At the end of December, we’re saying goodbye to a project that has long been part of the work of many researchers in the Department of Soil, Water, and Climate: the SPRUCE experiment, sponsored by the US Department of Energy and housed at the USDA Forest Service Marcell Experimental Forest just north of Grand Rapids, MN. SPRUCE stands for Spruce and Peatland Responses Under Changing Environments. Peatlands are wetland ecosystems with accumulations of partially decayed organic matter called peat. Globally, peatlands store ⅓ of terrestrial carbon, although they only cover 3% of the planet’s surface.
The SPRUCE experiment consists of several large domed structures located in a peat bog (a specific type of peatland). Each dome is controlled to a different temperature relative to the temperature outside to study the impact of climate change on peatland environments, including their vegetation and soil.
Over the last decade, the SPRUCE experiment has been a success story of interagency and transdisciplinary collaboration. Randy Kolka, SWAC faculty member and USDA Forest Service representative on the project, says that “the level of collaboration across disciplines and organizations has been unprecedented,” leading to discoveries not otherwise possible.
“There have been literally hundreds of collaborators working on SPRUCE over the decade,” Kolka says, “from undergrad students to the preeminent peatland and climate change scientists on the planet.” This massive group has included scientists at all stages in their careers, from professors and government agency professionals to graduate and undergraduate students.
Several SWAC faculty and their teams are among those who’ve been conducting research at SPRUCE over the last ten years. SWAC faculty members Jess Gutknecht, Brandy Toner, and Ed Nater (emeritus) have worked throughout the experiment on mercury and sulfur cycling at the site. Even within the SWAC team of researchers, the work is interdisciplinary, including soil microbiology, geochemistry, and more.
The ongoing work around mercury cycling has yielded a glimpse into how the element builds up in our natural environment. “The bottom line appears to be that warming leads to increased availability of the bioaccumulative form of mercury (methylmercury) in soil water and hence to downstream biota,” Kolka explains; in layman’s terms, the more warming occurs, the more mercury ends up building up in animals and plants downstream from the peatlands. Mercury in its gaseous form was also found to be higher as warming increases, which means it could be deposited in higher levels downwind of the peatlands.
Other key findings include a documented flip from peatlands as carbon sinks (storing carbon) to carbon sources (emitting carbon) as warming occurs, fueling future climate change, as well as a shift in peatland plant communities toward dominance by shrubs (especially blueberries), shading out the peatlands’ characteristic sphagnum moss, the most important plant in the system from a carbon storage perspective. The increase in plant activity has led to higher evapotranspiration rates, which lowers water tables and allows certain microbial communities to decompose more rapidly, releasing even more carbon. These results highlight the importance of peatlands to the understanding how our climate will continue to change in the future.
At the beginning of the experiment, according to Kolka, the goal was to build a large, one-of-kind experiment that could test the effect of climate change on the terrestrial ecosystem that stores the most carbon on the planet. “We hoped it would interest the scientific community enough to bring additional leveraged resources to the research,” he says. “That has happened many times over; as a result, the level of collaboration across disciplines and organizations has been unprecedented, leading to discoveries not possible without the truly transdisciplinary nature of SPRUCE.”
“It’s really exciting to work on these bigger projects where you have all this data, and knowledge, and history,” says SWAC professor Brandy Toner, who has been a part of the SPRUCE experiment from the start. “There’s a special feeling at the beginning of a project like this, and now an equally special feeling at the end.”
After the experiment closes at the end of 2025, a phase of “destructive sampling” begins. Throughout the experiment, access has been limited to certain planned sampling events to protect the integrity of the site throughout the life of the project and make sure there was material (soil, vegetation) left at the end. During destructive sampling, the restrictions are loosened and many more samples are allowed to be collected.
"As SPRUCE winds down and we get our last samples and measurements, the end is really the beginning,” Kolka says. “It will be the 10 year results that will have the most scientific impact and lead to the integration of peatlands in the development of better global circulation models that predict our future climate.”
Over the summer, we visited the SPRUCE experiment during a soil sampling event and had the chance to see first hand the science happening there. To see for yourself, check out the video below:
Story, photos, and video by Nora Poole