Análise sistêmica de ambientes lacustres do semiárido tropical: suporte para projetos de manejo e mitigação da eutrofização

Abstract

Eutrophication is considered one of the main water quality problems in lake ecosystems today, leading to losses of important ecosystem goods and services, as well as consequences of reduction and reduction of biodiversity. Eutrophication is the result of the input of nutrients transported to aquatic ecosystems, which are later deposited in the system. The selection of eutrophication management and mitigation measures requires an adequate systemic (diagnostic) analysis of each lake. In addition, semi-arid aquatic ecosystems are among one of the most independent systems to eutrophication. The general objective of this thesis was to provide information to support projects for the management and mitigation of eutrophic environments in the tropical semi-arid region, through integrated systemic analysis involving water quality, in addition to the analysis of phosphorus sources and fluxes. Chapter 1 addressed the temporal dynamics and a diagnosis of water quality in a semi-arid tropical reservoir used for multiple uses. The results show the process of degradation of the reservoir's environmental health over prolonged periods, being intensified by a period of prolonged drought, causing a reduction in the stored water volume, also favoring characteristics of a shallow and mixed environment with dominance of cyanobacteria. Characteristics such as the absence of background anoxia events, high concentrations of humic substances and high pH can make certain mitigation measures and strategies unfeasible. Chapter 2 analyzed land use and occupation and its influence on the spatial distribution of mobile forms of phosphorus in the sediment. The focus of this chapter was to quantify the potential sources of eutrophication, external and internal. Thus, the results of the chapter showed the anthropic activities along the drainage basin and area of influence, and its potential contribution of mobile phosphorus present in the sediment, which is spatially distributed in a heterogeneous way along the reservoir. These results point to agriculture, livestock and floodplain vegetation as priority activities and coverage for proper management, in addition to the preservation of the riparian zone. Chapter 3 showed a temporal analysis of the mass balance, using a P load estimation model, as well as evaluating the effects of this load on water quality. The results of the chapter showed a high and constant internal phosphorus load due to a reduction in the volume of stored water and susceptibility to the action of winds for resuspension of nutrients. In addition, there is evidence of a delay in the reduction of internal loads, which may continue to intensify the eutrophication phenomenon even with the reduction of external loads. The results of this thesis emphasize that the management and mitigation of eutrophic environments in this region is still deficient, as evidenced throughout this thesis cause the intensification of the effects of eutrophication on the water quality of the reservoirs. Finally, this thesis represents an important systemic analysis, and this methodology can serve as a reflection for reserves in the world and support the choice of strategic management measures for the recovery of eutrophic environments in the semi-arid region.