Abstract
BackgroundLong-term trends in freshwater bacterial community composition (BCC) and dynamics are not yet well characterized, particularly in large lake ecosystems. We addressed this gap by temporally (15 months) and spatially (6 sampling locations) characterizing BCC variation in lakes Erie and St. Clair; two connected ecosystems in the Laurentian Great Lakes.ResultsWe found a spatial variation of the BCC between the two lakes and among the sampling locations (significant changes in the relative abundance of 16% of the identified OTUs at the sampling location level). We observed five distinct temporal clusters (UPGMA broad-scale temporal variation) corresponding to seasonal variation over the 15 months of sampling. Temporal variation among months was high, with significant variation in the relative abundance of 69% of the OTUs. We identified significant differences in taxonomic composition between summer months of 2016 and 2017, with a corresponding significant reduction in the diversity of BCC in summer 2017.ConclusionsAs bacteria play a key role in biogeochemical cycling, and hence in healthy ecosystem function our study defines the scope for temporal and spatial variation in large lake ecosystems. Our data also show that freshwater BCC could serve as an effective proxy and monitoring tool to access large lake health.
Highlights
Long-term trends in freshwater bacterial community composition (BCC) and dynamics are not yet well characterized, in large lake ecosystems
After removing singleton and doubleton sequence reads, as well as operational taxonomic units (OTUs) with ≤20 reads from the data set, 2100 OTUs were included in this study
We observed no significant replicate effect with 3–9 samples/location in our recently published study of aquatic bacterial community dynamics in north temperate lakes [17], we combined sequence read data of the two replicates for each week at each location to increase the read depth for all further statistical analyses
Summary
Long-term trends in freshwater bacterial community composition (BCC) and dynamics are not yet well characterized, in large lake ecosystems. We addressed this gap by temporally (15 months) and spatially (6 sampling locations) characterizing BCC variation in lakes Erie and St. Clair; two connected ecosystems in the Laurentian Great Lakes. The smallest and shallowest of the LGLs, has undergone dramatic swings in water quality over the past century due to nutrient loading (primarily phosphates) from agricultural and urban sources [3]. Lake St. Clair is heavily impacted by densely populated urban areas, and because of its location upstream [6]. Clair is very shallow and highly affected by recurrent eutrophication symptoms [7]
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