Internal loading of phosphate in Lake Erie Central Basin

• Published in: The Science of the total environment 2017-02, Vol.579, p.1356-1365
• Main Authors: Paytan, Adina, Roberts, Kathryn, Watson, Sue, Peek, Sara, Chuang, Pei-Chuan, Defforey, Delphine, Kendall, Carol
• Format: Article
• Language: English
• Subjects: Environmental Monitoring; Freshwater; Geologic Sediments - chemistry; Great Lakes Region; Lake Erie; Lakes - chemistry; Oxygen isotopes of phosphate; Phosphates - analysis; Phosphorus - analysis; Phosphorus flux; Sediments; Water Pollutants, Chemical - analysis
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.11.133

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. [Display omitted] •Eutrophication and hypoxia in Lake Erie are fueled by phosphorus (P); yet P loads are unconstrained.•We use pore-water profiles, core incubations and isotopes to estimate P loading from sediments.•Sediment P loading amounts to as much as 20% of external loading.•P loading from sediments is in the form of biologically available phosphate.