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Abstract Inland waters are an important component of the global carbon budget. However, our ability to predict carbon fluxes from stream systems remains uncertain, aspCO2varies within streams at scales of 1–100 m. This makes direct monitoring of large‐scale CO2fluxes impractical. We incorporate CO2input and output fluxes into a stream network advection‐reaction model, representing the first process‐based representation of stream CO2dynamics at watershed scales. This model includes groundwater (GW) CO2inputs, water column (WC), benthic hyporheic zone (BHZ) respiration, downstream advection, and atmospheric exchange. We evaluate this model against existing statistical methods including upscaling and multiple linear regressions through comparisons to high‐resolution streampCO2data collected across the East River Watershed in the Colorado Rocky Mountains (USA). The stream network model accurately captures GW, evasion, and respiration‐drivenpCO2variability and significantly outperforms multiple linear regressions for predictingpCO2. Further, the model provides estimates of CO2contributions from internal versus external sources suggesting that streams transition from GW‐ to BHZ‐dominated sources between 3rd and 4th Strahler orders, with GW, BHZ, and WC accounting for 49.3%, 50.6%, and 0.1% of CO2fluxes from the watershed, respectively. Lastly, stream network model atmospheric CO2fluxes are 4‐12x times smaller than upscaling technique predictions, largely due to relationships between streampCO2and gas exchange velocities. Taken together, this stream network model improves our ability to predict stream CO2dynamics and efflux. Furthermore, future applications to regional and global scales may result in a significant downward revision of global flux estimates.
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Spatiotemporal variability of gas transfer velocity in a tropical high‐elevation stream using two independent methods
Abstract Streams in high‐elevation tropical ecosystems known as páramos may be significant sources of carbon dioxide (CO2) to the atmosphere by transforming terrestrial carbon to gaseous CO2. Studies of these environments are scarce, and estimates of CO2fluxes are poorly constrained. In this study, we use two independent methods for measuring gas transfer velocity (k), a critical variable in the estimation of CO2evasion and other biogeochemical processes. The first method, kinematick600(k600‐K), is derived from an empirical relationship between temperature‐adjustedk(k600) and the physical characteristics of the stream. The second method, measuredk600(k600‐M), estimates gas transfer velocity in the stream by in situ measurements of dissolved CO2(pCO2) and CO2evasion to the atmosphere, adjusting for temperature. Measurements were collected throughout a 5‐week period during the wet season of a peatland‐stream transition within a páramo ecosystem located above 4000 m in elevation in northeastern Ecuador. We characterized the spatial heterogeneity of the 250‐m reach on five occasions, and both methods showed a wide range of variability ink600at small spatial scales. Values ofk600‐Kranged from 7.42 to 330 m/d (mean = 116 ± 95.1 m/d), whereas values ofk600‐Mranged from 23.5 to 444 m/d (mean = 121 ± 127 m/d). Temporal variability ink600was driven by increases in stream discharge caused by rain events, whereas spatial variability was driven by channel morphology, including stream width and slope. The two methods were in good agreement (less than 16% difference) at high and medium stream discharge (above 7.0 L/s). However, the two methods considerably differed from one another (up to 73% difference) at low stream discharge (below 7.0 L/s, which represents 60% of the observations collected). Our study provides the first estimates ofk600values in a high‐elevation tropical catchment across steep environmental gradients and highlights the combined effects of hydrology and stream morphology in co‐regulating gas transfer velocities in páramo streams.
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- Award ID(s):
- 1847331
- PAR ID:
- 10449532
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecosphere
- Volume:
- 12
- Issue:
- 7
- ISSN:
- 2150-8925
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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