Lakes with vegetated edges are powerful carbon sinks

Lakes are often labeled as steady emitters of carbon dioxide, yet new research suggests that view misses what happens along their edges, where plants work fast and sediments hold tight.

A peer-reviewed analysis finds that when these fringes are included, lakes may act as net carbon sinks at the global scale.

Lake edges are known as littoral zones – the shallow belts where land and water meet, and they wrap around an astonishing length of shoreline.

In fact, the total shoreline of the world’s lakes and reservoirs is estimated to be roughly four times longer than the global ocean coastline. The research was led by Charlotte Grasset of Uppsala University.

Vegetated edges and lake carbon

Add the vegetated littoral zone to the ledger and the balance shifts in surprising ways. A commentary describes how including these zones can substantially alter, and in some cases reverse, whole-lake carbon budgets by boosting burial and trimming apparent outgassing.

The key is that littoral plants take in atmospheric carbon dioxide (CO2) during photosynthesis, send a portion of that carbon below ground, and help trap organic matter in low-oxygen sediments.

Those sediments can store carbon for long periods, changing the net ledger of what lakes contribute to the atmosphere versus what they lock away.

Plants trap and store carbon

Aquatic plants, known as macrophytes, often grow densely in littoral zones and can be highly productive per square foot.

Independent global work has shown that carbon burial in lakes and reservoirs is on the same order as burial in the oceans, underscoring how potent these inland sinks can be.

That background makes the new accounting intuitive. If the most productive, plant-rich parts of lakes were omitted from global budgets, the scale would tilt toward emissions by default, even if sediments at the edges were quietly piling up carbon year after year.

Calculating carbon balance

The study links littoral zones to open-water areas using a simple transport model and a mass-balance approach.

The research builds on recent syntheses showing that global inland waters emit substantial greenhouse gases (GHGs) but also bury a lot of carbon, with regional variation and strong dependence on surface area estimates.

By integrating shoreline vegetation into the budget, the authors report scenarios in which the annual carbon buried in lake sediments exceeds the annual carbon released to the air.

This flips the global lake balance from net source to net sink in their estimates – a change driven by the sheer footprint and productivity of vegetated edges.

Lakes can switch to carbon sinks

One detail is important for interpretation. Part of the CO2 escaping from open-water zones may actually come from carbon originally fixed in the littoral zone, transported horizontally, and then respired offshore.

This suggests that previous attributions may have overestimated the portion coming directly from land.

This adjustment doesn’t eliminate emissions – it clarifies them. It highlights the multiple pathways carbon takes within lakes and shows that the littoral zones do more than just support reeds, frogs, and shallow shelves: they actively process and store carbon on a continental scale.

Lake edges and the carbon budget

“We were planning to write a conceptual paper about how aquatic plants in the littoral zone are overlooked in lake carbon cycling,” said Grasset.

“But after doing some initial calculations quantifying the role of these plants, we quickly realized that littoral zones could be a significant player in the global carbon budget!”

The team’s calculations revealed that factoring in vegetated lake edges can change the overall carbon balance, often transforming lakes from net carbon sources into net carbon sinks.

According to Grasset, the team hopes their findings will encourage further investigation into the importance of littoral zones and highlight the potential benefits of restoring these habitats as part of nature-based climate solutions.

Restoration takes center stage

Marine blue carbon ecosystems such as mangroves, seagrasses, and salt marshes have been treated as nature-based climate solutions for more than a decade, backed by extensive monitoring and finance frameworks.

The new lake analysis argues that freshwater shorelines deserve a similar look, not only for carbon but also for water quality and biodiversity.

There is practical support for that move. Studies show that healthy macrophyte communities help stabilize clearer water states, reduce algal blooms, and retain nutrients, all of which can reinforce carbon burial in sediments while improving ecological conditions for fish and invertebrates.

What’s next for lake edges

Accounting choices for methane (CH4) matter because methane warms more per pound than CO2 over a century, and littoral habitats can be methane hotspots.

Current assessments use IPCC AR6 100-year global warming potentials, where non-fossil methane has a value of about 27 with climate-carbon feedbacks considered, a standard that sharpens cross-gas comparisons and helps frame tradeoffs.

Improved maps of vegetated littoral coverage, better separation of terrestrial versus littoral carbon sources, and year-round measurements in underrepresented tropical and productive lakes would tighten the error bars.

As these data become available, planners can more precisely balance shoreline restoration with other measures to achieve climate, water quality, and habitat objectives.

The study is published in Nature Geoscience.

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