Addition of dissolved inorganic carbon stimulates snow algae primary productivity on glacially eroded carbonate bedrock in the Medicine Bow Mountains, WY, USA

Abstract

Snow is a critical component of the Earth system. High-elevation snow can persist into the spring, summer, and early fall and hosts a diverse array of life, including snow algae. Due in part to the presence of pigments, snow algae lower albedo and accelerate snow melt, which has led to increasing interest in identifying and quantifying the environmental factors that constrain their distribution. Dissolved inorganic carbon (DIC) concentration is low in supraglacial snow on Cascade stratovolcanoes, and snow algae primary productivity can be stimulated through DIC addition. Here we asked if inorganic carbon would be a limiting nutrient for snow hosted on glacially eroded carbonate bedrock, which could provide an additional source of DIC. We assayed snow algae communities for nutrient and DIC limitation on two seasonal snowfields on glacially eroded carbonate bedrock in the Snowy Range of the Medicine Bow Mountains, Wyoming, United States. DIC stimulated snow algae primary productivity in snow with lower DIC concentration despite the presence of carbonate bedrock. Our results support the hypothesis that increased atmospheric CO2 concentrations may lead to larger and more robust snow algae blooms globally, even for sites with carbonate bedrock.

Keywords: algae; carbon; isotopes; nitrogen; phototroph; primary productivity; snow.

Figure 1.

Sampling location. (A) Satellite image of the Snowy Mountain Range in the Medicine Bow Mountains, WY. Inset shows the western United States, with an open star indicating the location of the Snowy Mountain Range. Open rectangle indicates the area shown in panel B. (B) Zoomed-in satellite image of the sampling area indicating the locations near Round Lake (with images of the sample site shown in panel C) and Jeep Lake (with images of the sample site shown in panel D). Snow fields that were visible in the satellite image but were not present at the time of sampling are noted. (C) Panoramic image of the Round Lake field site looking east with the two snow algae sample sites indicated. Inset images show snow algae samples being collected for carbon uptake experiments (a-inc) or only geochemistry and molecular samples (a), as well as examples of contextual samples, including plants [evergreen trees (p-e), broadleaf plants (p-b), and grasses and sedges (p-g)] and soil (s). (D) Panoramic image of the Jeep Lake field site looking east with the snow algae incubation site indicated by a dashed open black circle. Inset images show snow algae samples being collected for carbon uptake experiments (a-inc), as well as examples of contextual samples, including plants [evergreen trees (p-e); broadleaf plants (p-b); moss (p-m); grasses and sedges (p-g); soil (s); and scat (sc)].

Figure 2.

Percent relative abundance of the top 10 most abundant algal small subunit rRNA (18S rRNA) OTU transcripts recovered from snow, lake and stream sediments (seds) and lake biofilms. Taxonomy was assigned using the best BLASTN hit. The Round and Jeep Lake samples that corresponds to the site where microcosms were performed is indicated by an asterisk. Orange indicates the color of the snow sampled at Round Lake; pink indicates the color of the snow sampled at Jeep Lake.

Figure 3.

Rates of carbon assimilation in microcosm assays. The horizontal line in each box indicates the median, and closed circles represent the mean (n  =  3 or 4 for each treatment).

Figure 4.

Biomass C and N stable isotope analyses. (A) C and N stable isotope analyses from Round and Jeep Lake snow algae biomass and contextual samples. (B) Round and Jeep Lake snow algae C and N stable isotope values plotted with C and N stable isotope values from snow algae collected from snowfields and glaciers in the Cascade Range of the Pacific Northwest (Hamilton and Havig , Havig and Hamilton 2019). Values for contextual samples in (A) are provided in Supplementary Table S2. Values for Pacific Northwest snow algae are provided in Supplementary Table S3.

Figure 5.

Percent relative abundance of the most abundant bacterial small subunit rRNA (16S rRNA) OTU transcripts recovered from snow, lake, and stream sediments (seds) and lake biofilms. The highest level of classification is shown (based on mothur). The Round Lake sample that corresponds to the site where microcosms were performed is indicated. Microcosms at Jeep Lake were performed in the snow sample.