This article was written by Serge, MSc. Plant Biologist and Environmental Scientist with a BSc in Plant Biology and an MSc in Environmental Biology and Biogeochemistry. My background covers plant biochemistry, botany, and field research in forest and soil ecosystems. I write from real experience, not just literature.
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Peatlands store more carbon than all the world’s forest vegetation combined, roughly twice as much. That single fact stopped me when I first encountered it during my biogeochemistry training.
We spend enormous energy discussing forest conservation and atmospheric CO₂, yet the ecosystem sitting quietly under our feet in bogs and fens holds a carbon archive that dwarfs anything above ground. Wetlands carbon storage is one of the most underrated parts of the climate story.
Wetlands are not scenic backdrops. They are among the most biogeochemically active ecosystems on Earth, and understanding how they work changes how you think about climate, water and land use.
What Wetlands Are
Wetlands are ecosystems where water saturation of the soil dominates the environment and shapes the plants and animals living there. That saturation is what makes them biogeochemically extraordinary.
When soil is waterlogged, oxygen cannot penetrate. Decomposition slows dramatically, because the microbes that break down organic matter most efficiently are aerobic and need oxygen. In waterlogged conditions, anaerobic decomposition takes over instead.
It is slower, less complete, and produces different by-products, so organic matter accumulates rather than fully breaking down. It is the opposite of a well-turned compost heap, where plenty of oxygen keeps decomposition fast, as I explain in how composting works.
The plants themselves help too. Sphagnum moss, the main peat-builder in northern bogs, makes its surroundings acidic and nutrient-poor, and its tissues contain phenolic compounds that inhibit the enzymes microbes use to break organic matter down. It is a striking example of the defence chemistry I describe in why plants produce secondary metabolites, working at the scale of a whole landscape.
Over thousands of years, this accumulation builds peat: compressed layers of partially decomposed plant material that can be many metres deep. The carbon fixed by plants over millennia stays locked in that peat rather than cycling back to the atmosphere.
This is the fundamental mechanism behind wetland carbon storage, and it works because of the chemistry of oxygen-depleted soil.
The Carbon Numbers That Matter
In my biogeochemistry training I studied the global carbon cycle in detail, including how different ecosystems act as carbon sources or sinks. The wetland carbon story is striking.
Peatlands cover only around 3 percent of the Earth’s land surface but store an estimated 550 to 650 gigatonnes of carbon, roughly equal to 60 years of current global fossil fuel emissions held in one type of ecosystem.
Northern boreal peatlands, the type most relevant to the high-latitude environments I studied, are particularly significant stores, because cold temperatures slow decomposition even further. My own soil respiration measurements showed how sensitive that decomposition is to warming, which I describe in soil temperature and carbon cycling.
The carbon density of peat is extraordinary compared with other land ecosystems. A deep peat bog holds more carbon per square metre than almost any forest, because the carbon has been accumulating for thousands of years rather than cycling through a few decades of forest growth and decay.
The Methane Complication
Wetlands are also the largest natural source of methane, and this deserves an honest look rather than being glossed over.
Anaerobic decomposition in waterlogged soils produces methane as a major carbon by-product. Methanogenic archaea, the microbes responsible, cannot function in the presence of oxygen and thrive in the permanently saturated lower layers of wetland soils.
The methane they produce is either oxidised in the oxygen-rich surface layer before it reaches the air, or escapes as bubbles, by diffusion, or through the hollow stems of wetland plants such as sedges.
Methane is a far more potent greenhouse gas than CO₂ over short timescales, trapping roughly 80 times more heat per tonne over 20 years. Wetland methane emissions are therefore a real climate consideration, not just a footnote.
The net climate effect of a wetland depends on the balance between carbon sequestration and methane emission. In cold northern peatlands, carbon storage over millennia substantially outweighs the warming effect of their methane, making intact northern peatlands net climate coolers over long timescales. Tropical wetlands have a more complex balance.
The critical point is what happens when wetlands are drained. Drainage lets oxygen into the peat and triggers aerobic decomposition, which is rapid and releases CO₂ at rates that far exceed both the original sequestration rate and the methane emissions of the intact wetland. Drained peatlands become significant carbon sources almost immediately.
It is the same basic process, on a far larger scale, as the carbon loss from repeatedly disturbed farm soil that I discuss in no-till gardening.
Atmosphere-Biosphere Gas Exchange in Wetlands
During my postgraduate training in atmosphere-biosphere exchange, I studied how gases including CO₂, methane and water vapour move between ecosystems and the atmosphere.
Wetlands are particularly interesting in this context, because they are doing several things at once: taking in CO₂ through plant photosynthesis, releasing CO₂ through aerobic decomposition near the surface, releasing methane from anaerobic decomposition deeper down, and exchanging water vapour at high rates thanks to their saturated conditions.
Eddy covariance systems, the measurement approach I trained in, are used widely to measure net ecosystem exchange in wetlands.
The data generally shows that intact temperate and boreal peatlands are net carbon sinks over the year, absorbing more carbon through photosynthesis than they release through decomposition and methane combined, although individual sites can flip to being sources in unusually dry or warm years.
Mangroves: The Coastal Carbon Story
Mangroves deserve specific attention, because their carbon dynamics differ from inland peatlands in important ways.
Mangrove forests store carbon in both their biomass and their waterlogged soils, where the same anaerobic mechanism that builds peat is at work. Mangrove soil carbon densities are among the highest measured in any ecosystem, partly because mangroves trap sediment and organic matter carried in by coastal waters.
Mangroves also protect coastlines by absorbing wave energy and reducing storm surges, improve water quality by trapping sediment and nutrients, and provide nursery habitat for commercially important fish. Their loss has cascading effects well beyond carbon.
Globally, mangrove cover has declined significantly because of coastal development, aquaculture and land clearing. When mangroves are cleared, the carbon stored in their soils is released, often quickly, because disturbance exposes previously stable carbon to aerobic decomposition.
Water Quality and Nitrogen Cycling
My Water Risk Management training covered how wetlands interact with agricultural and urban water systems. This is where wetland function has the most direct practical relevance for most people.
Wetlands remove nitrogen from water through denitrification, in which anaerobic bacteria convert nitrate into nitrogen gas that returns to the atmosphere. This is the same nitrogen cycling process I studied in my biogeochemistry training in the context of soil nutrient dynamics.
Some nitrous oxide, a potent greenhouse gas, can be released along the way, but well-placed wetlands between farmland and water bodies can often remove half or more of the nitrate flowing through them, significantly reducing eutrophication in downstream lakes and rivers.
Phosphorus is removed through binding to sediment particles and uptake by wetland plants. How efficiently a wetland does this depends on hydraulic residence time: the longer water spends in the wetland, the more nutrients are removed.
This makes wetland restoration in farming catchments one of the most cost-effective water quality measures available, often far cheaper than engineered water treatment for the same nutrient removal. Forests do similar work for water further up the catchment, as I explain in deforestation and the water cycle.
Why Wetland Loss Matters Beyond Carbon
I want to be direct about something the standard wetland conservation story often softens. Wetland loss is not mainly a future risk. It has already happened at scale.
The Ramsar Convention’s 2018 Global Wetland Outlook estimated that around 35 percent of the world’s wetlands were lost between 1970 and 2015, although estimates vary with the method used. In many temperate farming regions, more than half of historical wetland area has been converted to farmland.
The carbon released by that drainage is already in the atmosphere, and the loss of wetland species is part of a wider pattern I discuss in biodiversity loss and human health.
Restoring degraded wetlands rewets the peat, slows aerobic decomposition and lets carbon accumulation resume. But the carbon lost during drainage is not recovered on any human timescale. Rewetted peatlands take hundreds to thousands of years to rebuild the stores that drainage destroyed in decades.
This asymmetry, fast loss and slow recovery, is the core argument for protecting wetlands rather than relying on restoring them. Prevention is orders of magnitude more effective than repair.
What Gardeners Can Do
One of the most direct links between your garden and peatland carbon is the bag of compost you buy. Many potting composts are still made from extracted peat, and every bag means peat that was drained and dug from a bog. Choosing peat-free compost, or making your own, keeps that carbon in the ground.
My free mulch and compost calculator tells you exactly how much you need, so nothing goes to waste. Food choices matter too, since a great deal of drained wetland now grows crops and animal feed, as I explore in plant-based food and climate change.
FAQs
How do wetlands store carbon?
Through slow, anaerobic decomposition in waterlogged soils, which is less complete than decomposition with oxygen. Peat-forming plants like sphagnum add compounds that slow decay even further. Organic matter builds up over thousands of years instead of fully breaking down, forming deep peat deposits that keep carbon out of the atmosphere.
Do wetlands emit greenhouse gases?
Yes, mainly methane from anaerobic decomposition in saturated soils. Intact northern peatlands are still net climate coolers over long timescales, because their carbon storage outweighs the warming from their methane. Drained peatlands become significant net carbon sources.
What happens to wetland carbon when they are drained?
Drainage lets oxygen into previously waterlogged peat, triggering rapid aerobic decomposition that releases CO₂ far faster than the wetland ever stored it. Drained peatlands become carbon sources almost immediately and can stay that way for decades.
How do wetlands improve water quality?
Through denitrification, in which anaerobic bacteria convert nitrate into nitrogen gas, and through sediment trapping that removes phosphorus. Well-placed wetlands in farming catchments can often remove half or more of the nitrate flowing through them.
Are mangroves more valuable than other wetlands?
They serve different functions. Mangroves have exceptional soil carbon density and provide coastal protection that inland wetlands cannot. Inland peatlands store more carbon in total worldwide. Both are important, and both are under significant threat.
Can wetland restoration reverse carbon losses?
Rewetting stops active carbon loss and lets storage resume, but the carbon lost during drainage is not recovered on human timescales. Restored wetlands take centuries to millennia to rebuild what drainage destroyed in decades. Preventing drainage is far more effective than restoration for the climate.
What is the Ramsar Convention?
An international treaty signed in Ramsar, Iran, in 1971, which commits member countries to the conservation and wise use of wetlands. It designates wetlands of international importance and provides a framework for national wetland policy. More than 170 countries have joined.
