Carbon dynamics of a freshwater marsh ecosystem

淡水沼泽是一种湿地类型，其特点是其高大的、新兴的植被和典型的洪水环境，在加拿大约有1600万公顷，在全球约有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，但对其碳循环的研究很少。沼泽地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。对这些大通量的驱动因素了解甚少，但可能对环境变化高度敏感。沼泽甲烷排放的研究仍然特别不足，在生态系统尺度上的连续测量很少。甲烷的产生是一个厌氧过程，而富含易分解碳的水浸沼泽为甲烷的产生提供了理想的环境。存在三种不同的运输途径：通过水柱扩散，沸腾（冒泡）和植物通过中空植物组织介导的运输。然而，这些和控制机制之间的平衡仍然缺乏研究。因此，我们对系统中控制甲烷生产、运输和释放的过程所知有限，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。改进对沼泽甲烷排放的量化和了解，反过来将使人们更好地了解它们在全球碳循环中的作用以及它们可能如何影响气候。我们不能简单地应用其他研究得更好的湿地类型的知识；沼泽具有独特的特征——浅层有机土壤沉积物、新兴水生植物、营养丰富和被淹没的环境——这导致了与其他湿地不同的碳通量动态。如果我们考虑到这个生态系统的碳交换潜力，以及它长期固碳的能力如何依赖于对甲烷释放的控制，沼泽的长期命运也会引起我们的兴趣。本研究将结合实地、实验室和建模方法，以改善我们对安大略省东部温带淡水沼泽生态系统中生态系统微量气体交换的有限理解。这项研究将为以下方面提供新的见解：优势植被物种和开放水域特征在沼泽净碳交换中的作用，干扰如何改变年度和年际碳排放，并将减少当代与大气碳交换率的不确定性。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.