NSF Postdoctoral Fellowship in Biology FY 2019: Hydropower May Enhance Riverine Productivity Through Chemoautotrophic Pathways

这项行动资助了2019财年NSF生物学博士后研究奖学金，使用生物收集的研究。该研究金支持研究员的研究和培训，以创新的方式利用生物收藏。该研究员将研究柬埔寨湄公河流域新形成的水电水库如何将甲烷中的碳贡献给水生食物网。众所周知，水库是向大气排放温室气体甲烷的来源，而甲烷通常被视为水力发电的一部分。如果这些甲烷产生的碳在水库形成后也支持食物网顶端的鱼类，那么这些水库可以说是提高了河流的生产力，渔业和经济繁荣。该研究员将分析从湄公河支流（色桑河）上采集的鱼组织样本中的碳，在湄公河上修建大坝改变之前和之后。水电正在湄公河等大型热带河流上扩张，因此了解其生态影响可能会发生变化非常重要。 这位研究员还将在华盛顿的蛇河重复这项研究，以提供一个老化的水电系统的比较。以前的工作表明，湖泊沉积物中的大多数微生物生产可能是厌氧的，如甲烷生成。然而，在水生生态系统中的净生态系统生产力（NEP）的估计忽略了甲烷或化能自养初级生产力。相对于其他碳源，这里产生的甲烷在两种丰富的稳定碳同位素之一，碳-13中高度贫化。这种消耗作为一个有用的示踪甲烷作为碳源，以水生食物网。在具有动态水位和陡峭的氧气和氧化还原梯度的水库漫滩上，这种甲烷可能被称为甲烷氧化菌的微生物群落的成员氧化。由于有氧氧化不影响碳比，甲烷生成的同位素特征是保守的，因为它是从甲烷氧化菌转移到浮游动物和鱼类在更高的营养水平。该研究员将对来自柬埔寨农业部、史密森学会和哈佛比较动物学博物馆的历史鱼类组织样本进行质谱分析。 该研究员还将测量Sesan和Snake河大坝上游的光合作用和甲烷生产与氧化的原位速率，以a）确定水库食物网底部初级生产的地理变异性和B）更准确地说明NEP估计中的氧化过程。 所有的研究成果和出版物都将包括科学家，在新一代中建立科学专业知识。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

This action funds an NSF Postdoctoral Research Fellowship in Biology for FY 2019, Research Using Biological Collections. The fellowship supports research and training of the fellow that will utilize biological collections in innovative ways. The fellow will study how newly formed hydropower reservoirs in Cambodia's Mekong watershed contribute carbon from methane to aquatic food webs. Reservoirs are well known sources of the greenhouse gas methane to the atmosphere, which is usually counted against hydropower. If this methane produced carbon also supports fish at the top of the food webs after reservoirs are created, these reservoirs can be said to enhance river productivity, fishing, and economic prosperity. The fellow will analyze carbon in fish tissue samples gathered from a tributary of the Mekong (the Sesan River) before and after it was altered by having a dam built upon it. Hydropower is expanding on large tropical rivers like the Mekong, so it is important to understand how its ecological impacts may vary. The fellow will also replicate this study in Washington's Snake River to provide a comparison to an aging hydropower system.Previous work has shown that the majority of microbial production in lake sediments may be anaerobic, such as methanogenesis. Yet, estimates of Net Ecosystem Production (NEP) within aquatic ecosystems ignore methanogenesis or chemoautotrophic primary production. Methane produced here is highly depleted in one of two abundant stable carbon isotopes, carbon-13, relative to other carbon sources. This depletion serves as a useful tracer for methane as a carbon source to aquatic food webs. On reservoir floodplains with dynamic water levels and steep oxygen and redox gradients, this methane may be oxidized by members of the microbial community known as methanotrophs. Because aerobic oxidation does not affect carbon ratios, the isotopic signature of methanogenesis is conserved as it is transferred from methanotrophs to zooplankton and fish in higher trophic levels. The fellow will carry out mass spectrometry on historical fish tissue samples from the Cambodian Ministry of Agriculture, the Smithsonian Institution, and the Harvard Museum of Comparative Zoology. The fellow will also measure in-situ rates of photosynthesis and coupled methane production and oxidation upstream of both the Sesan and Snake River dams to a) determine geographic variability in primary production at the base of reservoir food webs and b) more accurately account for oxidative processes in estimates of NEP. All research and resulting publications will include Cambodians, building scientific expertise in a new generation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.