Dissolved organic matter from surface and pore waters of a discontinuous permafrost watershed in central Alaska reveals both compositional and seasonal heterogeneity

In areas of active permafrost thaw, changes in organic carbon pools may significantly impact water quality and ecosystem services across the landscape. Surface and pore waters were collected from streams and lakes in the Goldstream Valley near Fairbanks Alaska over a period of three years, 2016–2018, to compare and contrast different thermokarst regimes, their water quality, and dissolved organic matter (DOM). Waters were characterized by elemental analysis, major ions, and optical characterization of DOM. We found DOM composition to be spatiotemporally heterogeneous, and influenced by complex hydrology. This result is evidenced by analyzing DOM character between differing water bodies and depths, seasonality, as well extent of metal association with DOM. Pore water DOM overall varied from the surface waters, with respect to both optical metrics and seasonality. Optical parameters typically associated with terrestrial signals were observed to become more prevalent in pore waters as summer progressed toward winter in an active thermokarst lake, potentially corroborating a hypothesis of downward flow into the talik or rapid turnover of authochthonous-sourced DOM. In addition, winter sampling, where surface inputs were assumed to be frozen, is essential to observe annual patterns of DOM composition. A principal components analysis separated water bodies based on their thermokarst activity and by season. Dissolved organic matter in these permafrost-impacted systems was found to be more complex than simply terrestrial or microbial, and extracted isolates from these waters were not necessarily bounded by existing end-member references.