ST. PAUL and DULUTH, Minn. — A new study led by Minnesota Sea Grant researchers finds that shallow lakes with invasive common carp, which are common across Minnesota, can produce less methane than lakes without carp, but the reduction is linked to degraded lake conditions, not improved water quality.
“This was almost a shocking outcome. We expected methane emissions to rise in lakes with carp because of higher nutrient levels,” said co-author and Minnesota Sea Grant Director John A. Downing. “But over time, carp alter the sediments in ways that reduce the lake’s ability to produce methane.”
The paper, published in Limnology and Oceanography Letters in April, analyzed greenhouse gas emissions from 18 shallow lakes in southern Minnesota, comparing lakes with and without carp.
"This study shows that invasive species can fundamentally change how lakes process carbon, sometimes in very unexpected ways,” said lead author Joseph S. Rabaey, postdoctoral fellow at the University of Minnesota Duluth Large Lakes Observatory and Minnesota Sea Grant.
Methane is a potent greenhouse gas, and emissions from lakes are often expected to increase as nutrient levels rise. Carp are known to increase nutrients and turbidity in lakes, so researchers initially expected methane emissions to be higher where carp are present. Instead, the study found the opposite pattern. Lakes with carp had significantly lower methane emissions than carp-free lakes.
The explanation lies in what carp do to lake bottoms. Carp feed by disturbing sediments, a process known as bioturbation. Over time, this activity reduces the amount of organic matter and phosphorus stored in sediments. Those materials help fuel methane production. With less of that material available, methane emissions decline.
“Lower methane emissions might sound like a benefit, but it reflects a loss of sediment quality,” said Rabaey. “Lake sediments are a key part of how lakes function. When they are disturbed and depleted, it affects the entire system.”
The study also found that lakes with carp had poorer water quality overall, including higher nutrient concentrations, more turbidity, and fewer aquatic plants. These changes are consistent with previous research on carp impacts in Minnesota lakes.
For lake managers and communities, the findings add context to how carp affect lake health. Reduced methane emissions do not indicate a healthier lake. Instead, they signal long-term changes to sediment processes that support water quality, fish and other aquatic life.
“Sediments are where much of a lake’s biological activity happens,” Downing said. “When that system is disrupted, it has consequences for habitat, water clarity, and how nutrients cycle through the lake.”
The study focused on shallow lakes, which are common across Minnesota and especially vulnerable to carp invasion. More than 70 percent of lakes in the study region have established carp populations.
Carp management is a major public investment, and for Minnesota lake managers, the takeaway is straightforward. Controlling carp remains important for protecting water quality, habitat, and the underlying processes that support lake ecosystems.
Co-authors include Brian J. Huser of the Swedish University of Agricultural Sciences and Przemyslaw G. Bajer of the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota.
The study was funded in part by the Minnesota Environment and Natural Resources Trust Fund and the Minnesota Aquatic Invasive Species Research Center. Minnesota Sea Grant contributed to the research through federal and state support.
Minnesota Sea Grant is a system program of the University of Minnesota and one of 34 federal-university Sea Grant partnerships across the country supported by the National Oceanic and Atmospheric Administration in Great Lakes and coastal states that encourage the wise stewardship of our marine resources through research, outreach, communication, education and technology transfer.
CONTACTS:
John A. Downing, Director, Minnesota Sea Grant, University of Minnesota and University of Minnesota Duluth, [email protected].
Joseph Rabaey, Postdoctoral Fellow, Minnesota Sea Grant, University of Minnesota and University of Minnesota Duluth, [email protected].
Marie Thoms, Associate Director, Communications Director, Minnesota Sea Grant, University of Minnesota and University of Minnesota Duluth, [email protected].