# _Vallisneria spiralis_ Promotes P and Fe Retention via Radial Oxygen Loss in Contaminated Sediments
## 3 Results and Discussion
### Net \(O_{2}\) and DIP Fluxes Measured in the Light and the Dark
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameter** & **Source of Variation** & **DF** & **SS** & **MS** & **F** & \(p\) \\ \hline \multirow{8}{*}{O\({}_{2}\) fluxes} & Treatment & \multirow{2}{*}{1} & \multirow{2}{*}{8,625,871.36} & \multirow{2}{*}{8,625,871.36} & \multirow{2}{*}{72.83} & \multirow{2}{*}{**<0.001**} \\  & (S vs. S + V) & & & & & \\ \cline{2-6}  & Condition & \multirow{2}{*}{1} & \multirow{2}{*}{40,040,426.36} & \multirow{2}{*}{40,040,426.36} & \multirow{2}{*}{338.06} & \multirow{2}{*}{**<0.001**} \\  & (D vs. L) & & & & \\ \cline{2-6}  & Time & \multirow{2}{*}{2} & \multirow{2}{*}{144,181.34} & \multirow{2}{*}{72,090.67} & \multirow{2}{*}{0.61} & \multirow{2}{*}{0.547} \\  & (D1 vs. D2 vs. D3) & & & & \\ \cline{2-6}  & Treat. \(\times\) Condit. & 1 & 36,375,693.71 & 36,375,693.71 & 307.12 & **<0.001** \\ \cline{2-6}  & Treat. \(\times\) Time & 2 & 54,762.21 & 27,381.10 & 0.23 & 0.794 \\ \cline{2-6}  & Condit. \(\times\) Time & 2 & 63,928.11 & 31,964.05 & 0.27 & 0.764 \\ \cline{2-6}  & Treat. \(\times\) Condit. \(\times\) Time & 2 & 1722.28 & 861.14 & 0.007 & 0.993 \\ \cline{2-6}  & Residual & 60 & 7,106,348.76 & 118,439.14 & & \\ \cline{2-6}  & Total & 71 & 92,412,934.15 & 1,301,590.62 & & \\ \hline \multirow{8}{*}{DIP fluxes} & Treatment & \multirow{2}{*}{1} & \multirow{2}{*}{1633.11} & \multirow{2}{*}{1633.11} & \multirow{2}{*}{182.96} & \multirow{2}{*}{**<0.001**} \\  & (S vs. S + V) & & & & & \\ \cline{2-6}  & Condition & \multirow{2}{*}{1} & \multirow{2}{*}{509.97} & \multirow{2}{*}{509.97} & \multirow{2}{*}{57.13} & \multirow{2}{*}{**<0.001**} \\  & (D vs. L) & & & & & \\ \cline{2-6}  & Time & \multirow{2}{*}{2} & \multirow{2}{*}{3.19} & \multirow{2}{*}{1.59} & \multirow{2}{*}{0.18} & \multirow{2}{*}{0.837} \\  & (D1 vs. D2 vs. D3) & & & & & \\ \cline{2-6}  & Treat. \(\times\) Condit. & 1 & 342.94 & 342.94 & 38.42 & **<0.001** \\ \cline{2-6}  & Treat. \(\times\) Time & 2 & 8.12 & 4.06 & 0.45 & 0.637 \\ \cline{2-6}  & Condit. \(\times\) Time & 2 & 16.70 & 8.35 & 0.93 & 0.398 \\ \cline{2-6}  & Treat. \(\times\) Condit. \(\times\) Time & 2 & 7.21 & 3.60 & 0.40 & 0.669 \\ \cline{2-6}  & Residual & 60 & 535.54 & 8.92 & & \\ \hline Total & 71 & 3056.81 & 43.05 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Three-way analysis of variance of dissolved O\({}_{2}\) and inorganic phosphorus fluxes measured on 3 different days in the light and in the dark in microcosms with bare sediment (S) and with sediment and _V. spiralis_ (S + V). Significant values are printed in bold. Figure 3: Rates of measured dark respiration (R) and net ecosystem metabolism (NEM) and of calculated gross primary production (GPP=NEM-R) in reconstructed microcosms containing bare sediment (S) (**a**) and bare sediment with transplanted individuals of _V. spiralis_ (S + V) (**b**). Light and dark incubations were carried out over 3 different days after a 3-week conditioning period. Averages \(\pm\) standard errors (n = 6) are reported. The three-way analysis of variance on DIP fluxes suggests that also, for this solute, the factor time was not significant (Table 1). In treatment S, DIP fluxes were always positive (from the sediment to the water column) and not statistically different in the light and dark incubations (Table 1 and Figure 5). They averaged \(7.5\pm 1.0\) umol m\({}^{-2}\) h\({}^{-1}\) (pooled data for the 3 incubation days and the two incubation conditions, n = 36). Sediments with _V. spiralis_ regenerated in the dark significantly lower amounts of DIP to the water column as compared to treatment S (2.3 \(\pm\) 1.2 umol m\({}^{-2}\) h\({}^{-1}\), Figure 5) whereas in the light they were net DIP sinks with an uptake averaging \(7.3\pm 1.7\) umol m\({}^{-2}\) h\({}^{-1}\) (pooled data for the 3 light incubations, n = 18).