Assessing interacting stressors in lakes

湖泊是加拿大最具代表性的景观之一，也是我们最敏感的环境变化哨兵。这些系统的压力源包括养殖富营养化、栖息地丧失、物种引入和气候变化。确定单个压力源对湖泊浮游生物群落的影响通常具有挑战性，因为压力源通常是组合出现的。先前的研究表明，相互作用的压力源可能包括从累加效应到更复杂的情况，在这些情况下，它们会增强（协同作用）或相互抑制（拮抗作用）。在这个建议中，我将结合空间和时间上的湖泊采样，实验中观和建模来创建一个对主要相互作用压力源的预期反应的景观。开发该模型的主要现场将是伊利湖西部。这个盆地可以经历蓝藻（主要是铜绿微囊藻）在主要流入河流附近的梯度开花，这些河流促进了开花，而盆地的其他部分则没有开花。与此同时，该流域每年都有重要的引进捕食者水蚤（Bythotrephes longimanus）的发展，其丰度和影响随季节和空间的变化而变化。主要浮游动物群体对蓝藻菌落的敏感性各不相同，专业捕食者（如轮虫）几乎没有受到影响，而其他动物，如主要食草动物水蚤，则受到强烈的负面影响。同样是这些浮游动物群体，它们对食虫的脆弱性也各不相同，轮虫不受影响，而水蚤则受到严重影响。有趣的是，伤害水蚤等食草动物种群的两种共同发生的压力源可能同时对轮虫产生中性或积极的影响（由于不敏感和竞争性释放）。这些反应的复杂性表明，定义相互作用的压力源的影响将是一个具有挑战性的问题。在本研究中，我们将结合蓝藻华和嗜水藻种群的发展，评估浮游动物群落组成和丰度的空间和季节变化，期望群落组成和丰度的变化能够反映对相互作用的压力源的敏感性。中环境实验将在微囊藻和大囊藻密度梯度下进行，并在实验室饲养一种关键的枝海动物（水蚤）和轮虫（角虫）的混合群落。建模练习将探索在没有压力源和有一个或两个压力源存在的情况下，这个混合社区之间相互作用的本质。最后，我们将使用内陆湖泊和五大湖的其他地区来验证我们的模型，在这些地区，巨藻和微囊藻同时大量繁殖。我们的项目将揭示相互作用的压力源的复杂性，预计共同发生的嗜水线虫和微囊藻华蔓延到加拿大更多的湖泊。

Lakes are among Canada's most defining landscapes and most our sensitive sentinels of environmental change. Stressors of these systems include cultural eutrophication, habitat loss, species introductions, and climate change. Identifying the impact of an individual stressor on a lake's plankton community is often challenging because stressors commonly occur in combination. Previous work identified that interacting stressors may encompass everything from additive effects to more complex situations in which they enhance (synergism) or damp one another (antagonistic effects). In this proposal I will use a combination of lake sampling over space and time, experimental mesocosms, and modeling to create a landscape of expected responses to major interacting stressors. The main field site for development of the model will be western Lake Erie. This basin can experience gradients in cyanobacteria (mainly Microcystis aeruginosa) blooms near major inflowing rivers that foster blooms while other sections of the basin are bloom-free. At the same time, the basin experiences annual development of a key introduced predator, the waterflea Bythotrephes longimanus, whose abundance and impact vary seasonally and spatially. Major zooplankton groups vary with respect to sensitivity to presence of cyanobacteria colonies, with specialist feeders (e.g. rotifers) little affected, while others, like the major herbivore Daphnia spp., are strongly and negatively impacted. These same zooplankton groups also vary with respect to vulnerability to ingestion by Bythotrephes, with rotifers not affected and Daphnia heavily impacted. Interestingly, then, the same two co-occurring stressors that harm populations of grazers like Daphnia could simultaneously either neutrally or positively affect rotifers (owing to insensitivity and competitive release). The complexity of these responses indicates that defining the impact of interacting stressors will be a challenging problem. In this proposal we will assess zooplankton community composition and abundance spatially and seasonally in conjunction with development of cyanobacteria blooms and Bythotrephes populations, with the expectation that shifts in community composition and abundance will reflect sensitivity to the interacting stressors. Mesocosm experiments will be conducted across a gradient of Microcystis and Bythotrephes densities with lab-reared mixed community of a key cladoceran (Daphnia) and rotifers (Keratella). Modeling exercises will explore the nature of the interactions between this mixed community in the absence of stressors, and with one or both stressors present. Finally, we will validate our models using inland lakes and other areas of the Great Lakes where both Bythotrephes populations and Microcystis blooms co-occur. Our projects will shed light on the complexity of interacting stressors that are expected as co-occurring Bythotrephes and Microcystis blooms spread to more lakes across Canada.