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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
slide2
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.
slide3
Objective:

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

slide4
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.
slide6
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

slide13
SEM/EDS images

SEM secondary image

EDS elemental dot maps

slide15
Chemical properties of Mg-bearing minerals

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

slide19
Conditions favoring turbidity:
  • Lake chemistry (pH, ionic strength)
  • Mineral properties (density, size, shape)
  • V = g (sp - sl) D2 / 1.8η

Solids

Solids data for samples we collected

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Effect of cation valence

Upper - hydrated Na, a monovalent cation

Middle - hydrated Ca, a divalent cation

Lower - "specifically adsorbed" Al, trivalent

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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.
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Mud mineralogy similar to that for geologic phosphate deposits. Might mud have accumulated by stream transport from these deposits?
slide28
Torry Muck has sepiolite and smectite.

Prevalent to S and E of Lake Okeechobee

From EVERGLADES AGRICULTURAL AREA SOIL SUBSIDENCE AND LAND USE PROJECTIONS, Dr. George Snyder,

Prepared December, 2003

After

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.

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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 …”
slide33
Provenance!

(No divine revelation forthcoming)

A mystery that cries for a solution

slide34
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)

slide35
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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