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Ground and surface water interactions in karst terrains: Some observations from along the Cody Scarp. Jon Martin Liz Screaton, PJ Moore Acknowledgements: NSF, DEP, SRWMD O’Leno State Park, Ichetucknee State Park Sheryl Gordon, Randy Dean, Brooke Sprouse, Jennifer Martin.

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Ground and surface water interactions in karst terrains: Some observations from along the Cody Scarp

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Ground and surface water interactions in karst terrains:Some observations from along the Cody Scarp

Jon Martin

Liz Screaton, PJ Moore

Acknowledgements: NSF, DEP, SRWMD

O’Leno State Park, Ichetucknee State Park

Sheryl Gordon, Randy Dean, Brooke Sprouse, Jennifer Martin


How does flow in conduits and matrix interact?- What can be learned from chemistry of spring discharge?

Modified from White, 2002


  • Karst aquifers have two distinct ground water reservoirs:

    • Conduits (> 1 cm2)

    • Matrix (fracture and intergranular porosity)

      • Flow unimportant in low porosity matrix, e.g. Paleozoic aquifers

      • High porosity matrix important flow path and for storage, e.g. Floridan aquifer

Martin and Screaton, 2001


StudyArea:Cody Scarp


Mill Pond Spring, Ichetucknee River

~21 cm of rain

Dye return

Martin and Gordon, 1997


Santa Fe RiverSink/Rise area

Sink Well

Rise Well


Travel time: Sink  Rise


Flow velocity, two “floods”

  • Velocity constant through conduits

  • Velocity depends on stage and discharge

  • Discharge can be used to determine conduit size

  • Determine residence time – chemical sampling


2.2 million

m3 lost

1.1 million

m3 lost

19 million

m3 gained

Discharge at sink and rise:evidence for conduit-matrix exchange


Cl- concentrations vs. distance and through time following 1998 El Nino floods


Seawater Sr Isotopes Through Time


Mixing: Ocala Ls and seawater + radiogenic Sr?Some wells have more Ocala Sr than othersRadiogenic Sr from Hawthorn Gp?

Modern Seawater

0.70917

0.7079Upper Ocala


222Rn Geochemistry

222Rn derived from decay of 238U

Alkaline earth element; easily fits in clay and carbonate mineral structures.

226Ra

t½ = ~1600 yrs

 Source of 222Rn to ground water.

222Rn

t½ = 3.8 days

 Loss from radioactive decay.

218Po

Noble gas; non-reactive in inorganic or organic reactions.

 Loss from evasion to atmosphere.


Rn input and decay

10.53 masl

Excess

Rn

222Rnmeas.-222Rncalc.

9.78 masl

Rn

Deficit

~12.2 masl

Distance from sink (m)

N = 222Rn activity

N0 =initial 222Rn activity

l = decay constant

t = time


Conclusions and Questions

  • Water exchanges between conduits and matrix (T, physical models, Cl concentrations)

  • Several sources of recharged water from confined region (Sr and Rn isotopes)

  • What roles do diffuse recharge and epikarst have in flow in conduits and matrix?


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