Functional and Compositional Responses of Periphyton Mats to Simulated Saltwater Intrusion in the Southern Everglades
Periphyton plays key ecological roles in karstic, freshwater wetlands and is extremely sensitive to environmental change making it a powerful tool to detect saltwater intrusion into these vulnerable and valuable ecosystems. We conducted field mesocosm experiments in the Florida Everglades, USA to test the effects of saltwater intrusion on periphyton metabolism, nutrient content, and diatom species composition, and how these responses differ between mats from a freshwater versus a brackish marsh. Pulsed saltwater intrusion was simulated by dosing treatment chambers monthly with a brine solution for 15 months; control chambers were simultaneously dosed with site water. Periphyton from the freshwater marsh responded to a 1-ppt increase in surface water salinity with reduced productivity and decreased concentrations of total carbon, nitrogen, and phosphorus. These functional responses were accompanied by significant shifts in periphytic diatom assemblages. Periphyton mats at the brackish marsh were more functionally resilient to the saltwater treatment (~ 2 ppt above ambient), but nonetheless experienced significant shifts in diatom composition. These findings suggest that freshwater periphyton is negatively affected by small, short-term increases in salinity and that periphytic diatom assemblages, particularly at the brackish marsh, are a better metric of salinity increases compared with periphyton functional metrics due to functional redundancy. This research provides new and valuable information regarding periphyton dynamics in response to changing water sources in the southern Everglades that will allow us to extend the use of periphyton, and their diatom assemblages, as tools for environmental assessments related to saltwater intrusion.
KeywordsCoastal freshwater wetlands Salinity Microbial mats Diatoms Indicator species
We thank Shawn Abrahams, Michelle Blaha, Marbelys Garriga, Adam Hines, Rowan Johnson, Oliver Ljustina, Melinda Martinez, Fabiola Santamaria, Chris Sillivan, Frank Skiff, Emily Standen, Ryan Stolee, and Mary Grace Thibault for help in the field; Andres Leon and Sara Osorio for help in sample processing and data entry; and Franco Tobias for laboratory assistance particularly with species identification. This manuscript was greatly improved by feedback from two anonymous reviewers. This is contribution number 866 from the Southeast Environmental Research Center in the Institute of Water and Environment at Florida International University.
Funding for research was supported by Florida Sea Grant R/C-S-56, including cooperative agreements with the South Florida Water Management District, the Everglades Foundation, and Everglades National Park. Additional funding was provided through the National Science Foundation’s Florida Coastal Everglades Long Term Ecological Research Program (DEB-1237517).
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