## 4 Discussion  
In the past decades, previous to the construction of wastewater treatments plants, the River Magro suffered regular sewage inputs, either domestic or industrial, that resulted in a great disturbance of its natural ecological functioning [4; 5; 6; 36]. In most of its upper-middle course, the high oxygen demand of the streambed makes the site an ideal candidate for the use of bioremediation techniques that stimulate the anaerobic degradative metabolisms of organic matter. The NG-TAS analysis demonstrated the natural occurrence of a relatively diverse prokaryotic assemblage where different microbial guilds involved in the anaerobic degradation of organic matter dominated the native prokaryotic community of the River Magro sediments. However, these native microbial communities are not totally able to handle this excess of organic pollution following its accumulation rhythm and, consequently, OM accumulates in the sediments of dammed river stretches [5]. Nowadays, the implementation of wastewater treatment plants (WWTP) has improved the quality of water poured into the river, and few  
Figure 5: Principal coordinate ordination (PCO) based on the Euclidean distances for the response to the studied variables in the different experiments. The color lines numbered from 1 to 3 represent the hierarchical structure (i.e., subdivision points in the tree) for the Euclidean distances among cases. Abbreviations of treatments (in blue bold) are as follow: Control (non-amended control), BAP-50 (one dosage of 50 g/m\({}^{3}\) of BAP), BAP-25 (one dosage of 25 g/m\({}^{3}\) of BAP), BAP-75 (one dosage of 75 g/m\({}^{3}\) of BAP), BAP-SP (one dosage of 50 g/m\({}^{3}\) of BAP, more spatially distributed), BAP-2 inj (two dosages of 25 g/m\({}^{3}\) of BAP), BAP-3 inj (three dosages of 20, 15, and 15 g/m\({}^{3}\) of BAP), NO\({}_{3}\) (50 g/m\({}^{3}\) KNO\({}_{3}\)), BAP-NO\({}_{3}\) (BAP-50 + 50 g/m\({}^{3}\) KNO\({}_{3}\)), Fe (10 g/m\({}^{3}\) FeCl\({}_{3}\)), BAP-Fe (BAP-50 + 10 g/m\({}^{3}\) FeCl\({}_{3}\)), BAP-Mo (BAP-50 + Na\({}_{2}\)MoO\({}_{4}\) 5 mM), BAP-BES (BAP-50 + BES 3.5 mM), BAP-Ace (BAP-50 + CH\({}_{3}\)COONa 5 g/m\({}^{3}\)), BAP-NH\({}_{4}\) (BAP-50 + NH\({}_{4}\)+), BAP-P (BAP-50 + PO\({}_{4}\)\({}^{3-}\)), BAP-Olig (BAP-50 + Trace elements), AllNut (NH\({}_{4}\)+ PO\({}_{4}\)\({}^{3-}\) + Trace elements), BAP-AllNut (BAP-50 + AllNut). Abbreviations of variables (in black bold) are as follow: %OM (percentage of organic matter content), COD (chemical oxygen demand), BOD\({}_{5}\) (biological oxygen demand), TN (total nitrogen), TP (total phosphorus), Loosely-P (loosely-binding P). inputs of organic matter occur. Accordingly, the analysis of the overlying water during the experiment indicates a relatively low concentration of particles experiencing a rapid settling. Still, some minimal deposition of OM might occur inside mesocosms during incubations, which otherwise did not affect the results of the experiment. The improvement of the quality of waters poured into the river now puts the focus on the main pollution problems in the river sediments, which keep a high organic and nutrient load, thus challenging the recovery of the river ecological quality. The BAP selected for our experiments (Acti-zymeTM) has been used to treat wastewater under both aerobic and anaerobic conditions [5; 9; 10; 11]. Biochemical tests conducted with this product show the occurrence of a general hydrolytic activity of catalases, amylases, and proteases. However, other enzymatic activities related to the nitrogen cycle (i.e., tryptophanase, urease) are apparently lacking [11]. Attending to that composition, this BAP is expected to accelerate the initial hydrolytic phases of OM degradation, which are followed by a sequential process of acidogenesis, acetogenesis, and finally, methanogenesis [37]. The treatment operating optimally in our study consisted in the addition of BAP supplemented with sodium acetate.