Abstract
Streams are significant sources of CO2 to the atmosphere. Estimates of CO2 evasion fluxes (fCO2) from streams typically relate to the free flowing water but exclude geomorphological structures within the stream corridor. We found that gravel bars (GBs) are important sources of CO2 to the atmosphere, with on average more than twice as high fCO2 as those from the streamwater, affecting fCO2 at the level of entire headwater networks. Vertical temperature gradients resulting from the interplay between advective heat transfer and mixing with groundwater within GBs explained the observed variation in fCO2 from the GBs reasonably well. We propose that increased temperatures and their gradients within GBs exposed to solar radiation stimulate heterotrophic metabolism therein and facilitate the venting of CO2 from external sources (e.g. downwelling streamwater, groundwater) within GBs. Our study shows that GB fCO2 increased fCO2 from stream corridors by [median, (95% confidence interval)] 16.69%, (15.85–18.49%); 30.44%, (30.40–34.68%) and 2.92%, (2.90–3.0%), for 3rd, 4th and 5th order streams, respectively. These findings shed new light on regional estimates of fCO2 from streams, and are relevant given that streamwater thermal regimes change owing to global warming and human alteration of stream corridors.
Highlights
We found the Gravel bars (GBs) in OSB to be a site of increased fCO2 to the atmosphere
Because ecosystem metabolism contributions to fCO2 and the solubility and release of CO2 depend on temperature[23], we explored the effect of temperature within the GB on fCO2 to the atmosphere
Our findings from a broad range of GBs across several stream orders, show that mean diurnal fCO2 from GBs were on average 2.19 ± 1.43 times higher than the fCO2 from streamwater. Thereby, these results reveal GBs as hitherto potentially significant sources of CO2 to the atmosphere and link these critical carbon fluxes to the thermal regime in GBs
Summary
Gravel bars (GBs) induce hydrodynamic exchange where streamwater typically enters the streambed (that is, downwelling) at the head and returns (that is, upwelling) downstream of the GB tail to the streamwater[12,15,16]. Owing to this enforced hydrodynamic exchange, GBs are sites of increased biogeochemical reactions, as has been shown for dissolved organic carbon (DOC)[17,18] and nitrate[19]. The role for carbon dynamics, including CO2 evasion to the atmosphere from GBs (and likely from other geomorphological features) within stream corridors remains poorly studied at present[11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
