Adam Rexroade
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Current Research

Greenhouse gas emissions in Australian streams
Tropical aquatic systems have been identified and potential hotspots for CO2 and CH4 emissions. Particularly in Australia, lack of direct observations of CO2 and CH4 have limited our ability to accurately quantify the contribution of these systems to global carbon budgets. By combining extensive field campaigns, data mining, and high frequency monitoring I am working to better understand what drive greenhouse gas emissions from stream across Australia and how much CO2 and CH4 is emitted from tropical streams in Australia. 
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Understanding sources and sinks of CO2 and CH4 in a tropical wetland stream
Key to estimating the contribution Australian streams have in the global carbon budget is understanding how streams receive, transform, transport, and emit carbon gasses. Using a key study site that is monitored heavily in both space and time, we hope to gain invites on these processes. In a small stream in Litchfield National Park, we are measuring CO2 and CH4 inputs from shallow riparian soils, upstream export, and overland flow. We also are measuring exports of these gases downstream and to the atmosphere. By using diel time series of dissolved oxygen, we are also quantifying internal metabolism. We hope that, collectively, this wide array of data will help us understand processes that drive concentrations and fluxes of CO2 and CH4. 

PictureConceptual diagram of nationwide GHG flux model.
Estimating greenhouse gas Emissions form tropical streams in Australia
By combining field observations of CO2 and CH4 with stream network models, we aim to model the total greenhouse gas emissions from streams in Australia. We sampled CO2 and CH4 at nearly 150 different locations across the tropics of Australia and aggregated additional observations from other published papers. Using these data, we upscaled GHG emissions to all streams across the continent. Key to this work is a surface area model which predicts surface area of streams across the year–this step is critical given that nearly 70% of streams in Australia are intermittent. 
Selected works
Ulloa-Cedamanos, F., Rexroade, A. T., Li, Y., Hutley, L. B., Wong, W. W., Wallin, M. B., Canadell, J. G., Lintern, A., and Duvert, C.: OzRiCa: An Australian riverine carbon database of concentrations, gas fluxes and isotopes, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2025-233, in review, 2025.
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Gas Evasion from Steep Streams
Streams and rivers emit greenhouse gases and the rate at which this process occurs is called the gas transfer velocity. This parameter can be measured or estimated in different ways, yet few studies compare these different methods. We aimed to understand how existing methods compare to each other and how well these methods work in systems other than flat temperate and boreal streams. Our results show that methods that use a biologically inert tracer gas to measure gas transfer velocity work better than other in-situ methods. Models that estimate gas transfer velocity tend to overestimate this parameter when it is low and underestimate this parameter when it is high. We also found that while gas transfer velocity varies substantially in space, it remains relatively stable over time. The differences we observed between the different methods highlight the need for further research on how to best measure or model gas transfer velocity, particularly in steep streams.

Selected works
Rexroade, A. T.,  Wallin M., and Duvert, C. 
(2025) Measuring Gas transfer velocity in a steep tropical stream: method evaluation and implications for upscaling. JGR: Biogeosciences, 130, e2024JG008420. https://doi.org/10.1029/2024JG008420 . 


Previous Research

PictureGreenhouse gas sampling on Allequash Creek, Wisconsin USA, Summer 2020
Temporal and Spatial Variation and Drivers of GHG Fluxes in Temperate Streams
My master's thesis aimed to compare differences in day and night emissions of carbon dioxide and methane as well as identify drivers of each gas flux. For two summers, we measured CO2 and CH4 concentration as well as water temperature, dissolved oxygen, dissolved organic carbon, and discharge during midday and midnight. ​We also aimed to understand spatial variability of CO2 and CH4 within a stream system. 

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Algae collected from a bloom on Lake Mendota, Wisconsin USA, Summer 2019
Algal Blooms and Greenhouse Gas Emissions 2019-Present
My undergraduate senior thesis looked to explore the impact of increased algal biomass and algal blooms on greenhouse emissions from Lake Mendota in southern Wisconsin, USA. This was done through routine simultaneous measurement of algal pigment concentration in the surface water, gas emissions from the surface using a floating chamber and portable gas analyzer, and dissolved gas concentrations throughout the water column using headspace sampling. Data collection occurred over summer 2019 and the journal article is currently in progress. This work was done through UW-Madison and was made possible by LTER funding. The advisor was Dr. Emily Stanley. 

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  • About Me
  • Research
  • Education
  • CV
  • Contact