MAPPING MICROBIAL COMMUNITY COMPOSITION AND GEOCHEMICAL GRADIENTS AT HIGH SPATIAL RESOLUTION IN A MEROMICTIC LAKE (GREEN LAKE, FAYETTEVILLE, NEW YORK)

Meromictic lakes are composed of non-mixing geochemically distinct strata. Green Lake is perhaps the most studied meromictic lake in the world with regard to its geology and limnology; however, its microbiological characterization remains limited. Here we present the first high-resolution molecular based survey of microbial community composition and geochemistry in Green Lake. A novel multilevel sampler was used to synchronously and aseptically acquire samples at 0.25 m to 1 m intervals throughout the water column. Cells were collected by filtration and extracted to isolate genomic DNA for subsequent community characterization by next-generation sequencing (Illumina MiSeq). Sonde profiles and geochemical analyses of sample filtrates were used to establish depth resolved gradients of dominant biologically relevant oxidants (O₂, NO₃^-, NO₂^-, SO₄^2-) and reductants (Fe(II), Mn(II), NH₄⁺, S₂O₃^2-, H₂S). Considering the bioenergetics of counter diffusing oxidizing and reducing equivalents, we use one dimensional eddy diffusion box models to estimate reaction rates and ultimately chemotrophic power consumption as a function of lake depth. By mapping community composition against depth-resolved geochemistry we will examine the correlation between dominant microbial populations, prevailing redox reactions and local chemotrophic bioenergetics.