Investigating Cross-Scale Dynamics at Terrestrial-Aquatic Interfaces in Temperate Forests
Authors
Jaclyn Hatala Matthes1* (jmatthes@fas.harvard.edu), Noel Michele Holbrook1,2, Charles Harvey3, Naomi Hegwood1, Jonathan Gewirtzman4, Hannah Burrows1
Institutions
1Harvard Forest, Harvard University, Cambridge, MA; 2Deptartment of Organismal and Evolutionary Biology, Harvard University, Cambridge, MA; 3Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA; 4School of the Environment, Yale University, New Haven, CT
Abstract
Terrestrial-aquatic interfaces are critical sites of biogeochemical processing, and the location of these interfaces is increasingly impacted by rising total annual precipitation and extreme rain events that rapidly move the water table. Small and ephemeral wetlands are particularly dynamic in space and time within temperate forests. In the saturated zone below the water table, conditions are anaerobic, and methane (CH4) is produced. Dissolved gas may diffuse or bubble up to the water table or escape to the atmosphere through plant roots and stems. In the unsaturated zone above the water table, conditions are oxic, carbon dioxide (CO2) is produced, and CH4 is oxidized. Additionally, CH4 transported by ebullition and tree stems have high variation across the landscape and through time, and the mechanisms driving plant-mediated methane transport are not well understood.
In this project, which began in September 2023, researchers are conducting cross-scale field measurements of methane dynamics at the Harvard Forest in Petersham, MA within uplands, ephemeral wetlands, and two small perennial wetlands: an approximately 14-thousand-year-old forested peatland and an approximately 20-year-old beaver-constructed wetland. Researchers are leveraging data and infrastructure from core AmeriFlux towers to add new ecosystem-scale measurements of CH4 and CO2 exchange and are measuring the lateral flow of carbon (C) in gaged streams and CH4 flux from tree stems. At the process-scale, researchers will characterize rates of CH4 production, consumption, ebullition, and diffusion and will develop a novel reactive transport model to represent these processes.
Future work will synthesize new field measurements within a spatiotemporal modeling framework that brings together process-based measurements with net CH4 flux constraints from eddy flux towers and lateral flow data. The observational design will facilitate understanding of the dynamics of CH4 within this complex ecosystem that dynamically changes across space and through time with precipitation.