Gênese e dinâmica de nascentes: contribuições a partir da investigação hidrogeomorfológica em região tropical

Abstract

The springs are environmental systems with recognized singularity and fragility, responsible for the passage of underground water to the surface. Nevertheless, a pronounced blank in this subject is related to the river springs geneses and dynamics: how do springs arise, evolve and behave through time? This question guides the research and points the hypothesis to be investigated. There is a great physiographic heterogeneity of river springs, due to its geomorphological, hydrological and hydrogeological characteristics. So, its believed that the origins and the dynamics of springs are diverse and complex, but can be explained by superficial and underground hydrogeomorphological processes. From this affirmative, two main objectives are pointed: to comprehend the hydrogeomorphological processes that leads to the geneses of springs and to interpret the dynamics of springs due to their seasonal hydrogeomorphological variations. Trying to reach general lines from case studies, 24 river springs in Serra do Cipó (MG) and Lagoa Santa (MG) were monthly monitored for one hydrological year, to keep up with their hydrogeomorphological aspects. Besides, water samples were collected to laboratorial analysis (ICP-OES, Ion Chromatography and Titration), used in hydrochemistry and geomorphological models. Further, it was performed the dating of springs water through the environmental tritium concentration. The results showed the importance of the surface coverage to control the hydrological dynamics of springs, including its perennial/temporary behavior. The geochemistry signature of the springs water identified five main aquifer systems in the studied areas. Furthermore, the TDS and geochemical denudation of the springs were calculated leading to the conclusion that the geomorphological work of river springs can be more important than previous researches have shown. As expected, the age dating pointed to modern waters in the majority of studied springs, but in a few cases pre-modern water was found. All these results led to the spatial conditions of river springs dynamics and geneses, so, it was possible to develop five theoretical models for the origin of springs, based in five main hydrogeomorphological processes in a multiscale perspective: rill erosion; piping/sapping; seepage erosion; karst conduits; cavitation. Besides the importance of hydrogeological and hydrological phenomena, the interpretation of the results reaffirmed that the geomorphological processes control the geneses and the dynamics of the springs. However, it is expected that the reflections of this work can contribute to the expansion of the knowledge of the hydrogeomorphology of springs, as well as for the planning and management of natural resources in Brazil.