Using Oxygen Isotopes of Phosphate To Trace Phosphorus Sources and Cycling in Lake Erie

Water samples collected during three sampling trips to Lake Erie displayed oxygen isotopic values of dissolved phosphate (delta O-18(p)) that were largely out of equilibrium with ambient conditions, indicating that source signatures may be discerned. delta O-18(p), values in the Lake ranged from +10 parts per thousand to +17 parts per thousand, whereas the equilibrium value was expected to be around +14 parts per thousand. The riverine weighted average delta O-18(p), value was +11 parts per thousand and may represent one source of phosphate to the Lake. The lake delta O-18(p) values indicated that there must be one or more as yet uncharacterized source(s) of phosphate with a high delta O-18(p) value. Potential sources other than rivers are not yet well-characterized with respect to delta O-18(p) of phosphate, but we speculate that a likely source may be the release of phosphate from sediments under reducing conditions created during anoxic events in the hypolimnion of the central basin of Lake Erie. Identifying potential phosphorus sources to the Lake is vital for designing effective management plans for reducing nutrient inputs and associated eutrophication.