Aplicação da simulação de habitats físicos para avaliar vazões ecológicas em um riacho de Mata Atlântica do Sudeste do Brasil: um estudo piloto

Abstract

Simulation of the physical habitat is a key component of the incremental methodology - Instream Flow Incremental Methodology (IFIM) that uses hydraulic variables (depth, velocity and type of substrate) and habitat suitable indices for targeted species. From these simulations, a quali-quantitative index is obtained for each species, named weighted usable area (WUA) that relate flow with usable habitat. In this study, we use the high waters of an Atlantic Forest stream, as a model for application of the physical habitat simulation in two contiguous stretches (upper and lower stretches) to assess the flow that maximizes the WUA for three fish species of different orders: the Characiformes Bryconamericus ornaticeps, the Siluriformes Ancistrus multispinis and the Perciformes Geophagus brasiliensis. Two field excursions were carried out (winter 2013 and summer 2014) in these two 50 m long stretches, in periods of low rainfall and reduced flow. The topographic characteristics of each stretches were measured, as well as the hydraulics measurements of water depth, velocity and type of substrate for each transect (9 in the upper stretch and 10 in the lower stretch) divided in cells of 0,25m². To assess habitat suitability of fish species, we performed subaquatic census to characterize microhabitats use by fish species. After having all variables, we performed hydraulic simulation, habitat simulation and the models of usable habitat by the studied fish species, obtained as results of the flow curves versus WUA. These curves are the baseline for proposition of regimes of ecological flow that enable the maintenances of fish species in the system. We determined an ecological flow of 0.60 m3/s, considered ideal for supply the requirements of the three fish species in periods of reduced flow. This information are important subsides to be considered by environmental hydric resources managers, to establish ecological flow regimes to ecosystem conservation.