Mg-Rich Minerals in Sediment and Suspended Particulates of Lake Okeechobee and Tributaries in the No...
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Mg-Rich Minerals in Sediment and Suspended Particulates of Lake Okeechobee and Tributaries in the Northern Everglades: Implications for TurbidityWillie HarrisSoil and Water Science Department, University of FloridaOther contributors: Matt Fisher, Rocky Cao, Todd Osborne, Rex EllisAcknowledgments: Ramesh Reddy, Woody Dierberg, John White, Tom James

  • Topics Discussed

  • Objective of study and this talk.

  • Methods.

  • Summary of findings.

  • Data that document mineral ID.

  • Mineral properties and their relevance to turbidity.

  • Mystery and importance of provenance.


Determine if mineral components of sediments in Lake Okeechobee and water conveyances of N. Everglades also occur as suspended sediment and hence constitute potential abiotic contributors to turbidity.

Mission from God

  • Methods:

  • Sediment samples collected from:

    • 9 stations within the lake

    • 8 locations north of Water Conservation Area 2A

  • Water samples collected at selected locations.

  • Silt and clay mineralogy of sediment and suspended particles determined using XRD, TG, SEM, EDX, and HRTEM.

Summary of Results:

Lake sediment clay: sepiolite, smectite, dolomite, calcite, kaolinite, palygorskite.

Lake sediment silt: Dominated by carbonates and/or quartz; smaller amounts of Ca phosphates and sepiolite.

Lake suspended solids: Similar to sediment, except smectitemore prevalent.

Everglade samples (sediment and suspended solids): calcite, dolomite, palygorskite, aragonite, quartz, sepiolite

Blue: contain Mg

Orange: commonly contain some Mg

SEM/EDS images

SEM secondary image

EDS elemental dot maps

Discrete Ca-P phases commonly observed

Chemical properties of Mg-bearing minerals

M = exchangeable cations; can range from 0.2 to 0.6.

Physical properties of Mg-bearing minerals

From U. S. Geological Survey Open-File Report 01-041

  • Conditions favoring turbidity:

  • Lake chemistry (pH, ionic strength)

  • Mineral properties (density, size, shape)

  • V = g (sp - sl) D2 / 1.8η


Solids data for samples we collected

Effect of pH

Effect of ionic strength

Effect of cation valence

Upper - hydrated Na, a monovalent cation

Middle - hydrated Ca, a divalent cation

Lower - "specifically adsorbed" Al, trivalent

Mystery and importance of provenance.

Fluvial transport?

  • Prospect of Kissimmee River being significant mud mineral source raises questions:

  • Does its channelization exacerbate turbidity-related problems in the lake?

  • Would continued sediment delivery by river negate any benefit from dredging?

  • Prospect could be evaluated by mineral analysis of:

  • sediment cores from the river’s original bed, constructed channel, and mouth.

  • suspended solids at river mouth.

Mud mineralogy similar to that for geologic phosphate deposits. Might mud have accumulated by stream transport from these deposits?

Authigenic provenance?

Torry Muck has sepiolite and smectite.

Prevalent to S and E of Lake Okeechobee


Prepared December, 2003


Cox, S., D. Lewis, S. McCollum, M. Bledsol, and R. Marrotte. 1988. Subsidence study of the Everglades Agricultural Area. USDA, SCS, Greenacres, FL. pp. 25.

  • Summary of implications for turbidity

  • Mud is consistently rich in Mg-bearing minerals.

  • Small size, low density, and fibrous or platy habit favor re-suspension and slow settling.

  • Minerals didn’t originate from P-induced biogeochemical processes.

  • P load reduction (though needed) does not mitigate mineral effects.

  • “One thing thou lackest …”


(No divine revelation forthcoming)

A mystery that cries for a solution

Guoy-Chapman Model

• Reciprocal of double layer thickness:

K = A z [n0 / εkT]1/2

where: K = reciprocal of double layer thickness

A = a constant

z = counter ion charge

n0 = electrolyte conc

ε = dielectric constant of solvent

T = temperature (Kelvin)

  • Electric Double Layer

    • • Guoy-chapman model or diffuse double layer model

      • – Conducted independently by Gouy (1910) and Chapman (1913)

    • • Modification by Stern (Stern Theory)

    • • DLVO Theory

      • – Derjaguin, Landau, Verwey, and Overbeek

    • • Surface complexation models

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