Linking environmental gradients to diatom community distribution in the northwestern Florida Coastal Everglades watershed: applications to understanding long-term tropical storm dynamics

Florida coastal ecosystems are highly sensitive to changes in fresh water influx driven by tropical cyclone activity, changing climate cycles such as the Atlantic Multidecadal Oscillation and El Nino, and water management practices.  Such changes in freshwater flow drive changes in water chemistry that affect the composition of diatom communities because different species have different tolerances for environmental variables like salinity and nutrient availability.  Diatoms can be a powerful tool for understanding environmental variability because of their strong affinity for certain environmental conditions, short generation times that provide a fast response to change, and preservation in sediments that provides the potential for long-term analysis. 

Sediment and water samples were collected across the Charlotte Harbor watershed, in the northwestern Florida Coastal Everglades region.  Charlotte Harbor receives fresh water from three major rivers as well as several small streams.  One of the major rivers, the Caloosahatchee, is a highly managed waterway that was channelized and used for early Everglades drainage via a man-made connection with Lake Okeechobee.  The two other river inflows are relatively pristine but affected by farm and mining activity in their watersheds.  Sediment and water samples from the open harbor and three rivers were taken to capture the gradients of environmental conditions across the watershed during the dry season.  Samples were analyzed for diatom species relative abundance and environmental variables that change in response to freshwater flow such as salinity, nitrogen, phosphorus, and carbon availability.  Relationships between diatom community composition and environmental variables are described.  Additional samples taken following Tropical Storm Debby in June 2012 will be used to evaluate changes driven by a rapid change in flow and applied to long-term analysis using sediment cores.