Duluth, Minn. — It might come as a surprise to some Minnesotans, living in a state rich with lakes and rivers, that science has not always recognized the crucial role that inland waters play in transporting, transforming, and emitting carbon. That understanding changed significantly with a landmark 2007 paper, which has earned the authors one of the highest honors in the aquatic sciences.
The paper, "Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget," published in the journal Ecosystems, challenged the long-standing view that terrestrial ecosystems and oceans are the primary players in the carbon cycle. The research, conducted by 11 scientists, revealed that rivers, lakes, reservoirs, and streams do far more than simply transport carbon from land to sea—they actively process and release it, reshaping our understanding of carbon sinks and sources.
For their groundbreaking contributions, the study’s authors will receive the 2024 John Martin Award from the Association for the Sciences of Limnology and Oceanography (ASLO) at its 2025 annual meeting. The award recognizes aquatic science papers that have had a profound impact on subsequent research.
“This was a transformational study that changed how scientists perceive land-water-atmosphere interactions in the carbon cycle,” said co-author John A. Downing, a limnologist and Director of Minnesota Sea Grant. Downing will accept the award on behalf of the research team.
A major shift in carbon cycle science
Prior to this study, inland waters were mostly seen as passive conduits, merely moving carbon from land to the ocean. The research showed that these water bodies are, in fact, active players in the carbon cycle, significantly altering carbon’s form before it reaches the sea.
“We found that roughly twice as much carbon enters inland aquatic systems from land as is exported from the land to the sea,” said Downing. “This means a substantial amount of carbon doesn’t make it to the sea but is instead released into the atmosphere as carbon dioxide or buried in sediments.”
The study estimated the annual amount of carbon that inland waters process and how much carbon dioxide those waters emit into the atmosphere using a measure called a teragram (Tg). For comparison, San Francisco’s Golden Gate Bridge and New York City’s Chrysler Building each weigh about 1 teragram.
The research team estimated that inland waters process about 1,900 teragrams of carbon per year and emit about 750 teragrams of carbon as carbon dioxide to the atmosphere, a significant flux that had been previously overlooked in global carbon models.
Implications for climate science and policy
By revealing that carbon traditionally thought to be passed directly from terrestrial ecosystems to the ocean was actually moving through and being released from and sequestered by inland waters, the research rewrote conventional global models. Scientists now recognize that excluding inland waters creates major gaps in carbon cycle models—with direct implications for climate change mitigation and policy decisions.
Since its publication, the study has influenced how scientists, policymakers, and environmental managers approach carbon accounting, climate modeling, and freshwater ecosystem conservation.
“This publication has been cited by 4,360 other peer-reviewed publications and the research stimulated by this publication is covered more in the news than any other aquatic science topic,” said Downing.
A lasting legacy
The recognition of this research by the John Martin Award underscores its lasting impact on the field of limnology and beyond. As climate scientists continue refining carbon budgets and global models, the findings from this study remain crucial to ensuring accurate predictions and effective policy responses.
Nina Caraco, one of the authors and partner of the late Jon Cole, the first author, designated Downing to accept the award on behalf of the research team.
“I am deeply honored to have been chosen to accept this award on behalf of all the authors of this outstanding international team,” Downing said. “Jon was a brilliant scientist and will be greatly missed.”
CONTACTS:
John Downing, Director, Minnesota Sea Grant, University of Minnesota and University of Minnesota Duluth, [email protected].
Marie Thoms, Communications Manager, Minnesota Sea Grant, University of Minnesota and University of Minnesota Duluth, [email protected].