Seasonal changes in hydrology and permafrost degradation control mineral element-bound DOC transport from permafrost soils to streams

Mineral elements bind to dissolved organic carbon (DOC) in permafrost soils, and this may contribute to the stabilisation or the degradation of organic carbon along the soil to river continuum. Permafrost thaw enlarges the pool of soil constituents available for soil to river transfer. The unknown is how changes in hydrology upon permafrost degradation affect the connection between soil-derived mineral element-bound DOC and headwater streams. Here, we study Al, Fe, Ca and DOC concentrations in water from a headwater stream at Eight Mile Lake, Alaska, USA (colloidal (0.22 µm–1 kDa) and truly dissolved (< 1 kDa) fractions) and in soil pore waters sampled across a gradient of permafrost degradation at the same location. We target the peak flow to base flow transition to show that there is a narrow window of mineral element-bound DOC colloid transport from soils to streams. We show that during spring thaw and maximum thaw there is an enhanced lateral transfer of mineral element-bound DOC colloids in extensively degraded sites compared to minimally degraded sites. This is explained by a more rapid response of hydrology at peak flow to base flow transition at degraded sites. Our results suggest that ongoing permafrost degradation and the associated response of soils to changing hydrology can be detected by targeting the composition and size of mineral element-DOC associations in soil waters and headwater streams during peak flow-baseflow transitions.