Postdoctoral Fellowship: EAR-PF: Quantifying the hydrobiogeochemical controls on anaerobic oxidation of methane and methane emissions in wetland hyporheic zones

Wetlands are important ecosystems that are sensitive to changes in temperature and water flow. They are also the largest natural source of methane, a powerful greenhouse gas. However, it is difficult to predict how much methane produced in wetlands reaches the atmosphere, and how this might change in the future.

Through field, lab, and modeling work, this project studies the link between water flow and methane in wetlands. It will investigate how methane in wetlands responds to environmental changes, focusing on how microbes consume methane without oxygen. This work will provide mentoring and research opportunities for undergraduate students from backgrounds that are not currently well-represented in the Earth Sciences.

It will also develop data-intensive Earth Science teaching materials that include ways to engage ethically with Indigenous peoples and lands.

Dr. Samuel Shaheen has been awarded an NSF EAR Postdoctoral Fellowship in collaboration with Drs. G.-H.

Crystal Ng and Cara Santelli at the University of Minnesota. In this project, Dr. Shaheen will integrate field, experimental, and modeling work to examine how microbial-scale biogeochemical reactions and multi-scale processes such as hyporheic zone hydrology influence wetland methane dynamics.

Current uncertainties in our process-based understanding of the hydrobiogeochemical controls on wetland methane dynamics limit our ability to predict future changes to methane fluxes. While much attention has been focused on quantifying the microbial production of methane in wetlands, some of the methane produced is biogeochemically consumed before reaching the atmosphere, and major understanding gaps persist regarding methane consumption occurring under anoxic conditions.

The anaerobic oxidation of methane (AOM) is widely detected in wetland hyporheic zones, but estimates of its significance in mediating wetland methane emissions vary widely. This uncertainty may reflect that the significance of AOM depends on dynamic hydrologic conditions and a “cryptic” sulfur cycle able to resupply sulfate as an electron donor for AOM in anoxic settings.

This project will characterize hydrologic fluxes, redox processes, and methane emissions from wetland sites with varying availability of sulfate. In particular, the relationship between AOM, sulfur cycling, and methane emissions will be assessed to address this understudied aspect of wetland methane dynamics. Incorporating field measurements and laboratory experiments into a reactive transport model, redox processes relevant to methane cycling can be evaluated across hydrologic conditions and under potential global change scenarios.

Moving beyond the detection of AOM in wetlands, this project will build on emerging evidence of rapid sulfur cycling in wetlands to develop a quantitative understanding of AOM’s dependency on sulfur cycling and hyporheic fluxes and investigate how carbon and sulfur cycles in wetlands evolve across dynamic shifts in hydrology and temperature.

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.