shore transport, with the most pronounced effects observed in May and June when the offshore thermocline is shallow. In the northern part of the lake, dispersal predominantly occurs alongshore, mirroring the prevailing cyclonic (counterclockwise) coastal circulation during the stratified season. This pattern is a consequence of a 45% increase in upwelling events compared to three decades ago. In the northwestern and southern sectors of the lake, elevated cross-shore mixing is attributed to geomorphology-induced cross-basin currents.
安大略湖近岸生态系统的水质和资源面临着更大的压力，尤其是在西北海岸线一带。连接不同近岸和离岸营养结构的水动力过程在沿海岸和跨岸输送富含营养物质的水体方面起着关键作用。尽管藻类生长与滋扰性比例的发展之间存在关键联系，但这些过程的作用尺度仍知之甚少。本研究利用经过验证的三维数值模型，深入探讨了2018年全年安大略湖近岸和离岸区域之间的交换动态。使用虚拟被动年龄示踪剂来识别湖泊近岸区域（水深<30米）与离岸位置之间的水平混合时间尺度。从模型湖周边八个点释放的被动示踪剂显示的扩散模式表明，与混合期相比，在夏末全湖建立分层时扩散更为广泛。导致次表层水入侵的沿岸上升流事件对净跨岸输运有显著贡献，在5月和6月离岸温跃层较浅时观察到的影响最为明显。在湖的北部，扩散主要沿岸边发生，这与分层季节盛行的气旋式（逆时针）沿岸环流一致。这种模式是与三十年前相比上升流事件增加45%的结果。在湖的西北部和南部区域，跨岸混合加剧归因于地貌诱导的跨盆地水流。
