Exploring light-dependent manganese oxide formation in a meromictic metal-rich pond

金属锰广泛存在于环境中，与生物体的健康和功能密切相关。在某些环境中，在氧气存在的情况下，锰可以形成锰氧化物矿物。这些矿物具有极强的活性，它们在控制地球表面的营养物质、污染物和碳的命运方面发挥着重要作用。尽管它们对环境具有重要意义，但对天然氧化锰形成的控制仍然知之甚少；PI和其他人最近的发现提出了证据，表明存在光促进氧化锰形成的新途径。该项目的目标是确定在地表阳光照射的环境中控制氧化锰矿物形成的过程。研究小组将研究科德角当地的一个池塘，在那里已经发现了锰氧化物的形成并在光线存在的情况下持续存在。来自池塘的水将在不同的地点和深度收集，并在不同的环境和光照条件下在实验室进行反应，以确定允许形成锰氧化物的化学和生物途径。通过不同的光和环境条件形成的锰氧化物将被表征，以确定它们的形成途径和反应活性。这些发现将提高我们对地球和其他行星(如火星)上的锰循环和相关元素的理解。该项目还将有助于培养几名本科生和研究生。此外，与这项研究相关的推广工作将包括每年在当地一所高中进行讲座，以及指导高中科学博览会项目，这些项目将向学生介绍地球科学。最近的实验室和实地调查指出，光介导的反应是一些水体中被低估的锰循环的组成部分。此外，PI在当地一个富含金属的亚闪锌矿池塘(美国科德角Siders Pond)的初步数据表明，尽管可能发生了光还原过程，但光在表层水中锰氧化物的形成中发挥了关键作用。因此，在这里，PI建议对Siders池塘内的锰氧化和氧化锰形成的速率、产物和机制进行系统的野外和实验室调查。这项研究的总体目标是确定在该地点内允许光诱导形成锰氧化物的条件，这对于理解和预测地球上现在和过去光驱动的氧化锰的形成具有广泛的意义。指导本研究的目标是(1)量化Mn(II)和Mn(III)-L氧化以及Mn(III)-L和Mn氧化物还原在氧化还原跃层中的时空分布，(2)确定光跃层内Mn(II)氧化和Mn氧化物形成的潜在生物机制，(3)表征氧化锰的组成、结构和反应活性随深度和跨越氧化跃层的变化。这些目标将通过现场测量、实验室培养和微生物培养相结合来实现。来自池塘的水将在不同的地点和深度收集，并在不同的环境和光照条件下在实验室进行反应，以确定允许形成锰氧化物的化学和生物途径。通过不同的光和环境条件形成的锰氧化物将被表征，以确定它们的形成途径和反应活性。识别与光有关的氧化锰形成的潜在生物地球化学过程将改进现代生物地球化学模型和古记录解释。这些光介导的反应也可能有助于解释之前在地表阳光照射的水域中观察到的颗粒锰和锰氧化物。作为该项目的一部分，PI和博士生将为高中教育做出贡献，在初中/高中科学博览会项目中指导学生，并支持暑期本科生的研究经验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The metal manganese (Mn) is found widely throughout the environment where it is closely tied to the health and function of living organisms. Within some environments, in the presence of oxygen, Mn can form Mn oxide minerals. These minerals are extremely reactive, and they have an important role in controlling the fate of nutrients, contaminants, and carbon at the Earth’s surface. Despite their environmental importance, the controls on natural Mn oxide formation remain poorly understood; recent discoveries by the PI and others have put forth evidence that new pathways for light promoted Mn oxide formation exist. The goal of this project is to determine the processes controlling Mn oxide mineral formation in surface sun-lit environments. The research team will study a local pond on Cape Cod where Mn oxides have been found to form and persist in the presence of light. Waters from the pond will be collected at various sites and depths and reacted in the laboratory under different environmental and light conditions to identify the chemical and biological pathways allowing Mn oxides to form. Mn oxides formed via different light and environmental conditions will be characterized to determine their formation pathways and reactivity. These findings will improve our understanding of the Mn cycle and associated elements on Earth and other planets, such as Mars. This project will also contribute to the training of several undergraduate and graduate students. Further, outreach efforts associated with this research will involve lectures each year at a local high school and mentoring of high school science fair projects that will introduce students to Earth science.Recent lab and field investigations point to light-mediated reactions as underappreciated components of the manganese (Mn) cycle within some water bodies. Further, the PI’s preliminary data from a local meromictic metal-rich pond (Siders Pond, Cape Cod, USA) suggest that light plays a key role in the formation of Mn oxides in the surface waters, despite presumed photoreductive processes occurring. Accordingly, here the PIs propose a systematic field and laboratory interrogation of the rates, products, and mechanisms of Mn oxidation and Mn oxide formation within Siders Pond. The overall goal of the research is to determine the conditions allowing for light-induced formation of Mn oxides within the site, which has broad implications for understanding and predicting light-driven Mn oxide formation on Earth at present and in the past. Objectives guiding this research are (1) to quantify the distribution of Mn species and rates of Mn(II) and Mn(III)-L oxidation and Mn(III)-L and Mn oxide reduction along the redoxcline over space and time, (2) to identify the underlying (a)biotic mechanisms of Mn(II) oxidation and Mn oxide formation within the photic zone, and (3) to characterize the composition, structure, and reactivity of Mn oxides as a function of depth and transition across the redoxcline. The objectives will be addressed via a combination of field measurements, laboratory incubations, and microbial culturing. Waters from the pond will be collected at various sites and depths and reacted in the laboratory under different environmental and light conditions to identify the chemical and biological pathways allowing Mn oxides to form. Mn oxides formed via different light and environmental conditions will be characterized to determine their formation pathways and reactivity. Identification of the underlying biogeochemical processes allowing for light dependent Mn oxide formation will improve modern biogeochemical models and paleorecord interpretations. These light-mediated reactions may also help explain previous observations of particulate Mn and Mn oxides in surface sun-lit waters. As part of this project, the PI and PhD student will contribute to high school education, mentor students in middle/high school science fair projects, and support research experiences for summer undergraduate fellows.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.