Patterns and controls of carbon dioxide concentration and fluxes at the air–water interface in South American lowland streams

FEIJOÓ, CLAUDIA; ARROITA, MAITE; MESSETTA, MARÍA LAURA; ANSELMO, JULIETA; RIGACCI, LAURA; VON SCHILLER, DANIEL

AQUATIC SCIENCES

BIRKHAUSER VERLAG AG

Año: 2022 vol. 84

1015-1621

Carbon dioxide (CO2) emission from fuvial systems represents a substantial fux in the global carbon cycle. However, variation in fuvial CO2 fuxes at the air?water interface as well as its drivers are poorly understood, especially in non-forested headwaters. Here, we measured CO2 concentration and fuxes in 14 lowland open-canopy streams (Pampean region, Argentina) that cover a wide range of land use and water quality. We also analyzed drivers of CO2 concentration and fuxes, including factors related to metabolism, gas solubility, alkalinity, and gas transfer. Metabolic rates varied considerably among the study sites, but most streams (i.e., 8 out of the 11 where we were able to estimate ecosystem metabolism) were net heterotrophic. Metabolic diferences among sites were mostly driven by the aromatic carbon content and the percent of the stream reach covered by primary producers. All streams, even those that were not net heterotrophic were CO2 supersaturated. Alkalinity combined with in-stream primary production explained 52.3% of the variance in the partial pressure of CO2 (pCO2), but our observations suggest that pCO2 might be controlled by external groundwater inputs of dissolved inorganic carbon rather than by internal metabolism. All streams were net emitters of CO2 to the atmosphere. Signifcantly more variance inCO2 fux was explained by gas transfer velocity (63.7%) than by pCO2 (21.9%). We also observed high spatial heterogeneity in CO2 fuxes within each stream, which was associated with fow variation and the presence of diferent macrophyte and algae patches. Overall, our results indicate that CO2 emission in these extremely low turbulence streams is controlled by a combination of external and internal biogeochemical processes and limited atmospheric exchange.