The atmospheric concentration of methane has started to grow rapidly again, after a slow down between approximately 1999 and 2007. Our ability to attribute these dynamics to different methane sources and sinks is, however, very limited. One major source of uncertainty is the role of wetlands at the global scale, with some scientists proposing that increases in wetland methane emissions from the tropics and/or the Arctic could be driving the renewed methane growth rate. Currently, a range of models are used to predict wetland methane fluxes globally but we lack an observation-based estimate to help validate these. My work within the FLUXNET-CH4 aims to address this gap by bringing together methane emissions data collected at wetland sites around the world, to use machine learning approaches to predict methane under various conditions, and to make spatial predictions using global geospatial products.
What’s in a wetland’s breath?
Wetland ecosystems support lifeforms that exploit and adapt to saturated or flooded soils, leaving unique biogeochemical signatures. My dissertation focused on quantifying and understanding wetland carbon and nitrogen cycling, with a focus on carbon decomposition to carbon dioxide, and the emission of methane and nitrous oxide, greenhouse gases produced by microbes under low oxygen conditions.
Restored Agricultural Peatlands
Wetlands globally have been drained for agricultural purposes, to take advantage of the organic soils they support under flooded conditions. This is true in the Sacramento Delta where peat-forming marshes gradually accumulated meters of organic deposits over the last 6-8k years. When these ecosystem were diked and drained in the last 150 years, it was these peaty organic-rich soils that provided fertile grounds for agriculture; decomposition accelerated under drier conditions, releasing nutrients for crops, but also mineralizing large stores of carbon and releasing it to the atmosphere as carbon dioxide. With rapid subsidence in the California Delta, and elsewhere, wetland restoration via reflooding (or rewetting) is being explored to reverse carbon losses and rebuild peat soils. Restored agricultural peatlands therefore provide a management-driven experiment to understand the role of flooding on rates of soil decomposition and carbon dioxide emissions.