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

潮汐湿地从大气中去除大量的二氧化碳。这些碳的一部分被埋在土壤中，通常被称为“蓝碳”。然而，另一部分碳通过湿地沉积物的潮汐冲刷出口到沿海海洋。潮汐沼泽输出的碳量尚不为人所知。该项目使用最先进的方法研究控制盐沼碳出口的过程。本研究的首要目标是建立第一个碳出口预测模型。该模型将为预测海平面持续上升时沿海碳收支的未来变化提供一个工具。将横向碳输出作为“蓝碳”汇将大大增加潮汐湿地碳汇的存量，并通过湿地的保护和恢复来增加整套生态系统服务。本项目将培养两名博士研究生，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，以提高对与该项目有关的科学的认识。横向碳(C)出口被认为大大超过了全球的碳埋藏，在北美东部沿海地区，这一数字高达五倍。然而，这些估计是基于有限的数据。目前，控制各站点横向碳和总碱度（TA）通量的机制驱动因素和环境变量是一个知识缺口，限制了在有限数量的实地观测平均之外的缩放或建模工作。该项目的目的是调查沼泽平台淹没频率和洪水持续时间（由潮汐框架内的海拔决定）作为横向C和TA输出的驱动因素和预测因素的作用。该项目将检验DOC、DIC和TA输出随着潮架内沼泽平台海拔的降低而增加的假设，这是由于：1)孔隙水排水增加；2)溶解C通量比CO2逃逸比例更大。在为期一个月的夏季期间，将评估位于潮汐框架内独特海拔的新英格兰沼泽地的6个地点，捕捉由春季小潮变化和偶发事件调节的峰值C和TA输出。每个站点之间的变异将受到当地呼吸速率和净生态系统交换、土壤C含量和积累速率以及当地环境条件的测量的限制。本研究将使用原位溶解无机碳（DIC）传感器、生物地球化学和物理传感器，通过高分辨率、时间序列地表水测量，量化潮汐溪的横向碳和碳氧化物通量。沼泽排水深度和DOC/DIC/TA输出将由沉积物224Ra:228Th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侧向DOC/DIC/TA输出提供一个全面的框架，并作为预测通量大小和未来变暖气候的变率的基础。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。

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.