Many rivers in the tropics have very dark, coffee-like water. The colors of so-called black water rivers are due to organic acids that are formed when organic substances decompose – for example humic acids. Now, experts at ETH Zurich say they have discovered what may be the blackest river in the world. It is probably the Rocky River, a tributary of the Congo – comparisons with other tropical rivers show this. The institute writes on its website. A team led by ETH researcher Travis Drake became aware of the unusually dark river water while researching the carbon balance of the Rockies. Because of its high organic matter content, the river plays an important role in the carbon balance in the Congo Basin. The group reports in the journal Limonology and Oceanography.
Dark black water rivers are characterized by the fact that, in addition to the high content of organic acids, they transport very little suspended solids. They reflect light and thus illuminate the water. Rocky has very little gradation, so suspended solids settle easily. At the same time, the rich vegetation of the Congo Basin provides it with plant decomposition products. Rainwater leaches humic acids from the soil before it enters the river. In addition, during the rainy season, the river floods large areas of the forest for weeks and absorbs organic matter. Despite the low concentration of suspended matter, the water is almost opaque, reports ETH Zurich. “We were very impressed by the color of the river,” says Travis Drake. “Rocky is actually jungle tea.”
The Rocky River is also special because it is one of the last large rivers that remains largely unchanged. Its catchment area is covered by lowland rainforest and peat swamps. Not only does this make the river water exceptionally dark, but it is also a huge storehouse of carbon. The Drake team’s analyzes show that carbon reserves in peatlands are very stable – which is good news. Although the river contains a lot of dissolved organic carbon, it is not removed from the peat, but comes from fresh plants. The reason is that swamps are underwater almost all year round, ETH writes. However, if land use changes, for example, if forests are cleared, peat bogs may dry up, and in the long term a lot of carbon dioxide can be released.2 launch.
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