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“WATER COLUMN AMMONIUM DYNAMICS IN TWO LARGE, EUTROPHIC, FRESHWATER LAKES: LAKE TAIHU (CHINA) AND LAKE OKEECHOBEE (FLORIDA).” (E)

Lakes Taihu (China) and Okeechobee (Florida) are large, shallow, eutrophic lakes that experience seasonal harmful algal blooms. These Microcystis spp. blooms proliferate in aquatic ecosystems due to eutrophication, triggered by high external inputs of nitrogen and phosphorus. As non-N2-fixers, Microcystis spp. must compete with other primary producers, such as ammonia-oxidizing organisms, for combined nitrogen (e.g., ammonium). This competition may alter nitrification (ammonia and nitrite oxidation) and, subsequently, denitrification rates in lakes. To investigate the competition for ammonium, we used 15N stable isotope additions to quantify water column rates of ammonium regeneration and potential uptake and compared them to ammonia and nitrite oxidation rates. Our data show that, outside of the bloom, ammonia oxidation dominated total ammonium uptake and could be sustained by regeneration. However, during the high bloom season, uptake rates exceeded ammonia oxidation rates, suggesting that non-N2-fixing cyanobacteria were outcompeting nitrifiers. Nitrite oxidation rates were higher than ammonia oxidation rates in most of our sampling events, suggesting that nitrate reduction by photoautotrophs and/or particle-associated denitrifiers, and subsequent nitrite oxidation by nitrifiers, might be much more significant than previously thought.

Authors

Hampel, J. J., Wright State University, USA, hampel.4@wright.edu

McCarthy, M. J., Wright State University, USA, mjm.kingston@gmail.com

Gardner, W. S., The University of Texas at Austin Marine Science Institute, USA, wayne.gardner@utexas.edu

Lu, Z., Nanjing Institue of Geography and Limnology, China, luzhang@niglas.ac.cn

Zhu, G., Nanjing Institue of Geography and Limnology, China, gwzhu@niglas.ac.cn

Xu, H., Nanjing Institue of Geography and Limnology, China, hxu@niglas.ac.cn

Newell, S. E., Wright State University, USA, silvia.newell@wright.edu

Details

Oral presentation

Session #:021
Date: 03/01/2017
Time: 15:15
Location: 323 B

Presentation is given by student: Yes