Aplicação de técnicas químicas para mitigação da eutrofização e seus efeitos nos organismos planctônicos

Abstract

Geoengineering comprises chemical techniques to mitigate eutrophication, which aim to manipulate the biogeochemical cycle of phosphorus. The Floc & Sink and Floc & Lock techniques form geoengineering and have been extensively studied regarding their effects on water quality, however, there are few studies on the effects of these techniques on planktonic organisms (phytoplankton and zooplankton). Therefore, the general objective of this thesis was to analyze the responses of the planktonic community to chemical techniques for mitigating eutrophication, evaluating their efficiency in spring waters in the tropical semi-arid region. The first chapter aimed to carry out a scientometric analysis of the literature to observe the effect of chemical and physical techniques for controlling eutrophication on planktonic organisms in eutrophic environments, evaluating bibliometric production and determining existing knowledge gaps. The results showed that these techniques have been extensively studied and there has been more interest in them over the years. Despite this, few studies focus on the effects of the techniques on plankton. The effects of the technique on other phytoplankton groups, in addition to cyanobacteria and zooplankton, are poorly addressed and it is still unclear how these techniques act on these organisms, which is one of the gaps found in the first chapter. Furthermore, studies that observe the effects over time, showing the succession of the planktonic community and in mesocosms are a minority and, also need to be analyzed. Overall, all chemical techniques removed the biomass or biovolume of cyanobacteria. Unlike physical techniques that had conflicting results, with inconclusive results. The few studies following the application of the technique show positive effects on phytoplankton diversity after Floc & Sink and an increase in richness after Floc & Lock and aeration. All techniques negatively affected zooplankton, decreasing the biomass, survival or abundance of these organisms. Given this, some of these gaps sought to be answered in the following chapters, focused on the chemical technique of geoengineering, which has been gaining prominence in scientific publications over the last decade. The technique aims to manipulate the biogeochemical cycle of phosphorus (P), removing particulate P (algal biomass) by sedimentation, and dissolved P from water by adsorption and sediment capping. The technique uses a combination of coagulant and materials (natural or modified) for sedimentation. Chapter two sought to analyze the effects on biomass and phytoplankton composition, when applying the Floc & Sink (F&S) mitigation technique, in eutrophicated waters from reservoirs in the tropical semi-arid region. For this objective, a functional approach was used that addresses the morphological characteristics of phytoplankton (Morpholgy-Based Functional Groups –MBFG). The technique was able to remove algal biomass with the addition of coagulant (PolyAluminum Chloride – PAC) plus ballast (PAC+Planosso; PAC+Beige Limestone and PAC+White Limestone), and we observed its effects on the functional groups. The groups with a sedimentation resistance mechanism (MBFG VIII) were unable to sediment with the isolated use of the coagulant, especially due to the presence of aerotopes. The MBFG VII group, due to the presence of the mucilage sheath, did not sediment, unlike the MBFG IV group, which, as it did not have specialized characteristics, sedimented with just the use of the coagulant. The MBFG V group in contact only with the PAC increased and the MBFG VI group, despite its silica wall, did not show statistical differences in the removal of the group. Chlorophytes and cryptophytes (MBFG groups IV and V) are considered high quality foods, therefore, it is important to observe the palatability and nutritional value of phytoplankton species, after the Floc & Sink test, as it directly influences the flow of energy to the other trophic levels. Therefore, natural ballasts are capable of ssinking algal biomass combined with coagulants and can be used as an alternative to high-value commercial products. The third chapter aimed to test the efficiency of the Floc & Lock technique in controlling the eutrophication of reservoir water in the semi-arid region, by reducing the release of phosphorus and removing algal biomass through the combination of PAC, Lanthanum Modified Bentonite (LMB) and a material rich in calcium. Our study demonstrated that eutrophication control techniques can affect plankton in different ways, depending on the technique, its principle and the product. In the case of phytoplankton, organisms with mechanisms of resistance to sedimentation can impair the effectiveness of Floc & Sink. Furthermore, we recommend the use of natural ballasts using the Floc & Sink technique and the combination of beige limestone with BML and PAC. Therefore, natural materials can be an alternative to commercial products with the same efficiency and more economically viable