Carbon dynamics of a freshwater marsh ecosystem

淡水沼泽是一种湿地类型，由其高大的新兴植被和典型的洪水环境定义，在加拿大约有1600万公顷，全球约有9500万公顷。淡水沼泽提供了许多生态系统产品和服务，从水过滤和洪水控制到鸟类和昆虫物种的栖息地。尽管淡水沼泽是一种重要的湿地类型，但只有少数研究关注其碳循环。沼泽中的净碳交换是大量二氧化碳吸收和大量甲烷释放之间的平衡-两者都是温室气体。这些大通量的驱动因素知之甚少，但可能对环境变化高度敏感。沼泽地甲烷排放量仍然特别缺乏研究，在生态系统尺度上的连续测量很少。甲烷生产是一个厌氧过程，而富含易分解碳的沼泽湿地为甲烷生产提供了理想的环境。存在三种不同的运输途径：通过水柱的扩散、沸腾（起泡）和通过中空植物组织的植物介导的运输。然而，这些和控制机制之间的平衡仍然很少研究。因此，我们对控制系统中甲烷生产、运输和释放的过程的了解有限，而该系统已被证明可能比任何其他温带或北方湿地类型排放更多的甲烷。改善对沼泽甲烷排放的量化和了解，反过来将导致更好地了解它们在全球碳循环中的作用以及它们如何影响气候。我们不能简单地应用其他更好地研究湿地类型的知识;沼泽地包含独特的特征-浅层有机土壤沉积物，新兴水生植物，营养丰富，淹没环境-导致碳通量动态不同于其他湿地。如果我们考虑这个生态系统的碳交换潜力，以及它通过时间封存碳的能力如何取决于对甲烷释放的控制，那么沼泽的长期命运也很有趣。这项研究将使用基于现场，实验室和建模方法相结合，以改善我们有限的了解，在温带淡水沼泽生态系统中的生态系统微量气体交换在东部安大略。这项研究将提供新的见解的作用，占主导地位的植物物种和开放水域功能发挥的净碳交换沼泽，干扰如何修改年度和年际的碳排放量，并将减少当代的碳交换率与大气的不确定性。因此，建模工作将能够纳入未来变化对沼泽净碳平衡的影响。

Freshwater marshes are a wetland type that is defined by its tall, emergent vegetation and typically flooded environments and are found in ~16 million ha in Canada and ~95 million ha globally. Freshwater marshes provide many ecosystem goods and services from water filtration and flood control through habitats for avian and insect species. Despite freshwater marshes being an important wetland type, only a few studies exist that are focused on their carbon cycling. The net carbon exchange in a marsh is a balance between a large carbon dioxide uptake and a large methane release - both greenhouse gases. The drivers of these large fluxes are poorly understood but are likely highly sensitive to changes in the environment. Marsh methane emissions remain particularly understudied with very few continuous measurements at the ecosystem scale. Methane production is an anaerobic process and waterlogged marshes with highly available easily decomposed carbon provide an ideal environment for methane production. Three different pathways for transport exist: diffusion through the water column, ebullition (bubbling) and plant-mediated transport through hollow plant tissues. However, the balance between these and the controlling mechanisms remain poorly studied. We are thus left with limited knowledge about processes controlling methane production, transport and release in a system that that has been shown to potentially emit more methane than any other temperate or northern wetland type. Improved quantification and understanding of marsh methane emissions will, in turn, lead to better understanding of their role in the global carbon cycle and how they may affect climate. We cannot simply apply knowledge from other better-studied wetland types; marshes contain unique characteristics - shallow organic soil deposits, emergent aquatic plants, nutrient rich, and inundated environments - that lead to carbon flux dynamics that are distinct from those of other wetlands. The long-term fate of marshes are also of interest if we consider the carbon exchange potential of this ecosystem and how its ability to sequester carbon through time is dependent on the controls on methane release. This research will use a combination of field-based, laboratory and modelling approaches to improve upon our limited understanding of the ecosystem trace gas exchange in a temperate freshwater marsh ecosystem in eastern Ontario. This research will provide new insights into the role that dominant vegetative species and open water features play in the net carbon exchange of marshes, how disturbances modify annual and interannual carbon emissions and will reduce uncertainty about contemporary rates of carbon exchange with the atmosphere. Modelling efforts will thus be able to incorporate the effects of future change on the marsh net carbon balance.