Nutrient treatments alter microbial mat colonization in two glacial meltwater streams from the McMurdo Dry Valleys, Antarctica

Abstract

Microbial mats are abundant in many alpine and polar aquatic ecosystems. With warmer temperatures, new hydrologic pathways are developing in these regions and increasing dissolved nutrient fluxes. In the McMurdo Dry Valleys, thermokarsting may release both nutrients and sediment, and has the potential to influence mats in glacial meltwater streams. To test the role of nutrient inputs on community structure, we created nutrient diffusing substrata (NDS) with agar enriched in N, P and N + P, with controls, and deployed them into two Dry Valley streams. We found N amendments (N and N + P) to have greater chlorophyll-a concentrations, total algal biovolume, more fine filamentous cyanobacteria and a higher proportion of live diatoms than other treatments. Furthermore, N treatments were substantially elevated in Bacteroidetes and the small diatom, Fistulifera pelliculosa. On the other hand, species richness was almost double in P and N + P treatments over others, and coccoid green algae and Proteobacteria were more abundant in both streams. Collectively, these data suggest that nutrients have the potential to stimulate growth and alter community structure in glacial meltwater stream microbial mats, and the recent erosion of permafrost and accelerated glacial melt will likely impact resident biota in polar lotic systems here and elsewhere.

Catch and release: Hyporheic retention and mineralization of N‐fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams

“…Significance was set at a = 0.05, and all analyses were performed using R version 3.2.3 (R Core Team ). All data are available online through the Environmental Data Initiative repository (Kohler ).…”

Ecological Stoichiometry of the Mountain Cryosphere

“…Glacier-fed stream biofilms are generally limited by both N and P (Figure 4), but they exhibit stoichiometric flexibility and are capable of producing biomass with high C:P and N:P, which can in turn drive P limitation of consumers (e.g., macroinvertebrates, fish; Figure 4). Experimental addition of P increases microbial richness in glacier-fed streams (Kohler et al, 2016). Combined N and P additions stimulate biofilm primary production and shift microbial community composition (Robinson et al, 2003;Kohler et al, 2016 ; Figure 4).…”

“…Experimental addition of P increases microbial richness in glacier-fed streams (Kohler et al, 2016). Combined N and P additions stimulate biofilm primary production and shift microbial community composition (Robinson et al, 2003;Kohler et al, 2016 ; Figure 4). However, hydrological characteristics (e.g., flow and proportion of glacier influence) may override the influence of nutrient additions in some areas, such as the Swiss Alps (Rinke et al, 2001) and the Tian Shan Mountains of central Asia (Ren et al, 2017b).…”

“…In the short term, increased N and DOC inputs from glacial meltwaters may alleviate N limitation of primary producers and heterotrophic microorganisms in biofilms, increasing gross primary production and ecosystem respiration in glacier-fed streams (Uehlinger et al, 2010;Cauvy-Fraunié et al, 2016;Kohler et al, 2016 ; Figure 4). However, while DOC in glacier-fed streams may initially increase due to accelerated glacier melting, the lability (i.e., potential rate of turnover) will substantially decrease as the proportion of ice-locked DOC declines relative to less labile terrestrially derived DOC (Singer et al, 2012;Milner et al, 2017;Hemingway et al, 2019).…”

The Hydroecology of an Ephemeral Wetland in the McMurdo Dry Valleys, Antarctica

“…In nutrient addition experiments, Kohler et al () found that nitrate increased Chl‐a concentrations but had little effect on AFDM in two MDV streams. In the WHC wetland, there were no strong or significant relationships between surface water nitrate concentrations and mat AFDM, Chl‐a concentration or AI (Figure S2 and Table S1).…”