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Greg Druschel Department of Geology University of Vermont

Determination of sediment phosphorus concentrations in St. Albans Bay, Lake Champlain: Assessment of internal loading and seasonal variations of phosphorus sediment-water column cycling. Greg Druschel Department of Geology University of Vermont. Acknowledgements.

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Greg Druschel Department of Geology University of Vermont

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  1. Determination of sediment phosphorus concentrations in St. Albans Bay, Lake Champlain: Assessment of internal loading and seasonal variations of phosphorus sediment-water column cycling Greg Druschel Department of Geology University of Vermont

  2. Acknowledgements • Funding for this study through State of Vermont Clean & Clear Program, administered by the Department of Environmental Conservation • VT DEC, especially Eric Smeltzer and Pete Stengel, for providing logistical support • St. Albans Bay Watershed association and town administrator Dan Lindley • Students at UVM who assisted: Aaron Hartmann, Rachel Lomonaco, Deb Schulman, and Ken Oldyryd • Mary Watzin, Eric Smeltzer, Andrea Lini, Neil Kamman for thoughtful and insightful discussions

  3. Program Goals • Determine the amount of phosphorus currently contained in St. Albans Bay sediments • Determine how that phosphorus may be mobile within the sediments  what controls P profiles and how P may be released from sediments into the water column, providing nutrients feeding algal blooms

  4. Oxic Anoxic Redox ‘Fronts’ • Boundary between oxygen-rich (oxic) and more reduced (anoxic) waters • Oxygen consumed by microbes which eat organic material • When Oxygen is gone, there are species of microbes that can ‘breathe’ oxidized forms of iron, manganese, and sulfur

  5. Methods • Gravity Coring • Seasonal site  10 separate samplings, late May through early October • Early August collected 43 cores across the bay and Stevens Brook Wetland • In-situ pore water measurments to determine redox front • Chemical extractions of iron, manganese, and phosphorus in the sediment • Inductively-coupled plasma optical emission spectroscopy (ICP-OES) to measure iron, manganese, and phosphorus from extractant

  6. Results: Seasonal Work • Sediments generally become more reduced as summer progresses • Redox fronts move up and down in response to Temperature, wind, biological activity changes

  7. Summer 2004 • Summer 2004 was, in general, colder than average, windy, and rainy  these factors would drive redox fronts higher in the sediment column • Sediments at other locations (deeper, in the wetland) would be slightly different – possibly having a lower redox front

  8. Seasonal Phosphorus mobility • Ascorbic acid extractions of Fe, Mn, and P from 10 sediment cores collected in summer 2004 show strong dependence between P and Mn or Fe • Further, profiles show overall enrichment of all 3 parameters in upper sections of sediment • Fe and Mn would be primarily in the form of Fe and Mn oxyhydroxide minerals  transformation of these minerals is key to P movement

  9. Sediment P mobility and water column • Does the P mobilized in the sediment get into the water column and does it contribute to algal activity/ blooms? • From our data, it seems that Fe, Mn mineral changes and P mobility in the sediments is linked to both P release and algal activity • Our study methods were not specifically designed for this, but now that we know the processes involved, a better study of P transfer from sediment and use by algae is possible

  10. St. Albans Bay P Load • 43 cores subdivided into 7 depth sections each, extracted 5 different ways analyzed in triplicate • 1200 individual samples and 3000+ individual analyses • Results: • Top 4 cm contains ~500 tons of P • Top 10 cm of sediment contains ~1200 tons of P

  11. 1992 vs 1982 comparisons suggested P was being essentially flushed out of the sediments into the main lake This study finds no evidence to support P concentrations are substantially decreasing in time i.e.  the bay sediments will NOT clean themselves in the near future

  12. Spatial distributions • Profiles again reflect a general increase of P, Mn, and Fe in top few cm of these cores

  13. P Loading and sediment deposition • Constantly moving redox fronts affect Fe and Mn minerals, mobilize P and turn ideal profile into what we actually see…

  14. Summary of Findings • There remains significant P in the sediments of St. Albans Bay, and overall rates of P loss from the sediments should be much lower than previously thought • P mobility in the sediments is at least partly governed by Iron and Manganese mineralization which is strongly affected by redox fronts • This mobility has changed the profile of P in the sediments by smoothing out any recorded changes in P loading.

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