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

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.