Trace Metal Accumulation and Re-mobilization in Phreatic Karst Conduits
Little is known about how trace metals accumulate and cycle in conduits within the phreatic zone. These water-filled conduits can receive floodwater that allows metals to accumulate, similar to air-filled caves, but are more susceptible to reducing conditions following floods because oxygen is limited to dissolved concentrations. If sufficient reactive organic carbon is transported into the aquifer, oxygen consumption will lower Eh and mobilize manganese and iron. To evaluate this accumulation and mobilization of metals, we analyzed the geochemical and isotopic composition of water, solid metal oxide, and limestone samples from two phreatic systems in north-central Florida where river water displaces aquifer water following storms. River water was a net source of trace metals to the aquifer; however, manganese depletion in the interior of the metal oxides relative to concentrations in intruding river water indicates not all metals are retained in the aquifer as redox conditions changed. The metal oxides are actively incorporating metals from floods, with anthropogenically sourced lead from surface water on the outer portion of the metal oxide.
- Martin, H.W. 1990. Phreatite: A speleothem formed in phreatic limestone conduits. Underwater Speleology 17 (6): 6–10.Google Scholar
- White, W.B., C. Vito, and B.E. Scheetz. 2009. The mineralogy and trace element chemistry of black manganese oxide deposits from caves. Journal of Cave and Karst Studies 71 (2): 136–143.Google Scholar