Alberta Environment and Parks, Edmonton/Calgary, Alberta, Canada; Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
Alberta Environment and Parks, Edmonton/Calgary, Alberta, Canada; Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.
Water Res. 2020 Sep 15;183:116071. doi: 10.1016/j.watres.2020.116071. Epub 2020 Jun 20.
Wildfires can have severe and lasting impacts on the water quality of aquatic ecosystems. However, our understanding of these impacts is founded primarily from studies of small watersheds with well-connected runoff regimes. Despite the predominance of large, low-relief rivers across the fire-prone Boreal forest, it is unclear to what extent and duration wildfire-related material (e.g., ash) can be observed within these systems that typically buffer upstream disturbance signals. Following the devastating 2016 Fort McMurray wildfire in western Canada, we initiated a multi-faceted water quality monitoring program that suggested brief (hours to days) wildfire signatures could be detected in several large river systems, particularly following rainfall events greater than 10 mm. Continuous monitoring of flow and water quality showed distinct, precipitation-associated signatures of ash transport in rivers draining expansive (800-100,000 km) and partially-burned (<1-22 percent burned) watersheds, which were not evident in nearby unburned regions. Yields of suspended sediment, nutrients (nitrogen, phosphorus) and metals (lead, others) from impacted rivers were 1.2-10 times greater than from those draining unburned regions. Post-fire suspended sediment concentrations in impacted rivers were often larger than pre-fire 95% prediction intervals based on several years of water sampling. These multiple lines of evidence indicate that low-relief landscapes can mobilize wildfire-related material to rivers similarly, though less-intensively and over shorter durations, than headwater regions. We propose that uneven mixing of heavily-impacted tributaries with high-order rivers may partially explain detection of wildfire signals in these large systems that may impact downstream water users.
野火会对水生生态系统的水质造成严重且持久的影响。然而，我们对这些影响的了解主要基于对具有良好连通性径流水系的小流域的研究。尽管在易发生火灾的北方森林中，大而低地势的河流占主导地位，但尚不清楚在这些系统中，野火相关物质（如灰烬）在多大程度和多长时间内可以被观察到，因为这些系统通常缓冲上游干扰信号。在加拿大西部 2016 年麦克默里堡大火毁灭性发生后，我们启动了一个多方面的水质监测计划，该计划表明，在几个大河流系统中，特别是在降雨量超过 10 毫米的降雨事件之后，可以检测到短暂的（数小时到数天）野火特征。对流量和水质的连续监测显示，在排水面积广阔（800-100000 平方公里）和部分燃烧（<1-22%燃烧）流域的河流中，存在与降水有关的明显的灰烬运输特征，而在附近未燃烧地区则没有这种特征。受影响河流的悬浮泥沙、养分（氮、磷）和金属（铅等）的产量比未燃烧地区排水的河流高出 1.2-10 倍。受影响河流的洪水后悬浮泥沙浓度通常大于根据几年水质采样得出的洪水前 95%预测区间。这些多重证据表明，低地势景观可以将野火相关物质类似地输送到河流中，尽管输送的强度较低、持续时间较短。我们提出，受严重影响的支流与高等级河流的不均匀混合可能部分解释了这些大型系统中检测到的野火信号，这些信号可能会影响下游用水者。
