Carbon Storage in Mangrove Ecosystems via Abiotic Sulfurization

红树林沉积物是有机碳保存的重要热点，它们具有封存大量大气二氧化碳的潜力。然而，目前还不完全清楚为什么这些环境能够埋藏如此多的有机碳，或者它们将如何应对未来海平面、土地利用和气候的变化。该项目将研究一种可能有助于解释这种碳埋藏的机制：有机质硫化，硫化物对沉积有机质的转化和有效的“酸洗”。它的中心目标是了解是什么控制了红树林沉积物的硫化程度，并估计在不同的环境中有机质硫化对沉积物碳储量的贡献。通过提供一些关于红树林中有机物硫化如何、何时以及在何处发生的初步限制，这项工作的结果将指导决策者在面对土地利用、气候和海平面变化时管理沿海流域和碳储量。作为这项工作的一部分，加州大学圣巴巴拉分校的四名本科生和一名博士生将获得实地和研究经验。此外，该团队还将与现场相关的当地团体合作，制作一季“海洋解决方案”播客，内容涉及加勒比红树林的保护和人类对其的影响。该项目的总体目标是了解微生物硫循环如何影响植被海岸沉积物中的有机质保存，这对影响十年到千年时间尺度上的全球碳循环具有重大影响。它专门研究了有机物的硫化作用，它可以将新鲜的、容易呼吸的有机物转化为具有长期保存潜力的顽固的、聚合的碳库存。虽然已知在红树林沉积物中会发生有机物质硫化，但其影响的规模基本上是未知的。两组实地考察将在佛罗里达州西南海岸的一片红树林进行。在第一个野外季节，地球化学剖面将用于量化沉积物中的有机质硫化及其与碳储量、铁矿物学和沉积有机质输入特征的关系。在第二个油田季节，循环伏安法将用于毫米尺度的氧化还原动力学。将进行实验室实验，以测试各种当地有机物来源对硫化的敏感性，并描述其硫化形式。在整个项目中，通过同位素和光谱技术表征溶解、脂质、蛋白质/碳水化合物和原始干酪根池，对沉积有机质采用了整体方法。这项工作将产生第一个定量的机制框架，用于预测沿海植被栖息地中有机物硫化的程度及其对生态、土地利用或海平面变化的可能反应。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。

Mangrove forest sediments are important hotspots of organic carbon preservation, and they have the potential to sequester substantial amounts of atmospheric CO2. Currently, however, is it not fully understood why these environments are able to bury so much organic carbon, or how they will respond to future changes in sea level, land use, and climate. This project will investigate a mechanism that may help explain this carbon burial: organic matter sulfurization, the transformation and effective ‘pickling’ of sedimentary organic matter by sulfide. Its central aim is to understand what controls the extent of sulfurization in mangrove sediments, and to estimate the contribution of organic matter sulfurization to sediment carbon storage in different parts of the environment. By providing some of the first constraints on how, when, and where organic matter sulfurization happens in mangroves, the results of this work will guide decisionmakers managing coastal watersheds and carbon stocks in the face of land use, climate and sea level change. As part of this work, four undergraduate students and one PhD student at UC Santa Barbara will gain field and research experience. And, in collaboration with local groups associated with the field site, the team will produce a season of ‘Ocean Solutions’ podcast episodes related to conservation and human impacts of Caribbean mangroves. The overarching goal of this project is to understand how microbial sulfur cycling affects organic matter preservation in vegetated coastal sediments, which have substantial leverage to impact the global carbon cycle on decadal to millennial timescales. It specifically investigates organic matter sulfurization, which can transform fresh, easily respired organic matter into recalcitrant, polymerized carbon stocks with long-term preservation potential. Although organic matter sulfurization is known to occur in mangrove sediments, the scale of its impact is essentially unknown. A pair of field expeditions will be conducted at a mangrove forest on the southwestern coast of Florida. In the first field season, geochemical profiles will be used to quantify organic matter sulfurization in sediments and its relationships with carbon storage, iron mineralogy, and the characteristics of sedimentary organic matter inputs. In the second field season, cyclic voltammetry will be used to target redox dynamics at the millimeter scale. Laboratory experiments will be conducted to test the susceptibility of various local organic matter sources to sulfurization and characterize their sulfurized forms. Throughout, the project applies a holistic approach to sedimentary organic matter by characterizing the dissolved, lipid, protein/carbohydrate, and proto-kerogen pools with isotopic and spectroscopic techniques. This work will yield a first quantitative, mechanistic framework for predicting the extent of organic matter sulfurization in coastal vegetated habitats and its likely response to changes in ecology, land use, or sea level.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.