MODERN GEOLOGIC CHARACTERIZATION OF A GULF OF MEXICO COASTAL DUNE LAKE

Coastal dune lakes are shallow lacustrine ecosystems located within dune environments that share a permanent or sometimes intermittent connection with the sea. Because coastal dune lakes are only found in a few locations worldwide (e.g. Australia, New Zealand, Florida, etc.) they represent a unique environment worthy of protection. The ecological health of these lakes has become an important environmental concern in Florida, as the area has developed into a tourist center. Preserving and protecting these important lakes through environmental regulation offers significant challenges due to a lack of scientific data to support policy decisions at state and federal levels. Therefore, the purpose of this study was to characterize the modern sediments and foraminera of a coastal dune lake (i.e. Eastern Lake) in Walton County, FL and determine whether coastal dune lakes share geologic similarities with other nearby estuaries. A total of ten Ekman grab surface sediment samples were collected along a canoe transect spanning the length of Eastern Lake. The samples were dried, split, and processed to determine grain size distributions, fractions of organic carbon, grain shape, mineral composition, and foraminiferal assemblage patterns. Results from both sedimentological and foraminiferal analyses reveal at least three unique depositional environments including: (1) a coarse-grained, moderately well-sorted, organic-poor, sandy beach with a mixture of agglutinated and calcareous estuarine foraminifera, (2) a fine-grained, very poorly-sorted, organic-rich central mud basin with an abundance of calcareous foraminifera, and (3) a coarse-grained, poorly-sorted, organic-rich sandy marsh delta dominated by agglutinated foraminifera. The three identified environments are further elucidated by a principle component analysis of the sedimentological and foraminiferal data. It is worth noting that these three environments are found in much larger nearby estuaries including Choctawhatchee Bay, Pensacola Bay, Mobile Bay, and Tampa Bay. Our results therefore suggest that coastal dune lakes may serve as down-scaled “micro-estuaries” and are functionally related to larger estuaries of the gulf coast and throughout the world.