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Abstract High‐altitude tropical grasslands, known as “páramos,” are characterized by high solar radiation, high precipitation, and low temperature. They also exhibit some of the highest ecosystem carbon stocks per unit area on Earth. Recent observations have shown that páramos may be a net source of CO2to the atmosphere as a result of climate change; however, little is known about the source of this excess CO2in these mountainous environments or which landscape components contribute the most CO2. We evaluated the spatial and temporal variability of surface CO2fluxes to the atmosphere from adjacent terrestrial and aquatic environments in a high‐altitude catchment of Ecuador, based on a suite of field measurements performed during the wet season. Our findings revealed the importance of hydrologic dynamics in regulating the magnitude and likely fate of dissolved carbon in the stream. While headwater catchments are known to contribute disproportionately larger amounts of carbon to the atmosphere than their downstream counterparts, our study highlights the spatial heterogeneity of CO2fluxes within and between aquatic and terrestrial landscape elements in headwater catchments of complex topography. Our findings revealed that CO2evasion from stream surfaces was up to an order of magnitude greater than soil CO2efflux from the adjacent terrestrial environment. Stream carbon flux to the atmosphere appeared to be transport limited (i.e., controlled by flow characteristics, turbulent flow, and water velocity) in the upper reaches of the stream, and source limited (i.e., controlled by CO2and carbon availability) in the lower reaches of the stream. A 4‐m waterfall along the channel accounted for up to 35% of the total evasion observed along a 250‐m stream reach. These findings represent a first step in understanding ecosystem carbon cycling at the interface of terrestrial and aquatic ecosystems in high‐altitude, tropical, headwater catchments.
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Lake Morphometry and River Network Controls on Evasion of Terrestrially Sourced Headwater CO 2
Abstract Lakes are central components of the inland water system distinct from, yet inextricably connected to, river networks. Currently, existing network‐scale biogeochemistry research, although robust, typically treats each of these components separately or reductively. Here, we incorporate lake morphometry into a fully connected stream/lake network for the Connecticut River watershed and model potential evasion of terrestrially sourced headwater CO2as transported through the network, ignoring in‐stream production. We found that approximately 25%–30% of total potential soil CO2evasion occurs in lakes, and percent evasion is inversely related to streamflow. A lake's ability to evade CO2is controlled by residence time and size: most lakes with residence time over 7 days or surface area greater than 0.004 km2evade functionally all terrestrial CO2entering from upstream, precluding further downstream transport. We conclude that lakes are important for soil CO2degassing and that this coupled river/lake approach is promising for CO2studies henceforth.
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- Award ID(s):
- 1840243
- PAR ID:
- 10452802
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 1
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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