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

本行动资助NSF 2019年度生物学博士后研究奖学金，利用生物馆藏进行研究。该奖学金支持研究和培训将以创新的方式利用生物收集的研究员。这名研究员将研究柬埔寨湄公河流域新形成的水电站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，而甲烷通常被计入水电。如果这些甲烷产生的碳在水库建成后也支持食物链顶端的鱼类，那么这些水库可以说提高了河流的生产力、渔业和经济繁荣。这名研究员将分析从湄公河（塞桑河）的一条支流上采集的鱼组织样本中的碳，这些样本是在该支流被修建大坝改变之前和之后采集的。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如何变化是很重要的。该研究员还将在华盛顿的斯内克河（Snake River）重复这项研究，以与老化的水力发电系统进行比较。先前的研究表明，湖泊沉积物中的大部分微生物生产可能是厌氧的，如甲烷生成。然而，对水生生态系统内净生态系统产量（NEP）的估计忽略了甲烷生成或化学自养初级生产。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碳-13中的一种中已经高度枯竭。这种耗竭可以作为一种有用的示踪剂，作为水生食物网的碳源甲烷。在具有动态水位和陡峭的氧和氧化还原梯度的水库洪泛平原上，这些甲烷可能被称为甲烷氧化菌的微生物群落成员氧化。由于有氧氧化不影响碳比率，甲烷生成的同位素特征在从甲烷养生物转移到更高营养水平的浮游动物和鱼类时是保守的。该研究员将对来自柬埔寨农业部、史密森学会和哈佛大学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河水坝上游的光合作用和耦合甲烷生产和氧化的原位速率，以a)确定水库食物网基础初级生产的地理变异性，b)更准确地解释NEP估算中的氧化过程。所有研究和由此产生的出版物将包括柬埔寨人，在新一代中建立科学专业知识。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.