New insights into the carbon cycle of Amazonia's lakes, floodplains and waters have furthered the understanding of the scale and consequences of global warming.
The research, published in Hydrobiologia, revealed that the microbial food chain found in floodplains produces 10 times more carbon dioxide than the classical phytoplankton-zooplankton-fish food chain made up of decomposing organic matter.
Carbon is one of one of the most abundant elements found on Earth. Most of the carbon on this planet is stored in rocks, but it can also be found in the ocean, atmosphere, plants, soil and fossil fuel.The carbon cycle occurs when the element flows between each reservoir. Changes that put higher concentrations of carbon gases into the atmosphere result in warmer global temperatures.
The Amazon region plays a crucial role in this cycle. This South American biome encompasses 7,000,000 square kilometers, most of which is covered by the largest and most biodiverse tract of tropical rainforest in the world.
Most research studying the carbon cycle in this area focus on terrestrial biomass, such as plants and animals, or the biomass of major rivers.
Few studies, however, have concentrated on the floodplains and those that have analyzed the carbon cycle in the classical food chains comprised of phytoplankton, zooplankton, fish and invertebrates. Floodplains and related areas that include shallow lakes, secondary channels and wetlands comprise 20 percent of the Amazon landmass.
"The Amazon rainforest is know as the planet's lungs, but few people know that a the quantity of carbon emitted in Amazonian waters is equivalent to the quantity of the carbon fixed every day by the forest. It is important to understand the mechanisms behind those emissions," Hugo Miguel Preto de Morais Sarmento, a professor in the Hydrobiology Department of the Federal University of São Carlos (UFSCar) in São Paulo State, Brazil, told Laboratory Equipment.
The microbial food web is made up of all the interactions among microorganisms—including viruses, bacteria, algae, unicellular predators and invertebrates—in an aquatic environment.
Researchers collected and analyzed water samples in May 2014—during the rainy season when water levels are high and food is plentiful—and October 2014—when water levels are lower and the food web is complex during the dry season.
The 30 samples were obtained from the Puruzinho, a floodplain system in Brazil consisting of a narrow lake connected to the Madeira River, a tributary of the Amazon River, by a eight km long channel.
Using an inverted optical microscope, a flow cytometer and genomic screening, the research team counted the numbers of phytoplankton, zooplankton and bacteria in order to estimate the total carbon found in each sample.
The results revealed that 90 percent of all carbon in the Puruzinho circulate in the microbial food, with carbon making up an average of 245.5 micrograms per liter. This is significantly higher than the average of the classical food chain: 24.4 micrograms per liter.
"Our study demonstrate the importance of the tiniest organisms of the food web for the carbon cycle in Amazonian waters. These microbes were largely overlooked in previous studies because their small size require new approaches such as flow cytometry, epifluorescence microscopy and DNA sequencing," Sarmento said. "Working in the Amazon is always fascinating but also challenging by its enormous dimensions, the complexity of the landscape and the difficulty to reach. It was a major achievement being able to take these samples and make all the analyses in good conditions."
Editor-in-Chief, ALN Magazine