Constraining Carbon Dioxide and Methane Fluxes from Diverse Tidal Wetlands: Standardizing Measurements and Analysis Across a Network of Eddy Covariance Sites in North America and Canada

Authors

Patty Oikawa¹ ([email protected]), Ellen Stuart-Haëntjens²*, Maiyah Matsumura¹, Jessica Silberman¹, Christopher Gough³, Lisa Haber³, Sara Tenda³, Karina Schäfer⁴, Suman Dhakal⁴, Sara Knox⁵, Katrina Poppe⁵, Sarah Russell⁵, Rodrigo Vargas⁶, Andrew Hill⁶, Lisamarie Windham-Myers²

Institutions

¹California State University–East Bay, Hayward, CA; ²California Water Science Center, U.S. Geological Survey, Sacramento, CA; ³Virginia Commonwealth University, Richmond, VA; ⁴Rutgers, The State University of New Jersey–Newark, NJ; ⁵The University of British Columbia, Vancouver, British Columbia, Canada; ⁶University of Delaware, Newark, DE

Abstract

Tidal wetlands and other blue carbon systems are the strongest long-term carbon (C) sinks per unit area, yet these ecosystems, and the biogeochemical processes regulating C exchange, are not well represented in Earth system models. In 2021, NATURA (A Network of North American Tidal Wetlands: Understanding Through Coordinated Research Activities) was established, funded by DOE. This project unites seven eddy covariance flux sites along the east and west coasts of the United States and Canada and aims to improve empirical understanding and assist process-based biogeochemical modeling of these critical ecosystems. The team coupled field measurements, statistical analyses, and experimental mesocosms in a ModEx approach to: (1) improve net ecosystem exchange (NEE) partitioning into gross primary production (GPP) and ecosystem respiration (RECO); (2) quantify the influence of elevation, nitrate, and salinity on GPP and methane fluxes; (3) derive thresholds and responses of C fluxes to nonperiodic pulses of salinity and nitrogen; and (4) inform and improve biogeochemical models, MEM-PEPRMT and PFLOTRAN-E3SM. Analysis of three NEE partitioning approaches revealed high variability in performance both within and across tidal wetlands (n=6 eddy covariance sites). This variability likely resulted from pulses of nitrate and salinity as well as tidal pumping of dissolved carbon dioxide and other forms of respired C. Stable isotope partitioning and lateral C flux measurements were used to evaluate and improve partitioning algorithms. Researchers improved MEM-PEPRMT model performance across sites by incorporating nitrate and salinity data from the tidal channel to help predict GPP, RECO, and methane exchange. The team is now in the process of standardizing nitrogen, salinity, water level, and additional measurements in all seven NATURA sites and, in spring 2023, will begin running mesocosm experiments using a ModEx approach to isolate the effects of nitrogen and salinity on GPP and methane fluxes.