Fig. S1. Example scatter plots from FCM showing contrast between (a) unstained and (b) stained response to blue (488 nm) laser excitation, highlighting the SGII shift in green fluorescence and a threshold (∼ 102 DN) for separating biological and non-biological particulates for a stream sample taken on DOY196. The threshold was defined from samples in which autofluorescent particles appeared absent. Panel c illustrates the SSC vs. FSC scatter plot for biological particles in a supraglacial stream sample and the size classification boundaries derived independently from the use of a pseudo-blank sample containing beads.

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