Iron phosphate sedimentation in a meromictic kettle lake: A Holocene record of geochemistry and paleoenvironment in Teapot Lake, Southern Ontario

Abstract

High iron phosphate mineralization in sediments (>3 m with 15 to 20% vivianite) and the water column (up to 6 ppm PO4 and 9 ppm Fe) of Teapot Lake, a meromictic kettle lake in Brampton, Ontario, was investigated to understand the origins of such remarkable phosphorus enrichment. The lake is surrounded by palimpsest topography composed of Halton Till and Holocene organic matter. Groundwater is the primary recharge source of Teapot Lake, contributing dissolved ferrous iron to the system. Phosphorus concentrations remain low in lake sediments deposited over the past 1335 years, therefore anthropogenic phosphorus contributions are negligible compared to natural accumulations over the Holocene. The source of phosphorus was concluded to be airborne, likely from waterfowl faeces entering the lake from the surface and is subsequently assimilated by algae in the mixolimnion. Phosphorus released from decomposing biomass below the redox boundary is then sequestered by iron as vivianite in the reduced sediments. Currently, the acidic monimolimnion prevents vivianite from precipitating from the lake water, however vivianite can form in the sediments when iron and phosphorus activities are high and the Eh remains above the sulfate/sulfide reduction zone.