Terrestrial inputs of carbon and nutrients, as well as within-water physical and biological processes, conspire to produce significant but highly variable emissions of greenhouse gases to the atmosphere from inland waters. Flickr user Fc Nikon, CC BY-SA 2.0

Inland waters generate significant emissions of carbon dioxide, methane, and other greenhouse gases (GHGs). Recent papers have estimated that these emissions could offset a significant fraction of the terrestrial carbon sink. However, published estimates rely nearly exclusively on extrapolation of point-in-time observations made over limited regions.

To foster improvement of GHG aquatic emissions quantification and incorporation of new measurement technologies and approaches in aquatic ecology, more than 60 ecologists, limnologists, and micrometeorologists, including early career scientists, attended this inaugural freshwater gas exchange workshop. The workshop brought together researchers studying the cutting edge of measurements and modeling of processes relevant to aquatic fluxes at research sites from the tropics to the poles. Expertise included flux measurements in lakes, streams, and wetlands; hydrodynamics; biogeochemistry, including microbial processes; and modeling.

The workshop was timely because its goals tied closely to the need to define specifications for inland water GHG observations in the Global Lake Ecosystem Observatory Network (GLEON), the International Research Staff Exchange Scheme (IRSES) Greenhouse Gas Lake Project, and the Integrated Carbon Observation System (ICOS). The group identified that networks similar to ICOS are needed in multiple regions.

Over 4 days, participants focused on the current understanding of GHG emissions, measurement and model limitations, and needs for database and synthesis development. Keynote and research talks reviewed the importance of inland systems to landscape carbon cycling; the role of stream transport of organic, inorganic, and gaseous carbon; the complexity of modeling methane mixing across sediment, in water, and in atmospheric interfaces; and the difficulties in scaling chamber and eddy covariance flux measurements from point to lake to landscape. Regional synthesis and upscaling of aquatic emissions found significant spatial and temporal variability in all components of the carbon budget, with advances made in understanding key biological and physical processes that drive this variation.

Poster presentations emphasized the importance of next-generation flux measurement and modeling techniques, including the use of over-water eddy covariance and automated flux chambers, high-resolution in-water profiling including turbulence, and improvements to one- and three-dimensional models of aquatic systems and their atmospheric exchanges. Two-day breakout sessions discussed in-water biogeochemical, physical, and microbial observations; direct flux measurement approaches, including incorporation of the dynamic atmospheric boundary layer in flux calculations; and required improvements for coupled hydrodynamic-biogeochemical models.

Two additional discussions motivated new syntheses. In one, an inland water GHG flux forum was initiated to facilitate communications and support collection of comparable data. In the other, a synthesis manuscript on eddy covariance flux tower observations of lake carbon and energy exchanges was begun. Other outcomes included identifying minimum and ideal required measurements for sites conducting over-lake flux measurement, initiating a review paper on observational and modeling needs to improve numerical models incorporating methane biogeochemistry, and synthesizing gas transfer coefficients.

Researchers interested in contributing observations or approaches to the evolving eddy covariance synthesis and the GHG flux forum should contact Malgorzata Golub (mgolub@wisc.edu) and David Bastviken (david.bastviken@liu.se), respectively.

A photo of the participants and a list of workshop organizers can be found here.

—Ankur Rashmikant Desai, Department of Atmospheric and Oceanic Sciences, University of Wisconsin–Madison; email: desai@aos.wisc.edu; Timo Vessala, Department of Physical Sciences, University of Helsinki, Finland; and Miitta Rantakari, Finnish Environment Institute, Helsinki

Citation: Desai, A., T. Vessala, and M. Rantakari (2015), Measurements, modeling, and scaling of inland water gas exchange, Eos, 96, doi:10.1029/2015EO022151.

© 2015. American Geophysical Union. All rights reserved.

© 2015. American Geophysical Union. All rights reserved.