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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 l.jpg

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


Slide2 l.jpg

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

Modified from White, 2002


Slide3 l.jpg

  • 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


Study area cody scarp l.jpg

StudyArea:Cody Scarp


Mill pond spring ichetucknee river l.jpg

Mill Pond Spring, Ichetucknee River

~21 cm of rain

Dye return

Martin and Gordon, 1997


Santa fe river sink rise area l.jpg

Santa Fe RiverSink/Rise area

Sink Well

Rise Well


Travel time sink rise l.jpg

Travel time: Sink  Rise


Flow velocity two floods l.jpg

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


Discharge at sink and rise evidence for conduit matrix exchange l.jpg

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 l.jpg

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


Seawater sr isotopes through time l.jpg

Seawater Sr Isotopes Through Time


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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


Slide13 l.jpg

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 l.jpg

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 l.jpg

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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