## Materials and Methods
### Experimental Design and Setup
Thus, the intermediate dose of 50 g/m\({}^{3}\) was divided to be added according to two temporal patterns: (**1**) in two injections of 25 g/m\({}^{3}\) each, conducted at the beginning of the experiment and after 15 days; or (**2**) in three injections, one of 20 g/m\({}^{3}\) done at the beginning of experiment, and two of 15 g/m\({}^{3}\) performed after 15 and 30 days, respectively. Experiment 4 (a supplementary addition of electron acceptors for anaerobic respirations): This experimental setting was designed to evaluate the potential of alternative anaerobic metabolisms \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Treatment** & **Code** & \multicolumn{6}{c}{**Experiment**} \\ \cline{3-8}  & **1** & **2** & **3** & **4** & **5** & **6** \\ \hline Non-amended controls (2) & Control & ✓ & ✓ & ✓ & ✓ & ✓ \\ One dosage of 50 g/m\({}^{3}\) of BAP & BAP-50 & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ \\ One dosage of 25 g/m\({}^{3}\) of BAP & BAP-25 & & ✓ & & & & \\ One dosage of 75 g/m\({}^{3}\) of BAP & BAP-75 & & ✓ & & & & \\ One dosage of 50 g/m\({}^{3}\) of BAP, more & & & & & & & \\ spatially distributed & & & & & & & \\ Two dosages of 25 g/m\({}^{3}\) of BAP & BAP-2 inj & & ✓ & & & & \\ Three dosages of 20, 15, and 15 g/m\({}^{3}\) of BAP & BAP-3 inj & & ✓ & & & \\
50 g/m\({}^{3}\) KNO\({}_{3}\) & NO\({}_{3}\) & & & ✓ & & \\ BAP-50 + 50 g/m\({}^{3}\) KNO\({}_{3}\) & BAP-NO\({}_{3}\) & & & ✓ & & \\
10 g/m\({}^{3}\) FC\({}_{13}\) & Fe & & & ✓ & & \\ BAP-50 + 10 g/m\({}^{3}\) FC\({}_{13}\) & BAP-Fe & & & ✓ & & \\ BAP-50 + Na\({}_{3}\)MoO\({}_{4}\) 5 mM & BAP-Mo & & & ✓ & & \\ BAP-50 + BES 3.5 mM & BAP-BES & & & & ✓ & \\ BAP-50 + 5 g/m\({}^{3}\) CH\({}_{3}\)COONa & BAP-Ace & & & ✓ & \\ BAP-50 + NH\({}_{4}\)\({}^{+}\) & BAP-NH\({}_{4}\) & & & & & ✓ \\ BAP-50 + PO\({}_{4}\)\({}^{3-}\) & BAP-P & & & & ✓ \\ BAP-50 + Trace elements & BAP-Olig & & & & ✓ \\ NH\({}_{4}\)\({}^{+}\) + PO\({}_{4}\)\({}^{3-}\) + Trace elements & AllNut & & & ✓ \\ BAP-50 + AllNut & BAP-AllNut & & & ✓ & \\ \hline \hline \end{tabular} H\({}_{0}\) experiment 1: There is no effect of the BAP. H\({}_{0}\) experiment 2: The effect of BAP is not concentration-dependent at the conditions assayed, nor depending on the spatial distribution. H\({}_{0}\) experiment 3: There is not an effect of temporally dosing the BAP. H\({}_{0}\) experiment 4: There is not an effect of adding NO\({}_{3}\)\({}^{-}\) and Fe\({}^{3+}\) as alternative electron acceptors. H\({}_{0}\) experiment 5: The acetoclastic metabolisms are not involved in the process. H\({}_{0}\) experiment 6: Inorganic nutrients are not limiting factors of the process.  
\end{table} 
Table 1: Summary of the different mesocosoms used to conduct the experiments made in the middle course of the River Magro. The table also indicates the treatments tested by ANOVA (post hoc [PERSON]’s pairwise comparisons) in each experiment. The H\({}_{0}\) in the table footnote are the null hypotheses for each experiment. The codes shown here are used as labels for plotting cases in the chart of the principal coordinates analysis (PCO). Two control mesocosms were shared for all experiments. “\(\checkmark\)” was used for indicating if each treatment is part of an experiment. other than methanogenesis and sulfate-reduction to degrade OM, such as the dissimilatory denitrification and the reduction of ferric iron, respectively, which are more thermodynamically favorable than the former. Thus, four different treatments were conducted, whether containing or lacking 50 g/m\({}^{3}\) of BAP, and combined with **(1)** 50 g/m\({}^{3}\) of potassium nitrate (KNO\({}_{3}\)); or **(2)** 1 g/m\({}^{3}\) of ferric chloride (FeCl\({}_{3}\)). Experiment 5 (role of the acetoclastic metabolisms): A set of incubations were carried out to test the relative role and eventual inhibition of the main acetoclastic microorganisms potentially involved in the process.