Small‐Scale Spatial Variability in Carbon Fluxes Driven by Soil and Vegetation Characteristics in Wetlands of Trail Valley Creek, Canada

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Abstract
The microtopography of the Arctic tundra and the associated soil moisture (SM) gradient influence the net ecosystem‐atmosphere exchange of methane (CH 4 ) and carbon dioxide (CO 2 ). To quantify fine‐scale variability in a permafrost ecosystem, we measured growing‐season carbon fluxes with closed chambers at Trail Valley Creek, Canada from 2022 to 2024. A total of six landforms were sampled, spanning a wetness gradient from dry (upland tundra, gully) over intermediate (polygons, degraded wetland centers) to wet (transitional zones, trenches) microsites. All landforms were net sources of CH 4 ; only trenches had high (0.58 mg CH 4 m −2 h −1 ) fluxes, while the other landforms had fluxes close to zero. Drier elements (upland tundra, polygons) were net CO 2 sinks, while wetter depressions (gully, degraded centers, transitional zones) were net sources; trenches were a wet exception that still acted as a sink. All fluxes were strongly influenced by air temperature ( T air ), peaking during the hot summer of 2023. CH 4 flux variability was dominated by belowground variables (SM and temperature). For CO 2 fluxes, aboveground ( T air , and photosynthetically active radiation (PAR)) and belowground controls contributed equally. For CH 4 , ecosystem respiration, and gross primary production, fitting separate models per landform reduced absolute prediction error (despite lower R 2 ), making it preferable when minimizing error. For net ecosystem exchange, a single model fit to all landforms was sufficient. These results show that field studies focusing on small‐scale variability in carbon fluxes should prioritize detailed soil‐layer measurements, T air , and PAR, while vegetation metrics are optional.
Funding Information
  • HORIZON EUROPE European Research Council (951288)
  • Gordon and Betty Moore Foundation (8414)
  • Canada Research Chairs (CRC‐2018‐00259)

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