Department of Physical and Environmental Sciences, University of Toronto, Toronto, Ontario, M1C 1A4, Canada.
Department of Physical and Environmental Sciences, University of Toronto, Toronto, Ontario, M1C 1A4, Canada; Ontario Ministry of Environment, Conservation and Parks, Toronto, Ontario, M9P 3V6, Canada.
Environ Pollut. 2018 Dec;243(Pt A):777-789. doi: 10.1016/j.envpol.2018.07.070. Epub 2018 Jul 23.
We examine the spatio-temporal trends of mercury, a well-known global legacy contaminant, in eleven fish species across all of the Canadian Great Lakes. These particular fish species are selected based on their ecological, commercial, and recreational importance to the biodiversity and fishing industry of the Great Lakes. We present a two-pronged Bayesian methodological framework to rigorously assess mercury temporal trends across multiple fish species and locations. In the first part of our analysis, we develop dynamic linear models to delineate the total mercury levels and rates of change, while explicitly accounting for the covariance between fish length and mercury levels in fish tissues. We then use hierarchical modelling to evaluate the spatial variability of mercury contamination between nearshore and offshore locations, as well as to examine the hypothesis that invasive species have induced distinct shifts on fish mercury contamination trends. Our analysis suggests that the general pattern across the Great Lakes was that the elevated mercury concentrations during the 1970s had been subjected to a declining trend throughout the late 1980s/early 1990s, followed by a gradual stabilization after the late 1990s/early 2000s. The declining trend was more pronounced with top fish predators, whereas benthivorous fish species mainly underwent wax-and-wane cycles with a weaker evidence of a long-term declining trend. Historically contaminated regions, designated as Areas of Concern, and bays receiving riverine inputs are still characterized by mercury concentrations that can lead to consumption restrictions. Lake Erie displayed the lowest mercury levels across all the fish species examined. However, several species of commercial importance showed a reversing (increasing) trend in the 2000s, although their current levels do not pose any major concerns for consumption advisories. These recent trend reversals can be linked with systematic shifts in energy trophodynamics along with the food web alterations induced from the introduction of non-native species, and the potentially significant fluxes from the atmosphere.
我们研究了汞（一种众所周知的全球性遗留污染物）在加拿大五大湖中所有 11 种鱼类中的时空趋势。这些特定的鱼类物种是根据它们对大湖生物多样性和渔业的生态、商业和娱乐重要性选择的。我们提出了一种双管齐下的贝叶斯方法框架，以严格评估多种鱼类和地点的汞时间趋势。在我们分析的第一部分，我们开发了动态线性模型来描绘总汞水平和变化率，同时明确考虑了鱼类长度和鱼类组织中汞水平之间的协方差。然后，我们使用分层模型来评估近岸和远岸地点之间的汞污染空间变异性，并检验入侵物种是否导致鱼类汞污染趋势发生明显变化的假设。我们的分析表明，五大湖的总体模式是，20 世纪 70 年代升高的汞浓度在整个 80 年代末/90 年代初呈下降趋势，随后在 90 年代末/21 世纪初逐渐稳定。在顶级鱼类捕食者中，下降趋势更为明显，而底栖鱼类主要经历了波动周期，长期下降趋势的证据较弱。历史上受污染的地区，被指定为关注区域，以及接收河流输入的海湾，仍然以可能导致消费限制的汞浓度为特征。在所有检查的鱼类中，伊利湖的汞含量最低。然而，几种具有商业重要性的物种在 21 世纪出现了逆转（增加）趋势，尽管它们目前的水平不会对消费建议构成任何重大担忧。这些最近的趋势逆转可能与沿能量营养级的系统变化以及由引入非本地物种和潜在的大量大气通量引起的食物网变化有关。
