Cornell scientists divided 3 ponds into different plant plots; some had more methane in the water, yet gas escaping into the air did not increase as expected

Ponds play a larger role in the planet’s climate than their size would suggest, and new research from Cornell University shows that the plants growing in them may matter more than previously thought. A 2025 study titled “Freshwater plant communities influence water column greenhouse gases,” published in the journal Aquatic Botany, found that the composition of plants in a shallow freshwater pond, such as duckweed, algae and underwater ‘water weeds,’ can cause significant changes in the amount of methane, carbon dioxide and nitrous oxide produced and stored. Ponds and other small bodies of water make up a large proportion of the greenhouse gases on our planet, and this research demonstrates that we may be able to alter the way they are landscaped and maintained to help.

The experiment: plant corrals in real ponds

Meredith Theus, a doctoral student at Cornell and the study’s lead author, carried out the experiment, setting up plant corrals (mesocosms) in three separate ponds at the Cornell Experimental Ponds Facility. Each mesocosm contained either fully submerged plants rooted in the sediment, partially submerged plants plus floating plants such as duckweed, or phytoplankton, microscopic algae that float freely on the water’s surface. Every two weeks, she measured the concentration of dissolved gases in the water and the flux of the gas.


The twist nobody expected

Surprisingly, those mesocosms containing partially submerged and floating plants had the highest concentrations of dissolved methane and carbon dioxide. This would logically mean that there would be the highest amount of gas being released into the atmosphere, but flux measurements showed no real difference.

Meredith A. Holgerson, an assistant professor of ecology and evolutionary biology at Cornell and senior author of the study, explained that duckweed floating in a thick mat may act like “a lid” that usually traps gases within the pond, under normal, undisturbed conditions. Her previous research had highlighted that the duckweed can trap gases within the pond. Additionally, duckweed roots are known to be home to methane-eating bacteria called methanotrophs, which may be consuming some of the gas.

Why this matters beyond one pond in New York

Per EPA’s own overview of methane’s climate impact, methane is around 28 times more efficient at trapping heat in the atmosphere than carbon dioxide when measured over a 100-year period, a far longer window than the two-week sampling intervals used in this experiment, so the comparison speaks to methane’s long-term warming potential rather than anything directly measured in the study itself. Freshwater systems are a much larger source of global methane emissions than most people realize. A highly-cited 2021 study titled “Half of global methane emissions come from highly variable aquatic ecosystem sources,” by Holgerson et. al., published in the journal Nature Geoscience, found that aquatic environments including lakes, ponds, wetlands, and rivers are responsible for around 50% of the methane emitted on our planet.

As a generation of Americans are purchasing homes with backyard water features or HOA retention ponds, this information becomes relevant. Many people will feel the urge to remove messy underwater plants to create a ‘swimmable’ pond or allow duckweed to take over due to its lush appearance; however, this is actually an environmental decision.

The honest caveat

Theus did not claim the research would prevent climate change. Because flux measurements weren’t taken daily, duckweed mats may have been pushed aside by wind on occasion, meaning some emission spikes could have gone uncaptured, a limitation distinct from, not contradictory to, the general “lid” effect described above. The chemistry behind the experiment: the pond’s “black box,” was still not fully understood at the time of publication. However, the researchers said the work opens up a new area of study, demonstrating that managing plants within a pond could offer a small but useful way to help with climate change for the millions of small bodies of water across America’s backyards, parks and golf courses.