Lake Ontario water levels were the highest in recorded history in 2017 and 2019, resulting in significant impacts to shoreline properties and observable (but not previously quantified) changes in coastal wetland vegetation. In this study, we assessed differences in coverage of five plant community guilds (submerged aquatic vegetation, Typha, meadow marsh, shrub, and upland) along the shoreline elevation gradient from 12 Lake Ontario coastal wetlands surveyed from 2009 to 2019. This time period included a span of relatively stable water levels (2009–2016), followed by the two high-water years. In general, we found that extreme high water levels led to a decrease in vegetation coverage, most notably at the lower extent of the elevation ranges for the meadow marsh, shrub, and upland vegetation guilds. We also found a modest increase in Typha coverage at the upper extent of its elevation range in 2019, indicating that Typha advanced into the meadow marsh zone during the study period. These findings can be used to calibrate and validate predictive models that inform adaptive management of the new outflow regulation plan for Lake Ontario and can aid in modelling the dynamics of wetland vegetation in relation to predicted changes in Great Lakes water levels due to climate change.

安大略湖的水位是2017年和2019年有记录以来的最高水平，从而对海岸线特性产生了重大影响，并导致沿海湿地植被的可观察到的（但未量化）变化。在这项研究中，我们评估了五个植物群落行会（淹没的水生植被，香蒲）的覆盖范围差异，草甸沼泽，灌木和高地）沿安大略省12个沿海湿地的海岸线海拔梯度（从2009年到2019年进行了调查）。这段时间包括相对稳定的水位范围（2009-2016年），其次是两次高水位年份。总的来说，我们发现极高的水位导致植被覆盖率下降，最明显的是草甸沼泽，灌木和高地植被行会的海拔范围较低。我们还发现，在2019年高海拔范围内，香蒲覆盖率有所增加，这表明香蒲在研究期间进入草地沼泽地带。这些发现可用于校准和验证预测模型，这些模型可为适应性管理安大略湖新的出水调节计划提供信息，并可帮助对与大湖水位因气候变化而预测的变化有关的湿地植被动力学进行建模。