Publication Date:
2022-04-06
Description:
Small headwater streams are recognized for intense outgassing to the atmosphere of climate‐relevant carbon dioxide (CO2) and methane (CH4). Though these headwaters are markedly oversaturated for both CO2 and CH4, the origins and controls over the fate of these two carbon‐gases are still poorly constrained, especially for the stronger greenhouse gas CH4. Here, by measuring stream‐based production of CO2 and CH4, concurrently with their rates of outgassing to the atmosphere, we identify distinct biophysical control mechanisms for each gas. We show that while CO2 is largely imported from the catchment in proportion to discharge, CO2 outgassing can be modulated by in‐stream metabolism to offset outgassing by up to 30% in spring and summer. In contrast, CH4 shows a non‐linear response to seasonal changes in discharge and is predominantly produced in the streambed in relation to sediment type. Further, once released from the streambed, outgassing of CH4 at the surface and flow‐driven dilution occur far more rapidly than biological methane oxidation and CH4 leaves the water largely unaltered by biology. Incorporating the intense carbon cycling of headwater streams into the global carbon cycle will require distinct parameterizations for each carbon gas in Earth system models.
Description:
Plain Language Summary:
There is growing interest in the global carbon cycle and how carbon is transformed in the landscape into the greenhouse gases carbon dioxide (CO2) and methane–with methane being by far the more potent than CO2. Streams and rivers are recognized hotspots of carbon cycling in the landscape, commonly harboring large amounts of CO2 and methane–yet what controls either gas in streams is not fully understood. Without that understanding, we cannot predict how carbon cycling will respond to climate change or to other human alteration of the landscape. Here we researched different components of the carbon cycle in streams to show that each gas is influenced by quite distinct “biophysical” control mechanisms. While CO2 in streams results largely from physical run‐off from the land, once in a stream it can be changed by the stream biology that ebbs and flows with the seasons. Contrastingly, methane is largely created by biology within the streambed itself but once released into the wider stream that methane is then dispersed by the physical forces of stream flow. Put more simply, CO2 is physically carried to the stream to then be altered by biology, whereas as methane is borne from biology in the stream, to then be physically carried away.
Description:
Key Points:
There are different controls on the outgassing of the greenhouse gases carbon dioxide and methane in streams.
Carbon dioxide results largely from physical run‐off from the land and is then altered in stream by biology depending on season.
In contrast, methane is created in the streambed but once released to the stream is then dispersed by the physical forces of stream flow.
Description:
Natural Environment Research Council (NERC)
http://dx.doi.org/10.13039/501100000270
Description:
Deutsche Forschungsgemeinschaft (DFG)
http://dx.doi.org/10.13039/501100001659
Description:
EC | H2020 | H2020 Priority Excellent Science | H2020 European Research Council (ERC)
http://dx.doi.org/10.13039/100010663
Description:
FNU
Description:
Danish National Research Foundation
Keywords:
ddc:551.48
Language:
English
Type:
doc-type:article
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