This data package provides analytic results for a laboratory assay on sediment samples collected in January 2019 from a transect (“P2”) across Von Guerard Stream (as described by Heindel et al. 2021), located in Taylor Valley, McMurdo Dry Valleys, Antarctica. We used excess sample from that study in a laboratory desorption assay to assess conductivity dependent desorption of ammonium. The assay was performed by mixing samples with potassium chloride treatment solutions that replicate the range of specific conductivities observed in Von Guerard Stream, shaking and centrifuging slurries, and analyzing filtered supernatant.