![]() These efforts have generated extensive inventories of microbial taxa inhabiting such ecosystems. ![]() Microbial community characterization in freshwater lakes has been the subject of a wide range of studies using culturing approaches, culture-independent diversity surveys, and–omics based investigations. Our work documents the development of multiple spatially and temporally distinct niches during lake stratification, and supports the enrichment of multiple yet-uncultured and poorly characterized lineages in the lake’s deeper oxygen-deficient layers, an ecologically relevant microbial niche that is often overlooked in lakes diversity surveys.įreshwater lakes are biologically complex ecosystems that contribute several economic and societal services and provide habitats for a wide range of micro- and macro-organisms. Within the oxygen-deficient thermocline and hypolimnion, the sedimentation of surface biomass induced the development of a highly diverse community, with the enrichment of Chloroflexi, “Latescibacteria”, Armatimonadetes, and Delta-Proteobacteria in the particle-associated fraction, and Gemmatimonadetes and “Omnitrophica” in the free-living fraction. Within the oxic epilimnion, samples were characterized by the propagation of phototrophic ( Prochlorococcus), and heterotrophic (Planctomycetes, Verrucomicrobia, and Beta-Proteobacteria) lineages. The onset of phototrophic blooming in June induced the progression of this baseline community into two distinct trajectories. Pre-stratification samples (March) harbored a homogeneous community throughout the oxygenated water column dominated by typical oligotrophic aquatic lineages (acl clade within Actinobacteria, and Flavobacterium within the Bacteroidetes). Here, we conducted a spatiotemporal survey of the particle-associated and free-living microbial communities in a warm monomictic freshwater reservoir (Grand Lake O’ the Cherokees) in northeastern Oklahoma, USA. While the limnological aspects of this process are fairly well documented, relatively little is known regarding the microbial community response to such events, especially in the deeper anoxic layers of the water column. This autochthonously produced biomass represents a major seasonal organic input that impacts the entire ecosystem. Additional nutrient dispersion data from the two reservoirs will be analyzed, as well as the timing of the lake turnover.Many freshwater lakes undergo seasonal stratification, where the formation of phototrophic blooms in the epilimnion and subsequent sedimentation induces hypoxia/anoxia in the thermocline and hypolimnion. Additionally, the dispersion of some nutrients also do not appear to be affected by induced mixing as the total nitrogen concentration is similar between the two reservoirs, with the epilimnion and metalimnion having lower total nitrogen concentrations, and a higher concentration being found at a depth of 9 meters. Preliminary results suggest that induced mixing does not affect the depths of the thermocline or the oxycline. Additional water chemistry variables, such as dissolved oxygen and pH, have been collected using a multiparameter water probe. Nutrients analyzed include total nitrogen, nitrate, phosphate, and sulfate. Water samples have been collected throughout the water column from both reservoirs using a horizontal water sampler to investigate the potential effects of induced mixing on nutrient dispersion in the water column, as well as the locations of the thermoclines and oxyclines. Two warm monomictic reservoirs were investigated in this study – one that is younger (Hard Labor Creek Reservoir established in 2018) and does not utilize solar mixers, and one that is older (Lake Varner established in 1993) and does utilize solar mixers. Much of the published literature focuses on the beneficial effects of mixing on controlling algae blooms, but does not address the potential larger implication on overall lake thermoclines, oxyclines, and biogeochemistry. In order to reduce anoxic conditions and prevent eutrophication in the hypolimnion, solar-powered mixers are often utilized to facilitate water movement in the top 10 feet of a reservoir. Stratification may alter the dispersion of nutrients in the water column. During periods of stratification, the water separates into three distinct thermal layers – the upper epilimnion, the metalimnion, and the lower hypolimnion. ![]() Each year, warm monomictic lakes undergo a period of thermal stratification during warmer months, and when the temperature drops, the lake undergoes turnover and mixes.
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