Fine sediment dynamics in Quesnel Lake: the regulation of contaminant and nutrient transfers from the Mt Polley mine spill

2014年8月，加拿大最大的矿难发生在不列颠哥伦比亚省可能附近的波利铜金矿。尾矿库壁决口，释放出25 Mm3的尾矿、废水和建筑材料。在进入奎斯奈尔湖西部盆地之前，沿着9公里的河段发生了进一步的植被和地表物质冲刷。与尾矿库相邻的一个较小的湖泊波利湖（Polley Lake）也被注入了尾矿，但第一年研究人员仍禁止进入。本研究旨在评估奎斯奈尔湖和波利湖细沉积物过程对污染物（金属/类金属）和磷(P)动态的调节及其对食物网的中期影响。2016年沿着包含尾矿库的湖泊样带和更远的地方进行的岩心采样项目的观测表明，在天然沉积物或尾矿库材料之上，有一层几毫米至数十厘米厚的絮凝表面物质未固结。实验发现，这种物质具有很强的流动性，因此很可能在一年中的不同时间被重新引入水柱，可能是在捕集（风混合）事件和秋冬环流期间。这种再悬浮沉积物的质量将对湖泊的功能产生影响，因为它含有大量的磷（~5% wt）和金属——这两种物质都可能对过量的水生生物造成问题。这些污染物的生物利用度将取决于沉积物-水界面的化学和侵蚀条件。这两个变量的季节性变化将调节沉积物相关营养物质是否可用于湖中初级生产，以及沉积物相关污染物是否被滤食性无脊椎动物（湖中运动鱼类和鲑科鱼类的主要食物来源）所吸收。这个提议的项目的独特之处在于对提供全湖施肥的灾难性事件的评估，但同时伴随着高负荷的金属和类金属。虽然尾矿废料中引入的磷可能作为肥料增加了该湖泊的初级产量，但这些生物也可能含有金属，从而扩大了它们在食物网中的影响。由于波利山泄漏的大多数金属已被确定为与沉积物有关，这些未固结的絮凝沉积物在沉积物-水界面的命运是一个问题。为了解决这些问题，Petticrew和她的HQP将在未来五年内开展一系列现场和实验室项目。该项目还将提供有关大中型湖泊生态系统对大规模干扰（如与矿难有关的干扰）和原始流域其他类似事件的恢复能力的宝贵信息，从而有助于保护加拿大的水生生态系统。

In August 2014, Canada's largest mining disaster occurred at the Mt Polley copper-gold mine, near Likely, British Columbia. The tailings pond wall breached, releasing 25 Mm3 of tailings, wastewater and construction materials. Further scouring of vegetation and surface materials occurred along a 9 km reach before entering the west basin of Quesnel Lake. Polley Lake, a smaller lake adjacent to the tailings pond was also dosed with tailings but remained off limits to researchers for the first year. This proposal aims to assess fine sediment processes regulating contaminant (metals/metalloids) and phosphorus (P) dynamics and their medium-term effects on foodwebs in both Quesnel and Polley Lakes. Observations from a 2016 core sampling program along a lake transect incorporating the tailings deposit and further afield indicated a layer, several millimeters to tens of centimeters thick, of flocculated surface material that remained unconsolidated above either natural sediments or tailings material. This material was experimentally found to be very mobile and therefore likely to be reintroduced into the water column at various times of the year, potentially during seiching (wind-mixing) events and fall and winter turnovers. The quality of this resuspended sediment will have an impact on the lake functioning in that it contains a large mass of phosphorus (~5% wt) as well as metals - both of which can be problematic for aquatic organisms in excess. The bioavailability of these contaminants will be dependent upon the chemical and erosive conditions at the sediment-water interface. Seasonal changes in both of these variables will regulate if sediment-associated nutrients are available for in-lake primary production and if sediment-associated contaminants are incorporated by filter feeding invertebrates, which are a main food source for the sport and salmonid fishes in the lake. The uniqueness of this proposed project is the evaluation of a catastrophic event providing full-lake fertilization, but delivered in concert with high loads of metal and metalloids. While the phosphorus introduced in the tailings waste may act as a fertilizer increasing primary production in this lake, these organisms may also incorporate metals, thereby magnifying their impact within the foodweb. As most of the metals from the Mt Polley spill have been identified as being sediment-associated, the fate of these unconsolidated flocculated sediments at the sediment-water interface is in question. A series of field and laboratory projects will be undertaken by Petticrew and her HQP over the next five years to address these issues. This project will also provide valuable information on the resiliency of large and medium-sized lake ecosystems to massive disturbances such as those associated with mining disasters, and other similar events in pristine watersheds, thereby helping to protect Canada's aquatic ecosystems.