Changes in the Community Structure of Under-Ice and Open-Water Microbiomes in Urban Lakes Exposed to Road Salts.

Isabelle B Fournier,Connie Lovejoy,Warwick F Vincent

doi:10.3389/fmicb.2021.660719

Isabelle B Fournier, Connie Lovejoy + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2021.660719

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Abstract

Salinization of freshwater is increasingly observed in regions where chloride de-icing salts are applied to the roads in winter, but little is known about the effects on microbial communities. In this study, we analyzed the planktonic microbiomes of four lakes that differed in degree of urbanization, eutrophication and salinization, from an oligotrophic reference lake with no surrounding roads, to a eutrophic, salinized lake receiving runoff from a highway. We tested the hypothesis that an influence of road salts would be superimposed on the effects of season and trophic status. We evaluated the microbial community structure by 16S rRNA sequencing for Bacteria, and by four methods for eukaryotes: 16S rRNA chloroplast analysis, 18S rRNA sequencing, photosynthetic pigment analysis and microscopy. Consistent with our hypothesis, chloride and total nitrogen concentrations were among the most important statistical factors explaining the differences in taxonomic composition. These factors were positively correlated with the abundance of cryptophytes, haptophytes, and cyanobacteria. Ice-cover was also a major structuring factor, with clear differences between the winter communities and those of the open-water period. Nitrifying and methane oxidizing bacteria were more abundant in winter, suggesting the importance of anaerobic sediment processes and release of reduced compounds into the ice-covered water columns. The four methods for eukaryotic analysis provided complementary information. The 18S rRNA observations were strongly influenced by the presence of ribosome-rich ciliates, but revealed a much higher degree of taxonomic richness and greater separation of lakes, seasonal changes and potential salinity effects than the other methods.

Highlights

In many cold temperate lakes and rivers, the use of road de-icing salts in their catchments during winter has resulted in a pronounced increase of major ion concentrations, especially of the main road salt constituents sodium and chloride (Dugan et al, 2017; Kaushal et al, 2018)
The four lakes selected for this study (Lake Saint-Charles, Lake Clément, Lake Saint-Augustin, and Lake Clair) are located within a 40 km-radius of Quebec City, Canada, and span a range of morphometries, trophic states, mixing regimes and other environmental conditions, including a gradient of urbanization impacts (Table 1)
The 25 samples clustered into four water chemistry groups that separated according to lake (ANOVA, p < 0.05; nonmetric multidimensional scaling (NMDS), Figure 2), and there was no distinction between the ice-cover and the open-water periods (ANOVA, p > 0.05)

Summary

Introduction

In many cold temperate lakes and rivers, the use of road de-icing salts in their catchments during winter has resulted in a pronounced increase of major ion concentrations, especially of the main road salt constituents sodium and chloride (Dugan et al, 2017; Kaushal et al, 2018). Road-contaminated snow has a high salt content, and the subsequent meltwater inflow into lakes can cause a sudden rise in major ion concentrations; for example, salinity rose by a factor of two within a few hours of a snowmelt event in Lake Saint-Charles, Quebec (Fournier et al, 2020) These acute seasonal peaks, as well as chronic long-term salinization, have the potential to affect aquatic communities. Smaller salinity gradients within the freshwater range have been less studied (Wallace and Biastoch, 2016), and consideration has not been given to salt impacts on freshwater microbiomes, here defined as the complete assemblage of Bacteria, Archaea, and microbial eukaryotes that underpin biological productivity, food webs and biogeochemical cycling processes (Grossart et al, 2020) Such consideration requires a focus on natural microbial communities, with their diversity of taxa and their potential responses to the presence of multiple stressors and other variables that may lessen or exacerbate the influence of salt inputs in the environment

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