DISSERTATION RESEARCH: How do saltwater intrusion and drought interact to change the soil carbon balance of a brackish water coastal marsh?

滨海湿地在全球碳循环中发挥着重要作用，在植被和沉积物中储存了大量的碳。咸水入侵和干旱对沿海湿地的稳定性构成了严重威胁，因此可能导致它们储存碳的能力发生重大变化。沿海湿地，包括佛罗里达大沼泽地，在海平面上升速度相对较低的情况下，通过积累足够快的土壤碳来保持湿地上升的步伐。在佛罗里达沿海的大沼泽地，海平面上升更快，再加上干旱和淡水分流的增加，导致咸水进入沿海淡水湿地，改变了影响碳储存速度的过程，潜在地改变了湿地海拔上升的速度。这篇博士论文改善赠款将提供资金，在半咸水的大沼泽地沼泽实验模拟咸水入侵和干旱，以确定生产力、土壤碳库和水化学的变化如何影响土壤海拔的损失和向河口输出养分。这项研究的结果不仅将为大沼泽地的保护和恢复工作提供信息，也将为全球沿海湿地的保护和恢复工作提供信息。该项目还将为一家主要的拉美裔服务机构的本科生提供研究和实验室经验。研究人员将利用该项目通过各种外展活动向公众宣传和参与沿海环境问题。在沿海湿地，初级生产力的速度往往超过分解速度，并可能导致土壤碳的大量储存。初步结果表明，咸水入侵和干旱对沿海湿地土壤碳储量的速度有很强的相互作用，但这些反应背后的规模和机制仍存在疑问。这项研究使用了一种可控的实验操作，其中滨海湿地中观系统受到盐度升高和模拟干旱的影响，以理清这两个驱动因素的相互作用。碳储量的变化将通过二氧化碳气体交换和有机碳储量(地上和地下)、投入(根生产力、沉积物表面积累)和输出(有机碳分解)来衡量。这项研究将：(1)确定经历盐度升高和长期干旱的微咸水沿海泥炭沼泽中碳和生物地球化学循环的变化；(2)通过对干旱后恢复阶段的评估，测试沿海沼泽的抗旱能力；以及(3)评估盐度上升和干旱导致泥炭海拔下降和转向开阔水域湿地的可能性。

Coastal wetlands play an important role in the global carbon cycle and store large amounts of carbon in vegetation and sediments. Saltwater intrusion and drought represent serious threats to the stability of coastal wetlands, and may therefore cause substantial changes in their ability to store carbon. Coastal wetlands, including the Florida Everglades, persist under relatively low rates of sea level rise by accumulating soil carbon fast enough for wetland elevation to keep pace. In the Florida coastal Everglades, faster sea level rise, combined with increases in drought and freshwater diversion, have resulted in saltwater moving into coastal freshwater wetlands, changing processes that affect the rates of carbon storage, potentially altering the pace of wetland elevation increases. This Doctoral Dissertation Improvement Grant will provide funds to experimentally simulate saltwater intrusion and drought in a brackish Everglades marsh to determine how changes in productivity, soil carbon pools, and water chemistry affect losses in soil elevation and nutrient export to estuaries. Results from this research will provide information for conservation and restoration efforts not only in the Everglades but also for coastal wetlands globally. The project will also give research and lab experience to undergraduates at a major Hispanic-serving institution. Researchers will use this project to inform and engage the public on coastal environmental issues through a variety of outreach activities.In coastal wetlands, the rates of primary production often exceed decomposition, and can result in significant storage of soil carbon. Preliminary results have suggested a strong interaction between saltwater intrusion and drought on the rates of soil carbon storage in coastal wetlands, but questions remain about the magnitude and mechanisms behind these responses. This research uses a controlled experimental manipulation in which coastal wetland mesocosms are subjected to elevated salinity and simulated drought to disentangle the interactive effects of these two drivers. Changes in carbon storage will be measured through carbon dioxide gas exchange and organic carbon stocks (above and below ground), inputs (root productivity, sediment surface accretion), and outputs (organic carbon decomposition). This research will: (1) Identify changes in carbon and biogeochemical cycling in brackish water coastal peat marshes experiencing elevated salinity and prolonged drought; (2) Test the resilience of coastal marshes to drought through evaluation of a post-drought recovery phase; and (3) Assess the potential for elevated salinity and drought to cause the loss of peat elevation and conversion to open water wetlands.