『Abstract
　Phosphorus has historically been a limiting nutrient in the Florida Everglades. Increased P loading to the Everglades over the past several decades has led to significant changes in water quality and plant communities. Stormwater runoff that drains agricultural lands and enters the Water Conservation Areas (WCAs) are known to contain elevated levels of P, but the exact source of this P has not been fully determined. Here the results of an O isotope study of dissolved inorganic phosphate (DIP) in both polluted and relatively pristine (or reference) areas of the Everglades are reported. The data reveal spatial and temporal variations in the δ¹⁸O signature of DIP, reflecting the source and the degree of cycling of P. The δ¹⁸O values of DIP collected from the Everglades National Park were close or equal to the predicted δ¹⁸O values of DIP formed in situ in equilibrium with ambient water, indicating that P is quickly cycled in the water column in oligotrophic ecosystems with very low P concentrations. However, most DIP samples collected from areas impacted by agricultural runoff yielded δ¹⁸O values that deviated from the predicted equilibrium DIP-δ¹⁸O values based on the δ¹⁸O of water and water temperature, suggesting that biological cycling of P was not rapid enough to remove the fertilizer δ¹⁸O signature in the DIP pool from areas receiving high P loading. The δ¹⁸O signature of DIP in impacted areas reflects a mixing of fertilizer P and biologically cycled P, where the relative proportions of biologically cycled vs. fertilizer DIP are controlled by both biological (microbial activities and plant uptake) and hydrologic factors (loading rate and residence time). Using a two-end-member (i.e., fertilizer P and biologically cycled P) mixing model, fertilizers were estimated to contribute about 15-100％ of the DIP pool in the highly impacted areas of the northern Everglades, whereas the DIP pool in the reference (i.e., relatively pristine) wetlands in the Everglades National Park was dominated by biologically cycled P. This study shows that O isotopic measurements of dissolved PO4^3- can be a useful tool for tracing the fertilizer P inputs to freshwater ecosystems.』

1. Introduction
2. Study sites
3. Methods
4. Results and discussion
5. Conclusions
Acknowledgements
References