What’s in a wetland’s breath? Wetland Fluxes from Microsite to Globe
Is a wetland just… wet land? The short answer is yes. But the physical saturation of Earth’s surface soils with water has cascading effects on chemical and biological processes. For example, because oxygen is so insoluble in water, plants and microbes need to be adapted for life with little or no soil oxygen. Plant adaptations include specialized stem tissues that can transport oxygen, whereas microbes adapt with specialized biochemical lifestyles that in turn produce greenhouse gases like nitrous oxide and methane. Moreover, depending on the environmental context, these adaptations take can different forms. Wetlands are therefore at once unique and diverse ecosystems.
In the McNicol Lab, we study the signature processes of wetlands soils. We ask deceptively simple methodological questions, such as, how do we measure, estimate, or model complex wetland-atmosphere exchanges? But we also ask fundamental questions, such as, how do energetics control wetland microbial processes? Finally, we also ask global change questions like, how does human disturbance impact wetland functions?
In the Lab: Microscale Controls
Despite their important climate impacts, we have a relatively poor understanding of the processes that govern wetland greenhouse gas emissions. Wetland gas fluxes emerge from a complex interplay of dynamic biogeochemical gradients and soil microbial ecology. It is, however, an exciting time to break new scientific ground in ecosystem exchange, with advances in gas analyzers allowing ephemeral methane and nitrous oxide fluxes to be measured continuously, and advances in genomics providing new insights into the soil microbiome and the functional traits that structure microbial communities.
In the McNicol Lab, we use laboratory experiments to explore the effects of water on soil greenhouse gas emissions. We focus on the effects of oxygen depletion on patterns and rates of carbon dioxide and methane emissions. This fundamental knowledge helps provide a framework for interpreting greenhouse gas emissions at larger scales.
In the Field: New Wetland Flux Measurements
Wetlands globally have been drained for agricultural purposes, to take advantage of the organic soils they support under flooded conditions. When these ecosystems 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. Illinois lost almost all of its wetland and wet prairie cover in this same period, however pockets remain here and there, and more are being created through restoration.
Drained and restored wetlands provide management-driven experiments to understand the role of flooding on rates of soil decomposition and carbon emissions. Very few measurements of these processes have been made across Illinois’ wetland ecosystems. In the McNicol Lab, we use a mixture of manual chamber sampling and a low disturbance tower-based technique called eddy covariance (pictured above), to measure gas exchanges in wetlands and prairies.
In Collaboration: Global Synthesis
Methane contributes to over a quarter of all post-Industrial climate warming and 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 in the global methane budget 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.
Our lab participates in the FLUXNET-CH4 synthesis, which was launched in 2018 by the Global Carbon Project to address these methane budget uncertainties. FLUXNET is a global network for scientists who use micro-meteorological techniques to estimate biosphere-atmosphere exchanges of gas and energy. We work with FLUXNET scientists, especially those from the regional AmeriFlux and EuroFlux networks, to bring together methane emissions data collected at wetland sites around the world. Data are being used in various synthesis projects, such as through the USGS Powell Center. The main objective of the McNicol Lab’s participation is to use machine learning to develop a global wetland methane emissions map.