title: Internal loading of phosphate in Lake Erie Central Basin.
abstract: After significant reductions in external phosphorus (P) loads, and subsequent water quality improvements in the early 1980s, the water quality of Lake Erie has declined considerably over the past decade. The frequency and magnitude of harmful algal blooms (primarily in the western basin) and the extent of hypoxic bottom waters in the central basin have increased. The decline in ecosystem health, despite meeting goals for external P loads, has sparked a renewed effort to understand P cycling in the lake. We use pore-water P concentration profiles and sediment cores incubation experiments to quantify the P flux from Lake Erie central basin sediments. In addition, the oxygen isotopes of phosphate were investigated to assess the isotopic signature of sedimentary phosphate inputs relative to the isotopic signature of phosphate in lake water. Extrapolating the total P sediment flux based on the pore-water profiles to the whole area of the central basin ranged from 300 to 1250metric tons per year and using the flux based on core incubation experiments an annual flux of roughly 2400metric tons of P is calculated. These estimates amount to 8-20% of the total external input of P to Lake Erie. The isotopic signature of phosphate in the extractable fraction of the sediments (~18‰) can explain the non-equilibrium isotope values of dissolved phosphate in the deep water of the central basin of Lake Erie, and this is consistent with sediments as an important internal source of P in the Lake.
authors.affiliation: Institute of Marine Sciences, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA. Electronic address: apaytan@ucsc.edu.
authors.forename: Adina
authors.initials: A
authors.lastname: Paytan
authors.affiliation: Institute of Marine Sciences, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Roberts
authors.affiliation: Water Science and Technology, Environment and Climate Change Canada, 867 Lakeshore Rd, Burlington, Ontario L7S 1A1, Canada.
authors.forename: Sue
authors.initials: S
authors.lastname: Watson
authors.affiliation: United States Geological Survey, 345 Middlefield Rd, Menlo Park, California 94025-0434, USA.
authors.forename: Sara
authors.initials: S
authors.lastname: Peek
authors.affiliation: Institute of Marine Sciences, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA.
authors.forename: Pei-Chuan
authors.initials: PC
authors.lastname: Chuang
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA.
authors.forename: Delphine
authors.initials: D
authors.lastname: Defforey
authors.affiliation: United States Geological Survey, 345 Middlefield Rd, Menlo Park, California 94025-0434, USA.
authors.forename: Carol
authors.initials: C
authors.lastname: Kendall
mesh_terms: D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry; D006114:Great Lakes Region; D060106:Lakes / Q000737:chemistry; D010710:Phosphates / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D010710:Phosphates; D014874:Water Pollutants, Chemical; D010758:Phosphorus
keywords: Lake Erie; Oxygen isotopes of phosphate; Phosphorus flux; Sediments