Rapid and Intense Phosphate Desorption Kinetics When Saltwater Intrudes into Carbonate Rock
It is important to understand how phosphate sorption dynamics of coastal carbonate aquifers are affected by seawater intrusion, because many coastal aquifers are composed of carbonate rocks and subject to an increase in saltwater intrusion during relative sea-level rise. Twelve carbonate rock and unconsolidated sediment specimens were acquired from a test corehole spanning the full thickness of the Biscayne aquifer in southeastern Florida. All 12 samples exhibit low phosphorus content but variable contents of iron. Column leaching experiments were conducted with two carbonate aquifer samples, alternating between freshwater and saltwater flow. With the first influx of saltwater, phosphate concentration in leachate increased rapidly from a freshwater value of approximately 0.2 μM to peaks of between 0.8 and 1.6 μM. The phosphate concentration began to diminish as saltwater continued to flow, but sustained desorption continued for over 2 h. Overall, seawater drove sorption behavior much more than chemical composition for the aquifer rocks and sediment from the seven rock samples for which we did isotherm sorption experiments. Our results indicate that an immediate and intense pulse of phosphate desorption from carbonate rock and sediment with low phosphorus content occurs in response to an influx of seawater and that the duration of desorption will vary by layer within a single aquifer.
KeywordsFlorida Everglades Groundwater Submarine groundwater discharge
- Cotecchia, V., G. Tazioli, and G. Magri. 1974. Isotopic measurements in research on seawater ingression in the carbonate aquifer of the Salentine Peninsula, southern Italy. In Isotope techniques in groundwater hydrology 1974, Vol. I. Proceedings of a symposium.Google Scholar
- Cunningham, K.J., D. Bukry, T. Sato, J.A. Barron, L.A. Guertin, and R.S. Reese. 2001. Sequence stratigraphy of a South Florida carbonate ramp and bounding siliciclastics (late Miocene–Pliocene). Geology and hydrology of Lee County, Florida: Florida Geological Survey Special Publication 49: 35–66.Google Scholar
- Cunningham, K.J., M.A. Wacker, E. Robinson, J.F. Dixon, and G.L. Wingard. 2006. A cyclostratigraphic and borehole-geophysical approach to development of a three-dimensional conceptual hydrogeologic model of the karstic Biscayne aquifer, southeastern Florida. In U.S. Geological Survey Scientific Investigations Report 2005–5235, 69 p., plus CD.Google Scholar
- Cunningham, K.J., M.A. Wacker, E. Robinson, C.J. Gefvert, and S.L. Krupa. 2004. Hydrogeology and ground-water flow at Levee 31N, Miami-Dade County, Florida, July 2003 to May 2004. In U.S. Geological Survey Scientific Investigations Map I-2846, 1 sheet.Google Scholar
- Flower, H., M. Rains, D. Lewis, J.-Z. Zhang, and R. Price. 2017. Saltwater intrusion as potential driver of phosphorus release from limestone bedrock in a coastal aquifer. Estuarine Coastal and Shelf Science 184: 166–176.Google Scholar
- Froelich, P.N. 1988. Kinetic control of dissolved phosphate in natural rivers and estuaries: a primer on the phosphate buffer mechanism1. Limnology and Oceanography 33: 649–668.Google Scholar
- Gaiser, E.E., J.C. Trexler, J.H. Richards, D.L. Childers, D. Lee, A.L. Edwards, L.J. Scinto, K. Jayachandran, G.B. Noe, and R.D. Jones. 2005. Cascading ecological effects of low-level phosphorus enrichment in the Florida Everglades. Journal of Environmental Quality 34: 717–723.CrossRefGoogle Scholar
- Kohout, F., and H. Klein. 1967. Effect of pulse recharge on the zone of diffusion in the Biscayne aquifer. In International Association of Scientific Hydrogeology Symposium, Haifa, Israel, pub, 252–270.Google Scholar
- NRC. 2010. National Research Council: Progress Toward Restoring the Everglades: The Third Biennial Review. Washington, D.C.: The National Academies Press, 326 p.Google Scholar
- NRC. 2014. National Research Council: Progress Toward Restoring the Everglades: The Fifth Biennial Review. Washington, DC: The National Academies Press, 302 p.Google Scholar
- Price, R.M. 2001. Geochemical determinations of groundwater flow in Everglades National Park, Ph.D. Dissertation, University of Miami, 307 p.Google Scholar
- Prinos, S.T., M.A. Wacker, K.J. Cunningham, and D.V. Fitterman. 2014. Origins and delineation of saltwater intrusion in the Biscayne aquifer and changes in the distribution of saltwater in Miami-Dade County, Florida. U.S. Geological Survey Scientific Investigations Report 2014–5025, 101 p. Google Scholar
- Rudnick, R., and S. Gao. 2003. 3.01 Composition of the continental crust. Treatise on geochemistry 3 The Crust: 1–64.Google Scholar
- Spence, V. 2011. Estimating groundwater discharge in the oligohaline ecotone of the Everglades using temperature as a tracer and variable-density groundwater models, Masters Thesis, University of South Florida at Tampa, 36 p.Google Scholar
- USGS. 2003. Lithologic and Geophysical Log for G-3784. U. S. Geological Survey, Center for Water and Restoration Studies, Miami, Florida, 1 sheet Accessed online January 10, 2015 at http://sofia.usgs.gov/exchanget/L31_wells/L-31-N_G-3784_COMBO.pdf.
- Yakubu, M., M. Gumel, and A. Abdullahi. 2008. Use of activated carbon from date seeds to treat textile and tannery effluents. African Journal of Science and Technology (AJST) Science and Engineering Series 9: 39–49.Google Scholar
- Zhang, J.-Z., C.J. Fischer, and P.B. Ortner. 2004. Potential availability of sedimentary phosphorus to sediment resuspension in Florida Bay. Global Biogeochemical Cycles 18(4): GB4008. doi:10.1029/2004GB002255.