Meanders in river beds help the climate
River beds that can shift naturally are more efficient carbon sinks than straightened rivers

Date:
October 29, 2021
Source:
GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
Summary:
River beds that can shift naturally are more efficient carbon
sinks than straightened rivers.



FULL STORY ==========================================================================
It takes about 8500 years for a grain of sand from the Andes to be washed across the Argentine lowlands into the Ri'o Parana'. The 1200-kilometer
journey in the river called Ri'o Bermejo is interrupted by many stops in
river floodplains, where the grain is deposited, sometimes over thousands
of years, and then washed free again. The sand is accompanied by organic carbon, washed in from soil and plants. The transport in water thus gains relevance for the climate: Rivers carry the carbon, which was previously removed from the atmosphere via photosynthesis, as sediment into the sea,
where it is stored for thousands of years without harming the climate.


========================================================================== Researchers at the GFZ German Research Centre for Geosciences have now quantified the individual processes of the journey for the first time and report on them in the journal Nature Geoscience. An important result of
the work: It is in particular undisturbed meandering sections of a river
where carbon is deposited and reabsorbed, and then transported further
into the sea.

In river sections with straight, stable banks, on the other hand,
only the suspended particle load passes through, while the carbon
in the river floodplains is slowly decomposed again to CO2 by
microorganisms. GFZ working group leader Dirk Sachse says, "The Ri'o
Bermejo was an ideal natural laboratory for us because it has no
significant tributaries." Sachse is also director of the "Landscapes
of the Future" topic in the Helmholtz program "Changing Earth --
Sustaining Our Future." He says, "This means that natural river courses
that have space to erode floodplains can remove more carbon from the
atmosphere than straight river sections. In this respect, straightening
of rivers by humans could also contribute to the increase in atmospheric
CO2 concentration. What's exciting now is answering the question of
whether we can help the climate by giving rivers more space again and
not impeding natural river meandering." The international team led by
first author Marisa Repasch of GFZ studied the processes in the river
and its floodplains with a diverse set of instruments.

Analyses of cosmogenic beryllium-10 content, for example, indicated
the duration of sediment transport. Dating based on the unstable carbon
isotope 14C, in turn, allowed conclusions to be drawn about the age of
the particles of organic origin. During fieldwork in Argentina, samples
were taken from the river at multiple stations along the source-to-sink pathway. "Naturally meandering rivers erode material from floodplains
and transport it to the sea, where it remains for a long time," says
Marisa Repasch, summarizing the results, "in contrast, artificially
stabilized river courses are far less effective carbon sinks." ========================================================================== Story Source: Materials provided by GFZ_GeoForschungsZentrum_Potsdam,_Helmholtz_Centre. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Marisa Repasch, Joel S. Scheingross, Niels Hovius, Maarten Lupker,
Hella
Wittmann, Negar Haghipour, Darren R. Gro"cke, Oscar Orfeo,
Timothy I.

Eglinton, Dirk Sachse. Fluvial organic carbon cycling regulated by
sediment transit time and mineral protection. Nature Geoscience,
2021; DOI: 10.1038/s41561-021-00845-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211029113959.htm

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