Bioturbação por macroinvertebrados bentônicos sobre a eficiência de imobilização de fósforo pela técnica “Floc & Lock” em águas eutrofizadas

Abstract

Artificial eutrophication is a phenomenon that has been decreasing water quality due to the rapid entry of nutrients, such as phosphorus (P) and nitrogen (N), into aquatic bodies and, in order to mitigate it, it is necessary to stop their contribution from both from external, point and diffuse sources, such as internal sources, which occurs due to the recirculation of P from the sediment. For the control of internal sources of P, there is a technique called Floc & Lock, which uses coagulants (Floc) and clays (Lock), to precipitate this nutrient, inactivating it in the sedimentary layer and preventing it from returning to the water column. However, after the application of these products, greater attention is needed on benthic macroinvertebrates, which can disturb the sediment due to bioturbation, which can modify the efficiency of the technique. In this study, we carried out an experimental test in microcosm using polyaluminium chloride (PAC) as coagulant and lanthanum-modified bentonite (LMB) as clay in the Floc & Lock technique, which were added singly and combined, in triplicate, to evaluate the efficiency. removal of total phosphorus (TP), soluble reactive phosphorus (SRP) and chlorophyll-a (Chlor-a) from eutrophic water. In addition, the effect of bioturbation caused by two species of benthic macroinvertebrates (Melanoides tuberculata and Chironomus sancticaroli) on TP, SRP and Chlor-a concentrations in surface water and bottom water was observed, verifying if there was any interference in the application of the technique and whether different species, with different types of bioturbation, had significant effects on it. It was observed that the addition of PAC and its combination with LMB reduced the concentrations of P and Chlor-a in the water, whereas LMB alone had no significant effect on the reduction of the nutrient. C. sancticaroli larvae helped in the removal of TP, SRP and algal biomass from the water column and its deposit in the sediment, while the presence of M. tuberculata increased the amounts of TP and Chlor-a in surface water and decreased in the bottom water in the PAC and PAC treatments combined with LMB. Some species of benthic macroinvertebrates are dominant in eutrophic environments because they are resistant to pollution and it is important to understand the changes they can cause in the Floc & Lock technique due to application costs and also to verify the possible impacts that their use can cause.