| Summary: | Does iron (Fe) act to stabilise (e.g., via attachment to ferrihydrite) or degrade (e.g., via photo-degradation) organic carbon (OC) in Arctic Rivers? Characterising the interaction between Fe and OC in headwaters, prior to transport along the continuum, is key to answering this question. Here we ask: what is the role of water residence time on the interaction between Fe and dissolved organic carbon (DOC) transported from a sub-Arctic Fen (Stordalen, N Sweden)? River waters were collected from a mountain stream – representing waters entering the fen and an outflow stream – representing waters leaving the fen. Soil pore waters were collected from palsa, bog and fen sites. Samples were collected every three days between September 16th and November 11th 2021, spanning a period of Autumn rain and snowfall. Water discharge, precipitation, snowfall and oxygen isotopes (δ18O) on river waters were used to characterise water residence time. Fe and DOC concentrations were determined in the colloidal and truly dissolved fraction of river waters. SUVA254 and S275-295 were determined on soil and river waters. Visual MINTEQ modelling was used to characterise the colloidal Fe-DOC interaction. During the rain event, the Fe and DOC transported out of the fen are mainly derived from the mountain stream. During Autumn freeze-up, the Fe and DOC transported out of the fen are derived from processes occurring within the fen system. We highlight that the increased residence time of water during the Autumn freeze-up period alters the interaction between Fe and DOC, with possible impact on the degradability of DOC along the continuum.
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