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 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

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

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 Anoxic Oxic

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

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

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

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

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

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

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

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

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…

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.