Distribution and abundance of microbial biomass in Rocky Mountain spring snowpacks

Snowpacks in both Colorado and Wyoming were sampled on 15 dates for total microbial biomass, ratio of bacteria to fungi, and major inorganic ions. Levels of viable microbial biomass remained low throughout the period, peaking at 0.05 micrograms carbon/ml. Microscopic analyses indicated this biomass was composed primarily of bacteria. Fungi were not detected in samples taken at or above tree line. With the exception of one date in early May at the Colorado site, bacteria were confined to a band within the snowpack approximately 20 cm above the snow/soil interface. Laboratory incubations using two Gram negative motile rods isolated from this layer indicated these organisms were capable of growth at 0degC ± 0.5degC but had optimum growth temperatures between 20degC and 37degC. Based on observed population sizes and growth rates it is unlikely these organisms were capable of significantly affecting trace gas emissions or altering the chemical composition of snowmelt.