5th UF Water Institute Symposium Abstract

Submitter's Name Joshua Papacek
Session Name Poster Session - Coastal Waters
Poster Number 14
Author(s) Joshua Papacek,  Wetland Biogeochemistry Laboratory (Presenting Author)
  Edward  Phlips,  Fisheries & Aquatic Sciences
  Patrick  Inglett, Wetland Biogeochemistry Laboratory
  An investigation of nitrogen fixation in the northern Indian River Lagoon, Florida
  Nitrogen fixation, the conversion of atmospheric nitrogen (N2) to a biologically-available form, represents a potential source of new nitrogen (N) to aquatic systems. Although N2 fixation has been largely overlooked in estuaries, increasing eutrophication and occurrence of harmful algae blooms in the northern Indian River Lagoon (IRL) has led to an investigation of potential internal nutrient sources, including N2 fixation by several distinct IRL pools: 1) the water-column 2) benthic vegetation and 3) IRL sediments. This research aims to address the seasonal and spatial importance of each of these pools to supplying N to the IRL. Water column fixation was tested from samples collected at three locations within the major IRL basins, Mosquito Lagoon (ML), Banana River (BR), and the northern Indian River (IR). Collections occurred on a bi-monthly basis between September 2014 and October 2015, and N2 fixation response was measured via the acetylene reduction assay (ARA) technique under light (100-200 µE) and dark conditions. Fall and winter rates remained low (< 0.01 ng N/ml/hr; < 2 ng N/µg chlorophyll/hr) and June 2015 rates were significantly higher for both dark and light treatments on a per volume basis. When normalized for chlorophyll, however, June rates were comparable to dark rates in winter. Two-way ANOVA results confirmed a significant temporal effect as well as a significant interaction between month and treatment (p<0.05). This may suggest higher heterotrophic bacterial contributions over winter months while photosynthetic N2 fixers were most active as temperature increased in the IRL. Preliminary data for ARA of benthic vegetation showed that epiphytic coverage of seagrasses (e.g. Halodule wrightii) and macroalgae act as an additional N source. Overall, results from this research indicate that N2 fixation is a potentially important processes in supplying new N the IRL.