Water samples for this study were collected at two sites in the vicinity of the town of Cherskiy: one representing the Kolyma mainstem (at 68.755 °N, 161.305 °E) and the other a small headwater stream called Y3 (watershed size ~17 km2), draining Yedoma-rich soils (sampling site at 68.759 °N, 161.448 °E). Surface water samples of 5-20 L were collected every 4-7 days from late May until late September/early October to cover the entire open-water season in 2013 and 2015, resulting in a total of 36 POM samples for the lower Kolyma mainstem and 35 POM samples for headwater stream Y3.