Karst estuaries are governed by interactions between inland hydrological conditions and sea level

Abstract

Summary Karst estuaries represent unique systems created by freshwater inputs that flow directly into the sea through karst conduits and/or matrices. In order to determine the characteristics of a karst estuary resulting from the brackish discharge of Double Keyhole Spring into the Gulf of Mexico, we monitored short-term tidal fluctuations, long-term rainfall patterns, aquifer levels, spring discharge, and multiple geochemical parameters along a transect from the spring through the estuary. We monitored four sites along a spring/estuary transect and a nearby inland freshwater spring to represent the freshwater portion of the Upper Floridan Aquifer. Datasondes were deployed in Double Keyhole Spring to measure discharge volume, tidal fluctuations, and physical water parameters for two years. Water samples were collected quarterly from both springs and the surrounding surface sites over the same time period. An isotopic/trace element mass balance tracer method was used to determine the hydrogeological components of the spring discharge from three possible sources: (1) freshwater from the upper portion of the Upper Floridan aquifer, (2) freshwater from the lower portion of the Upper Floridan aquifer, and (3) saltwater from the Gulf of Mexico. Within the water column of the submarine spring conduit, there were no significant differences of the sampled parameters over short sampling distances (