From Tides to Seasons: How Cyclic Tidal Drivers and Plant Physiology Interact to Affect Carbon Cycling at the Terrestrial-Estuarine Boundary

Authors

Inke Forbrich^1,2* ([email protected]), Zoe Cardon¹, Yongli Zhou¹, Anne Giblin¹, Mikaela Martiros¹, Teri O’Meara³, Ben Sulman³, Cove Sturtevant⁴

Institutions

¹Marine Biological Laboratory, Woods Hole, MA; ²University of Toledo, Toledo, OH; ³Oak Ridge National Laboratory, Oak Ridge, TN; ⁴National Ecological Observatory Network, Boulder, CO

Abstract

The goal is to improve mechanistic process understanding and modeling of tidal wetland hydro-biogeochemistry in coastal Terrestrial-Aquatic Interfaces (TAIs). Key characteristics distinguish coastal wetlands, including tidal oscillation, sulfur biogeochemistry, and plant structural adaptations to anaerobic soil. These characteristics have only very recently been incorporated into land surface models such as ELM-PFLOTRAN and there remains large uncertainty in their parameterization. Particularly challenging are: (1) the small-scale, dynamic, heterogeneous redox conditions in wetland soils; (2) the aerenchyma tissue in wetland plants that greatly facilitate gas flow into and out of sediment; and (3) the temporal and spatial variability in salinity, which is a key determinant for plant species distribution and productivity, as well as organic matter decomposition. In 2022, researchers successfully established the sampling site (AmeriFlux site US-PLo) in a brackish marsh in the Parker River estuary, MA. In addition to the flux tower installation, two sampling locations (marsh interior, creek bank) were equipped with automated sensors (soil temperature, water level, salinity, redox profile) to contrast different soil and hydrological conditions. Researchers also did an initial field test with the new spatially explicit sediment redox measurements. The measurements captured the system response to an extreme drought, which caused high salinity levels (20ppt) early in the growing season.

Researchers will use these field measurements to help constrain three phases of ELM-PFLOTRAN development designed to improve simulations of brackish marsh biogeochemistry under fluctuating oxygen availability and salinity influenced by tides, diel and seasonal changes in plant physiology and river discharge. Researchers have already implemented aerenchyma-mediated oxygen transport into PFLOTRAN using data from the sites. Using a simplified reaction network, researchers find impacts on belowground biogeochemical cycling due to the heterogenous distribution of oxygen in the soil.

Ultimately, researchers will be poised to combine the new process understanding and model formulation with existing long-term data already in hand from two more saline salt marsh sites in the Parker Estuary.