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Abstract Increases to summer Arctic rainfall and tundra thermal degradation are altering hydrological cycling in coastal watersheds with implications for carbon (C) cycling and transport of C to the atmosphere and coast. Arctic riverine research has focused on large rivers; however, small streams contribute significantly to vertical and longitudinal carbon dioxide (CO2) fluxes. Despite the well‐established connection between hydrology and biogeochemistry, the impact of extreme rainfall events on Arctic aquatic C cycling remains a knowledge gap. This study characterized how hydrology, biogeochemistry, and geomorphology control the supply of CO2to low order streams and their propensity to act as atmospheric CO2sources. We characterize biogeochemical and hydrologic processes in unique reaches from a beaded stream and stream impacted by thermal erosion. Rainfall and its resulting increases to terrestrial‐aquatic connectivity drove the movement of CO2and biodegradable dissolved organic C (BDOC) from soils into streams, however, BDOC mineralization only contributed a small portion of surface CO2fluxes. Rain events likely stimulated stream benthic respiration, which led to CO2contributions from net ecosystem production often exceeding surface CO2fluxes and downstream CO2transport. In addition, thermal degradation played a role in terrestrial‐aquatic connectivity of the streams. The erosion‐affected stream had inconsistent and smaller inputs of CO2, had weaker heterotrophic conditions, and smaller CO2emissions. Understanding how hydrologic regime, influenced by late summer rain events and stream morphology, controls the transport of CO2and metabolism in small tundra streams will help improve predictions of landscape scale CO2emissions from these critically understudied systems.
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Improving Predictions of Stream CO 2 Concentrations and Fluxes Using a Stream Network Model: A Case Study in the East River Watershed, CO, USA
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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- Award ID(s):
- 2103520
- PAR ID:
- 10362044
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 35
- Issue:
- 12
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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