Interacting effects of <i>Azolla</i>, rain and wind on salinity stratification. A

<p>) Salinity (mg L⁻¹ ± standard error) in the top water layers (solid lines) and in the bottom water layers (dotted lines) of the beakers in the absence of <i>Azolla</i> (rounds), in the presence of <i>Azolla</i> (squares), with no influence of wind (closed figures) or with influence of wind (open figures) hours after the rain event. <b>B</b>) Salinity (mg L⁻¹) profiles in the beakers 20 hours after the rain event.</p

Calibration and validation statistics of partial least-squares regression models.

<p>Calibrations were evaluated as follows (Saeys et al (2005): excellent (R²/r² ≥ 0.9, RPD ≥ 3.0), reliable quantitative predictions (R²/r² ≥ 0.75 and <0.9, RPD ≥ 2.0 and <3.0), differentiation between high and low values (R²/r² ≥ 0.65 and <0.75, RPD ≥ 1.5 and <2.0, unsuccessful (R²/r² <0.65, RPD <1.5).</p><p>Transf: transformations for regression analyses.</p><p>Abs: Log1/R (R = reflectance).</p><p>1D: first derivative.</p><p>R²: coefficient of multiple determination (calibration).</p><p>SEC: standard error of calibration.</p><p>SECV: standard error of cross validation.</p><p>r²: regression coefficient NIRS predicted vs. observed values.</p><p>SEP: standard error of prediction (validation).</p><p>RPD: ratio of SD of reference values (validation) to SEP.</p><p>RPIQ: ratio of the interquartile distance IQ ( = Q3–Q1) of reference values (validation) to SEP.</p><p>Corr. OM: Pearson correlation with organic matter content.</p

Mesocosm experiment.

<p><b>A</b>) Development of the biomass density of <i>Azolla filiculoides</i> (g dry weight m⁻² ± standard error) grown in freshwater or brackish water basins. <b>2B</b>) Chloride concentrations and <b>2C</b>) phosphate concentrations (µM ± standard error) in the top, middle and bottom water layers of the freshwater and brackish water basins during the mesocosm experiment. Significant differences between water layers are indicated by different letters. The cumulative amount of rainfall during the experiment (mm) is shown on the right axis in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050159#pone-0050159-g002" target="_blank">figure <b>2B</b></a>.</p

Exemplary observed vs. NIR predicted values for NaCl-extractable Ca and N-NH₄ and oxalate-extractable Fe and P.

<p><i>Open circles</i> calibration data set, <i>filled circles</i> external validation.</p

Nitrate mobilization.

<p>Mobilization of nitrate (NO₃^-) over time (t = 0, 30 and 127 days) in the pore water of 40 soil cores that differ in experimental water level treatment (rewetted or drained) and initial soil iron content (high or low). Soil cores were classified into 4 groups: rewetted iron-poor fens (n = 10 cores from 2 sites), drained iron-poor fens (n = 10 cores from 2 sites), rewetted iron-rich fens (n = 10 cores from 2 sites), and drained iron-rich fens (n = 10 cores from 2 sites). Dots represent group means ± SE.</p

Increase in cover of the water layer by <i>Stratiotes aloides</i> (mean + SEM) subjected to different PAR levels and CO₂ availability.

<p>Low PAR significantly reduced final cover (<i>P</i><0.001), whereas CO₂ limitation resulted in slower colonisation rates (<i>P</i> = 0.001). Results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Experimental set-up.

<p>40 intact vertical soil cores were collected in 4 drained fens using sharpened PVC tubes (45 x 12.5 cm), and were then placed in individual containers filled with stagnant de-oxygenized artificial groundwater. Tubes were perforated at the bottom to allow water inflow. Rhizons were placed at 5, 15 and 25 cm below the soil surface, and connected to vacuum-syringes. Half of the cores were rewetted to peat surface level, while the other half was kept moderately drained (water level 27 cm below peat surface level).</p

Depths of the rosettes (mean and SEM) of <i>Stratiotes aloides</i>, grown at different CO₂ availabilities and 100% PAR.

<p>Plants from 90 μmol L^-1 CO₂ treatments sank within two weeks, after which plants remained significantly lower in the water layer than those grown at limited 230 and 930 μmol L^-1 (<i>P</i><0.001), as indicated by different letters. Additional results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Output of the linear mixed-effect models.

<p>The models included two fixed factors “Water level (rewetted or drained)” and “Iron content (low or high)” and were corrected for the random factor “Site ID” (ZB, ES, BM or LH), with tests for interactions between soil iron content and water level. Dependent variables are mean pore water pH, EC, and concentrations of total dissolved iron (Fe), total inorganic carbon (TIC), dissolved organic carbon (DOC), methane gas (CH₄), ammonium (NH₄⁺), nitrate (NO₃^-) and total dissolved phosphorus (P) measured at the start (t = 0 days) and at the end of the experiment (t = 127 days).</p

Relationship between iron, TIC, DOC and NH4+.

<p>Correlations between the change in pore water Fe concentrations (ΔFe) and the change in concentrations of (a) total inorganic carbon (ΔTIC), (b) dissolved organic carbon (ΔDOC) and (c) ammonium (ΔNH₄⁺) (in <b>μ</b>mol L^-1) in 20 rewetted and 20 drained soil cores over 127 days (n = 4 sites).</p