EAR-PF Salinity Influence on Methane Emissions from Tidal Wetlands Determined by Clumped Isotopes

Haghnegahdar Mojhgan, College Park MD

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Methane (CH4) is the most abundant organic gas in Earth’s atmosphere, and a greenhouse gas. The EPA estimates indicate that methane accounts for 10% of national greenhouse gas emissions (www.epa.gov/ghgemissions). Methane emissions to the atmosphere include both anthropogenic and natural sources. Of these, wetlands not only play a significant role in the global methane budget, but are also one of the sources with the greatest associated uncertainties. This proposal focuses on wetland methane emissions within the Chesapeake Bay region. This region consists of a variety of environments that produce methane, most notably freshwater tidal wetlands. The proposed research will help characterize the regional methane budget and role of microbial processes that are driven by both natural and anthropogenic forcing of estuarine salinity. This work will support a longer-term project to construct a regional methane cycle model and to model atmospheric methane in this part of the world. Understanding the evolution of the atmospheric methane budget has important implications for local tidal wetlands restoration projects and national climate change policy decisions. Estimates of methane emissions from tidal wetlands are subject to high uncertainty and commonly suffer from the lack of information, but essential for determining the atmospheric methane budget and its change over time. The proposed research will evaluate the role of salinity (seasonal and regional changes) on microbial methane production and consumption in Maryland wetlands using new methane isotopologue fingerprinting approach. This work will document signatures of carbon and hydrogen in clumped isotopes that depend on varying environmental conditions and seek to develop an isotopologue tracer to track rates of microbial methane production and consumption influenced by environmental factors in different tidal wetlands systems. Using doubly substituted methane isotopologues (clumped isotopes) offers an additional way to resolve uncertainties about the biogenic methane formation pathways under various environmental conditions including the salinity and electron acceptors variability. This study will also address key questions regarding the pathways in methane production and consumption by microbes under the influence of various salinity regimes in tidal wetland systems. The work is a combination of in-situ methane measurements and laboratory (under controlled conditions) experiments. The results of this study will improve our understanding of the role of tidal wetlands in methane budget in Maryland and will be beneficial in environmental policy decisions. 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.