The NGEE-Arctic Barrow, Alaska eddy flux site on the North Slope of Alaska undergoes pre-winter maintenance while the sun sits at its highest point in the sky, three days before disappearing behind the horizon for 66 days. Photo by Sigrid Dengel/Berkeley Lab.
Scientists who work to address challenges ranging from vegetation productivity under increasing temperatures to the impact of future drought at continental scale need to rely on data that can connect the biology taking place on land with changes in atmospheric concentrations of water and trace gases like carbon dioxide. Climate and ecosystem modelers, soil microbiologists, and researchers working to improve tools that enable autonomous sensing of remote field environments also need this information. For decades now, this data has been collected at hundreds of sites globally using eddy covariance towers set up to monitor how fluxes of carbon dioxide (CO2), water vapor, and energy (heat) are exchanged between the biosphere and the atmosphere.
The latest consolidated release of these eddy flux measurements collected over two decades, from the early 1990s to 2014, is available in the FLUXNET2015 dataset, with data from 200-plus sites throughout the world. How these data were processed at the network levels and new ways to make this data easier to access, use, and acknowledge, are described in a paper published online earlier this month in the Nature journal Scientific Data. The FLUXNET data teams at Berkeley Lab and University of Tuscia coordinated the preparation of the dataset updates and the paper, “The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data,” also co-authored by site team members and with lead author Berkeley Lab research scientist Gilberto Pastorello.
“When FLUXNET2015 was introduced it included some of the longest continuous records of ecosystem-level flux data ever taken,” Pastorello said. “We have now made that data more complete and easier to access and acknowledge by the thousands of researchers around the world who rely on it. The data is already being used in a number of applications, including ecophysiology, remote sensing studies, and development of Earth and ecosystem models.”
Computer scientists at the Department of Energy’s (DOE’s) Lawrence Berkeley National Laboratory (Berkeley Lab) contributed to the development of the FLUXNET data processing pipeline, now available as an open-source software package called ONEFlux, also described in the paper. They also helped build tools that allow researchers to easily upload, download, and share datasets, as well as track how and where each site’s data will be used.
The AmeriFlux Management Project team, which is funded by the DOE and led by Berkeley Lab, the European Ecosystems Fluxes Database and FLUXNET project, worked with several regional networks to process and harmonize all of the information in the initial FLUXNET2015 release and to finesse the recent enhancements to the dataset.
The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe. This adds up to more than 1500 site-years, up to and including the year 2014. The paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.
The eddy covariance technique has been used to measure land-atmosphere exchanges of greenhouse gases and energy at sites around the world for over three decades. There are estimates that more than 2,000 towers operating worldwide allow noninvasive measurement of these fluxes at high temporal resolution and ecosystem level, and over an area that extends up to hundreds of meters beyond the point of measurement. The tool provides important insights into changes taking place within tundra, grasslands, savanna, and crops, to conifer, deciduous, or tropical forest.
Each of these sites contributes data to a regional network such as the European Database and AmeriFlux which were established to connect research using eddy covariance at field sites across Europe and the Americas. Later FLUXNET was created as a global network to foster collaboration among these two regional networks, and in 2000 the first FLUXNET dataset made it possible for researchers to create global eddy covariance datasets from these observations for the first time.
“Apart from eddy covariance, there’s literally no other way to show what’s happening between surface and the atmosphere at an ecosystem level,” said Pastorello. “There is more and more awareness of how useful a tool eddy covariance can be to understanding what is happening to the water cycle and the carbon cycle, in particular.”
The improvements to the FLUXNET2015 dataset–which has already been used by authors of 400 scientific papers since its debut in 2015–came from an awareness of the need for making it easier to use and cite the data.
“We really wanted to give the scientific community a reference guide for using the dataset,” Pastorello said. “This paper serves as that guide. We’ve also moved to a more standardized use policy. Now the citation process has been streamlined so that data contributors are easy to acknowledge. ”
The team also added metadata to the datasets to simplify their use. For example, they collected information on the position of different sensors used in the acquisition of certain data. “If you have data on soil sensors, but don’t know where they are positioned this makes the data about soil more difficult to use,” Pastorello said.
This data and data like it are essential to answering so many different scientific questions. “Climate modelers, carbon and water modelers, researchers who look at how vegetation behaves, and others, rely on this data derived using eddy covariance,” Pastorello said. “So do microbiologists and scientists looking for ways to improve remote-sensing techniques. The enhancements to the FLUXNET dataset make this data more accessible to helping answer some of the most important environmental questions of the times.”