Collaborative Research: Deciphering drivers and variability in salt marsh lateral carbon export

潮汐湿地从大气中去除了大量的二氧化碳。这些碳的一部分被埋藏在土壤中，通常被称为“蓝碳”。然而，这些碳的另一部分通过湿地沉积物的潮汐冲刷输出到沿海海洋。潮汐沼泽输出的碳的数量并不为人所知。该项目使用最先进的方法调查控制盐沼碳出口的过程。这项研究的首要目标是开发第一个碳出口预测模型。该模型将为预测未来海平面持续上升时沿海碳预算的变化提供一种工具。将横向碳出口列为“蓝碳”汇将大大增加潮汐湿地碳汇的库存，并增加通过保护和恢复湿地而得到保护的生态系统服务。该项目将培养两名博士生，并为多名本科生提供研究机会。研究人员将参加当地的推广活动，以提高人们对与该项目相关的科学的认识。全球范围内，横向碳(C)出口量被认为远远超过碳埋藏量，北美东海岸的出口量高达5倍。然而，这些估计是基于有限的数据。目前，控制横向C和总碱度(TA)跨站点通量的机械驱动因素和环境变量是一个知识缺口，限制了缩放或建模工作，超出了有限数量的现场观测的平均值。该项目的目标是调查沼泽平台淹没频率和洪水持续时间作为横向C和TA出口的驱动和预测因素的作用，这些因素由潮汐框架内的海拔决定。该项目将检验这一假设，即在潮汐框架内，DOC、DIC和TA出口随着沼泽平台高程的降低而增加，这是因为：1)增加了孔隙水排放；2)溶解C通量相对于二氧化碳逃逸的比例更大。在为期一个月的夏季期间，将对潮汐框架内位于独特海拔的六个新英格兰湿地站点进行评估，捕捉受大潮-小潮变化和插曲事件调制的C和TA出口峰值。每个地点的可变性将受到当地对呼吸速率和净生态系统交换、土壤碳含量和累积率以及当地环境条件的测量的限制。这项研究将使用现场溶解无机碳(DIC)传感器、生物地球化学和物理传感器，从高分辨率、时间序列的地表水测量中量化通过潮汐小溪的横向C和TA通量。沼泽排水和DOC/DIC/TA输出的深度将根据沉积物224Ra：228次不平衡确定，并将与使用地表水方法确定的通量进行比较。总体而言，该项目将为评估潮汐湿地的横向DOC/DIC/TA输出提供一个全面的框架，并作为预测未来更温暖气候的通量大小和变异性的基础。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。

Tidal wetlands remove large amounts of carbon dioxide from the atmosphere. Some portion of this carbon is buried as soil, often referred to as “blue carbon.” However, another portion of this carbon is exported to the coastal ocean through tidal flushing of wetland sediments. The amount of carbon exported from tidal marshes is not well known. This project investigates the processes that control carbon exports from salt marshes using state-of-the-art methods. The overarching goal of this study is to develop the first predictive model of carbon exports. This model will provide a tool for predicting future changes in coastal carbon budgets with continued sea level rise. Inclusion of lateral carbon exports as a “blue carbon” sink would greatly increase the inventory of tidal wetland carbon sinks and add to the suite of ecosystem services that are preserved through conservation and restoration of wetlands. This project will train two PhD students and provide research opportunities for multiple undergraduate students. The researchers will participate in local outreach activities to increase awareness of the science related to this project.Lateral carbon (C) exports are thought to greatly exceed C burial globally, and by as much as a factor of five along the eastern coast of North America. However, these estimates are based on limited data. At present the mechanistic drivers and environmental variables that control lateral C and total alkalinity (TA) fluxes across sites are a knowledge gap that limits scaling or modeling efforts beyond averaging a limited number of field observations. The objective of this project is to investigate the role of marsh platform inundation frequency and flooding duration, as determined by elevation within the tidal frame, as a driver and predictor of lateral C and TA exports. This project will test the hypothesis that DOC, DIC and TA export increases with decreasing marsh platform elevation within the tidal frame due to: 1) increased porewater drainage and 2) a greater proportion of dissolved C flux versus CO2 evasion. A total of six New England marsh sites at unique elevations within the tidal frame will be evaluated during a one-month summer period, capturing peak C and TA exports modulated by spring-neap tidal variation and episodic events. Variability across each site will be constrained from local measurements of respiration rates and net ecosystem exchange, soil C content and accumulation rates, and local environmental conditions. This study will quantify lateral C and TA flux through tidal creeks from high-resolution, time-series surface water measurements using an in-situ dissolved inorganic carbon (DIC) sensor, biogeochemical and physical sensors. The depths of marsh drainage and DOC/DIC/TA export will be determined from sediment 224Ra:228Th disequilibria and will be compared with fluxes determined using the surface water approach. Overall, this project will provide a comprehensive framework for the evaluation of lateral DOC/DIC/TA exports from tidal wetlands and serve as a basis for the prediction of flux magnitude and variability into a future, warmer climate.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.