The effects of nutrient enrichment on benthic periphyton mat communities in a South Florida freshwater coastal wetland habitat

Within the long hydroperiod freshwater marshes of the South Florida Everglades, low intensity enrichment promotes functional, chemical and compositional changes in floating periphyton mats, while high intensity enrichment causes the breakdown and disappearance of mats, a phenomenon not reported elsewhere.  To date no comprehensive studies have been conducted regarding nutrient effects on the benthic periphyton communities of these coastal wetlands. It is therefore not known whether these communities, which are influenced by both water and soil nutrient levels, would exhibit similar responses to nutrient enrichment as seen in floating mats.  With federally-approved plans to change freshwater flow patterns from the interior of the Everglades towards the coast, the potential for nutrient enrichment in coastal habitats is significant.  This project therefore sought to examine periphyton mats from a freshwater coastal Everglades wetland habitat and determine the effects of nutrient enrichment on mat development.  The study was conducted from May to August 2006.  Three experimental sites were subjected to a weekly dosing of 1000 μgL-1 Sodium Phosphate, while three control sites remained un-enriched.  Mat development under enriched and control conditions was assessed using artificial substrates, which were placed at each site and monitored on a weekly basis. Preliminary results show (i) periphyton mat total phosphorus and nitrogen were higher in enriched treatments, (ii) nitrogen:phosphorus ratios, chlorophyll a levels and ash free dry weight (AFDW) were higher in control treatments, but not significantly so, (iii) total phosphorus and nitrogen levels and nitrogen:phosphorus ratios showed no distinct pattern of change over time and (iv) chlorophyll a levels and AFDW increased over time in control treatments but not in enriched treatments.  Furthermore, enriched benthic periphyton mats did not disintegrate as seen in enriched floating mats and diatom community composition did not differ significantly between treatments.  These results along with their implications are discussed.