Spectroscopic investigation of the speciation of phosphorus forms entering and leaving Everglades Stormwater Treatment Areas.

Five large-scale treatment wetlands, the Everglades Stormwater Treatment Areas (STAs), have been constructed in south Florida to reduce phosphorus (P) transport into the Florida Everglades. While the STAs have successfully reduced P entering downstream waterbodies by at least 77%, concentrations in outflow waters still exceed target values in many cases. It has been well documented that P compounds have varying effects on biotic and abiotic processes due to differing stability, bioavailability, and transport characteristics, making it critical to understand the nature of different P pools for improving long-term treatment wetland performance. Here, we used 31P nuclear magnetic resonance (31P NMR) spectroscopy and P X-ray absorption near edge spectroscopy (XANES) to characterize P in surface water particulates entering and leaving the STAs. The most abundant P component at the inflows, as determined via 31P NMR, was orthophosphate (∼36% of P). XANES analyses of inflow waters indicated a lack of iron (Fe)-P bonds and suggested the presence of organic P. Though not commonly documented in this magnitude, polyphosphates were detected in all samples, ranging up to 39% at the outflows. Very little orthophosphate was detected at the outflows, while XANES analysis indicated the presence of hydroxyapatite in STA-2, suggesting internal transformation processes within the wetland. These findings suggest that outflow particulate P may be largely biogenic and that inorganic P may be apatitic in nature, as seen in STA-2. While STA research is relevant for Everglades ecosystem health, the approaches addressed here are informative for treatment wetland research and stormwater P management globally.