Uncovering the melt: Unmanned Aircraft System (UAS) and in-situ sensor synergies reveal dissolved organic carbon (DOC) pathways in a northern peatland

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Abstract. Spring snowmelt is a critical period for dissolved organic carbon (DOC) export from northern boreal peatlands, yet the spatiotemporal dynamics of this process remain poorly understood. To reveal the spatial patterns, we used a novel combination of high-resolution Unmanned Aircraft System (UAS) snow depth mapping, topographic wetness index, and high-frequency stream monitoring during the peak snowmelt in 2024. The study took place in a small 6 ha fen in northeastern Finland. Our results show that DOC leaching is triggered after widespread snow cover depletion, likely due to thawing of surficial peat layers and increased connectivity in the peatland. High-resolution UAS snow surveys captured the progression of snowmelt from drier, south-facing slopes and forested areas toward wetter fen areas, with the expansion of snow-free areas in high-wetness zones initiating hydrological connectivity and pathways for DOC transport. Event-based hysteresis and flushing analyses enabled by high-frequency stream monitoring revealed transitions from deeper to more surficial flow paths towards the final peak melt. The integration of high-resolution spatial and temporal datasets enabled the detailed identification of DOC transport mechanisms during the snowmelt period. These findings underscore the sensitivity of peatland carbon dynamics to late winter processes and snow conditions, highlighting their potential vulnerability to future shifts in climate.

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