Study on emissions breaks new ground in Peru’s palm-swamp peatlands

Degraded peatland area. CIFOR/Kristell Hergoualc'h

A new study marked a series of “firsts” for understanding greenhouse gas (GHGs) emissions and land degradation in the palm-swamp peatlands of the Pastaza-Marañon Basin in Peru.

The palm-swamp peatlands, dense in Mauritia flexuosa palms, store vast amounts of carbon. Their waterlogged conditions allow organic matter in the soil to slowly decompose and accumulate over thousands of years. However, this ecosystem is still largely misunderstood and understudied. Between 2015 and 2018, a collaborative team of research institutions led by the Center for International Forestry Research and World Agroforestry (CIFOR-ICRAF) — and with joint efforts from the Peruvian Amazon Research Institute (IIAP) — pioneered the first long-term study on soil nitrous oxide (N₂O) and methane (CH₄) fluxes in palm swamps of the Peruvian Amazon.

It was also among the first to look at how these GHG emissions vary with different levels of forest degradation.

“Our research offers really important data for the country [Peru] if they want to report their emissions from peatlands,” said lead author and CIFOR senior scientist, Kristell Hergoualc’h. “These are local, robust estimates that policy makers and governments can use in their national reporting. The default emission factors for peatlands, up until now, were taken from the IPCC guidelines, which were developed using data from Southeast-Asian peatlands.”

Unsustainable fruit harvesting leads to deforestation

One of the main causes of degradation in the palm swamps, known locally as “aguajales,” is the unsustainable harvesting of aguaje fruits. These fruits grow on the M. flexuosa palms and are key ingredients in traditional drinks and recipes. Because the fruit grows so high up in the trees, it is often easier to cut down the whole palm to harvest it. Such forest degradation has had measurable effects on the landscape.

Thirty-one percent of palm swamps are severely degraded, 42 percent are moderately degraded and 27 percent have low levels of degradation, according to a 2017 study which looked at a 350,000 ha sample area in Peru. Degradation could affect the ratio of the palm swamps’ natural mosaic of hummocks — raised areas made up of the palms’ root structures — and hollows — the low, flooded areas in between. In the most recent publication,

Hergoualc’h and her team theorized that GHG emissions could be affected by continued changes in site-level microtopographies as well as macro-level changes, which combine microscale measurements with tree density.

“In Indonesia, the ratio of hummocks to hollows is about 50:50,” said Hergoualc’h. “In our study, which also helped to quantify this ratio for South American, palm-swamp peatlands, hollows made up more than 80 percent of the total surface area. These environmental differences between Southeast Asia and South America, in addition to degradation gradients, could affect the amount of GHG emissions that is released from peatlands.”

Linking GHG emissions to peatland degradation and other environmental factors

Over the study’s three-year period, the team examined three sites representing an undegraded (intact) site, moderately degraded site and highly degraded site. They measured soil nitrous oxide and methane fluxes along with environmental factors such as temperature, water table depth (WT) and water-filled pore space (WFPS) in the soil.

While degradation levels did lead to changes in GHG emissions at the microscale, there was little to no change in emissions at the macroscale, according to the study. However, water levels did play a large role in GHG fluxes at the three sites.

Soil net nitrification rates and both WT and WFPS levels significantly influenced nitrous oxide emissions. In addition, the research team found a strong relationship between methane emissions and rainfall: more rain leads to greater methane emissions. This is because the lack of oxygen in flooded palm-swamps stimulates microorganisms to produce more methane than they consume.

Satellite images have already shown that tropical South American wetlands have higher methane emissions than those in tropical Southeast Asia. However, the link this study found between rainfall and methane is significant considering that climate-change estimates for this region in South America predict long-term increases in rainfall. Hence, the study suggests the palm swamps will also see long-term increases in emissions.

“There has already been global concern about increased methane emissions from melting permafrost associated with higher global temperatures,” said Hergoualc’h. “For the Amazon, we still do not have much data, but our study shows that more rainfall due to climate change could be yet another cause of increased methane emissions.”

Additionally, the scientists found that nitrous oxide levels in Peruvian palm swamps were significant, despite the water-flooded environment. Normally, one would expect the reduced oxygen levels in the swamps to cause nitrous oxide to reduce to N₂, leading to minimal emissions.

However, nitrous oxide emissions in the peatlands have remained counterintuitively high, remarked Hergoualc’h. The magnitude of emissions for both gases observed in this study, as well as their correlation with the peatland’s water levels, highlights the need to improve bio-geochemical modeling of these GHGs, according to the study.

The way forward

While Hergoualc’h noted that this study’s findings may not be representative of all sites in the Amazon, it is a first step towards understanding their contributions to mitigate or exacerbate climate change.

“We are working with the Peruvian government because they want to include peatlands in their Nationally Determined Contributions (NDCs),” said Hergoualc’h. “They want to know how much they could decrease GHG emissions if they put in place a plan for sustainable management of these forests.”

The context-specific knowledge that studies like these provide help support sustainable policy shifts at the national level and beyond.

During the COP26 in Glasgow, a representative from Peru’s Ministry of the Environment spotlighted opportunities for private investment in Peru’s aguajales that would encourage sustainable fruit-harvesting practices.

Cross-sectoral opportunities like these that bring together policy makers, local communities, corporations and scientists are key to developing sustainable value chains and restoring peatlands.