Microbial composition of dust from alpine snow

Abstract:

Dust deposited on snow profoundly impacts overall snowpack properties, altering snow physical and chemical composition at the deposition site. Microorganisms inhabit the dust deposited on snow as well as within the snowpack itself in alpine and polar regions. We examined snow microstructure and microbial composition at alpine sites in western Colorado, including Senator Beck Basin maintained by the Center for Snow and Avalanche Studies and the Berthoud Pass Colorado Dust on Snow study site. Snow samples were collected during the late spring at the primary study sites. Samples consisted of dust layers comprised of multiple past dust events that had merged into a single layer over time, as well as samples collected immediately after individual dust events. We developed a methodology to quantify the amount, size, and location of dust particles within the snow matrix from X-ray micro-computed tomography (micro-CT) data. The micro-CT data were examined with the primary objective of determining where, within the snow matrix, the dust particles reside, with potential implications for microbial communities housed on the dust. We determined the microbial composition in sampled dust layers through DNA sequencing. Back trajectory modeling of dust deposition events was used to corroborate dust emission locations. We found that dust particles were generally surrounded by snow grains within the matrix, with a small, but critical in terms of microbial exposure, fraction of the dust particles' surface area exposed to air. Microbial community composition varied by alpine site and residence time of the dust within the snowpack. Freshly deposited dust layers had both the highest concentration of dust particles as well as the highest diversity of microbial species.

Figure: Micro-CT imagery of dust particles within snow samples from Senator Beck Basin in 2D and 3D.