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

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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  1. 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

  2. How does flow in conduits and matrix interact?- What can be learned from chemistry of spring discharge? Modified from White, 2002

  3. 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

  4. StudyArea:Cody Scarp

  5. Mill Pond Spring, Ichetucknee River ~21 cm of rain Dye return Martin and Gordon, 1997

  6. Santa Fe RiverSink/Rise area Sink Well Rise Well

  7. Travel time: Sink  Rise

  8. 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

  9. 2.2 million m3 lost 1.1 million m3 lost 19 million m3 gained Discharge at sink and rise:evidence for conduit-matrix exchange

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

  11. Seawater Sr Isotopes Through Time

  12. 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

  13. 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.

  14. 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

  15. 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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