The Laurentian Great Lakes (LGLs) contain approximately 20% of global surface freshwater, and therefore play important roles in global biogeochemical cycling. Despite this, we have a poor understanding of biogeochemical cycling within the LGLs, including not only traditional biogeochemical processes such as nutrient pools and processing rates, but also complex interactions between macro- and micro-elemental cycles. This is increasingly important, as anthropogenic impacts are intensifying and the LGLs are responding to multiple stressors (e.g., warming, water level fluctuations, strong storm-drought cycles, acidification, aquatic invasive species, harmful algal blooms). For example, large uncertainties in pools and processing rates of the three primary macronutrients (carbon, nitrogen, phosphorus) in the LGLs constrain our ability to forecast lake responses to future stressors. Although hydrologically interconnected, the LGLs encompass five distinct freshwater ecosystems concerning biogeochemistry. For example, Lake Superior’s carbon budget is 20+ years old and includes missing carbon inputs from unidentified sources (i.e., the carbon mass balance does not add up), and mechanisms contributing to high accumulation of nitrate in the water column are unclear. In contrast to the predominantly forested watershed of Lake Superior, the lower four Great Lakes are strongly influenced by nitrogen and phosphorus loading from agricultural sources, but coupling between these critical nutrient cycles has not been fully defined. As anthropogenic stress continues to compound, cycling of carbon, nitrogen, and phosphorus, as well as other nutrients, will be affected in yet unknown ways. In this session, we invite submissions that focus on macro- and micro-elemental cycles (both pools and processes) in the LGLs, especially those that focus on interactions among cycles, connections between cycles and anthropogenic stress, or novel or understudied controls on biogeochemical cycles. We hope to integrate findings from observational or experimental studies using diverse approaches (e.g., high frequency sensors, remote sensing, field surveys, modeling). The intended outcome from this session is to identify new linkages among cycles and areas for future research and refinement.

Lead Organizer: Christopher Filstrup, University of Minnesota Duluth (filstrup@d.umn.edu)

Co-organizers:

Kathryn Schreiner, University of Minnesota Duluth (kschrein@d.umn.edu)

Reagan Errera, National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory (Reagan.Errera@noaa.gov)

Presentations

06:00 PM

SPATIAL HETEROGENEITY AND DIVERSITY OF MICROBIAL COMMUNITIES IN LAKE HURON SEDIMENTS: IMPLICATIONS FOR BIOGEOCHEMICAL CYCLING (9375)

Primary Presenter: Britta Larson, Natural Resources Research Institute (lars5859@d.umn.edu)

Sediment microbial communities within freshwater ecosystems drive biogeochemical cycling, influencing the transformation and movement of nutrients and contaminants. However, there is a need to understand the coupling strengths of different biogeochemical cycles and how they vary across environmental gradients. As part of the Great Lakes Sediment Surveillance Program, we investigated spatial and temporal prokaryotic communities through surface sediment samples. We assessed the phylogenetic composition and functional traits of the potentially active community (RNA) compared to the total community (DNA) and identified contributing taxa to geochemical processes. Our results reveal microbial communities in Lake Huron are highly heterogeneous, suggesting local biogeochemistry is influenced by the variable land cover (e.g., forest types, cropland, urbanization) and environmental gradients. Distinctly, offshore sediment samples predominately harbor sulfur-transforming genera under the families Beggiatoaceae and Desulfosarcinaceae. Samples collected in the Georgian Bay, North Channel, and near river mouths showed distinct microbial communities and some overlap with sediments in Lake Superior. When compared to Lake Superior, Lake Huron has more diverse microbial communities with anaerobic and reductive metabolisms. Overall, local selective pressures shape microbial communities and their transformation of nutrients and contaminants. This approach is being applied to other Laurentian Great Lakes, which allows greater insight into the gradients found across the system.

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