Periphyton chemistry and nitrogenase activity in a northern Everglades ecosystem |
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Authors: | PW Inglett KR Reddy PV Mccormick |
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Institution: | (1) US Geological Survey, 430 National Center, Reston, VA 20192, USA;(2) Department of Biology and Southeast Environmental Research Center, Florida International University, Miami, FL 33199, USA |
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Abstract: | Cyanobacterial periphyton communities are a dominant feature of oligotrophic Everglades marshes, however, little is known regarding the biogeochemical aspects of this ecosystem component. This study was undertaken to investigate the potential for N2 fixation in the periphyton communities of a hydrologically-controlled portion of the northern Everglades marsh (Water Conservation Area 2A, WCA-2A). The objectives of this research were to characterize the temporal patterns of nutrient composition and N2 fixation of the natural WCA-2A periphyton communities and to compare fixation rates of periphyton with those of other ecosystem components in both natural and nutrient-impacted WCA-2A areas. In general, N2 fixation (measured by the acetylene reduction (AR) method) of natural WCA-2A periphyton was enhanced under light conditions showing a nitrogenase pattern characteristic of autotrophic cyanobacteria. Winter (November–March) rates of AR expressed per gram organic carbon (gOC) ranged from 147–240 nmol C2H2 g OC–1 h–1, while summer rates were elevated with an observed peak of 1148 nmol C2H2 g OC–1 h–1 in July 1998. This translates into an estimated yearly contribution of approximately 10 g N m–2 to an unimpacted WCA-2A slough ecosystem. Nitrogenase activity did not correlate seasonally with nutrients (Ca, Mg, Fe, N, P, Mn), but closely followed measured N stable isotopic ratios ( 15N) in floating periphyton. In oligotrophic marsh areas, AR (on a weight basis) decreased in the order floating periphyton > benthic periphyton floc > soil > water > detrital plant biomass, while highest AR rates were observed for detrital biomass in areas impacted by agricultural discharges. |
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