Mineralogy of particulate inputs and P-speciation and mineralogy of recently accreted soils within Everglades stormwater treatment wetlands

Abstract Phosphorus (P) biogeochemical processes in wetlands are influenced by the chemical composition of both recently accreted and native soils. The evaluation of biogeochemical processes influencing P transformations requires an understanding of the participating chemical components. Here, we use X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray fluorescence spectroscopy (EDS), X-ray absorption near-edge P spectroscopy (P-XANES), and microprobe X-ray fluorescence (μ-XRF) to examine the mineralogy and P speciation of solid phases entering and within selected Everglades Stormwater Treatment Areas (STAs). Suspended particulates in the source waters (upstream of the STAs) to the STAs were examined and compared with those of recently-accreted soil (RAS) from inflow, mid-flow, and outflow locations of two flowways (FWs) within STA-2: one dominated by emergent aquatic vegetation (EAV) and the other dominated by submerged aquatic vegetation (SAV). Source water particulates included carbonates and silicates, whereas mineralogies of STA RAS were less diverse, dominated by CaCO3 and having a lower silicate content, suggesting a strong autochthonous influence on STA RAS composition. No P minerals were detected via XRD. Discrete Ca P particles were evident, though uncommonly observed, in two of three STA RAS samples analyzed via SEM/EDS. P-XANES of STA RAS indicated the presence of apatitic minerals. The potential presence of apatitic minerals was supported by μ-XRF correlation analysis that revealed strong correlations of P with both Ca and K. Apatitic minerals are a relatively refractory form of P and their presence in the RAS of both EAV and SAV systems indicate that remobilization and release of this P from the STAs will have a smaller effect on the downstream oligotrophic conditions of the Florida Everglades than more labile forms of P.