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Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions., (© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Abundant phytoplankton and bacteria were identified by high-throughput 16S rRNA tag Illumina sequencing of samples from water and ice phases collected during winter at commercial fish ponds and a sand pit lake within the UNESCO Třeboň Basin Biosphere Reserve, Czech Republic. Bacterial reads were dominated by Proteobacteria and Bacteroidetes. Despite dominance by members of just two phyla, UniFrac principal coordinates analysis of the bacterial community separated the water community of Klec fish pond, as well as the ice-associated community of Klec-Sand Pit from other samples. Both phytoplankton and cyanobacteria were represented with hundreds of sequence reads per sample, a finding corroborated by microscopy. In particular, ice from Klec-Sand Pit contained high contributions from photoautotrophs accounting for 25% of total reads with reads dominated by single operational taxonomic units (OTUs) of the cyanobacterium Planktothrix sp. and two filamentous diatoms. Dominant OTUs recovered from ice were largely absent (< 0.01%) from underlying water suggestive of low floristic similarity of phytoplankton partitioned between these phases. Photosynthetic characterization of phototrophs resident in water and ice analysed by variable chlorophyll a fluorescence showed that communities from both phases were photosynthetically active, thus supporting ice as viable habitat for phytoplankton in freshwater lakes and reservoirs., (© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Lake St. Clair is the smallest lake in the Laurentian Great Lakes system. MODIS satellite imagery suggests that high algal biomass events have occurred annually along the southern shore during late summer. In this study, we evaluated these events and tested the hypothesis that summer bloom material derived from Lake St. Clair may enter Lake Erie via the Detroit River and represent an overlooked source of potentially toxic Microcystis biomass to the western basin of Lake Erie. We conducted a seasonally and spatially resolved study carried out in the summer of 2013. Our goals were to: 1) track the development of the 2013 summer south-east shore bloom 2) conduct a spatial survey to characterize the extent of toxicity, taxonomic diversity of the total phytoplankton population and the phylogenetic diversity of potential MC-producing cyanobacteria (Microcystis, Planktothrix and Anabaena) during a high biomass event, and 3) compare the strains of potential MC-producers in Lake St. Clair with strains from Lake Erie and Lake Ontario. Our results demonstrated a clear predominance of cyanobacteria during a late August bloom event, primarily dominated by Microcystis, which we traced along the Lake St. Clair coastline downstream to the Detroit River's outflow at Lake Erie. Microcystin levels exceeded the Province of Ontario Drinking Water Quality Standard (1.5 µg L(-1)) for safe drinking water at most sites, reaching up to five times this level in some areas. Microcystis was the predominant microcystin producer, and all toxic Microcystis strains found in Lake St. Clair were genetically similar to toxic Microcystis strains found in lakes Erie and Ontario. These findings suggest extensive genetic connectivity among the three systems.

Due to their ubiquity in aquatic environments and their contribution to total biomass, especially in oligotrophic systems, cyanobacteria can be viewed as a proxy for primary productivity in both marine and fresh waters. In this chapter we describe the development and use of picocyanobacterial bioreporters to measure the bioavailability of nutrients that may constrain total photosynthesis in both lacustrine and marine systems. Issues pertaining to bioreporter construction, performance and field applications are discussed. Specifically, luminescent Synechococcus spp. and Synechocystis spp. bioreporters are described that allow the bioavailability of phosphorus, nitrogen and iron to be accurately measured in environmental samples.