Uptake rates of ammonium and nitrate by phytoplankton communities in two eutrophic tropical reservoirs

Author(s)

Fernandes Cunha, Davi Gasparini ^[1] ; de Melo Lima, Vitoria Fernandes ^[1] ; Neri, Amanda Menegante ^[1] ; Marafao, Gabriela Albino ^[1] ; Poli Miwa, Adriana Cristina ^[1] ; Calijuri, Maria do Carmo ^[1] ; Bendassoli, Jose Albertino ^[2] ; Tromboni, Flavia ^[3] ; Maranger, Roxane ^[4]

Affiliation

^[1] Univ Sao Paulo, Escola Engn Sao Carlos, Dept Hidraul & Saneamento, Ave Trabalhador Sao Carlense 400, BR-13566590 Sao Carlos, SP - Brazil

^[2] Univ Sao Paulo, Ctr Energia Nucl Agr, Ave Centenario 303, BR-13400970 Piracicaba, SP - Brazil

^[3] Univ Estado Rio de Janeiro, Dept Ecol, Rua Sao Francisco Xavier 524, BR-20550900 Rio De Janeiro, RJ - Brazil

^[4] Univ Montreal, Grp Interuniv Limnol & Environm Aquat GRIL, Dept Sci Biol, Stn Ctr Ville, POB 6128, Montreal, PQ H3C 3J7 - Canada

• Document type: Journal article
• Source: INTERNATIONAL REVIEW OF HYDROBIOLOGY; v. 102, n. 5-6, p. 125-134, DEC 2017.
• Web of Science Citations: 4

Abstract

While excess phosphorus typically results in the eutrophication of inland waters, there is growing evidence that excess nitrogen (N) and the availability of different N forms influence phytoplankton community composition, often favoring potentially toxic genera. In this study, the environmental dynamics, phytoplankton community structure, and N uptake rates were investigated in two tropical reservoirs. Phytoplankton ammonium (NH4+) and nitrate (NO3-) acquisition was assessed through N-15 addition experiments over 2 years. We found that changes in ambient nutrient concentrations and temperature influenced different phytoplankton groups, which tended to have different N uptake strategies. The preferred N-source by Cyanobacteria was NH4+ while Dinophyceae and other groups seemed adapted to also take up NO3-, possibly due to competition. Potential uptake rates (maximum of 8.5 mu M-N hr(-1) for NH4+ and 1.3 mu M-N hr(-1) for NO3-) were high in comparison to previous reports from temperate freshwater or marine systems, likely due to elevated algal biomass and temperature. When normalized to biomass as chlorophyll-a (Chl-a), specific uptake rates varied between 0.01-3.4 mu mol-N mu gChl-a(-1) day(-1) for NH4+ and <0.01-0.8 mu mol-N mu gChl-a(-1) day(-1) for NO3- and were comparable to those reported for other eutrophic and hypereutrophic aquatic systems. In addition, higher temperatures favored Cyanobacteria (e.g., Cylindrospermopsis raciborskii and Microcystis aeruginosa), while a more diverse community was found during colder months. Results highlight how high loading of reduced forms of nitrogen and high temperatures can exacerbate harmful Cyanobacteria blooms in tropical reservoirs and be a concern for drinking water quality. (AU)

• FAPESP's process: 14/02088-5 - Nitrogen biological fixation and uptake by phytoplankton in subtropical reservoirs with different trophic status
• Grantee: Davi Gasparini Fernandes Cunha
• Support type: Regular Research Grants