Identifying and evaluating the main drivers of change in freshwater ecosystems

湖泊生态系统正陷入困境，受到全球变暖和更直接的人类活动的威胁。气候变化正在通过改变水柱的温度梯度、营养循环以及由于径流增加而增加营养物质和沉积物输入来影响湖泊。近年来，全球变暖对高纬度淡水生态系统的影响已经得到确认和研究，但对气候变化对热带湖泊的影响知之甚少，热带湖泊可能正在发生更加速的变暖，人为影响正在迅速蔓延。我的研究计划将通过研究沿海拔梯度分布的热带湖泊以及不同类型和程度的人为影响来弥合这一差距。热带的海拔梯度为研究气候变化对水生生态系统的影响提供了一个独特的机会，因为气候应激源在热带地区更加突出，上坡的变化比高纬度地区更加反差。安第斯山脉的大多数城市人口的饮用水来自安第斯高地湖泊，因此了解这种资源在发展中国家的命运至关重要。这项研究计划将利用以硅藻为基础的古生态和古湖泊重建，辅以颜料、粒度和稳定同位素，以了解全新世和人类世热带湖泊的演化和轨迹，并重建热带全新世的气候变异性。硅藻是湖泊变化的良好指示器，在大多数情况下反映了外部应激源的影响以及与自然内部过程的相互作用。通过这项研究，我将有助于回答最重要的问题：淡水生态系统如何因气候变化和人为影响而改变？该项目的结果将不仅适用于热带的大范围生态系统，也适用于加拿大的北方森林，那里的北方森林已经从纬度向南北移动，类似于热带森林的垂直迁移，并且严重的人类影响正在影响湖泊，削弱它们应对气候变化的能力。我的计划将有助于理解对加拿大气候有重大影响的气候现象的行为，如太平洋年代际涛动和厄尔尼诺南方涛动，以及关于热带全新世气候变异性的学术辩论。*该计划的目标是揭开热带湖泊沿海拔和植被梯度以及不同程度的人为影响的长期和短期历史，以便：(1)评估生态系统对气候变化和人类影响的脆弱性，以及(2)重建热带全新世的气候变异性。**

******Lake ecosystems are in trouble, threatened by global warming and more immediate anthropogenic activities. Climate change is affecting lakes by altering the thermal gradient of the water column, nutrient cycling, and by increasing greater nutrient and sediment inputs as a result of increasing runoff. The effect of global warming on higher latitude freshwater ecosystems has been identified and studied over recent years but very little is known about the effects of climate change on tropical lakes, where more accelerated warming may be occurring and where anthropogenic impact is spreading rapidly. My research program will bridge this gap by studying tropical lakes distributed along altitudinal gradients and under different types and degrees of anthropogenic influence. An altitudinal gradient in the tropics offers a unique opportunity to study the effects of climate change in aquatic ecosystems, since climatic stressors are more accentuated in the tropics and changes upslope are more contrasting than in higher latitudes. Most of the urban population in the Andes derive their drinking water from high Andean lakes, thus it is of utmost importance to understand the fate of this resource in developing countries. This research program will use paleoecological and paleolimnological reconstructions based on diatoms, complemented by pigments, grain size and stable isotopes, to understand the evolution and trajectories of tropical lakes in the Holocene and Anthropocene, and to reconstruct Holocene climate variability in the tropics. Diatoms are excellent indicators of limnological change, which in most cases reflect the effect of external stressors and interactions with natural internal processes.With this study I will contribute to answer the overarching question: How have freshwater ecosystems changed in response to climate change and anthropogenic impact? Results from this program will be applicable to a wide range of ecosystems not only in the tropics, but also in Canada where boreal forests have shifted latitudinally north and south, similarly to the altitudinal migration of the tropical forest, and where severe human impact is affecting lakes and diminishing their capability to respond to climate change. My program will contribute substantively to the understanding of the behaviour of climatic phenomena of great impact in Canadian climate, such as the Pacific Decadal Oscillation and the El Nio Southern Oscillation, and to scholarly debates regarding Holocene climate variability in the tropics. ***The objectives of this program are to unravel the long and short-term history of tropical lakes along an altitudinal and vegetation gradient and with varying degrees of anthropogenic impacts, in order to: (1) evaluate the vulnerability of ecosystems to climate change and human impact, and (2) to reconstruct climate variability for the Holocene of the tropics. **