Calcite dissolution by mixing waters: geochemical modeling and flow-through experiments
DOI:
https://doi.org/10.1344/105.000001652Keywords:
Calcite dissolution, Mixing waters, Flow-through experiments, Seawater intrusion, Geochemical modelingAbstract
Dissolution of carbonates has been commonly predicted by geochemical models to occur at the seawater-freshwater mixing zone of coastal aquifers along a geological time scale. However, field evidences are inconclusive: dissolution vs. lack of dissolution. In this study we investigate the process of calcite dissolution by mixing waters of different salinities and pCO2, by means of geochemical modeling and laboratory experiments. Our calculations show that saturation is not always a good indicator of the real dissolution potential of the mixture. In a closed system, the maximum subsaturation occurs for mixing ratios of about 15%-salty, while the dissolved calcite is maximum for 50%. Dissolution is affected by carbonate speciation, and by the dependence of activity coefficients on salinity. Laboratory experiments confirmed a strong dependence of the dissolution on the mixing ratio and pointed out the critical role of CO2 variations at the local atmosphere. The maximum dissolution was observed for mixtures less than 17%-salty, which is attributed to the CO2 exchange between the reaction cell and the laboratory atmosphere. The reaction cell gains CO2 for mixtures less than 17%-salty and calcite dissolution is enhanced with respect to a closed system. The opposite also occurs for mixtures higher than 17% salty. Including CO2 exchange, the model consistently predicts the experimental results. Both calculations and dissolution experiments at different flow rates demonstrated a high sensitivity of the amount of calcite dissolved to minor variations of CO2 partial pressure of the local atmosphere. This could be relevant in field scale interpretations. CO2 pressure measurements in the field are not easy to obtain and could account for the different and “contradictory” field observations.
References
Arvidson, R.S., Ertan, I.E., Amonette, J.E., Luttge, A., 2003. Variation in calcite dissolution rates: A fundamental problem? Geochimica et Cosmochimica Acta, 67, 1623-1634.
Back, W., Hanshaw, B.B., Herman, J.S., Van Driel, J.N., 1986. Differential dissolution of a Pleistocene reef in the groundwater mixing zone of coastal Yucatan, Mexico. Geology, 14, 137-140.
Back, W., Hanshaw, B.B., Pyle, T.E., Plummer, L.N., Weidie, A.E., 1979. Geochemical significance of groundwater discharge and carbonate solution to the formation of Caleta Xel Ha, Quintana Roo, Mexico. Water Resources Research, 15, 1521-1535.
Corbella, M., Ayora, C., 2003. Role of fluid mixing in deep dissolution of carbonates. Geologica Acta, 1, 305-313.
Corbella, M., Ayora, C., Cardellach, E., 2004. Hydrothermal mixing, carbonate dissolution and sulfide precipitation in Mississippi Valley-type deposits. Mineralium Deposita, 39, 344-357.
Corbella, M., Ayora, C., Cardellach, E., Soler, A. 2006. Reactive transport modeling and hydrothermal karst genesis: The example of the Rocabruna barite deposit (eastern Pyrenees). Chemical Geology, 233, 113-125.
Hanshaw, B.B., Back, W., 1980. Chemical mass-wasting of the northern Yucatan Peninsula by groundwater dissolution. Geology, 8, 222-224.
Harvie, C.E., Moller, N., Weare, J.H., 1984. The prediction of mineral solubilities in natural waters: The Na-K-Mg-CaH-Cl-SO4-OH-HCO3-CO3-CO2-H2O system to high ionic strength at 25°C. Geochimica et Cosmochimica Acta, 48, 723-751.
Magaritz, M., Luzier, J.E., 1985. Water-rock interactions and seawater-freshwater mixing effects in the coastal dunes aquifer, Coos Bay, Oregon. Geochimica et Cosmochimica Acta, 49, 2515-2525.
Maliva, R.G., Missimer, T.M., Walker, C.W., Owosina, E.S., Dickson, J.A.D., Fallick, A.E., 2001. Carbonate diagenesis in a high transmissivity coastal aquifer, Biscayne Aquifer, Southeastern Florida, USA. Sedimentary Geology, 143, 287-301.
Melim, L.A., Westphal, H., Swart, P.K., Eberli, G.P., Munnecke, A., 2002. Questioning carbonate diagenetic paradigms Evidence from the Neogene of the Bahamas. Marine Geology, 185, 27-53.
Metz, V., Ganor, J., 2001. Stirring effect on kaolinite dissolution rate. Geochimica et Cosmochimica Acta, 65, 3475-3490.
Ng, K.C., Jones, B., 1995. Hydrogeochemistry of Grand-Cayman, British-West-Indies - Implications for carbonate diagenetic studies. Journal of Hydrology, 164, 193-216.
Parkhurst, D.L., Appelo, C.A.J., 2006. PHREEQC, A hydrogeochemical transport model. Website (2004): http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/ Plummer, L.N., 1975. Mixing of seawater with calcium carbonate groundwater. Geological Society of America Memoir, 142, 219-236.
Plummer, L.N., Vacher, H.L., Mackenzie, F.T., Bricker, O.P., Land, L.S., 1976. Hydrogeochemistry of Bermuda: A case history of ground-water diagenesis of biocalcarenites. Geological Society of America Bulletin, 87, 1301-1316.
Price, R.M., Herman, J.S., 1991. Geochemical investigation of salt-water intrusion into a coastal carbonate aquifer: Mallorca, Spain. Geological Society of America Bulletin, 103, 1270-1279.
Pulido-Leboeuf, P., 2004. Seawater intrusion and associated processes in a small coastal complex aquifer (Castell de Ferro, Spain). Applied Geochemistry, 19, 1517-1527.
Rezaei, M., Sanz, E., Raeisi, E., Ayora, C., Vázquez-Suñe, E., Carrera, J., 2005. Reactive transport modeling of calcite dissolution in the fresh-salt water mixing zone. Journal of Hydrology, 311, 282-298.
Romanov, D., Dreybrodt, W., 2006. Evolution of porosity in the saltwater-freshwater mixing zone of coastal carbonate aquifers: An alternative modelling approach. Journal of Hydrology, 329, 661-673.
Saaltink, M.W., Batlle, F., Ayora, C., Carrera, J., Olivella, S., 2004. RETRASO, a code for modeling reactive transport in saturated and unsaturated porous media. Geologica Acta, 2, 235-251.
Sanford, W.E., Konikow, L.F., 1989. Simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers. Water Resources Research, 25, 655-667.
Singurindy, O., Berkowitz, B., Lowell, R.P., 2004. Carbonate dissolution and precipitation in coastal environments: Laboratory analysis and theoretical consideration. Water Resources Research, 40, 1-12.
Smart, P.L., Dawans, J.M., Whitaker, F., 1988. Carbonate dissolution in a modern mixing zone. Nature, 335, 811-813.
Stoessell, R.K., Ward, W.C., Ford, B.H., Schuffert, J.D., 1989. Water chemistry and CaCO3 dissolution in the saline part of an open-flow mixing zone, coastal Yucatan Peninsula, Mexico. Geological Society of America Bulletin, 101(2), 159-169.
Whitaker, F.F., Smart, P.L., 1997. Groundwater circulation and geochemistry of a karstified bankmarginal fracture system, South Andros Island, Bahamas. Journal of Hydrology, 197, 293-315.
Wicks, C.M., Herman, J.S., Randazzo, A.F., Jee, J.L., 1995. Water-rock interactions in a modern coastal mixing zone. Geological Society of America Bulletin, 107, 1023-1032.
Wigley, T.M.L., Plummer, L.N., 1976. Mixing of carbonate waters. Geochimica et Cosmochimica Acta, 40, 989-995.
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