Global dust emissions doubled during the 20th century with dramatic effects on ecosystems. Dust entrainment radically changes the timing of snow melt and deposits trace metals into montane ecosystems. Dust deposition contributes substantial loading of salts, metals, and metalloids to snowpack but it also contributes bacteria. Bacteria transported in snow may travel attached to colloid fine-earth particles, be influenced by atmospheric chemistry, and pollution, and ultimately act as seeding sources for new bacterial species. However, little is known concerning the importance of dust source or heavy metal chemistry in determining bacterial dispersal. We evaluated the bacterial community composition and dust chemistry at peak snowpack in three airsheds in northern Utah, USA. We sampled snowpack before any melting occurs because liquid water may facilitate the movement of bacteria from snow and alter the snowpack chemistry and dust composition. We filtered the bacteria from snow, extracted genomic DNA and sequenced the v4 region of the 16s DNA using an Illumina HiSeq 2500 sequencer. Dust chemistry and heavy metals were evaluated with inductively coupled plasma-mass spectrometry including elements: Li, Na, Mg, Al, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr,Sb, Cs, Ba, Ce, and Pb.
Results/Conclusions
Airsheds had a robust effect on the composition of snow bacterial communities. Based on our PCoA results, snow communities from the three airsheds separated in ordination space along axis 1, which explained 28.7% of community variation. The PERMANOVA results supported the ordination, with airshed location driving compositional difference among communities (F = 2.72, R2 = 0.34, P < 0.0001). Bacterial species richness and diversity were lowest in the airshed with high levels of heavy metals which potentially originate off of dry Lake Boniville sediments surrounding the Great Salt Lake (Red Butte, Salt Lake City, OTU number mean = 90.2 ± 21.1, Shannon diversity index mean = 3.0 ± 0.3). For example, heavy metal Sb (ANOVA, F = 27.9, P < 0.0001), As (ANOVA, F = 13.5, P < 0.0001), Sr (ANOVA, F = 10.1, P < 0.0001), which are often used as geological tracers, were higher in Red Butte snow than snow from the Provo and Logan airsheds. Conversely, elements, Pb and Cs, indicators of industrial pollution, did not differ between Red Butte and the Logan airsheds. Our findings suggest that bacteria dispersing through airsheds are chiefly dictated by mineral sources and not air pollution chemistry.