Draining Peatlands Turns Global Carbon Sinks Into Carbon Bombs, Massive Analysis Finds

Peatlands occupy less than three percent of Earth’s land surface, yet they hold roughly one third of all the carbon stored in the planet’s soils, an estimated 600 to 942 gigatonnes accumulated over millennia in waterlogged, oxygen-poor conditions that suppress decomposition. A sweeping new systematic review and meta-analysis, published in the journal Environmental Management, has now compiled annual carbon dioxide exchange measurements from 120 peatland sites across 28 countries to answer a deceptively simple question with profound climate implications: which peatlands still function as carbon sinks, which have flipped into carbon sources, and what drives the difference? The answer, distilled from 58 peer-reviewed studies, is stark. Agriculture converts peatlands into powerful emission engines, degraded peatlands are significant net sources of carbon dioxide, water table depth is the single most important environmental control on carbon exchange, and restoration, at least in the near term, does not reliably restore sink function.

The research team, led by Charuni Jayasekara of RMIT University together with colleagues at the University of Melbourne, Queensland University of Technology, the Queensland Herbarium and La Trobe University, conducted a systematic quantitative literature review following established PRISMA-style protocols. From an initial pool of 341 articles identified through databases including Web of Science, Scopus and Google Scholar, the authors applied strict inclusion criteria: only field-based studies reporting annual net ecosystem exchange values, meaning full-year measurements or repeated seasonal measurements extrapolated to a complete year, qualified for analysis. Plot-scale studies smaller than ten square meters, laboratory experiments and short-term snapshots were excluded to ensure that every data point represented the carbon balance of a functioning ecosystem at policy-relevant temporal scales. The final dataset of 58 articles and 120 sites spans both hemispheres, every continent except Antarctica, and measurement records ranging from a single year to an exceptional 17-year series.

The quantitative picture that emerges is one of dramatic divergence between land uses. Peatlands under their original, undrained land use were, on average, net carbon sinks absorbing about 30 grams of carbon per square meter per year, while agricultural peatlands emitted a mean of 490 grams of carbon per square meter per year, a statistically significant difference. Among agricultural categories, tropical plantations were the worst offenders, averaging 1,132 grams of carbon emitted per square meter annually, with the single highest recorded emission of 3,758 grams coming from an oil palm plantation established on drained tropical peat. Pastures and croplands each emitted roughly 420 grams per square meter per year. Peat extraction sites were also net sources, though less extreme, at around 137 grams. The underlying mechanism is well understood: drainage lowers the water table, exposing previously saturated peat to oxygen and accelerating aerobic microbial decomposition of organic matter that took centuries to accumulate, while the removal of natural vegetation simultaneously eliminates the photosynthetic uptake that once offset respiration.

Peatland condition told a parallel story. Degraded sites, about 55 percent of the dataset, averaged net emissions of 306 grams of carbon per square meter per year, significantly higher than intact sites, which averaged a net uptake of 124 grams. But the most consequential finding concerns restoration. Of the 18 restored sites in the analysis, the category as a whole remained a net carbon source, averaging 110 grams of emissions per square meter per year, and 39 percent of individual restored sites were still emitting carbon dioxide at the time of measurement. The authors attribute this to insufficient recovery time, incomplete hydrological recovery, legacy effects of severe degradation, and in some cases restoration methods that prioritize biodiversity or hydrological objectives over immediate carbon benefits. Severely degraded sites that have lost substantial peat may require many decades to regain sink function, and some may never return to it.

The single most powerful predictor of carbon exchange across all peatland types and climatic zones was water table depth. Across 98 sites with paired hydrological data, the regression analysis revealed that every centimeter of water table drawdown increases carbon dioxide emissions by approximately 7.2 grams of carbon per square meter per year. The relationship explained about 19 percent of the variance in net ecosystem exchange and, critically, identified a transition point: peatlands shift from net sink to net source when the water table drops to roughly 7.8 centimeters below the peat surface. This figure aligns closely with hydrological tipping points reported in other experimental studies, which place the threshold between about 14 and 24 centimeters depending on peatland type. The finding carries direct policy weight, because it converts an abstract ecological principle into a concrete management target: keep the water table within a few centimeters of the surface, and the peatland keeps functioning as a carbon bank; drain it, and the stored carbon begins flowing into the atmosphere.

Climatic geography added further nuance. Tropical peatlands were the strongest mean net sources, emitting on average 270 grams of carbon per square meter per year, and showed by far the greatest variability, a reflection of the intense land-use pressure they face, particularly in Southeast Asia where peat swamp forests are being rapidly converted to plantations. Alpine and sub-polar peatlands, by contrast, were the strongest sinks, absorbing roughly 34 to 37 grams per square meter per year. Temperate sites, which dominated the dataset at 77 percent of all locations, averaged as net sources overall, largely because so many European temperate peatlands have been drained for agriculture. Vegetation type mattered independently of land use: native shrub and grass systems and moss-dominated sites were mean sinks, while tree-dominated natural sites averaged as sources, and every agricultural vegetation category was a net emitter.

Perhaps the most sobering pattern in the data concerns the reliability of simple classification schemes. Nineteen percent of sites classified as intact were actually net carbon sources, while 21 percent of degraded sites were net sinks. This means that categorical labels based on land-use history or visual assessment cannot reliably capture the functional carbon status of a peatland. The authors point to several explanations: natural interannual variability means one or two years of measurement may misrepresent long-term trajectories; cryptic degradation through nitrogen deposition, invasive species or subtle hydrological shifts can erode sink function without visible structural change; and in some counterintuitive cases, vegetation changes following disturbance, such as dense tree establishment on a drained bog, can increase photosynthetic uptake enough to maintain or even strengthen net carbon sequestration despite lowered water tables.

The review also exposed a glaring geographic bias in the science itself. Eighty-six percent of the 120 sites lie in the Northern Hemisphere, and 60 percent are in Europe, with Germany, Denmark, Ireland and Latvia alone hosting dozens of studies. Only 14 percent of sites are in the Southern Hemisphere. Africa and South America contributed just three sites each, and Oceania six, despite these regions containing substantial, carbon-dense and highly threatened peatlands. The authors attribute the gap to technical, financial and political constraints on establishing long-term flux monitoring infrastructure, seasonal logistics in cold climates, and the likelihood that research from underrepresented regions exists in non-English or gray literature inaccessible to global syntheses. This underrepresentation is particularly troubling for tropical peatlands, which hold the largest share of global peatland carbon, accumulate carbon faster than their boreal counterparts, at rates of 59 to 145 grams per square meter per year, and face the fastest rates of conversion for agriculture and forestry.

Methodological fragmentation compounds the problem. The review identified 22 different software programs used to process carbon flux data, 15 for eddy covariance measurements alone, alongside fundamentally different measurement approaches: eddy covariance systems integrate fluxes over footprints of 100 to 1,000 square meters continuously, while chamber methods sample patches of less than one square meter and require spatial upscaling and temporal interpolation to estimate annual budgets. Different gap-filling algorithms, quality control protocols and chamber placement strategies introduce inconsistencies that may partly explain the enormous variability observed in restored peatland fluxes, which ranged from a sink of 397 to emissions of 1,170 grams of carbon per square meter per year. The authors argue that methodological standardization, combined with longer monitoring periods, since 43 of the 120 sites reported only a single year of data, is essential if net ecosystem exchange is to serve as a dependable restoration monitoring tool.

The implications extend from national greenhouse gas inventories to the growing portfolio of nature-based climate solutions. With approximately 65 million hectares, 16 percent of the world’s peatlands, already drained, and degraded peatlands responsible for roughly three percent of anthropogenic greenhouse gas emissions in 2020, the evidence assembled here supports a clear hierarchy of action: protect intact peatlands before they are lost, rewet drained ones with water table targets anchored to reference conditions from functioning sink systems, and commit to long-term monitoring and adaptive management rather than expecting rapid carbon payback from restoration. The authors also caution that raising water tables promotes methane production, meaning that the net climate benefit of any restoration project should be judged against the full greenhouse gas balance, not carbon dioxide alone. What the synthesis makes unmistakable is that the fate of hundreds of gigatonnes of soil carbon now hinges on a hydrological variable measurable with a ruler: centimeters of water above or below the peat surface.

Subject of Research: Global patterns and drivers of net ecosystem exchange in peatlands across land use and environmental gradients

Article Title: Global Patterns of Net Ecosystem Exchange in peatlands: A Systematic Review and Meta-analysis of Drivers Across Land Use and Environmental Gradients

Article References: Jayasekara, C., Leigh, C., Shimeta, J., Silvester, E., & Grover, S. (2026). Global Patterns of Net Ecosystem Exchange in peatlands: A Systematic Review and Meta-analysis of Drivers Across Land Use and Environmental Gradients. Environmental Management, 76(9), Article 310. https://doi.org/10.1007/s00267-026-02621-y

Image Credits: AI Generated

DOI: 10.1007/s00267-026-02621-y

Keywords: peatlands, net ecosystem exchange, carbon cycle, water table depth, peatland restoration, land use change, CO2 emissions, carbon sink, drainage, tropical peatlands, meta-analysis, nature-based climate solutions