Comparative effects of urea, ammonium, and nitrate on phytoplankton abundance, community composition, and toxicity in hypereutrophic freshwaters

• Published in: Limnology and oceanography Vol. 56; no. 6; pp. 2161 - 2175
• Main Authors: Donald, Derek B., Bogard, Matthew J., Finlay, Kerri, Leavitt, Peter R.
• Format: Journal Article
• Language: English
• Published: Waco, TX John Wiley and Sons, Inc 01.11.2011; American Society of Limnology and Oceanography
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Ecotoxicology, biological effects of pollution; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; Marine; Microcystis; Planktothrix agardhii; Synecology; Canada, Saskatchewan; Freshwater environment; Community structure; Urea; Composition; Plant community; Toxicity; Fresh water; Ammonium nitrate; Abundance; Phytoplankton; Ureas; Community
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2011.56.6.2161

Dissolved nitrogen (N) as urea ([NH₂]₂CO), nitrate (NO⁻₃), and ammonium (NH⁺₄) was added to naturally phosphorus (P)-rich lake water (up to 175 μg P L−1) to test the hypotheses that pollution of hypereutrophic lakes with N increases total algal abundance, alters community composition, and favors toxic cyanobacteria that do not fix atmospheric N₂. Monthly experiments were conducted in triplicate in polymictic Wascana Lake, Saskatchewan, Canada, during July, August, and September 2008 using large (> 3140 liters) enclosures. Addition of all forms of N added at 6 mg N L−1 increased total algal abundance (as chlorophyll a) by up to 350% relative to controls during August and September, when soluble reactive P (SRP) was > 50 μg P L−1 and dissolved N: P was < 20 : 1 by mass. In particular, NH⁺₄ and urea favored non-heterocystous cyanobacteria and chlorophytes and NO⁻₃, urea promoted chlorophytes, some cyanobacteria, and transient blooms of siliceous algae, whereas N₂-fixing cyanobacteria and dinoflagellates exhibited little response to added N. Added N also increased microcystin production by up to 13-fold in August and September, although the magnitude of response varied with N species and predominant algal taxon (Planktothrix agardhii, Microcystis spp.). These findings demonstrate that pollution with N intensifies eutrophication and algal toxicity in lakes with elevated concentrations of SRP and low N: P, and that the magnitude of these effects depends on the chemical form, and hence source, of N.