Partitioning inorganic carbon fluxes from paired O2-CO2 gas measurements in a Neotropical headwater stream, Costa Rica

The role of streams and rivers in the global carbon (C) cycle remains unconstrained, especially in headwater streams where CO2 evasion (F-CO2) to the atmosphere is high. Stream C cycling is understudied in the tropics compared to temperate streams, and tropical streams may have among the highest F-CO2 due to higher temperatures, continuous organic matter inputs, and high respiration rates both in-stream and in surrounding soils. In this paper, we present paired in-stream O-2 and CO2 sensor data from a headwater stream in a lowland rainforest in Costa Rica to explore temporal variability in gas concentrations and ecosystem processes. Further, we estimate groundwater CO2 inputs (GW(CO2)) from riparian well CO2 measurements. Paired O-2-CO2 data reveal stream CO2 supersaturation driven by groundwater CO2 inputs and large in-stream production of CO2. At short time scales, CO2 was diluted during storm events, but increased at longer seasonal scales. Areal fluxes in our study reach show that F-CO2 is supported by greater in-stream metabolism compared to GW(CO2). Our results underscore the importance of tropical headwater streams as large contributors of carbon dioxide to the atmosphere and show evaded C can be derived from both in-stream and terrestrial sources.

Automated summary

This paper explores the role of tropical headwater streams in the global carbon cycle, particularly in terms of carbon dioxide evasion to the atmosphere. The study finds that tropical headwater streams are significant contributors of CO2 to the atmosphere, with inputs from both in-stream and terrestrial sources.