Environmental flow assessment based on physical habitat simulation in a small river in the Southeastern Brazil

Martínez Capel Francisco, Rodrigues da Costa Marcus, T. M. Mattos, Muñoz Mas Rafael, Victor Hugo Fernandes, F. G. Araujo

2015

Environmental flow assessment based on physical habitat simulation in a small river in the Southeastern Brazil

The physical habitat simulation system within the framework of the IFIM (Instream Flow Incremental Methodology) uses hydraulic variables and habitat suitability indices of target aquatic species to predict how different in-stream flows affect their habitats. This habitat modelling approach was adopted to simulate and to assess the effects of different stream flows on three tropical fish species of different orders (Bryconamericus ornaticeps, Ancistrus multispinis and Geophagus brasiliensis) in two stretches of an Atlantic Forest stream in Southeastern Brazil during the Summer 2013 and the Winter 2014. Topographic and hydraulic characteristics (depth, velocity and substrate type) were measured, and underwater direct observation of the fish by snorkelling was performed to assess microhabitat use. Microhabitat suitability curves were developed for the three fish species; based on those curves we performed the physical habitat simulation in a representative stretch. Thus, we obtained the average Habitat Suitability Index (HSI) and Weighted Usable Area (WUA) vs. flow curves, and the relevant flow rates upon such curves to conserve the fish habitat for the three fish species. The results indicated a minimum flow rate of 0.25 m3 s-1 as a minimo-minimorum to conserve the fish habitat; an optimum range of 0.65-0.85 m3 s-1 was considered relevant for setting e-flow regimes to conserve the fish habitat in this Atlantic Forest stream. These results can support the first proposal of an e-flow regime in the frame of an adaptive management process of the water resources, in order to conserve healthy rivers with the diverse social benefits they provide.