Amazon River digests trees swept away
Vandré Fonseca - 28/05/13
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A team of Brazilian researchers and Americans discovered the origin of the large amount of carbon present in the rivers of the Amazon basin.
Based on studies conducted at the mouth of the Amazon River, they concluded that, contrary to popular thought, there are bacteria in fresh water able to digest the hard woody plant stems. The study was published in Nature Geoscience. (see below).
In the Amazon, the rivers carry large amounts of plants, trunks and branches torn off by the tropical rains. It was believed that there was no time for this stuff to be decomposed before reaching the ocean and thus all carbon contained there to be stocked in the sea for centuries or even millennia.
But during the doctoral studies in Oceanography from the University of Washington, Nick Ward demonstrated that only 5 per cent carbon loaded by the Amazon River reaches the Atlantic Ocean.
Much of the carbon (40 per cent) is stored in plant debris deposited on the soil during the course of the river. But for the most part, 55 per cent of all material is decomposed in the waters of the river.
Degradation of terrestrially derived macromolecules in the Amazon River
- Nature Geoscience
- 6,
- 530–533
- doi:10.1038/ngeo1817
- Received
- Accepted
- Published online
Temperate and tropical rivers serve as a significant source of carbon dioxide to the atmosphere1, 2, 3, 4. However, the source of the organic matter that fuels these globally relevant emissions is uncertain. Lignin and cellulose are the most abundant macromolecules in the terrestrial biosphere5, but are assumed to resist degradation on release from soils to aquatic settings6, 7, 8. Here, we present evidence for the degradation of lignin and associated macromolecules in the Amazon River. We monitored the degradation of a vast suite of terrestrially derived macromolecules and their breakdown products in water sampled from the mouth of the river throughout the course of a year, using gas chromatography time-of-flight mass spectrometry. We identified a number of lignin phenols, together with 95 phenolic compounds, largely derived from terrestrial macromolecules. Lignin, together with numerous phenolic compounds, disappeared from our analytical window following several days of incubation at ambient river temperatures, indicative of biological degradation. We estimate that the net rate of degradation observed corresponds to 30–50%of bulk river respiration. Assuming that a significant fraction of these compounds is eventually remineralized to carbon dioxide, we suggest that lignin and other terrestrially derived macromolecules contribute significantly to carbon dioxide outgassing from inland waters.
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