Modelagem ecohidrológica e caracterização biótica e abiótica da bacia hidrográfica do ribeirão do Espírito Santo

Abstract

Under tre framework of the water scarcity that is imposed as a global threat, it is urgent that we rethink man's relationship with water resources and the reconstruction of approaches management. Given that subsidies for the management of large river basins are based on the dynamics of small basins and their interrelations, this thesis aims to pursue a holistic view for the Espírito Santo Stream Basin (ESSB), located in Juiz de Fora, Minas Gerais, Brazil, identifying their biotic and abiotic characteristics, researching up in more detail the ecological flow. Due to the difficulties of deepening ecohydrological research across ESSB, we determined two river stretches to be studied, one bedside and the other near the mouth. In these two stretches, we sought to know its topobathymetry, sediment, hydrodynamic characteristics, water quality, fish populations and the relationship with the ecological flow. The results indicated that the two stretches studied have biotic and abiotic characteristics of moderately polluted environments. However, the particularities of the marginal areas of the two stretches imply very different flood characteristics. The first stretch has some marginal depressions, forming small ponds, with such an environment widely recognized for its importance in the maintenance and integrity of aquatic biodiversity. The two sites studied, though situate themselves in very different positions in ESSB, do not differ significantly with respect to the grain size of the sediment, water quality parameters, abundance, richness, diversity and composition of fish populations. These characteristics allowed the construction of univariate habitat suitability curves of fish populations investigated for the river basin as a whole. The habitat methodology associated to a river natural flow recognition tool identified the water surplus in the two stretches studied, signaling greater caution with respect to granting right of water use in bedside stretches since it did not identify up water surplus; in the driest months of the year. In contrast, natural streams already impose stressful condition to the analyzed species. On the other side, the mouth stretch has a water surplus flow superior than Minas Gerais State flow reference for granting in the wettest months and is still able to support it in the driest months. It should be noted, that the remaining minimum flows determined by the Brazilian legislation appears to be incompatible with the needs for ecosystem maintenance.