Periphyton nitrogenase activity as an indicator of wetland eutrophication: Spatial patterns and response to phosphorus dosing in a northern Everglades ecosystem

P. W. Inglett, E. M. D'Angelo, K. R. Reddy, P. V. McCormick, S. E. Hagerthey

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


The use of periphyton nitrogenase activity (biological N2 fixation) as an indicator of wetland P impact was assessed using patterns of nutrient content (C, N, P, Ca, Mg, K, Fe, and Mn) and acetylene reduction (AR) in floating cyanobacterial periphyton mat (metaphyton) communities of a P-enriched portion of the Florida Everglades, USA (Water Conservation Area-2A, WCA-2A). Spatial patterns of nutrients indicate the enrichment of floating mat periphyton N, P, Fe, and K, and the reduction of Mn and TN:TP in enriched marsh areas. In highly enriched areas, floating mat periphyton AR was approximately threefold greater than that in less enriched, interior marsh zones. Multiple regression models indicated AR dependence on P in eutrophic WCA-2A areas while the AR of more interior marsh periphyton mats was more closely related to tissue levels of Ca and Fe. Nitrogenase activity of floating mat periphyton from P-loaded mesocosms revealed a significant enhancement of N2 fixation in samples receiving approximately 2-3 mg P m-2 of cumulative P dosing or with biomass TP content of 100-300 mg kg-1. At P contents above the optimum, mat periphyton AR was suppressed possibly as a result of changes in species composition or increased levels of NH 4 +. After 3 years of dosing, consistently high AR occurred only at low rates of P enrichment (0.4-0.8 g P m-2 yr-1), and the patterns appeared to be seasonal. These findings agree with the hypothesis that P availability is a key determinant of nitrogenase activity in aquatic systems, and thus, may support the use of periphyton nitrogenase to indicate P impacts in P-limited systems. These results also demonstrate the potential existence of a P threshhold for biogeochemical alteration of periphyton mat function in the Everglades, and that cumulative loading of limiting nutrients (i.e., P), rather than instantaneous concentrations, should be considered when evaluating nutrient criteria.

Original languageEnglish
Pages (from-to)131-144
Number of pages14
JournalWetlands Ecology and Management
Issue number2
StatePublished - Apr 2009

Bibliographical note

Funding Information:
Acknowledgements This research was funded in part by the South Florida Water Management District (SFWMD). The authors thank the following for their cooperation in this work: Q. Clark (University of Florida, UF), M. O’Dell, and C. Kennedy (SFWMD) for field assistance, and Y. Wang (UF) for laboratory analyses.


  • Acetylene reduction
  • Cyanobacterial mat
  • Metaphyton
  • Nitrogen fixation
  • Phosphorus

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science
  • Management, Monitoring, Policy and Law


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