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| Submitter's Name |
Todd Osborne |
| Session Name |
Springs III - Chemical Processes and Nutrient Fluxes |
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| Author(s) |
Leah Laplaca, Whitney Laboratory for Marine Bioscience |
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Todd Osborne,
Whitney Laboratory for Marine Bioscience (Presenting Author) |
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Michael Coveney, St. Johns River Water Management District |
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Robert Mattson, St. Johns River Water Management District |
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Nitrate Inhibition of Submerged Aquatic Vegetation: Investigation of the Nitrogen Overload Hypothesis |
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Current observations of water quality in groundwater discharge from springs in Florida show anthropogenic enrichment of nitrate plus nitrite (NOx-N) generally attributed to fertilizer application and/or wastewater or manure sources in individual spring sheds. Excessive levels of NOx-N have been implicated in eutrophication of, and observed changes in, submerged aquatic vegetation (SAV) communities in several spring runs. While the indirect effects of nitrogen (N) enrichment on aquatic macrophytes are well-documented (i.e. algal productivity resulting in shading of macrophytes) in aquatic ecosystems globally, there is considerably less information available concerning direct effects of NOx-N such as toxicity or inhibition of macrophyte growth. This research aims to understand the direct effects of elevated nitrate on SAV by using growth indices in roots and shoots, allocation of biomass and changes in plant cellular structure and health associated with elevated NOx-N in several spring ecosystems in Florida. We tested the nitrogen overload hypothesis in mesocosms by growing Sagittaria kurzianna and Vallisneria americana under treatments of 0.1, 0.5, 1.0 and 5.0 mg l-1 NOx-N. Indicators of nitrate inhibition such as unregulated nitrate reductase activity, decreased root to shoot ratios, and decreased cellular starch storage were compared across all treatments. Results of this work are presented in the context of current spring ecosystem restoration efforts. |
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