Effects of urea fertilization rate (mg N L^-1 week^-1) on mean planktonic parameters.

<p>Results averaged for days 7–21. Response variables include (a) phytoplankton biomass (as Chl <i>a</i>), (b) bacterial density, (c) gross primary production (GPP), (d) bacterial C consumption (BCC; productivity + respiration), (e) the approximate metabolic balance of plankton communities, measured as GPP: BCC, and (f) dissolved oxygen concentration (DO). Data in each panel includes July (black circles and thick black lines), August (grey triangles and grey lines), and September (white squares and thin black lines) experiments. Solid lines indicate best-fit regression models detailed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188652#pone.0188652.t001" target="_blank">Table 1</a>, dashed lines indicate direction of change for trial in which statistically-significant regression models could not be fit. Error bars = ± 1 S.E, and <i>n</i> = 9.</p

Seasonal limnological trends in Wascana Lake, Saskatchewan May–August 2009.

<p>(a) total dissolved (TDP) and soluble reactive phosphorus (SRP) concentrations, (b) total dissolved nitrogen (TDN) concentration and phytoplankton biomass (as Chl <i>a</i>), and (c) final concentrations of Chl <i>a</i> (fertilized treatment minus control) after 72-h bottle bioassay incubations of Wascana Lake water receiving growth-saturating concentrations of NH₄ (N), PO₄^3- (P), or both N and P (N+P). Analysis of variance with Tukey’s post hoc tests identified statistically significant (asterisk) phytoplankton biomass response (<i>p</i> < 0.05) relative to control bottles. Vertical dashed grey lines show the start dates of the monthly mesocosm experiments.</p

Model fits describing N effect on mesocosm plankton dynamics.

<p>Least squares regression analysis (<i>n</i> = 15) of phytoplankton and bacterial abundance and production (y) as functions of urea load (x). Models were selected using Akaike information criterion corrected for small sample sizes (AIC_c), and ranked based on AIC_c score, with best-fitting models in bold. Models with no explanatory power (i.e. r² = 0) are omitted. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188652#pone.0188652.g002" target="_blank">Fig 2</a> for graphical representation of best-fit models.</p