We collected water samples from the river surface in the center of the Olenekskaya Channel near Samoylov Island using a pre-rinsed HDPE 1 L bottle. During the open water period (June to October), water was sampled from a small boat, and during ice-covered period (November to May), through a hole drilled through the river ice. Some samples during the river ice break-up (between May and June) as well as some samples during the ice freeze-up in October were taken from the shore due to the inaccessibility of a more centered location on the river channel. For DOC and TDN, the sample was filtered through a 0.45 μm cellulose acetate filter which had been rinsed with 20 mL sample water. Samples were filled into a pre-rinsed 20 mL glass vial and acidified with 25 μL HCl Suprapur (10 M) and stored in the dark at 4°C. After transport, samples were analyzed at Lomonosov Moscow State University in Moscow, Russia (MSU). DOC and TDN concentrations were analyzed using a TOPAZ NC manufactured by Informanalitika LLC (Russia). For analysis, ISO 11905-2:1997 for nitrogen and ISO 8245:1999 for carbon was followed. Three replicate measurements of each sample were averaged and three standards (5,15, and 100 mg L-1) as well as blanks (Milli-Q water) were used to ensure high accuracy of the measurements.
