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

Abstract

The use of periphyton nitrogenase activity (biological N 2 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 N 2 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.

Nutrient enrichment in tropical wetlands: shifts from autotrophic to heterotrophic nitrogen fixation

“…Two types of organisms are often responsible for N fixation in wetlands: autotrophic cyanobacteria, which occur in benthic, floating, or periphytic cyanobacterial mats (Rejmánková and Komárková 2000;Rejmánková et al 2004;Inglett et al 2004Inglett et al , 2009Scott et al 2005Scott et al , 2007Lee and Joye 2006), and heterotophic N fixers in the rhizosphere or in bulk sediments (Moseman 2007;Č erná et al 2009). Autotrophic N fixation prevails in oligotrophic and mesotrophic wetlands where cyanobacterial mats are often the main primary producers because macrophytes are nutrient limited (Rejmánková and Komár-ková 2000;Scott et al 2007).…”

Biological Nitrogen Fixation in Periphyton of Native and Restored Everglades Marl Prairies

“…In particular, phosphorus (P) levels are a key regulator of a variety of processes in the Everglades periphyton including species composition (McCormick and O'Dell 1996;, production and respiration (Iwaniec et al 2006). Everglades periphyton also show the ability to fix atmospheric N 2 (biological N 2 fixation) (Inglett et al 2004(Inglett et al , 2009). This process was estimated to contribute 10 gN m −2 yr −1 to a northern oligotrophic Everglades system.…”

“…Though studied intensely in other parts of Everglades, no study has been focused on periphyton in this unique restored calcareous ecosystem where this component is a key target and evaluation metric for restoration (Gaiser 2009). Furthermore, few studies have assessed N 2 fixation in P-limited ecosystems (Inglett et al 2004;Rejmánková and Komárková 2000;Rejmánková 2001;Inglett et al 2009), so it is important to understand the role of periphyton in Everglades marl prairies (Davis et al 2005). For these reasons, the following study was conducted to (1) characterize periphyton N 2 fixation between the restored and reference wetlands; (2) relate the N 2 fixation with nutrient limitation (i.e., N and P limitation); and (3) assess the potential of N stable isotopes as an indicator of N 2 fixation and nutrient limitation.…”

The Influence of Phosphorus on Periphyton Mats from the Everglades and Three Tropical Karstic Wetlands

“…La Hée et al, in prep). Because these wetlands are naturally depleted in nutrients, enhanced supplies coming from surface water runoff from agricultural and industrial activities and altered groundwater interactions have long-lasting cascading ecosystem effects (Hagerthey et al, 2009) that begin with the microbial community . Tools providing an early warning of these changes are valuable, as remediation practices can be established prior to a new hysteretic state is reached (Hagerthey et al, 2009).…”

“…Because these wetlands are naturally depleted in nutrients, enhanced supplies coming from surface water runoff from agricultural and industrial activities and altered groundwater interactions have long-lasting cascading ecosystem effects (Hagerthey et al, 2009) that begin with the microbial community . Tools providing an early warning of these changes are valuable, as remediation practices can be established prior to a new hysteretic state is reached (Hagerthey et al, 2009). Water column concentration of dissolved or total nutrients is not a useful metric of enrichment history due to high rates of abiotic adsorption and biotic assimilation, even as communities are irrevocably altered when exposed to even low-level increases in nutrient load .…”