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Abstract. Peatlands store ∼ 20 %–30 % of the global soil organic carbon stock and are an important source of dissolved organic carbon (DOC) for inland waters. Recent improvements for in situ optical monitoring revealed that the DOC concentration in streams draining peatlands is highly variable, showing seasonal variation and short and intense DOC concentration peaks. This study aimed to statistically determine the variables driving stream DOC concentration variations at seasonal and event scales. Two mountainous peatlands (one fen and one bog) were monitored in the French Pyrenees to capture their outlet DOC concentration variability at a high-frequency rate (30 min). Abiotic variables including precipitation, stream temperature and water level, water table depth, and peat water temperature were also monitored at high frequency and used as potential predictors to explain DOC concentration variability. Results show that at both sites DOC concentration time series can be decomposed into a seasonal baseline interrupted by many short and intense peaks of higher concentrations. The DOC concentration baseline is driven, at the seasonal scale, by peat water temperature. At the event scale, DOC concentration increases are mostly driven by a rise in the water table within the peat at both sites. Univariate linear models between DOC concentration and peat water temperature or water table increases show greater efficiency at the fen site. Water recession times were derived from water level time series using master recession curve coefficients. They vary greatly between the two sites but also within one peatland site. They partly explain the differences between DOC dynamics in the studied peatlands, including peat porewater DOC concentrations and the links between stream DOC concentration and water table rise within the peatlands. This highlights that peatland complexes are composed of a mosaic of heterogeneous peat units distinctively producing or transferring DOC to streams.

La torrencialidad en el valle del Ariege : de las catástrofes del pasado a los riesgos de hoy. El estudio de la topografía, de la ocupación del espacio, y de los archivos disponibles evidencia la permanencia histórica de los riesgos que amenazan diversos conos de deyección, algunos ya en parte edificados, en el Valle del Ariege, entre Ax y Tarascón, riesgos que resultan de la recurrencia aleatoria de episodios torrenciales. Estos episodios, que suelen ocurrir desde la primavera hasta el otoño, no acompañan siempre aquellas crecidas del Ariege que pueden generar inundaciones. El hecho de que, en estas condiciones, son más difíciles de prever no disminuye la necesidad de precaverse contra los daños que pueden acarrear.

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