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Magnesium-Rich Minerals in Sediment and Suspended Particulates of South Florida Water Bodies: Implications for Turbidity

Soil and Water Science Dep., Univ. of Florida, Gainesville, FL 32611

View larger version (34K): [in this window] [in a new window]   Fig. 1. Map of locations for samples designated in Tables 1–5.

View larger version (24K): [in this window] [in a new window]   Fig. 2. X-ray diffraction (XRD) patterns of Okeechobee mud sediment clay (Mg-saturated, glycerol solvated) and silt from specified stations and depths. Minerals indicated are sepiolite (Se), palygorskite (Pa), quartz (Qz), aragonite (Ar), calcite (Ca), and dolomite (Do). The peaks without a mark are from the XRD slide mount. Smectite was also present in most Okeechobee mud samples (including O7, above), but smectite XRD peaks were only marginally evident before K saturation (not shown) (Whittig and Allardice, 1986).

View larger version (106K): [in this window] [in a new window]   Fig. 3. High-resolution transmission electron microscope (HRTEM) image of Mg silicates (fibrous particles) in Okeechobee mud sediment (left; station P9) and in suspended particulates from Everglades stormwater treatment area (Cell 3). Micro-elemental analysis confirmed the presence of Mg and Si (data not shown).

View larger version (80K): [in this window] [in a new window]   Fig. 4. Secondary electron image (top) of Okeechobee sediment silt collected at station O7 (20–30 cm) (Scale bar = 20 µm). Below this image are scanning electron microscope-energy-dispersive X-ray spectroscope (SEM-EDS) elemental dot maps showing zones of Mg, Si, P, S, Ca, and Fe concentrations based on K characteristic X-ray emissions. Dolomite is indicated by some correspondence between Mg and Ca. Silica bioliths (e.g., sponge spicule fragments, etc.) are evident in the sample, along with a Ca phosphate particle and an iron sulfide crystal. Similar Ca-P associations were confirmed for all six silt-fraction samples that were analyzed by SEM-EDS (Fig. 5).

View larger version (56K): [in this window] [in a new window]   Fig. 5. Elemental dot maps of the silt fractions from several Okeechobee mud sediment samples, showing localized zones of Ca-P association (upper row is P, lower row is Ca). Phosphorus is not associated with Ca in a general or diffuse way, but only as localized concentrations, often as discrete grains.

View larger version (19K): [in this window] [in a new window]   Fig. 6. X-ray diffraction (XRD) patterns of the suspended particles collected at Okeechobee stations K8, N6, M9, and O7. Minerals indicated are smectite (Sm), sepiolite (Se), kaolinite (Ka), quartz (Qz), calcite (Ca), dolomite (Do), and aragonite (Ar).

View larger version (13K): [in this window] [in a new window]   Fig. 7. X-ray diffraction (XRD) patterns of the sediment sample from Everglades Cell 3 inflow, showing concentration of palygorskite and quartz by selective dissolution of Ca carbonate minerals (calcite and aragonite).