The Cerrado savanna occupies approximately 26% of Brazil and is home to more than 12,000 plant species and diverse wildlife. It is also dotted with groundwater-fed wetlands that serve as stormwater for two-thirds of Brazil’s major waterways, including Amazon Rivermaking it not only a hot spot for biodiversity, but also a critical ecosystem to preserve water safety in the region.
These savanna wetlands also have another superpower: storing carbon in their waterlogged soils. According to a new article published today in New PhytologistThe Cerrado’s wetlands store carbon at a density approximately 6 times greater than the vegetation of the Amazon rainforest.
The article continues below
The team’s findings underscore the need to protect these critically important ecosystems, especially as land use changes, agriculture and climate change threatens to degrade the dark, wet soil and release the carbon into the atmosphere.
Digging for carbon
Previous studies in the Cerrado indicated that the soil contained high amounts of carbon. But researchers typically did not dig deeper than about one meter (three feet) or extend sampling beyond a few high areas in the region. The carbon storage potential of the savannah had been overlooked because it is not easy to spot the wetlands with groundwater from above ground, said Amy Zannean ecologist at the Cary Institute of Ecosystem Studies and co-author of the new study.
Because the ecosystems had been so overlooked, their carbon storage potential has also not been included in Brazil’s national carbon accounts, said Rafael Oliveiraan ecologist at the Universidade Estadual de Campinas in Brazil and co-author of the new paper. Without detailed scientific information, “we have no idea what the emissions are” when these wetlands are degraded. “What are we losing in terms of carbon?” he asked.
To answer that question, Verona and the research team retrieved meter-long soil cores from seven locations in the Cerrado, then tested the layers of those soil cores to determine how much carbon was stored in each. The study’s wealth of data makes an important contribution, said Julie Loisela peatland ecologist at the University of Nevada, Reno, who was not involved in the new study. “It fills a very large data gap,” she said. “When it comes to the importance of wetlands in the tropics to understanding current carbon cycles, most of our information comes from satellite-derived products. We have very little information from field science.”
“It’s really nice to see a study that has really gone above and beyond in terms of measurements.”
The researchers found that, on average, each layer of soil cores stored carbon at a density of 1,200 tonnes of carbon per hectare. That was a surprisingly high number for the soil types tested, Loisel said. Although scientific descriptions differ, a classic definition of peat—the type of carbon-rich soil typically considered in carbon accounting—requires soil to be about 30% organic matter; the soils studied by the research team contained about 16% on average. Still, the amount of carbon stored in the Cerrado soils was much higher than in some peatlands because the Cerrado soils were so dense, Loisel said.
“These are significant carbon sinks,” she said, adding that research like the new study “opens up interesting research questions about understanding carbon dynamics in the continuum between mineral soils, wetland soils and peat soils.”
However, these dense, carbon-rich soils do not occur throughout the Cerrado, so Verona and the research team set out to estimate the complete geographic area of the wetlands using remotely sensed land cover data, agricultural information from landowners, and a machine learning approach. They estimated that these ecosystems cover 16.7 million hectares, about 8% of the total area of the Cerrado.
The team then measured greenhouse gas emissions from Cerrado soil during the wet, dry and transitional seasons. They found that around 70% of wetland emissions occurred in the dry season. That could pose a problem as climate changes and the wetlands dry up — because a steady influx of water maintains the environment that allows the soil to store so much carbon, drought can release a lot of carbon quickly.
Protection of tropical wetlands
Further analysis of the soil using radiocarbon dating determined that, on average, the carbon stored in the Cerrado is more than 11,000 years old, with the oldest dated to be 20,000 years old. The age of the carbon stored indicates how critical ecosystem protection is: “If we lose the carbon in the Cerrado that has been accumulating for millennia, we can’t put it back that easily,” Zanne said.
Although Brazilian law provides legal protection for wetlands, the laws do not necessarily protect the water sources that feed the wetlands and make them a critical carbon storage system. “We have to maintain the hydraulic dynamics,” Verona said. “If you only protect the wetlands themselves and don’t protect the water in the landscape … we will lose the hydraulic system.”
Furthermore, Verona refers to the Cerrado as a “sacrificial biome” because it absorbs some of the water-intensive land-use needs that cannot occur in the better-protected Amazon rainforest. For Verona, it is counterintuitive: “If you sacrifice the Cerrado for agriculture so that you can protect the Amazon, then you remove part of the water that flows to the Amazon, which (was) protecting the Amazon.”
However, keeping the Cerrado’s wetlands functional could be crucial to meeting global climate goals. Better protections—for example, laws recognizing the connection of groundwater to the wetlands and better water use laws—could help maintain the Cerrado’s carbon storage capacity.
“We’re just losing a lot of these wetlands quietly, invisibly,” Oliveira said. “They remain invisible in the politics of Brazil, and even to the global scientific community. They really urgently deserve stronger protection and recognition at the global level.”
This article was originally published on Eos.org. Read original article.
