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

NSF Award Abstract:

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.